HANMER ATA . + Qers > ses = ig ™ bs 7 A --} uv THE DISTRIBUTION OF VEGETATION IN THE UNITED STATES, AS RELATED TO CLIMATIC CONDITIONS - BURTON E. LIVINGSTON AND FORREST SHREVE PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON ee Wee aed r a fh % THE DISTRIBUTION OF VEGETATION IN THE UNITED STATES, AS RELATED TO CLIMATIC CONDITIONS BURTON E? LIVINGSTON AND FORREST SHREVE PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 192] CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION No. 284 Gift fastitutior Aone | S SEP 8 imay PRESS OF GIBSON BROTHERS, INC. WASHINGTON, D. C. CONTENTS. ER BAGUACGA Dine RGR Os SAN BN ole ag eta Ni A DEUS OIE, U0) ANG aad ke an aT Se a rae ae A Ca Part I. THe VEGETATION OF THE UNITED STATES. INTRODUCTION: I. The distribution of vegetation in general, as related to climatic conditions. . Il. Study of the distribution of individual species...................+0+00- I1I. Manifold operation of environmental conditions.................0+000005 DV (Groweh-lOrms OL DIAWiSi coc ma i as Vorb axRe en tee eis) vile 5 Bible asm o1e'e'e «p TasBiE 1—Analysis of Drude’s criteria for distinguishing SOM TM -TORMNS eso Pee Sk eee ha the ee ocd gM os Nestea COMMUNITIES (ie MC corel tile bean A Nn aia Sate gtslids dice Be Web/e ale od sea WA upelinatation, OF VerelatlonalaAreasinn 4.0 Wi oe leo als ine ors a one o DISTRIBUTION OF VEGETATION IN THE UNITED STATES: I. Methods used in securing and presenting the distributional data......... II. Leading vegetation types of the United States and their geographical areas III. Distributional areas of conformic groups of plants IV. Distributional areas of selected individual species MO eo idid te feria ate siete 6) Miele sie a. \0 wid) aie otis aap ke) oo we One Ota 6 Sha) Ce) Part Il. ENVIRONMENTAL CONDITIONS. SAAASES OID US) © RON ay ic se Se LD RAE SRE, LT SORE SZ SERS 8S LAN SD gs OS AO a Ue 2 Nae oh GENERAL INFLUENCE OF THE ENVIRONMENT ON PLANT LIFE: I. External and internal conditions and plant activity ie heory ol physiological Wmmits oe eee tee to eT Ae III. Relation of plant distribution to the physiological limits of the various developmental whasesiis. sc suwtcr ain kee cde, eee tae Coe sane oe IV. Genetic continuity of protoplasm and its cyclic activities, in connection with problems of distribution Se; [e > eA ener gare e\@) (6) lalse)/ehie.e) se (4.6) ©). 6) eee «es @ (ese) \e, et Bi a) aie Cuirr ENVIRONMENTAL CONDITIONS AND THE GENERAL NATURE OF THEIR Errects Upon PLANTS: I. General classification of environmental factors..............000ee cece II. Moisture: 1... Water requirement) withimi the plantuy;. is oe 0.es ook ce bee 2: Supply ob water torthe lamest cman, fae Oe a i ie 3. Relations between water-requirement and water-supply........... III. Temperature: 1. Temperature requirement within the plant...................... 2. The relation of temperature within the plant to conditions of CHNATOMUACIIEE Agee Ge ine heteS OOS GONGEs Cth oO a walk whe Gera 3. The duration aspect of the temperature relation................-. lV. Light: iieGeneralinature:orhohte: leeitieoe ks vas eee e ee Reel cw tk ee Pieces ot lehhvapon plamisia ji ceR ie eee Cas. «.s Ses os Gece ees 3. Duration aspect of light relation of ordinary plants............... V. Chemical conditions: : 1. Requirement of material within the plant....................46. 2. Material exchanges between the plant and its surroundings........ au Chemicalenvironimentsn netime «1. Seidl. oe Cd i ec ree tee wes 4, Duration aspect'of chemical conditions. ..... 0.0... ccc cee ceeeces VI. Mechanical conditions: at Chevren ad GM Sh QPabiIOMGh Naame held hi Gea la Ginidisne neice a aay sees wees ues 2. Destructive influences of mechanical conditions.................. 3. Favorable influences of mechanical conditions.................06+ VII. Interrelations of the environmental conditions................ 0600000 VIII. Experimental determination of relations between plant activity and QUIT OMMeCN GA CONGINIOUS a1. SkuidvisigVnbiaisiinis sb yale sadiveceesecenes PAGE. 101 | 84 CONTENTS. Tue Criimatic CoNnDITIONS OF THE UNITED STATES: 1: Introductory :.: Seer cent shane See Tach oe cee maak Rca ie II. Temperature conditions. 1. Duration of temperature conditions. A.. Preliminary. considerations ty. 630 2 agate on 5 oe eis wrace be B. The length of the period of the average frostless season (table 2, Plabe 54). Tiss Her Oe AUT ASME dics aec ea. yan se eke TABLE 2.—Frost data and length of average frostless sea- son for 1803 stations in the United States ............ C. Length of period of average frost season.................. D. Length of period of high normal daily mean temperatures (ables oplateus yet Ue Wee Pa CP wees De a TaBLE 3.—Length of period with normal daily mean tem- peratures of 68° F. or above, and of period with similar means of 32° F. or below, within the year............ E. Length of period of low normal daily mean temperatures (table Sqplate 36) Seki). 042.5 Bes ae, Go 2. Intensity of temperature conditions. A~ Prelaminany.iconsiderdtionsiins: lee sed is oe Sie SSE (1) Direct indices of temperature efficiency for plant growth (2) Remainder indices of temperature efficiency for plant growth, Merriam’s chart (plate 37)............... (3) Exponential indices of temperature efficiency for plant ERAN BRORLLE FHL IU Arg CO BOE noe nn care te open cee TaBLE 4.—Exponential indices of temperature efficiency for plant growth, based on a coefficient of 2.0 for each rise in temperature of 18° above 40° F., for each temperature from 41° to 100° F. (4) Physiological indices of temperature efficiency for Planiverowtn Mee BES ee oes ves ee ee TABLE 5.—Physiological indices of temperature efficiency for plant growth, based on Lehen- bauer’s 12-hour exposures with maize seedlings. B. Summations of direct indices of temperature efficiency for period of average frostless season.......... 0.20 e ee eee eee C. Summations of remainder indices of temperature efficiency for period of average frostless season (table 6, plate 38) TaBLE 6.—Summations of normal daily mean remainder indices of temperature efficiency for plant growth, for period of average frostless season, the daily indices being derived by subtracting 0, 32, 39, or 50, from the values of the normal daily mean temperature on the Bahrenheitsealle )/ew@ltist. iu, Juste chee ene one D. Summations of exponential indices of temperature efficiency for period of average frostless season (table 7, plate 39)... TABLE 7.—Summation of normal daily indices of tem- perature efficiency for plant growth, for period of aver- age frostless season, the mean daily efficiency indices being derived from the corresponding temperature indices, (1) by the exponential equation of chemical reaction velocities and (2) by the empirical growth- rate coefficients for maize seedlings as found by Lehen- bauer for a 12-hour exposure to maintained tempera- ture. The temperature efficiency for 40° F. is taken as whity an bothieases Uae ce ore ae ee E. Summations of physiological indices of temperature efficiency for period of average frostless season (table 7, plate 40, and fier, TY RO eS Be Bar ee AP oe ec eal P Absoltite: temperature maximas ) oc820. 0. dos eee es 217 225 CONTENTS. Tue Cuimatic ConDITIONS OF THE UNITED STATES—continued. II. Temperature conditions—continued. 2. Intensity of temperature conditions—continued. G. Absolute temperature minima (plates 41 and 42)........... H. Average daily normal temperature for coldest 14 days of year (tables, plate 4a nai iia Orr Soe te eae es TaBLE 8.—Average normal daily temperatures for coldestyis, daysior the weared wet ono.) co nae doe © I. Merriam’s mean normal temperature for hottest six weeks of year \Golate aA gneve PAA Mee bs hb de Be J. Normal mean annual temperature, U. 8S. Weather Bureau (plater Ase salen: Saini, Se ee Ree. eee 3. Conclusions from the study of temperature conditions............ III. Moisture conditions. di inibrodehony ss iia) Gewese IES oo bel bc wc een oe 2. Supply of water to the plant. Ay Preliminary. nconsid enations. iaewin . Bk: ideas se. ee wee ee B. Precipitation. (Lh): ntroductormattinawe neers ey pened eS: (2) Normal mean daily precipitation for period of average frostless season (P/S) (table 11, plate 46, and fig. 2) Tasie 11.—Precipitation and evaporation data for the period of the average frostless season....... (3) Total normal precipitation for period of average frost- less season plus preceding 30 days, divided by number of days in average frostless season (#/S) (table 11).. (4) Number of normally rainy days in period of average frostless season (table 13, plate 47)................ TaBLeE 13.—Number of days in period of average frostless season with normal precipitation of more than 0.10 inch and with normal precipita- tion of 0.10 inch or less, the latter also expressed as percentage of the number of days in the aver- Age TOStleSSvSEASOM. ty let c Lh. ba ewe eee Ok ek ae (5) Number of normally dry days in period of average frostless season (table 13, plate 48)............... (6) Percentage of days in period of average frostless season that are dry days (with normal daily precipitation of 0.10 inch or less) (table 18, plate 49).............. (7) Length of longest normally rainy period in period of average frostless season (table 14, plate 50)......... Tas_LEe 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period within period of average fiosthessisensanss Say uiiaiodacee, la ce ee ae (8) Length of longest normally dry period in period of aver- age frostless season (table 14, plate 51)............ (9) Normal annual precipitation, after Gannett (plate 52) (10) Conclusions from study of precipitation conditions. . . 3. Removal of water from plant. A. Introductory. (General controliofwaterslossecc. oc eee cee ee (2) Atmospheric evaporating power. ..............0000. Marrortensiomi geneity: . swell. ci cc ccc ce cwensmes Relativewimaditgs C40 vents. ca ee ce cw wawee’ (Sip Acaneeirea etiam: U4. Gls Waietines wecaecc eee. B. Atmospheric evaporating power in the United States. (1) Very limited nature of available data................ (2) Russell’s data of evaporation in the United States. ... 260 260 264 VI CONTENTS. THe Criirmatic CONDITIONS OF THE UNITED STATES—continued. III. Moisture conditions—continued. 3. Removal of water from plant—continued. B. Atmospheric evaporating power in United States—continued. (2) Russell’s data of evaporation in United States—continued. Evaporation intensities for the period of the average frostless season (table 11, plate 53, and fig. 14)... Annual evaporation intensities (table 15, plate 54).. Evaporation intensities for the three summer months (hailey Siren eae 6 ee TaBLE 15.—Precipitation and evaporation data for the year and for the three summer months. . (3) Evaporation studies in 1908. Presentation of date 0-250 ber er PSs ee TaBLE 16.—Weekly precipitation (P) and weekly rates of evaporation (#), the latter from cylin- drical porous-cup atmometers, summer of 1908. Summer march of evaporation at selected stations. . Mean evaporation values for 5-week periods and for 15-week season (table 17, plate 56).......... TABLE 17.—Summary of precipitation and evapo- ration for summer of 1908, with averages and precipitation-evaporation ratios (P/E) for the 15 weeks, May 26 to Sept. 7................. Comparison between plates 55 and 56............. Summer evaporation, 1908, as shown by geographic prohiles (eda): F PI: BME ee (4) Conclusions from study of evaporation conditions (fig.14) C. Ratios of precipitation to evaporation. (1): Preluminary considerations. ... 0... a ee ee (2) Ratios of total precipitation, for the period of the average frostless season, to total evaporation for the same period, July 1887 to June 1888 (P/E) (table 11, PIstens Gn EUG Se. Oo kee a ee (3) Ratios of total precipitation to total evaporation, for the period of the average frostless season, July 1887 to June 1888 (P/E) (table 18 plate 58)............ TaBLE 18.—Data of precipitation and evaporation for the period of the average frostless season, for the year July 1887 to June 1888, and corre- sponding ratios of precipitation to evaporation, together with similar ratios derived by employ- ing normal data of precipitation instead of those for hhis Sinsle yeaR so. 5 PRIS say ois ek ae (4) Ratios of normal total precipitation, for the period of the average frostless season plus 30 days, to total evaporation for the same period, July 1887 to June 1888 (a /#)* Gable’1,; plateO)e. 2 ee (5) Ratios of normal total annual precipitation to total annual evaporation, July 1887 to June 1888 (PafE,) Gable 15; plate GOVE Mis: Ae oe oo es (6) Ratios of normal total precipitation for the three sum - mer months, June to August, to total evaporation for July and August 1887 and June 1888 (P;/E;) Gitte TS Mla Gh) oh 2 2 BPs BER eee (7) Ratios of total precipitation for 15 weeks, summer of 1908, to total evaporation for the same period and year (Ps 1908/Es 198) (table 17, plate 62)......... (8) Conclusions from study of precipitation-evaporation PAGO EIA Gees Sd Site se a eter ca als Si weet e elere PAGE. 292 296 298 298 304 306 dll 316 318 320 322 323 326 326 328 329 330 303 CONTENTS. Tae Curmatic ConpDiITIONsS OF THE UNITED STATES—continued. III. Moisture conditions—continued. 3. Removal of water from plant—continued. D. Aqueous-vapor pressure. (1): Preliminary, considerations) i.jic hock. oe oc os coe ee (2) Normal mean aqueous-vapor pressures for the period of the average frostless season (table 19, plate 63).. TaBLE 19.—Normal mean relative humidities, for year and for period of average frostless season, mean relative humidities for the three summer months, 1908, and normal mean vapor-pressures for the year and for period of average frostless (3) Normal mean aqueous-vapor pressure for the year Gable VOW mlAateiG4) ree Foyle oe ee ee eed E. Relative air humidity. ())), Brelimimary. considerations...0...60.200. 000 5.02 eee (2) Percentages representing normal mean relative air humidity for period of average frostless season Gable 19, plate 65 and Mig. VO)0e. oc ee ee we (3) Percentages representing normal mean relative air humidity for the year (table 19, plate 66).......... (4) Percentages representing mean relative air humidity for June, July, and August 1908 (table 19, plate 67). (5) Generalizations from the three charts of relative humid- ity values (plates 65 to 67 and fig. 17)............ FF.) Wind: (Gable. 20*leiter OR) vatyipnis 205 eS wok ole a oe TaBLE 20.—Average wind velocities for the year and for the period of the average frostless SCASONE Alyse. hie eelvesee cb: oc lce ean ee ac hee _G,. Sunlight as a condition influencing water-loss from plants (Gables 2 iplataGOreaces pest eee es bk nes's See wo oo TABLE 21.—Normal total number of hours of sunshine within the period of the average frostless season... .. 1V. Moisture-temperature indices. _ PA VTE TOCUCE ORY enna ket iit ® We, GREER oa a Sioa ek elena le ee eee B. Moisture-temperature indices based on temperature summa- tion-indices obtained by the remainder method (above 39° F.), for the period of the average frostless season (table 22, plate; ZOE ehh wet he WIR PS aA ya EAN EE ae TABLE 22.—Moisture-temperature indices for the period of the average frostless season, by remainder (above 39° F.), exponential, and physiological methods...... C. Moisture-temperature indices based on temperature summa- tion-indices obtained by the exponential method, for the period of the average frostless season (table 22, plate 71) D. Moisture-temperature indices based on temperature summa- tion-indices obtained by the physiological method, for the period of the average frostless season (table 22, plate 72, SAAC TTI), ah RMU wedseay - . i Paw ce 2° =e ee en ee ee a 6 THE VEGETATION OF THE UNITED STATES. observational experiences, and, indeed, whether such agreement would actually yield substantial advantages. The classification of vegetations is thus seen to be by no means an easy task, and it is no marvel that there is lack of agreement among those interested in it. Plant communities are usually made up of many species, and these species are usually of distinct floristic relationship, or dissimilar geographic range, and of varied physiological require- ments and behavior. Furthermore, a particular community does not range far without the acquisition of new members and the loss of old ones. The classification of such a complex material requires the adop- tion of arbitrary standards, and consequently leads to an unnatural system or else to one which is only of local applicability. Physiographic ecology affords a genetic basis for the classification of vegetation, and the logic of such a system has much to recommend it. Physiographic criteria are not, however, of universal applicability for the classing of vegetation, and lead to unnatural interpretations of vegetational phenomena in many regions, particularly in the tropics, in deserts, and in regions with diversified geological and soil conditions. Furthermore, physiographic ecology is inclined to lead to a false sense of satisfaction with the assembled results of the study of a series of successions, and has often failed to stimulate a study of the physical causes which underlie the observed successional phenomena. Several Scandinavian and German botanists have rightly urged that the classification of plant communities should be based upon the recognition of certain distinctive types or forms of plants. These “biological types,’ “life-forms,” “vegetation forms” or ‘“growth- forms’ are recognized without regard to phylogenetic relationships, and serve to distinguish such groups as deciduous broad-leaved trees, evergreen coniferous trees, perennial grasses, sclerophyllous shrubs, etc. Several systems of growth-forms have been proposed, each more elaborate and complete than the next preceding. In so far as these systems represent an attempt at a physiological classification of plants they are highly commendable, and must lie at the foundation of physi- ological plant geography. Unfortunately, however, our knowledge of the physiology of plants is chiefiy based on the behavior of a small number of kinds of plants, mostly cultivated forms growing under sets of conditions at best only partially controlled or measured, and the existing classifications of growth-forms have been based on the inference that the gross anatomi- cal features of plants are an index of their major physiological char- acteristics. We have not yet secured enough evidence to test this inference in more than a general way. We know that there are marked differences between the annual march of transpiration and photo- synthesis in evergreen conifers and in deciduous broad-leaved trees, and that there is no contradictory significance in the fact that such INTRODUCTION. 7 dissimilar trees often grow side by side. We know that arborescent cacti and microphyllous trees differ markedly in the character and activity of their root-systems, and that the annual course of absorption and transpiration in the two types is very unlike, in spite of the fact that the two are constant associates. In view of the incompleteness of the knowledge which might afford a basis for the classification of life forms, it behooves us to recognize a limited number of such forms and to extend the list only on securing evidence of the divergent behavior of groups of plants. The difficulties inherent in the classification of vegetation have led some of the German and British botanists to use the physical charac- teristics of the habitat either as the sole criterion for classification or else as a secondary criterion, employed together with the charac- teristics of the plants themselves. Such a procedure may be looked upon as an indirect method of securing evidence of the physiological character of the plants involved and is logically allowable only on such ground. In any case in which plants of identical growth-form occur in two situations of very unlike physical conditions, an excellent opportunity is afforded to investigate the comparative physiology of the plants. If, as is very unlikely, the two groups should be found to be physiologically alike, there would then be no ground whatever for the separation of the two vegetations in classification. If physiological distinctions should be discovered, these, rather than the unlikeness of the habitats, should then form the basis for separating the two vege- tations. Our deepest concern for the development of plant geography is that its activities may be diverted from the description and classifica- tion of vegetation on subjective grounds and that they may be directed toward experimental work so planned as to yield an actual physio- logical basis for the classification of vegetation. Starting with the small body of experimental data which now makes it possible to recog- nize certain groups of plants with a general coherence of physiological behavior, it will become possible in the course of time, and of much hard work, to extend our knowledge far enough to actually under- stand the different types of vegetation which we now photograph, map, list, and name. II. STUDY OF THE DISTRIBUTION OF INDIVIDUAL SPECIES. The investigation of correlations between climatic conditions and ° vegetation has been extended, in our work, to the relations between the climate and the distribution of certain individual species of plants. We are here treading upon fresher ground, on which extremely little work has been done. To attempt to define the factors which are responsible for the geographical distribution of any one plant species 8 THE VEGETATION OF THE UNITED STATES. is, indeed, to face a problem of considerable complexity. Even in the presence of the results of our own work we are not prepared to main- tain that the distribution of all species is at the present time strictly controlled by the complex of physical conditions for which we have tried to derive numerical values. We are in the position, however, of being convinced that certain species are thus controlled, the evidence in this direction being partly our own and partly due to an analysis of the work of others. It is very generally maintained that the distribution of many plants is due to certain “historical factors,’ which is merely to say certain physical conditions which have operated in the past, or the conditions which determined the distribution of the ancestral stock of the plant in question. When we speak of the historical factors and the present factors operative in determining plant distribution, we must bear in mind that we are embracing in the former term two very dissimilar things which have registered a combined effect. We must look to evolutionary history and to paleobotany to tell us where a particular genus originated, at what epoch, and from what stock. We must look to paleobotany and paleoclimatology to tell us what have been the movements, the extensions, and the retreats of this genus. The initiation of a species is, from our standpoint, purely an evolutionary event; the history and fate of the species after its initiation are con- sidered as dependent upon the changes in orography or climate which it may encounter, always with the possible cooperation of physiological changes in the stock which are unaccompanied by morphological modifications of diagnostic value. It is conducive to clearer thinking, therefore, to distinguish between the evolutionary factors and the palecclimatic factors which compose the historical factor. This dis- tinction has its principal value in compelling us to regard the present distributional phenomena of the earth as merely a momentary stage in the prolonged and incessantly active procession of change due to secular or sudden changes of climate, or to destructive or constructive events in surface geology, and discontinuously marked by evolutionary activity. We are made to realize that there is no gulf between the climate of the past and that of the present, and that there has been no sudden, extensive, or unaccountable readjustment of distributions. The réle of the evolutionary factor can not be escaped in any con- sideration of distribution. For example, we owe it to facts in the shistory of the great plant stocks that Yucca arborescens occurs in the Mohave Desert of Southern California and that Aloe dichotoma, somewhat similar to it in form, grows in the deserts of Southwest Africa. It is likewise a part of phylogenetic history that very many plants were formerly confined to particular regions, whereas they now have been introduced overseas, into climates which prove to be wholly congenial to them. However, the reasons for the distributional ranges INTRODUCTION. 9 of Yucca and Aloe in their respective continents are to be sought in the operation of the environment, and the spread of an introduced plant in a new continent must be controlled by environmental con- ditions just as it was controlled in its native continent. Evolutionary activities may be thought of as supplying the raw materials out of which the physical environment has made the present distributional complex of the earth’s surface. We can not hope at present to understand why a strong development of the genus Yucca has occurred in the southwestern United States and a rich develop- ment of Aloe in South Africa, and the answer to such a question, if forthcoming, would have only a remote relation to the study of the present influences which are limiting the distribution of the members of these two stocks in their respective continents. The rodle of paleoclimatic factors is also an immanent one in the determination of plant distribution. Many species have a known ancestry and a known ancestral range, at the same time that they now inhabit areas of such small size that it is difficult to believe that any present physical conditions are restricting them. The history of these plants has been one of extinction and retraction, due to changes in their old extended environment. They are now unable to regain their old ranges, or even to spread over relatively short distances. These species may well be looked upon as physiologically and genetically decadent, and either decadent because they are geologically old or else old because they have failed to change their requirements to that slight extent which might permit a greater extension, or to that greater extent that would have reacted upon form in such a manner as to make us regard the resulting plants as distinct species from the old ones. In addition to the old and restricted, or relict, species we have another class of plants of limited range, those which are apparently just appearing on the scene and have not yet had time to occupy the entire area in which they might be expected to find congenial condi- tions. These plants are generally members of large genera, such as Opuntia, Antennaria, and Crategus, or else of genera which have been recently subdivided, whereas the relict species are usually members of small genera. It is not always easy to decide whether a given restricted distribution is of the relict type or of the ‘‘novitiate’’ type, as we may call the emerging species. Our decision, in the lack of other evidence, is apt to be based upon the existence or absence of fossil records of the species or its allies, or else upon the size and phylogenetic position of the genus or family. Such a restricted conifer as Pinus mayriana may well belong in either class, and the members of many small or monotypic genera of Mexican Compositz may also stand in a doubtful position. A very considerable number of our plants belong neither to the relict nor to the novitiate class. They are of such age that they have had 10 THE VEGETATION OF THE UNITED STATES. time to extend themselves as far as the subtle factors of their environ- ment, the crude power of great barriers, or the operation of suitable agents of dispersal have permitted, and their course has not run so far that climatic and orographic calamities have overtaken and restricted them. This great class of physically controlled plants can not be specifi- cally enumerated at the present time. There are many good reasons for believing it to contain the bulk of the species which form the dominant element in all vegetation, whether these are plants of extended range and frequent occurrence, plants of more restricted range, or plants whose occurrence is determined by complexes of con- ditions which are themselves rare. We may find areas of vegetation in which a relict plant is dominant, as is true of the groves of Cupressus macrocarpa near Monterey, California, or others in which a novitiate plant is very abundant, as is true of the Cababi Hills in southern Arizona, where an undescribed Opuntia, known nowhere else, is extremely abundant. Although cases of this sort are fairly common,- they are usually readily detected by a more thorough study of the adjacent regions. Such trees as Liriodendron, Taxodium, and Liquid- ambar are known to have undergone distributional recessions, but they occupy such large areas at present that they can scarcely be classed as relict species, and can surely be placed among the plants whose distributional controls are worth looking for among factors at present operative. Whether the physically controlled plants form a large or a small percentage of our flora, we can at least state with some assurance, based upon the correlation of distribution and climatic conditions, that they form the predominant part of our vegetation. The great bulk of the tiees, shrubs, grasses, root-perennials, and other plants which make up the dominant natural vegetation of the world may safely be held to have had their present distributional limits imposed by physical factors which are either now operative or were operative in very recent time. Such factors may be acting directly through the conditions of climate or may be acting indirectly through soil conditions, through geographic or physiographic changes, through the influence of associated plants, through animal, fungal, or bac- terial enemies, through fire or mechanical agencies, or through the means of animate or inanimate agents of dispersal. Since these indirect factors of environment can affect plants only through the same kinds of physiological influences as are exerted by the direct factors of the climate, they are at bottom of the same nature, whether we allude to them as “‘biotic’”’ factors, “mechanical factors,’ or what not. In the isolated desert mountains of southern Arizona the great bulk of the species are physically controlled in their distribution, as is abundantly shown by the universality of each of these species through- out a given altitudinal range or a given set of habitats, and by the definiteness with which it is limited by rather sharply drawn lines. INTRODUCTION. 11 When one of these mountains is compared with another the floras _ are found to be closely similar but not identical. Certain species range over the western cordillera of Mexico or over the central Rocky Mountains and have reached certain of the isolated desert mountains without having reached all of them. At least a few cases are known in which a given species is common throughout several mountains and is known from only one or two restricted localities in another moun- tain, although it is there surrounded by an area possessing a favorable environment for it. In view of the universality of the distribution of most of the mountain species, these cases appear to be the opening invasions by which new components are being added to the flora. They are in a way analogous to the novitiate species of larger areas, and their presence in no way vitiates the evidence for the physical control of the distribution of the major portion of the mountain flora. In determining the limits of the types of vegetation which are shown in plate 1, no consideration whatever has been given to the ranges of individual species of plants. It is true, nevertheless, that each of these ereat vegetations possesses many species, particularly among its dominant forms, which are roughly confined to the area occupied by the vegetation itself. Picea sitchensvis, for example, is nearly coincident in distribution with the Northwestern Hygrophytic Evergreen Forest; Pinus teda extends very little beyond the range of the Southeastern Mesophytic Evergreen Forest, and Bulbilis dactyloides extends over nearly the same area as the Grassland and the Grassland-Deciduous Forest Transition. Other forms are nearly coincident with groups of areas, as is the case with Covillea tridentata, which is found in the California Microphyll Desert, the Arizona Succulent Desert, and the Texas Succulent Desert. Since the limits of groups of dominant plants have been unconsciously and necessarily taken into account in delimiting the vegetational areas, it is to be expected that there should be many cases in which the physical conditions concomitant with the distribution of a given type of vegetation and those concomi- tant with the distribution of some of its dominant species should prove to be nearly identical. We regard the view that vegetation is determined in its distribution by complexes of physical conditions, as established beyond all cavil by the work of a large number of men, if indeed it is not almost axio- matic. That the distribution of individual species is also controlled by physical conditions is equally well demonstrated, so long as we con- fine our attention to the common forms which are important elements of the vegetation. There are doubtless many of the novitiate and relict species of plants which find the physical conditions of the present time a barrier to their spread, but such cases have not yet been demon- strated. We have, therefore, confined our consideration of individual species to forms which are extremely abundant, except in a few cases which will be noted. 12 THE VEGETATION OF THE UNITED STATES. Ill. MANIFOLD OPERATION OF ENVIRONMENTAL CONDITIONS. Our knowledge of the modes in which the nature of the environment may affect the activities of plants, and thereby affect or determine their distribution, is sufficiently great to give a profound impression of the complexity of the problem of the physical control of distribution. The experiences of agriculturists and horticulturists, the work of plant physiologists, and the observations and deductions of ecologists, have all combined to give us a very large body of facts relative to the mani- fold. features of the physical environment which may be of critical importance for the spread or survival of particular plants under par- ticular conditions. We are very well informed, both empirically and experimentally, with regard to many of the conditions which are harmful to cultivated crops and the climatic conditions which make it impossible to cultivate them beyond certain well-defined boundaries. A large part of this information relates to the ability or mability of plants to withstand frost or freezing temperatures, and to their ability to survive and grow under given limitations of water-supply. Enough has been done in the selection and breeding of economic plants to show that closely related forms may often exhibit great differences in ability to withstand low temperatures, low soil-moisture content, great ranges of soil texture, and the like. Enough is known of the distributional limits of plants which are associated in given regions to indicate that these are not limited by the same sets of condi- tions; they range to different distances and into regions of diverse character in such manner as to indicate that they have very dis- similar distributional controls. In spite of the manifold nature of the environmental controls and the well-known diversity among plants with respect to the nature and intensities of the conditions which control them, it is possible, never- theless, to distinguish certain classes of controlling conditions. The broadest line that may be drawn is the one separating the simple or direct factors of a climatic character and those which are not directly attributable to the climate. Later pages will be devoted to an elabora- tion of some of the major types of direct climatic conditions, but little will be said hereafter regarding the non-climatic conditions, such as the nature of the soil, such “‘biotic factors” as competing plants and preying animals, and such mechanical factors as the influence of wind (in causing mechanical injury), lightning, fire, landslips, inundations, active erosion, and other agencies of very real importance but usually of local or comparatively infrequent occurrence. So much is known regarding the importance of the character of the soil that it is custom- ary to speak of “‘climatic and soil conditions” as if the two were of co- ordinate importance. The réle of the soil in maintaining a water- supply for plants is of vastly greater importance to them than any of INTRODUCTION. 13 the other réles which it plays. Although the texture of the soil is of prime importance with relation to the penetration, movement, and con- servation of a water-supply for plants, it is fundamentally the climatic elements of rainfall and evaporation that determine what the soils of a given texture are able to do in presenting a moisture-supply of a given amount. We are compelled, therefore, to regard the soil as a medium through which the climate acts upon plants. The supply of moisture to the plant, due primarily to climatic conditions, is secondarily determined by the soil, just as the loss of moisture from the plant is determined through the medium of the atmosphere. The soil is a medium which differs from place to place independently of the climate, while the atmosphere is alike in all places, except in so far as it is directly affected in its movements, temperature, and moisture- content by the primary conditions of climate. Such a view of the réle of the soil in forming a portion of the environ- ment of plants takes no account of the cases in which the chemical nature of the soil and the amount and character of the salts and other solutes in the soil-water become factors of great moment. In the con- sideration of saline and alkaline areas, and certain limestone and ser- pentine regions, it is necessary to do more than investigate the texture of the soil in its réle as a stabilizer of the climatic moisture conditions. It has been customary to speak of competition as if it were a distinct condition of elemental character, capable of admitting or excluding a given plant to a given area in much the same manner as that in which a purely climatic condition would operate. The results of competition are registered upon a plant, however, in exactly the same manner as the results of a given climatic condition or set of conditions. Com- petition may exclude light, may restrict water-supply, or may operate in any one of a number of ways. The end-effects upon the processes of the plant are exactly such as might be exerted through climatic agencies, except it be in those cases in which there is an addition of toxic root-excretions to the soil. Even in such cases, the toxic substances act as chemicals and the plants producing them are not directly effec- tive. Competition may be of importance in determining the com- position of small areas of vegetation, but even then the competing plants must be regarded as struggling not with each other, but with physical conditions which are of precisely the same general nature as the conditions due in other places solely to climatic causes. The cases in which plants grow so closely as to exert an effect on the environ- mental conditions are similar to the cases in which the major plants modify the climate for the minor plants. Both of these cases must be left out of consideration in an attempt to determine the larger features of the réle of climate in relation to vegetation. It is possible to lay down a program for the study of distribution and its controlling conditions, applicable almost equally well to a given 14 THE VEGETATION OF THE UNITED STATES. species or to a given type of vegetation, and idealistic only in that it would require extension or modification to fit the necessities of any given case. Such a program, briefly outlined, is as follows: A. The securing of the distributional facts. 1. Securing an exact knowledge of the geographical range of the given plant. 2. Determining the ecological distribution of the plant. a. Its region of greatest abundance. b. Its region of greatest size. c. Its region of most rapid growth. d. Its region of greatest productivity. e. Its region of greatest catholicity of habitat. 3. Determining the behavior of the plant at the limits of its range. a. The character of its limital habitats. b. The evidences for its limitation. B. Ascertaining the apparent climatic controls on a correlational basis. 1. Determining the isoclimatic lines which follow nearest to the geographical limits of the plant form considered. 2. Determining its habitat behavior with respect to climatic elements discovered in 1. 3. Determining its comparative behavior at different portions of the periphery of its geographical range. C. Ascertaining the actual climatic controls by experimentation. IV. GROWTH-FORMS OF PLANTS. When we undertake to regard the vegetable kingdom from the ecological standpoint, and to investigate the importance of the physio- logical characteristics of plants as related to their distributional fea- tures, it is clear that considerations of phylogenetic relationship become of little importance. If we attempt to arrange the multifarious plant-forms of the earth in a series of groups according to their physio- logical affinities, so as to bring together the plants which have solved the same problems of environmental adjustment in the same manner, we shall have to depart very far from the families and genera of the natural system of classification. This is very obvious from a consideration of the diversity that exists in some of the large plant families. In the Composite, for example, we have trees, shrubs, and herbs, terrestrial plants and aquatics, large-leaved, small-leaved, and leafless perennials, mat- forming or cushion plants, slender climbers, etc. In the southwestern United States we have, conversely, a group of small-leaved or leafless woody perennials which are green-stemmed and richly branched and bear a close resemblance to each other, in so far as vegetative structures are concerned, in spite of the fact that they may belong to entirely different families. Among these plants are Thamnosma montanum (Rutaceze), Keberlinia spinosa (Koeberliniacee), Holacantha emoryt (Simarubacez), Canotia holacantha (Celastracee), and Parkinsonia microphylla (Leguminossz). Among the criteria used in the phylogenetic Brean sr of plants are: the structure of the flower, the developmental history of the floral INTRODUCTION. 15 organs, the systems of arrangement of leaves (phyllotaxy), the stelar anatomy of the stem, the existence and character of vestigial structures, and the recapitulation of ancestral features in the early life history of the plant. The facts which fall under these categories have been of long-standing use in phylogenetic classification, but have no direct bearing upon the present relation of the plants to their environmental conditions. Therefore these are not the criteria that would be useful in classifying plants for the purposes of ecology and plant geography. For these purposes we require a classification which shall give first attention to the vegetative rather than the reproductive organs of the plants, and to those features and structures which have to do most obviously with their relation to the conditions of the soil and atmos- phere. When plant geographers first began to break away from floristic considerations and commenced to consider plants collectively, as vegetation, they felt the need of a means by which it would be possible to express physiological relationships. It was a very difficult thing to depart from the point of view by which plants could be placed in such definite categories as the Saxifragacee or the Liliacez, or in such groups as ‘arctic circumpolar”’ or “‘littoral pantropist.”’ It was still more difficult to attempt, for example, to arrange the plants of heath, moor, tundra, and alpine meadow, in a series of groups that would bring out their physiological affinities. The very instant that we distinguish between the vegetation of any two areas we have taken into account, consciously or unconsciously, certain features of differ- ence between the plants of these areas. We notice the difference between the soft carpet of short grass which lies just above mean high tide in a brackish marsh and the tall, coarse grass which inhabits the quiet shallows below the high-tide line. We notice the difference between the forests of the southern Alleghenies and those of the Gulf Coast. In each case we have had our attention called to certain differences in the gross anatomy of the plants involved. In spite of the fact that the plants which characterize the two areas of marsh are both grasses, we recognize in them plants of different type, just as we distinguish the pines of the Gulf Coast and the oaks and chestnuts of the Alleghen- lanregion. It is these obvious differences between plants, conspicuous even to the man who knows no Latin names for them, that form the basis for all the distinctions between vegetational areas. Considerable attention has been given, from time to time, to the definition of these anatomically and physiologically distinctive types of plants which are best designated as growth-forms. These attempts have a very fundamental importance to plant geography, for, although many of them have been extremely crude, they represent an attempt to express an ecological similarity that exists between many plants of distant phyletic relationships. They represent an effort to establish 16 THE VEGETATION OF THE UNITED STATES. categories in which we can place the rich variety of types that the plant organism has assumed. They constitute the beginnings of an ecological classification of plants from a physiological standpoint. Everyone must be aware that such a classification should have its beginnings in physiological work and not in the descriptive work of plant geography. It is not strange, however, that need for it should arise in geographical work and should be felt more by plant geographers and ecologists than by most physiologists. In a brief review of the attempts that have thus far been made to establish systems of growth-forms that will be of service in plant geography, it will suffice to mention only afew. The first was proposed by Humboldt! in 1805, in connection with his effort to determine the features that give distinctive character to the vegetation of different altitudes in tropical America. Humboldt saw, in the types which he recognized, the distinctive vegetational units that serve to bring about the physiognomic diversity of the different regions of the earth, rather than groups oi possible physiological affinity. His list of 19 types included the coniferous tree, the palm, the cactus, the tamarind- like tree, grasses, aroids, and the like. Grisebach? described 60 vege- tative forms, and his classification, like that of Humboldt, had to do largely with the conspicuous types of plants which determine the physiognomy of vegetation and aid in differentiating the great floral regions of the earth. Following upon these early classifications have come the systems of Drude,’ Krause,* Pound and Clements,’ Raun- kidr,° and Warming.’ The systems proposed by these men are far more elaborate than the earlier ones; they embrace all cryptogamic as well as phanerogamic plants; they include aquatics as well as land plants; they take into account seasonal behavior as well as form and differentiation, and, what is best of all in an attempt to devise a natural system, they introduce subordinate categories. The system of growth-forms most widely used at the present time, and the one that seems to have attracted the most attention to this subject, is that proposed by Raunkidr. His system is based entirely — on the character of the perennating organs of plants and their position with respect to the substratum. His five groups are as follows: 1Humboldt, Alexander von., Essai sur la Géographie des Plantes, Paris, 1805. ?Grisebach, A. R. H., Die Vegetation der Erde, Leipzig, 1872. Drude, O., Deutschlands Pflanzengeographie, 1896, and earlier papers. ‘Krause, E. H. L., Die Eintheilung der Pflanzen nach ihrer Dauer., Ber. d. deut. Bot. Ges. 9: 233-237, 1891. 5Pound, R., and F. E. Clements, The phytogeography of Nebraska, Lincoln, 1898. 6Raunkiar, C. Types biologiques pour la géographie botanique, Bull. Acad. Roy. Sc. Dane- mark, Copenhague, 1905.—Livsformernes Statistik som Grundlag for biologisk Piantegeografi. Botan. Tidssk., 29, Kjobenhavn, 1908 (translation in Beih. Bot. Centralbl. 87, 1910).—Formations- underségelse og Formationsstatistik. Botan. Tidssk., 30, Kjobenhavn, 1909 (English abstract in Bot. Centralbl. 113:662, 1910). TWarming, E., Om Planterigets Livsformer, Festskr. ugd. af Universitet, Kjobenhavn, 1908. INTRODUCTION. 17 Phanerophytes: Trees and shrubs with buds exposed on branches. Chamephytes: Plants with their dormant buds on the surface of the soil or just above it (30 cm.). Hemicryptophytes: Plants with buds in the surface layer of the soil. Cryptophytes: With subterranean dormant buds. Therophytes: Perennating as seeds; annuals. This classification expresses the physiological diversities of the vege- table kingdom in a very inadequate manner. It lays stress upon the resting organs, with total disregard of what we may term the “‘work- ing organs.” Its author has more recently! proposed a subdivision of his group ‘“hanerophytes,”’ based on the size of the leaves. These six “size- classes”’ make it possible to use somewhat more definite terms in descriptive plant geography, but they do not satisfy the requirement for a more precise knowledge of the physiological significance of leaf- size. The fact that the transpiring power of leaves is not definitely related to their size is one of the considerations which makes this criterion of doubtful value even for a preliminary classification of growth-forms. Raunkiir, Paulsen, and other workers have used the above system of growth-forms to derive what they have designated as “biological spectra.’’ By this method the entire flora of a given region is appor- tioned among the five classes of the system, and the values are thus secured for the percentage of the total flora which is formed by each class. These spectra possess little value to the student of vegetation, inasmuch as they are based upon a consideration of the flora rather than the vegetation. The biological spectrum of a pine forest with 175 species of root perennials growing in its shade would be very slightly changed by the removal of the pines, although this would effect a very profound change in the character of the vegetation. The securing of the biological spectrum for a given number of the com- monest plants of an area, as has been done by Taylor’ for Long Island, gives results of some value, but their ecological importance is still limited by the inadequacy of the classification. The most carefully elaborated system of growth-forms is that of Drude, proposed in his Oekologie der Pflanzen.* This system is thoroughgoing and complete at the same time that it is eminently natural, in the sense that it comprises almost no subjective or phylo- genetic distinctions. The principal subdivision of the vegetable king- dom is into terrestrial, aquatic, and non-vascular plants, and the total ‘Raunkiir, C., Om Bladstérrelsens Anvendelse i den biologiske Plantegeografi, Bot. Tidssk — 1916.—Translation by G. D. Fuller and A. L. Bakke in The Plant World 21: 25-37, “Taylor, Norman, Flora of the vicinity of New York, a contribution to plant geography, Mem. New York Bot. Gard., v. v1-+683 p. New York, 1915. ’Drude, Oscar, Die Okologie der Pflanzen, 308 p., 80 figs., Braunschweig, 1913. 18 THE VEGETATION OF THE UNITED STATES. number of growth-forms recognized is 55. The number of growth- forms apportioned to each of the various classes of plants is shown by the following table: I. Terrestrial plants (38): IT. Aquatic plants (6): AirCesiey ts ote Wor! scare cis gholiens a Amphibious, ...4..... 4-2 3 PS) ETT OTS aM 2m apne Re es MRR 9 Submerged. <... +. 4 aah 2 Glib eEs eae ours Ce serra aW eels 4 Floating... 2.5... 1 Parasites and saprophytes...... 2 | Itt. Non-vaseular plants... 59s. eee if GRASSES. Fe a2 ATE Ot EE 3 Sweculem Gs ss iia nee eens 3 Simallsperenmals cures ese ees of VANETTH 10 C21 Sig Na Heh esp abat acter aa 3 The importance for us of a carefully elaborated and natural system of growth-forms such as that of Drude lies not so much in its details as in the criteria on which it is based. Some of the gross anatomical or physiognomic criteria are of profound and obvious physiological importance, such as the major distinction between terrestrial and aquatic plants, the distinction between perennials and annuals, and that between succulent and .non-succulent forms. Other criteria are of known physiological importance, such as the distinction between saprophytic, parasitic, and autonomous plants, or between the decidu- ous and perennial habits of leaves. When, however, we approach such distinctions as those between broad and narrow leaves, between pov- erty and richness of branching, and between the possession of rhi- zomes and that of bulbs, we are on extremely controversial ground. There is much evidence to indicate that the form and size of leaves has been overestimated as a criterion of importance in the ecological classification of plants. Palecbotanical evidence shows that many unusual forms of leaf, such as those of Liquidambar, Platanus, and Artocarpus, have persisted through long periods of time. The fact that these trees have undergone extensive migrations and recessions, undoubtedly encountering substantial changes of environment, affords some basis for a belief that leaf-form is often as conservative as the structure of the floral organs'. The importance of mere leaf-size in relation to water-loss has also been overestimated, as it has been shown that the transpiring power of a leaf bears no invariable relation to its size. This explains the existence, side by side in the deserts of southern Arizona, of such plants as Franseria ambrosioides, with leaves from 25 to 40 sq. cm. in area, and such plants as Hymenoclea monogyra and Baccharis emoryi, with leaves from 1 to 2 sq. em. in area; or the con- comitant occurrence, in relatively dry habitats in the mountains of Jamaica, of Bocconia frutescens, with leaves often 200 sq. cm. in area, and Micromeria obovata, with leaves less than 0.25 cm. in area. 1For a discussion of this topic from the paleobotanical standpoint, see: Berry, Edward W., The Lower Eocene Floras of Southeastern North America, U. 8. Geol. Surv., Professional Paper 91, 351 p., 1916 (p. 73). INTRODUCTION. 19 The nature of the growth-forms recognized by Drude has been examined with a view to determining what features of plant structure have been used by him as criteria for his subdivisions. The chief of these criteria are listed in table 1, together with the divisions based upon these criteria, and the environmental conditions to which these features seem, in the present state of our knowledge, to be most closely related. An examination of this table will show that Drude has used, in the main, criteria to which a definite physiological importance can be attached, or to which, in some cases, several lines of importance can be ascribed. The definitions which Drude has given some of his srowth-forms employ the words ‘‘dicotyledonous” and ‘‘monocoty]l- edonous.” It is difficult to decide whether these words indicate a recognition of phylogenetic divisions or whether they are used as a brief and convenient means of distinguishing types of stem, of leaf, and of branching, which may have a physiological as well as a phylogenetic significance. TasLEe 1.—Analysis of the criteria used by Drude in distinguishing growth-forms. Sad a yehee ; Environmental conditions to which it is Criterion and subdivisions based upon it. - related. Premiers, SHTUbS. 2 ae ee General favorableness of all conditions. Length of life: Perennial (or biennial); an- | General favorableness of all conditions. nual. Status: Autonomous; climbing; epiphytic; | Source of food materials. Ratio of material parasitic, saprophytic (?). expended in mechanical tissues to extent of leaf surface. Stem: Caulescent; acaulescent..............| Ratio of material expended in mechanical tissues to extent of leaf surface. Exposure to atmospheric factors. Habit of stem: Hrect; procumbent..........| Ratio of material expended in mechanical tissues to extent of leaf surface. Exposure to atmospheric factors. Type of stem: Woody; succulent; herbaceous | General favorableness of all conditions. Sea- sonal incidence of water-supply. Memewedhy teatless. oo. Lk ee General water-relations. Shape of leaf: Broad; needle-like............ General water-relations (phylogeny). Type of leaf: Deciduous; perennial.......... Seasonal distribution of rainfall. Branching: Absent (palms); poor (screw- | General water and temperature conditions pines); rich (polster plants). (phylogeny). Arrangement of foliage: Generalized; uni- | General water and light conditions. centric. Type of subterranean organs: Rhizome; | Incidence and duration of cold or dry seasons. woody root; bulb. We are here brought to face the difficult question as to whether the distinction between the dicotyledonous and monocotyledonous types of stem should be maintained in a classification of this kind. Is the distinction to be regarded as a purely phylogenetic one, or is there sufficient difference between the physiological efficiency of these very dissimilar organs of conduction and leaf display to warrant separating them? A similar question is raised as to the physiological importance of the parallel-veined and net-veined condition of leaves. Again, 20 THE VEGETATION OF THE UNITED STATES. should the unicentric foliage of a Yucca be distinguished from the similar leaf arrangement of Echeveria, in which the leaves are separated by internodes? Should the sessile foliage of Agave be regarded as per- forming its functions in precisely the same manner as the similar leaf- rosette of Aloe, which is raised well above the ground on a stout stem? It is only to future investigations that we can look for knowledge that will enable us to draw a line between the structural features that are of physiological or ecological importance and those that are due to what we might designate as evolutionary inertia. It is still impossible for us to distinguish between structures that are vestigial, in the sense that they no longer perform an office that they were able to perform in the early history of their race, and structures or structural features that arose fortuitously and never served a vital function, at the same time that they were not of such a nature as to be eliminated by selection. It does not require an examination of the physiological significance of the criteria used in any of the classifications of growth-forms to discover the fact that the water-relations of plants have done far more to influence their external form than have any other set of relations to environmental conditions. Anyone familiar with the cultivation of plants could predict with great certainty the relative water require- ments of Parosela spinosa, a hoary, small-leaved tree of the Colorado Desert, and such a tree as the red maple. It is not an invariable rule, however, that the water requirements are obvious, as witness the close similarity of Baccharis scoparia of the Jamaican mountains and Bac- charis emoryi of the Colorado Desert, or the general similarity of the grasses of dunes and swamps. The water requirements of a plant may, however, be much more commonly read from its outward form than may its temperature requirements. There is nothing, for example, in the appearance of Pinus divaricata and Pinus caribea to indicate that the former grows in the cold taiga of Canada and the latter in the West Indian Islands and Florida. Schimper recognized the importance of giving equal weight to the water and temperature requirements of plants in grouping them for ecological purposes. Heaccordingly divided each of the general classes of plants which are recognized on a basis of their water-relations— xerophytes, mesophytes, and hydrophytes—into three classes based on temperature requirements—microtherms, mesotherms, and mega- therms. In this manner nine categories were secured, in which it was possible to place plants only after securing some knowledge of their habitat requirements. | The only logical basis on which we can proceed to a classification of the vegetation of the world is one in which we take account of the nature of the vegetation itself, and give no weight whatever to any of the natural conditions or circumstances by which vegetation is affected. It is for this reason that importance attaches to the study of growth- INTRODUCTION. 21 forms. If we wish to understand vegetation we must understand the individual species of which it is composed. If we wish to understand the relation of each plant species to its environment we must under- stand the nature of its functions and the character and réle of each of the organs through which they are carried on. Whatever features of the gross anatomy of plants may be discovered to have no apparent importance in any aspect of their adjustment to environment will have no place in shaping our ultimate system of growth-forms. Progress toward such an ultimate system is beset by two dangers: that which would lead us to be satisfied with a system which is too simple, and that which would lead us to adopt a system in which anatomical features of questionable importance would be recognized along with those of demonstrated importance. Vegetational units have been grouped or classified by various workers according to the nature of the habitats in which they are found, according to their floristic make-up, and according to their successional relation to one another. A large body of work has been done by these methods, giving us a substantial part of our knowledge of the vegeta- tion of the globe. The only one of these methods which is purely vegetational is the last. If it were possible to demonstrate changes of vegetation in a state of nature which were not accompanied by changes of environmental conditions, it would indeed be necessary to sive strict attention to the stages of succession in making any attempt to correlate vegetation and conditions. If it were true that identical conditions might sometimes present different vegetations, our problem of correlation would be made still more complicated than it already is. It has been amply shown, however, that successional changes of vege- tation are both preceded by and accompanied by changes of environ- ment. The well-known work of Cowles has shown the importance of the changes of soil-moisture which accompany physiographic develop- ment, and the work of Fuller, of Gates, of Weaver, and of Cooper has shown the importance of other conditions of both soil and atmos- phere. In addition to the physiographically initiated changes in the environment are those initiated by the vegetation itself, supplying conditions favorable for invasion by a new group of species. Although a large amount of work has been done in describing successions and in relating successional stages to each other, it is only recently that the workers just cited have made a beginning in the investigation of the physical conditions which underlie the separate stages. As soon as we begin to study the relation of physical conditions to successional stages, the relation of these stages to each other sinks to a position of minor importance, and our work emerges upon the broad field of causational plant geography. The imperfections of our present knowledge of the physiology of plants and the consequent imperfections of our system of growth- 22 THE VEGETATION OF THE UNITED STATES. forms are carried on into our classification of vegetation. The fact that the water-relations of plants are more easily known from external criteria, and the fact that they have been more thoroughly investigated, have not only influenced our prevailing system of growth-forms, but have determined the nature of our vegetational units. The classification of growth-forms and the classification of vege- tation are like all other scientific efforts to reduce natural phenomena to a logical system, in that the classification possesses its chief value as & concise expression of the results of research. A classification of growth-forms which had been highly perfected by our present methods and knowledge would still be roughly made from the point of view of the ecologist and physiologist of tomorrow. It is perhaps idealistic, and is surely premature, to hope that we may one day have an eco- logical classification of the vegetable kingdom on a physiological basis. Such a classification will merely be the perfecting of the begin- ning which has been made by Drude and his predecessors. It will not be possible without a great deal of physiological work that is not yet so much as planned, and it will not be of more than academic interest unless it is constructed from a broad ecological point of view. V. PLANT COMMUNITIES. The study of vegetation is essentially a study of plants which are growing together in a state of nature, it is an investigation of all the phenomena which these plants exhibit as an aggregation, as dis- tinguished from the behavior of any one of them when considered alone. The natural assemblages of plants which characterize given areas have been assiduously studied by a very large number of workers in all portions of the world. The contrast between the small aggre- gations of local character, the larger ones of more general occurrence, and the still larger ones of very wide distribution has given rise to the recognition of various ranks of aggregation or association and to the study of the relationship existing between aggregations of different rank. By common consent among plant geographers and ecologists, the term ‘‘community”’ has been adopted as a general designation for any assemblage of plants regardless of its rank in the formal schemes of classification. In our work with the vegetation of the United States we have had to do with the climatic conditions influencing certain of the plant communities, and we have been under the necessity of deciding upon the criteria to be used in differentiating the communities, as well as under the need of disregarding, for our immediate purpose, certain other communities which stand in definite relation to climatic con- ditions, as well as the communities which are affected by climate chiefly through the medium of the soil. We have, perhaps, been some- INTRODUCTION. Za what informal in our handling of this eminently formal subject, upon which so much has been written and so much has been enacted by botanical congresses. As already intimated, the study of vegetation has resulted in the recognition of different degrees of communal existence among plants. These degrees have been designated by names, among which may be found the words formation, region, zone, society, association, district, consocies, group, belt, strip, and a score of others. Scarcely any two workers have used the same term in precisely the same sense, and few of the workers have defined their terms in such a manner as to enable a botanist to recognize one of the communities in case he should find himself in its midst. There has been an organized effort in recent years to secure a general and international agreement regarding the classification and nomenclature of plant communities. The extensive areas such as the sagebrush plains of the Great Basin, the grasslands of Nebraska and Kansas, or the pine forests of the Atlantic Coastal Plain are designated as formations. The smaller and less markedly differentiated areas within a formation are designated as associations, as, for example, the forests of shortleaf pine in New Jersey, those of loblolly pine in Maryland and Virginia, and those of longleaf pine in the Gulf States, all lying within the Coastal Plain formation. The smallest units of vegetation are termed societies, and these are of small area and represent portions of the association in which a definite aggregation of species is to be found. This classification of communities is simple and natural and has much to commend it for general use in describing vegetation. It is to be noted that, just as the formation is defined in terms of growth- forms which are found to be most common and characteristic in that community, so the association is defined partly in terms of the growth- forms present and partly in terms of species, while the society is defined chiefly by the species which it contains. The most important criterion to be employed in the distinguishing of communities is always the kind or kinds of growth-forms which are present, and this is a criterion which can be used for societies as well as for formations. A community may present a single growth-form, represented by a single species or by a group of species, as is true of many saline marshes and of very many forest areas. It may present an intermingling of two or three growth-forms, as is true of those saline marshes that contain grasses, the succulent Salicornia and the large- leaved Statice. In certain localities there occur communities which are made up of a very large number of growth-forms, as, for example, in the Karroo Desert of South Africa and in the deserts of Tehuacan, Mexico. Communities may be of such a character as to contain only plants of a single order of size, as the short-grass prairies of Nebraska, or they 24 THE VEGETATION OF THE UNITED STATES. may contain individuals of a particular height, together with other smaller individuals, as is true of the fresh-water marshes of the tribu- taries of Chesapeake Bay. By far the most common condition is that in which several successive stages of height are found together, so that the vegetation is said to possess a stratification with respect to the foliage of the plants concerned. This is found in every forest and reaches a splendid climax in the tropical rain-forests. In the com- munities which possess several strata of plants, the highest one has been designated the “facies,” but its members will here be alluded to as the “‘major’”’ plants of the community and the several lower strata as the “minor’’ plants. A further salient feature of communities depends upon whether the plants cover the ground closely or stand in an open formation. We may discover open or closed communities among plants of every stature, from the smallest grasses to trees of a height of 50 or 60 feet. The greatest density of stand is reached by trees only under conditions which favor the attainment of a greater size than this. In open com- munities there may be plants of different heights, but in such cases the low plants are not dependent on the large plants for the conditions which render their existence possible. Even in open communities there may be a certain degree of stratification under the largest in- dividuals as is observable in southern Arizona, where many small annuals occur abundantly beneath the trees as well as away from them. Last among the criteria of the community is the number of species comprised init. Even if there is a uniformity of growth-form through- out the community, there is importance, from our standpoint, in know- ing whether this uniformity is caused by the existence of a single species or of many. It is customary to designate the species which is most common in a community as the ‘‘dominant”’ one and the other species as ‘“‘subordinate.’’ The salient features by which we distinguish types of vegetation are, then, to sum up: the growth-forms involved, the presence of one or many strata of plants, the open or closed condition, and the degree of simplicity or complexity of the specific content. These are all features which must be looked upon as products of the environmental conditions just as truly as are any of the structures or physiological reactions of the individual plants themselves. The presence of a single growth-form or of many, the existence of a low carpet of plants or of a lofty forest, the openness or density, and the dominance of a single species or the successful association of many, are all features which are determned by the environmental complex just as truly as is the rate of growth or that of photosynthesis for an individual plant or species. The only other criteria that have been used in defining communities are the physical nature of the habitat and the specific identity of the INTRODUCTION. BS plants concerned, each of which has been sufficiently discussed to indicate that they are counter to our purpose. In making a general study of the relation of climate to vegetation for as large an area as the United States, it has been necessary for us to disregard the small communities which are unlike the general vege- tation of the surrounding region, such as the local prairies of Arkansas and Mississippi and the bands of trees that border the rivers of the western plains. These require special treatment, in which soil condi- tions can be given a thorough investigation. It has also been neces- sary for us to leave out of reckoning all of the minor plants in the stratified communities, inasmuch as the conditions under which they live are unlike those for the major plants. The climatic conditions under which the major plants exist are modified by them in such a manner as frequently to give the minor plants a very different environ- mental complex. By means of these omissions we have done a great deal to simplify our problem from the standpoint of the demarcation of vegetational areas. It has been desirable, furthermore, to consider only the most general features of the vegetation, because we have only very general data as to the distribution of the climatic factors. The subsidiary communities of every region are so largely controlled through the soil conditions that it would have carried us beyond our investigation of climatic controls to have entered upon a consideration of them. The statement that the occurrence and geographical range of all plant communities is controlled by the physical, and rarely the chemi- cal, characteristics of the environment is almost axiomatic. The operation of these controls has been observed from time immemorial by men of no technical training but of keen powers of observation, and the knowledge of them has become more exact among the practical pioneers in the agriculture and forestry of many lands where the natural vegetation has been used as an index of the cultural capabili- ties of given situations. Any skepticism regarding the physical con- trol of communities would be dissipated by an extended course of travel in diversified regions, or equally well by a careful reading of Schimper’s Plant Geography, to say nothing of an examination of the many scattered papers which give proofs in regard to particular instances of such control. We can, in brief, put it down as a law of plant geography that the existence, limits, and movements of plant communities are controlled by physical conditions. The conditions that control the movements of the community are those of the soil; the conditions that control the broader geographicallimits are almost solely those of the climate. The existence of the community and the extent of the area occupied are, of course, controlled by conditions of both soil and climate. 26 THE VEGETATION OF THE UNITED STATES. VI. DELIMITATION OF VEGETATIONAL AREAS. The botanical areas that have formed a basis for the correlations discussed in the following pages have been outlined in such manner as to show either the distribution of particular types of vegetation or else the ranges of individual species or groups of species. The deter- — mining of the distributional area of a given species is a relatively simple matter, depending for its accuracy only on the exploration that has been carried out and the records of occurrence that are available. The delimitation of vegetational areas, however, demands a careful scrutiny of criteria and methods such as we have attempted to give above. We have endeavored primarily to classify and map the vege- tation of the United States upon a basis which is purely vegetational, without regard to floristics, climate, topography, or other features, however closely these may seem to be associated with the vegetation. The effort to observe this requirement, for the sake of the logical soundness of our work, is nevertheless far from removing all of the difficulties which beset an attempt to classify and map the vegetation of a large area. It is difficult for the worker to avoid a subjective treatment of his material and to escape the bias which his own particu- lar experiences or field of observation may have given him. A more tangible set of difficulties arises in deciding where to draw the lines of demarcation in subdividing a set of intergrading vegetations, and where, on the map, to place the lines of separation between vegeta- tions that merge into each other over areas of great extent. This difficulty has been met by drawing lines on the chart through all transitional regions, these lines being so drawn as to be regarded as connecting the points that exhibit the same stage in transition, after the manner of isotherms and other isoclimatic lines. After a series of vegetational areas has been distinguished’ and delimited, and each has possibly been subdivided, we must refrain from regarding these divisions or subdivisions as of coordinate value, for there is no means of putting the degree of their relationship to a test. The subdivisions of the forest areas and those of the desert areas appear, on the printed page, to be of the same rank in classification, but we have no actual knowledge upon which we can base such a supposition. We have already seen that the features of outward oni which are considered in distinguishing growth-forms have to do, to a predominant extent, with the water-relations of plants. When we examine into the other features which we use in distinguishing vegeta- tions, such as the height of the dominant plants, the density of stand, and the simplicity or complexity of the stand, we are impressed with the fact that these features stand also in dependence upon water- relations. INTRODUCTION. yA These considerations force us to realize that the most commonly used and most natural subdivisions of vegetation are based upon cri- teria which have to do with the relations of the communities to water- supply and water-loss. It is quite true that the water-relations of plants have more to do with the control of the local and general dis- tribution of vegetation than have any other conditions. This is not true of the local and general distribution of the species themselves, for we here find temperature relations playing a strong réle. For the pur- poses of our investigation into the correlations existing between vege- tation and climate it is therefore significant that we are under the necessity of using a classification of vegetation which rests so largely upon a basis of the water-relations of plants. We might foresee from this fact that strong correlations would be discovered between vegeta- tion and water conditions and weak correlations between vegetation and temperature conditions. In spite of the efforts of Schimper and of others to give the tempera- ture-relations of plants a place in vegetational distinctions, by the recognition of microtherms, mesotherms, and megatherms, we are as yet unable to place a given species in its proper thermal category with- out possessing facts which are still lacking for all but a very few plants. We can not tell a megathermous plant from a microthermous plant when we see them growing side by side, and it follows that we can not go into the field in Georgia or Texas and pick out the plants in each habitat which have great or small temperature requirements, as we can rather satisfactorily distinguish those of great or small water requirement. ‘These categories are consequently of no present use in delimiting vegetational areas. The system of life-zones which was worked out by Merriam! for the United States, and has been elaborated by members of the United States Biological Survey, constitutes an effort to delimit biological areas primarily with respect to the influence of temperature. With such a classification of biological areas in hand it is not possible, how- ever, to make an impartial effort to determine which of several climatic factors is primarily concerned in conditioning the existence and limits of the areas. This attempt would indicate a very close correlation of biological areas and certain temperature conditions, because the climatic maps showing these temperature conditions were used as a basis in the original form of the life-zone map. If we were to make a map of the mean rainfall of the growing-season in the United States it would be found to possess certain isohyetal lines which corresponded closely with the distribution of certain plants or vegetations. If we were, then, to modify the rainfall map in slight ‘Merriam, C. Hart. Laws of temperature control of the geographic distribution of Sarentaial animals and plants, Nat. Geog. Mag., 6:229-238, 3 maps, 1894.—Life zones and crop zones of the United States. U.S. Dept. Agric., Biol. Surv. Bull. 10, 1898. 28 THE VEGETATION OF THE UNITED STATES. particulars so as to make it conform more closely to the distribution of vegetation, using vegetation rather than additional rainfall data as a basis, we would secure a map of great interest and value as a delinea- tion of the vegetation of the United States. This map would be of no value for a correlational study, however, since it would be in inherent and foreseeable agreement with the map of mean rainfall of the growing - season, which is very similar to all other maps of moisture conditions. The drawing of this map would resemble in all particulars the con- struction of the life-zone map of the United States, both with respect to the manner in which it was made and with regard to its unsuita- bility for our purposes. It may also be emphasized in this connection that, although the temperature conditions and the moisture conditions of climate are con- sidered as distinct in analytical studies, yet they are not truly inde- pendent of each other. Since evaporation and precipitation are so largely influenced by temperature, neither the chart of rainfall nor that of temperature is wholly without indications of the influence of one condition upon the other. It frequently happens, for example, that a region of low temperature is one of high soil-moisture content, low evaporation, etc. These considerations will receive more attention in Part IT. ° DISTRIBUTION OF VEGETATION IN THE UNITED STATES. I. METHODS USED IN SECURING AND PRESENTING THE DISTRIBUTIONAL DATA. The botanical data on which we have based the correlations that are to be discussed in the succeeding pages are presented in carto- graphic form in plates 1 to 33. A detailed map of the vegetation of the United States (plate 1) has been executed as a basis for our cor- relations of climate with the vegetational areas of the country as a whole.! The features of the map will be discussed in a succeeding sec- tion, together with a general account of the vegetation of the 18 sub- divisions which it recognizes. This map is of very uneven merit for the different parts of the United States, owing to the fact that there is an abundance of literature for certain portions of the country, while there are very few descriptive treatments or maps of the vegetation for other portions. As it stands, however, this map is somewhat too detailed for use in correlation with the climatological data that we have been able to secure. For this reason we have deemed it desirable to make a generalized map based upon the detailed one (plate 2). The latter contains 18 vegetational areas, whereas in the former the number has been reduced to 9 by a combination of the areas which are most similar in character. Even after this is done there are some of the vegetational areas of the United States for which we have only a very small number of climatological stations. In order to investigate the correlations between climatic conditions and the distribution of certain common growth-forms, a series of 7 maps has been drawn, showing the cumulative occurrence of these forms (plates 3 to 9). The maps have been prepared by the method used by Transeau in his investigation of the forest-centers of the eastern United States.” It consists merely in indicating on a single map the distributional limits of all of the plants involved. The area in which all of them are found together represents the region of maximum development of the particular group which has been selected. In some cases these maps have been drawn for all of the species of a particular growth-form, whereas in other cases they have been drawn for a repre- sentative group of the most common species of a particular growth- form. These maps are of value, not only in showing the center of development of a particular form or group of species and in showing the extreme limits of the form, but also in showing the manner in which the abundance of the given form shades off in different direc- tions from the center. I ea the UY beat ‘oa tihesateE ‘Shreve, Forrest, A map of the vegetation of the United States, Geographical Rev. 3: 119 125. Wath map. 1917. This map is reproduced here as our plate 1. *Transeau, E. N., Forest Centers of Eastern America, Am. Nat., 39: 875-889. 1905. OQ 30 THE VEGETATION OF THE UNITED STATES. Three maps have also been prepared showing the ecological dis- tribution of individual species of plants (plates 8, 9, 10). On these maps an effort is made to show the features of distribution in such a way as to indicate the regions of greatest abundance and greatest catholicity of habitat, the regions of frequent occurrence, the regions of rare occurrence, and the extreme geographical limits of the species. Maps of this character afford a picture of the distribution of a single species which is similar to the picture afforded by the maps of cumu- lative distribution of groups of related growth-forms. As a basis for the correlation of climatic conditions with the ranges of individual species, 70 plants were selected, the distributional areas of which are shown by groups on plates 13 to 33. Some of the species selected for this purpose were chosen because they are common and dominant elements in important vegetations of wide extent. Others were selected because their geographical ranges seem to be typical of those exhibited by a large number of species. Certain other species were selected because of the interest which attaches, from our point of view, to the character and particular direction of their distribution. Several of these plants extend across the continent from the Atlantic to the Pacific, either in the northern or in the southern part of the United States, in such a manner that they cross the principal boun- daries between vegetational areas. Distributions of this character seem to indicate that the plants in question are probably controlled by temperature conditions rather than moisture conditions. Several plants of this character and of more limited range were selected, be- cause they are commonly found in swamps or marshes and may there- fore be thought of as growing through a wide range of atmospheric conditions, at the same time that they are subjected to a relatively uniform set of soil-moisture conditions. It is to be anticipated that plants of this character differ markedly in their distribution from those whose range is greatly influenced by soil-water conditions. The construction of the vegetational maps has involved the examina- tion of a large body of ecological, floristic, and geographical literature. It was originally our plan to publish a complete list of the sources that were used in the compilation of these maps, but the appearance of Harshberger’s Phytogeographic Survey of North America has since made it superfluous to do so, inasmuch as this author has given a very thorough bibliography of the literature of American vegetation, in- cluding nearly all of the publications that we have used.’ In the construction of the maps of vegetation we have been heavily indebted to the maps published by the United States Forest Service, to the maps of grazing-lands published by the United States Bureau of Plant Industry, and to the detailed maps which have been published l1Harshberger, J. W., Phytogeographic survey of North America, Die Vegetation der Erde, 13: 863 p., 32 figs., 18 pls., 1 map, Leipzig, 1911. DISTRIBUTION OF VEGETATION IN UNITED STATES. 31 for several States. We have not only drawn upon ecological literature and the publications of the United States Geological Survey, but have been greatly aided by consultation of the photographic illustrations in numerous works of a non-botanical character, and we are particularly indebted to many of our colleagues, who have generously given us the information at their disposal. In the preparation of the maps showing the cumulative distribution of growth-forms and the distribution of individual species we have used all of the manuals, floras, and local lists that it was possible to secure. We have not consulted the specimens that are to be found in any of the large herbaria, but have depended solely upon published statements of occurrence. We have done this because it is so frequently possible to secure, in ecological literature or in the publications of the United States Biological Survey, statements regarding the ranges of plants which would in all probability be represented in the herbaria by only a few collections, on the labels of which the information regarding the ecological occurrence would be extremely meager. Some of the ranges of individual species are naturally outlined much more accurately than others. The distribution of trees is in general much better known that that of herbaceous plants, and the distribu- tion of grasses is better known than that of plants whose economic importance is not so great. Some of the ranges exhibited in our maps have been based on extremely few stations, as is true particularly of such plants as Flerkea occidentalis and Trautvetteria grandis. It may be taken for granted that all of our distributional areas which are represented by smooth and wide-sweeping lines are in general based upon less precise information than are the areas limited by very sinu- ous lines. The limitations of our method of mapping have required that the range of numerous mountain plants occurring in the Western States be exhibited by passing a bounding-line around the entire region in which they are found locally at their appropriate elevations. In similar manner several of the aquatic and palustrine plants have been plotted as if growing continuously throughout extensive stretches of country in which they are really of very local occurrence. This is notably true for Sium cicutefolium and for Cephalanthus occidentalis, which is not actually known in New Mexico and is very uncommon in Arizona, although it reappears in great abundance in interior Cali- fornia. The scale of our maps has made it necessary to include in the ranges of very many of our plants certain extreme coastal locations in which they are actually absent. This matter is mentioned only because several important climatological stations are located on the coast in areas which differ very markedly from the adjacent mainland in the character of their vegetation. This is true of Key West, Cape Hatteras, and Point Flattery. Further details regarding the vege- tational maps will be given in the succeeding pages. 32 THE VEGETATION OF THE UNITED STATES. Il. LEADING VEGETATION TYPES OF THE UNITED STATES AND THEIR GEOGRAPHICAL AREAS. In subdividing the vegetation of the United States we have used primarily the old distinction of desert, grassland, and forest. The distinguishing of these formations involves practically all of the criteria that have been discussed in previous pages. Our ultimate units have resulted from a subdivision of the desert and the forest, but we have not attempted to subdivide the grassland, partly because of lack of descriptive literature for all parts of the grassland region, and partly because of the extreme complexity exhibited by this region, particu- larly in its central portion. The desert areas have fallen into two groups which may be designated as Continental Desert and Coastal Desert. The latter include the semidesert regions of coastal California and of extreme southern Texas, each of them regions in which truly desert areas are found together with areas which scarcely merit this designation. The Continental Desert falls naturally into two regions, one of which is dominated by sclerophyllous shrubs and the other by a mixture of such shrubs and succulent or semisucculent plants. The sclerophyllous desert has been subdivided into the Great Basin Desert and the California Desert, while the succulent desert has been subdivided into the Arizona and Texas areas. The two bodies of sclerophyllous desert are adjacent and merge into each other, whereas the succulent deserts are separated by regions of dissimilar character. The Grassland area is bordered on the southwest by the Desert- Grassland Transition and on the east by the Grassland-Deciduous Forest Transition. The forested portion of the United States has been subdivided into the Deciduous Forest and 4 areas of Evergreen Needle-Leaved Forest. Two of these evergreen-forest areas are mesophytic in character, one of them xerophytic, and one of them hygrophytic. We have included in the Northern Mesophytic Evergreen Forest all of the needle-leaved forests of the northeastern States as well as of the Rocky Mountain and Pacific regions, with the exception of the extreme Northwest. Although this large forest region exhibits marked differences in its floristic make-up and in minor features of its physiognomy and ecological characteristics, there are nevertheless more reasons for maintaining it as a single area than for separating it into minor sub- divisions, so far as the purposes of our work are concerned. The Southeastern Mesophytic Evergreen Forest, the Western Xerophytic Forest, and the Northwestern Hygrophytic Evergreen Forest are all regions of distinctive character which are neither similar to the Northern Mesophytic Evergreen Forest nor to each other. Two transitional areas have also been outlined, connecting the Deciduous Forest with the Evergreen Forests to the north and to the south of it. DISTRIBUTION OF VEGETATION IN UNITED STATES. 33 We have also recognized as alpine summits all of the areas lying above timber-line, and as Swamps and Marshes the areas with saturated soil in the Atlantic Coastal Plain. In selecting names for the vegetational areas thus distinguished we have felt it desirable to use designations which have to do with the ecological character of the plants found in these areas. We have avoided the use of such words as coniferous, which alludes to a mor- phological feature, and have also avoided using any designations which would imply that the vegetation of a particular area is controlled by a particular physical condition, as, for example, the use of such terms as ‘“‘monsoon forest”’ or ‘‘pinelands of the odlitic limestone.’’ We are well aware that the names that we have used are neither brief nor convenient, but they have been selected with the cautions that have been mentioned, for purposes of ecological consistency. An effort has been made to draw all of the vegetational boundaries on the map shown as plate 1 with relation to the original plant covering. This primeval condition has been so greatly disturbed over large portions of the country, particularly in the Northeast, that it is now very difficult to be certain as to the limits between the virgin forest formations. Our map is therefore undoubtedly much less accurate for the northeastern portion of the United States than it is for the Western States, in which the vegetational differences are more marked, the country is less disturbed by human activities, and the published ecological descriptions of vegetation are much fuller and more accurate. The following paragraphs serve to give a brief characterization of each of the vegetational areas found in our detailed map, plate 1: California Microphyll Desert—The southernmost part of Nevada and the interior portion of California form an area in which the vege- tation is closely related to that of the Great Basin by reason of the fact that the dominant plants in each are microphyllous shrubs. In the California Desert the creosote-bush (Covillea tridentata) and the sand- bur (Franseria dumosa) are the most common plants and the dominant ones over extensive areas. A large number of deciduous shrubs are found, large semisucculents occur throughout the more elevated por- tions of the desert (Yucca brevifolia, Y. arborescens), and stem-suc- culents (Opuntia spp.) are found in small numbers. In both the Great Basin and the California deserts the plants which perennate by under- ground parts are very rare and grasses are uncommon, while short- lived annuals are abundant in the spring months. Great Basin Microphyll Desert—This desert occupies the floor and low mountains of the Great Basin from southern Washington to southern Nevada and eastward to Colorado, lying at elevations of 1,000 to 5,000 feet. Throughout practically the whole of this area the vegetation is dominated by a single species, the sagebrush (Arte- misia tridentata), a small-leaved evergreen shrub which sometimes 34 THE VEGETATION OF THE UNITED STATES. occurs in very open stand with a height of a few inches or at other times grows so thickly as nearly to cover the ground, reaching a height of 4 feet or more. ‘Together with the sagebrush are to be found several other microphyllous shrubs of similar size and distribution (Sarco- batus vermiculatus, Grayia spinosa, Coleogyne ramosissima, Kunzia tridentata, Tetradymia glabrata, etc.). The Great Basin desert is dis- tinctively a region of microphyllous shrubs, in which succulent plants are rare and confined to the highest mountain-slopes. The simplicity of the vegetation and the uniformity in the character of the several shrubs which play a secondary réle in it are features very unlike the other desert areas about to be described. Texas Succulent Desert.—The central valley of the Rio Grande and the valley of the Pecos River form a desert area in which extensive tracts are dominated by evergreen shrubs in open stand, while other areas are chiefly occupied by deciduous shrubbery (Acacia, Flourensia, Brayodendron). Large areas are covered by the low leaf-succulent lechuguilla (Agave lechuguilla), but not to the exclusion of the shrub- bery. Other areas are dominated more conspicuously by the sotol (Dasylirion texanum), a plant with perennial foliage and with a store of water and reserve materials in its stout stem. Succulents are abundantly represented in this desert, but chiefly by small species which do not play an important part in the physiognomy of the vege- tation. Perennial bunch-grasses are common in certain portions of the Texas Desert, and the number of plants perennial by underground succulent or semisucculent parts is larger than in the Arizona Desert. This is distinctively a region of leaf-succulents and semisucculents as contrasted with the Arizona region of stem-succulents. Arizona Succulent Desert—This area comprises the southern por- tion of Arizona drained by the Bill Williams and Gila Rivers and lying below 4,000 feet. In this desert the vegetation is largely made up of microphyllous shrubs, but there is everywhere a rich commingling of other types of non-succulent plants and of several types of succu- lents. The vegetation is open and low, but of irregular height. The sclerophyllous shrubs comprise the evergreen creosote-bush (Covillea tridentata), deciduous acacias (Acacia paucispina, A. constricta), and bitter bush (Flourensia cernua), the drought-deciduous ocotillo (fou- quieria splendens), several small-leaved or leafless trees and shrubs with green bark and stems (Parkinsonia, Canotia, Holacantha, Keberlinia, Ephedra), as well as the columnar giant cactus (Carnegiea gigantea) and numerous species of flat-jointed and round-jointed cacti (Opuntia). This desert is by no means poor in perennial grasses, and the seasonal rains are followed by the appearance of carpets of annual grasses and other herbaceous plants. The leafy succulents are rare in this desert, except at its upper edges around the higher mountains, and the plants with subterranean water-storing organs are very infrequent. DISTRIBUTION OF VEGETATION IN UNITED STATES. 39 Texas Semidesert (Mesquital-Grassland Complex).—The valley of the Rio Grande below the Balcones Escarpment and the River Neuces presents a region in which the deciduous compound-leaved leguminous shrubs and trees form the dominant vegetation, interspersed with areas of more or less open grassland. The shrubs and trees form a more or less closed scrub from 3 to 6 feet high where the shrubs pre- dominate and a more open one from 15 to 25 feet high where the trees are most abundant. The commonest of the trees is the mesquite (Prosopis glandulosa), which has spread somewhat over adjacent areas since the advent of the white man. With it the evergreen broad- leaved live-oak (Quercus virginiana) is a minor component of the vege- tation. In the scrub the dominant species are huisache (Acacia farnesiana), guajillo (Acacia berlandierei), and other microphyllous forms (Momesia, Parkinsonia, Condalia, Sesban, etc.), while the succu- lents are confined to the frequent occurrence of a prickly-pear cactus (Opuntia lindheimert) and a yucca (Yucca treculeana). Ephemeral herbaceous plants are also present here. Pacific Semidesert (Chaparral-Encinal-Desert Complex).—The Pacific semidesert region is best designated thus in spite of the fact that it comprises many small areas which are far from being desert. There is no other portion of the United States in which such profound differ- ences of vegetation exist within such small areas, and in which it would be more difficult to map on a small scale the complex allocation of these areas. Over the low hills and around the bases of the Coast Ranges is to be found chaparral, varying from place to place in height and density; in the valleys and on the north faces of some of the hills are to be found groves of evergreen or deciduous oaks; while in other valleys, particularly the broad valleys of the Sacramento and San Joaquin Rivers, and on the interior hills of the Coast Ranges, are to be found some of the most truly desert areas in the United States. The chaparral is sometimes a very low aggregation of shrubs, or some- times reaches a height of 6 or 7 feet. It is also variable in its density, but is commonly so close-set that it can be traversed only very slowly. It is made up predominantly of evergreen shrubs (Ademostoma, Arctostaphylos, Heteromeles), but partly of deciduous shrubs (Ceano- thus spp.). The encinal is made up of evergreen oaks (Quercus agri- folia) and deciduous oaks (Q. lobata, Q. wislizeni), with the digger pine (Pinus sabiniana) an occasional component of it. In the desert of the interior hills and the great valley is to be witnessed a region almost totally devoid of perennial plants, in which the only cover of vegetation is due to the herbaceous annuals that appear in the spring. Desert-Grassland Transition.—This transition region comprises the Llano Estacado of Texas and certain plateau lands in Arizona and New Mexico above 5,000 feet in elevation. It is a region that is inter- mediate in all important respects between the Grasslands to the east 36 THE VEGETATION OF THE UNITED STATES. and the Desert regions to the west. It is essentially a very open stand of perennial grasses, together with the herbaceous annuals or peren- nials of the Desert and an extremely scattered stand of succulent or semisucculent plants. In the Llano Estacado and in southern New Mexico and Arizona the latter group comprises sotol (Dasylirion) and bear-grass (Nolina), while farther north in Texas and New Mexico the commonest succulent or semisucculent forms are a yucca (Yucca glauca) and a round-jointed cactus (Opuntia arborescens). In northern Arizona and northwestern New Mexico there are low, shrubby sages (Artemisia), Mormon tea (Ephedra), and other scattered bushes, and small cacti (Opuntia hystricina, O. whipplei). Throughout the Transi- tion region the grasses are omnipresent, sometimes forming nearly as dense a carpet as they do in the Grassland itself. There is a con- siderable variety in the grass flora, but the commonest forms are species of Bouteloua, Hilaria, Bulbilis, and Aristida. Grassland.—The Grassland region extends from central Texas to the Canadian boundary, merging on the east into the transition region which separates it from the Deciduous Forest, and on the west either merging into the Desert-Grassland Transition or else terminating at the eastern base of the Rocky Mountains. Smaller detached areas of Grassland also surround the northernmost salients of the desert. Throughout the Grassland region the vegetation is dominated by a more or less continuous cover of perennial grasses—in some localities by a dense sod, in others by an open sod, and in still others by an open stand of bunch-grasses. The types of grasses which form the grassland are varied, both in the region as a whole and in any small portion of it. A score of grass species form the great bulk of the vegetation, several of them being of very widespread occurrence throughout the region, as Bouteloua oligostachya, Bulbilis dactyloides, Keleria cristata, and species of Andropogon, while others are confined to different portions of the area or to particular soils, as the species of Hilaria in Texas, the species of Sporobolus and Stipa in Kansas and Nebraska, and the species of Agropyron in the northwestern part of the area. In addition to the score of commonest species, there are a hundred or more that are either frequent over large areas or common over smaller portions of the area. From a floristic standpoint the Grassland presents two grada- tions, one encountered in going from the eastern edge toward the Rocky Mountains, the other encountered in going from south to north through its entire length of over 1,200 miles. From a vegetational standpoint, however, this is allaregion of great uniformity. Its prin- cipal variations are in the relative density or openness of the grassy cover, in the character of the areas in which grasses are sparse or absent, and in the frequence of plants other than grasses. It may be said, in general, that the carpet of grasses is most evenly closed along the eastern edge of the area and in the central portion. In central Texas DISTRIBUTION OF VEGETATION IN UNITED STATES. 37 and in the extreme north much of the Grassland is relatively open, particularly in the sandhills of Nebraska, where Andropogon scoparius is predominant, and in the portions of the region lying in Washington and Oregon, where Agropyron spicatum and Poa sandbergii are pre- dominant. In the highly eroded “‘bad lands,” such as occur in southern South Dakota, low, shrubby perennials are predominant, as the rabbit- brush (Chrysothamnus graveolens), the white “‘sage’’ (Eurotia lanata), and greasewood (Sarcobatus vermiculatus). Throughout the portion of the Grassland which lies nearest the Rocky Mountains there is a complicated patchwork of vegetation, in which closed grassland, open grassland, and open stands of low bushes, with or without grasses, are found to alternate in habitats of different character. The shrubby perennials found in such areas are chiefly those which have just been mentioned, together with species of true sage (Artemisia tridentata, A. frigida). The Grassland is locally invaded by plants of the types which are dominant in all of the surrounding regions. In the south- western portion of the area arborescent round-jointed cacti (Opuntia arborescens) are sporadic, and also yucca (Yucca glauca), which is likewise common in the sandhills of Nebraska. Throughout the area a low prickly pear (Opuntia missourtensis) is abundant on coarse soil, particularly in the Bad Lands. ; In the vicinity of the mountains the Grassland is invaded by shrubs (Cercocarpus, Quercus, Symphoricarpus), and in some localities even by coniferous trees (Pinus ponderosa), while the bottomlands of the rivers are the westernmost localities for many eastern broad-leaved deciduous trees. In every portion of the Grassland there are to be found very many types of low annual or root-perennial plants other than grasses. Among these certain composites are perhaps the most abundant, as Grindelia squarrosa and Chrysopsis villosa, although there are many plants of other types. The seasonal habits of the grasses and of these associated non-gramineous plants are such as to give rise to one of the most striking characteristics of the Grassland, namely, its different aspect in different portions of the growing-season, and the difference in the conspicuously predominant plants in different months. Grassland-Deciduous Forest Transition —This is the broadest and most extensive of the transition areas, but is so purely transitional in its character that it does not merit recognition on any other basis. Its eastern limit has been fixed along the line at which the Deciduous Forest ceases to be an unbroken formation and begins to exhibit the islands of grassland locally known as ‘‘oak openings.’”’ The western limit has been placed where timber ceases to occur on the upland. The transition area is seen, therefore, to increase in the amount of timber found on going east and to increase in the extent of grassland exhibited on going west. 38 THE VEGETATION OF THE UNITED STATES. In the northern part of the Transition belt the commonest trees are black oak (Quercus velutina) and bur oak (Q. macrocarpa); in the southern part the commonest are post oak (Quercus minor) and blackjack (Q. marilandica). The grasses originally most abundant in the central part of the belt were Andropogon furcatus, Sorghastrum nutans, Andropogon virginicus, and Sporobolus cryptandrus. Deciduous Forest—The Deciduous Forest formerly occupied the lower elevations of the Northeastern States, the summits and slopes of the southern Allegheny Mountains, the Piedmont region, and the valleys of the Ohio, Cumberland, and Tennessee Rivers, with exten- sions into southern Texas and into northern Michigan and the Dakotas, and an attenuated edge that merges into the transition area toward the west. There is no one of the vegetational areas of the United States that has been more completely and profoundly altered by man than has this one. In fact, it is difficult at the present time to secure reliable information as to the exact original extent of this type of forest in the Northeastern States. The virgin stands of deciduous forest were made up solely of deciduous broad-leaved trees over extensive areas, and these forests were both dense and of a stature as great as 100 feet, or even more. At the western edge of the Deciduous Forest its con- tinuity becomes interrupted by open areas, while in the Texan exten- sion of it the stand of trees is even, but very open. In all of the moun- tainous or hilly portions of the area the needle-leaved evergreens frequently become components of the Deciduous Forest, and on steep bluffs, rocky slopes, and limestone ledges the needle-leaved trees are sometimes predominant. The floor of the Deciduous Forest is some- times thickly covered with shrubbery and young trees, or is often open and more conspicuously occupied by herbaceous perennials, among which the chief vegetative activity takes place in the spring, before the complete unfolding of the foliage of the trees. The number of tree species participating prominently in the make-up of the Deciduous Forest is large, and very many of the commonest ones are found almost throughout the area, as the white oak (Quercus alba), black oak (Quercus velutina), pignut hickory (Hicoria glabra), beech (Fagus ferruginea), and tulip-tree (Liriodendron tulipifera). The Appalachian region is the place in which the Deciduous Forest reaches its finest development, both in respect of density and stature of the stand and with regard to the number of tree species participat- ing in its composition. The most common trees of that region are the widespread ones which have just been mentioned, and also chestnut (Castanea dentata), chestnut oak (Quercus prinus), scarlet oak (Quercus coccinea), shagbark hickory (Hicoria ovata), Spanish oak (Quercus digitata), sugar maple (Acer saccharum), and red maple (Acer rubrum). On passing northward from the center of the Deciduous Forest, the number of tree species becomes smaller, as many are left behind and DISTRIBUTION OF VEGETATION IN UNITED STATES. 39 few new ones are met, as birch (Betula lutea) and popular (Populus balsamifera). On passing southward, the commonest forms of the Alleghenian region are found to be confined to the mountainous dis tricts, while their place is taken on the Piedmont and in the Mississippi Valley by a still larger group of species, many of which are found not only on the upland, but in the half-swampy areas of the level regions. Prominent among these trees are Spanish oak (Quercus digitata), water oak (Quercus nigra), willow oak (Quercus phellos), black gum (Nyssa sylvatica), red gum (Liquidambar styraciflua), and blue-jack oak (Quercus brevifolia). The most southwesterly portion of the Deciduous Forest in central Texas is made up almost solely of post oak (Quercus minory and black- jack oak (Quercus marilandica), while the most northwesterly islands of deciduous forest in the Dakotas are made up chiefly of bur oak (Quercus macrocarpa). Southeastern Evergreen-Deciduous Transition Forest.—This transi- tion lies between the coastal Evergreen Forest and the interior Deciduous Forest, occupying hilly and broken land, except at the extreme western end. Throughout this area there are small bodies of pure evergreen needle-leaved forest and other bodies of pure deciduous forest, but the vegetation consists in the main of an admixture of the two types of trees in such percentages that neither dominates strongly over the other. As in all other transition regions, the local conditions of soil and topography often determine the precise composition of the forest. East of the Mississippi the Evergreen-Deciduous Transition is formed chiefly of the loblolly pine and the species of deciduous oaks that will be mentioned in connection with the inner portion of the Southeastern Evergreen Forest. West of the Mississippi the loblolly pine occurs near the Gulf coast and is chiefly replaced by the shortleaf pine (Pinus echinata) above the Neches River, while the same species of deciduous oaks accompany each of the pines. Southeastern Mesophytic Evergreen Forest—This region stretches from Long Island to Louisiana along the Coastal Plain, with an exten- sion into peninsular Florida, and with outlying areas in central Ala- bama and in Arkansas, Louisiana, and Texas. This area is dominated by evergreens, and a secondary réle in the vegetation is played by deciduous broad-leaved trees and by evergreen broad-leaved trees. The forest stands of this region are nowhere dense in the same sense as are some of the evergreen stands of Montana or Maine; indeed, many of the pine stands in all parts of the area, and particularly in Florida, are rather open. Some of the heaviest stands are found in Louisiana and Texas and the lightest are those of Florida and New Jersey. As a rule the pinelands which lie nearest the coast, particu- larly in the Gulf States, are the purest, while those of Maryland and the Carolinas, as well as the interior areas of Alabama and Arkansas, 40 THE VEGETATION OF THE UNITED STATES. are much richer in deciduous broad-leaved associates. In the pine forests of New Jersey the floor is*extremely shrubby, and this is often the case as far south as South Carolina. In southern Georgia and the Gulf region the floor is much more open. In both of these cases it is difficult to decide how much the normal conditions may have been disturbed by fire and by clearing. Under present conditions, at least, the Gulf pinelands present a very clean floor, closely carpeted by grasses, palmetto, pitcher-plants, and a multitude of other herbaceous species. Along the branches and other depressions there is a dense stand of shrubbery and a slightly different type of forest. The half dozen species of pine which dominate the different sections of the Southeastern Mesophytic Evergreen Forest are very similar in their appearance, and there is consequently a general resemblance between the pinelands of the entire Coastal Plain. In Long Island and New Jersey the scrub pine (Pinus rigida) is the dominant species, and is scarcely found elsewhere in this forest. In Maryland, Virginia, and North Carolina the loblolly pine (Pinus teda) is the leading species, while in peninsular Florida the Cuban pine (Pinus caribea) is the chief form. Throughout the remaining major portion of the forest the long- leaf pine (Pinus palustris) is always the dominant tree, or at least abundantly represented in company with the loblolly pine. Through- out the Gulf region the slash pine (Pinus heterophylla) is found in moist soils and the pond pine (Pinus elliottiz) in wet soils. Throughout the interior portions of this forest the shortleaf pine (Pinus echinata) is a characteristic tree, seldom found in company with the longleaf pine. In the northern and interior portions of the Southeastern Forest, the broad-leaved deciduous oaks are frequent associates of the pines. The post oak (Quercus minor) and the Spanish oak (Quercus digitata) are common from Maryland to Texas, and the blue-jack oak (Quercus brevifolia) and turkey oak (Quercus catesbe1) from Georgia to Missis- sippi. The red gum (Liquidambar styraciflua), the black gum (Nyssa biflora), and the red maple (Acer rubrum) are also common broad- leaved deciduous elements of this forest, although usually most com- mon in poorly drained soil. From South Carolina to Texas the branches and moist depressions of the forest are characterized by many ever- green broad-leaved trees. Some of these are always evergreens, as the magnolia (Magnolia grandiflora) and the live oak (Quercus virgin- wana), while others are evergreen in the Gulf region and deciduous further north, as the water-oak (Quercus nigra) and the laurel oak (Quercus laurifolia). Throughout the portions of the area which are poorest in associated deciduous trees there are a number of evergreen broad-leaved shrubs which form a conspicuous element of the vegetation. The most notable of these are the gallberry (Jlex glabra), the red bay (Persea carolina), the waxberry (Myrica caroliniana), the ti-ti (Cliftonia monophylla), DISTRIBUTION OF VEGETATION IN UNITED STATES. 4] and the sweet illicium ([llicium floridanum). In the extreme coastal region and in peninsular Florida the saw palmetto (Serenoa serrulata) is more conspicuous than the shrubs, although there is an increasing number of species of the latter, including two dwarf oaks (Quercus pumila and Quercus minima). Northeastern Evergreen-Deciduous Transition Forest.—This type of forest fringes the Northern Mesophytic Evergreen Forest from Minne- sota to Maine and southward along the Alleghenies. It is sometimes well marked as a nearly equal admixture of deciduous and evergreen needle-leaved trees, but on its southern and northern edges it merges into the larger types of forest, except where sudden changes of soil break the influence of climate. The most important deciduous con- stituents are sugar-maple (Acer saccharum), beech (Fagus atropunicea), birch (Betula spp.), and basswood (Ttlza americana). The commonest evergreen trees are hemlock (T’suga canadensis), white pine (Pinus strobus), balsam fir (Abies balsamea), and jack pine (Pinus divaricata). Northern Mesophytic Evergreen Forest.—This forest occupies portions of the northern Pacific coast, all but the alpine portions of the Rocky Mountains above an elevation of 6,000 to 7,000 feet, and the higher summits of all the coastal and inland mountain ranges of the Western States. It also occurs in northern Minnesota, Wisconsin, and Michi- gan and extends from Maine over the higher elevations of the Appa- lachian region through New York, Pennsylvania, and West Virginia south to North Carolina. This widespread forest is essentially similar in its physiognomy throughout. It is dominated in all portions by the needle-leaved ever- green tree, although it is by no means free of an admixture of broad- leaved deciduous trees, and the latter are particularly common along the streams or as small trees beneath the canopy of evergreens. This forest is usually between 50 and 100 feet in stature, and it is commonly so dense that the entire ground is in shade, although this is notably untrue of the forests at elevations approaching timber-line on high mountains, and of those which approach the lower limit of timber on the desert mountain ranges of the interior. The heaviest stands of this forest are almost devoid of either shrubby or herbaceous under- growth, but are carpeted by beds of moss. In the more open stands there is usually considerable shrubbery, and when this exists it is made up of deciduous plants. In spite of the essential similarity of the Northern Mesophytic Evergreen Forest, throughout its extensive range of occurrence, it is made up of a large number of tree species, and its composition varies greatly from State to State, and especially when the eastern and western portions of the forest are compared. Owing to differences in habit of growth that exist between different coniferous trees there are Some very striking differences in the physiognomy of the forest that 42 THE VEGETATION OF THE UNITED STATES. are to be thus explained, as, for example, the contrast of the open yellow-pine forest with the very dense lodgepole-pine forest. In the mountains of the Western States there are also considerable differ- ences in the coniferous forests due to altitude, and these differences are visible in the floristic composition as well as in the physiognomy. The leading tree in the composition of all the western forests of this character is the western yellow pine (Pinus ponderosa), which often forms extensive pure stands at middle altitudes, is replaced by other species at the highest elevations, and is sometimes the tree of lowest range, as in the northern Rocky Mountains, or is mingled with the oaks, junipers, and nut pines of the Western Xerophytic Evergreen Forest at its lower range. The tree which most frequently replaces the yellow pine in the domination of this forest is the lodgepole pine (Pinus murrayana), which is extremely abundant in pure stands in Idaho and Montana, occupies a belt of dominance from 3,000 to 5,000 feet in portions of eastern Washington, is almost the sole forest tree in the Big Horn Mountains of Wyoming, grows with the Douglas fir (Pseudotsuga mucronata) on the western side of the Coast Range, and is locally dominant in the Rocky Mountains of Colorado. The most hygrophilous portions of the Mesophytic Evergreen Forest are the coastward slopes of the mountains of Oregon and the western slopes of the Rocky Mountains in Montana and Idaho. In the former of these regions the lowest belt of forest is formed by yellow pine, Douglas fir, and lodgepole pine; above 5,000 feet the Douglas fir is the dominant tree, growing with yellow pine, sugar pine (Pinus lambertiana), white fir (Abies concolor), lodgepole pine, and noble fir (Abtes nobilis); while the higher forested elevations are dominated by the alpine hemlock (T'suga pattoniz), together with lodgepole pine, noble fir, white-bark pine (Pinus albicaulis), western white pine (Pinus monticola), and alpine fir (Abies lasiocarpa). The moister forests of the northern Rocky Mountains lie between a pure stand of yellow pine at lower elevations and an open stand of alpine fir and white-bark pine above. The commonest trees of this forest are western white pine and western larch (Larix occidentalis). The Douglas fir is frequent and the alpine fir (Abies lasiocarpa), the lodgepole pine, and giant cedar (Thuja plicata) form a small percentage of the arborescent vegetation. In the Sierra Nevada the lowest coastward fringe of forest is formed by an open stand of the digger pine (Pinus sabiniana), and the main body of the forest is formed of yellow pine, incense cedar (Libocedrus decurrens), sugar pine (Pinus lambertiana), Jeffrey pine (Pinus jeffrey?) and white fir (Abies concolor). At the highest timbered elevations lodgepole pine, Jeffrey pine, and red fir (Abies magnifica) are the char- acteristic trees. In the San Bernardino and San Jacinto Mountains the forest below 6,000 feet is composed almost solely of yellow pine, DISTRIBUTION OF VEGETATION IN UNITED STATES. 43 and above that elevation of an admixture of yellow pine, white fir, and sugar pine. In the Rocky Mountains of Colorado the principal areas of forest are dominated either by yellow pine or lodgepole pine, or more rarely by an admixture of them. The higher elevations are characterized by Douglas fir (Pseudotsuga mucronata), Engelmann spruce (Picea engelmanni), and by the fox-tail and limber pines (Pinus aristata and P. flexilis) and the Parry fir (Picea parryana) and alpine fir (Abies lasiocarpa). The forest in the Black Hills of South Dakota and in the desert mountains of Arizona and New Mexico is chiefly formed by yellow pine. The Mesophytic Evergreen Forest of northern Minnesota is a com- posite of white pine (Pinus strobus) on the deeper soils; of Norway pine (Pinus resinosa) and jack pine (Pinus dwvaricata) on the lighter soils; with tamarack (Lari laricina), black spruce (Picea mariana), and white spruce (Picea canadensis) in wet soils; and arborvite (Thuja occidentalis) in the bogs. The deciduous broad-leaved trees are more conspicuous here than in any portion of the western half of this forest, bur oak (Quercus macrocarpa), basswood (Tilia americana), and sugar maple (Acer saccharum) being the commonest species. In Maine the principal trees in the evergreen forest are spruce (Picea nigra), balsam fir (Abies balsamea), white pine (Pinus strobus), and hemlock (Tsuga canadensis). This group of trees is also charac- teristic of the coniferous areas of the other New England States, of the Catskill and Adirondack Mountains in New York, and of the moun- tains of Pennsylvania. The small coniferous areas on the mountains of North Carolina are chiefly composed of black spruce (Picea mariana) and the Fraser fir (Abves fraserz). Western Xerophytic Evergreen Forest—The Xerophytic Evergreen Forest is a dwarf and open form of ‘‘woodland”’ or ‘‘semi-forest”’ that characterizes the edges of the Mesophytic Evergreen Forest through- out the southern half of the western portion of that forest. The Xerophytic Forest seldom covers extensive areas, except in northern Arizona, and in all localities it becomes more open at the lower edges, where it meets the Desert or the Desert-Grassland Transition, and more closed at the upper edge, where it merges with the Mesophytic Ever- ereen Forest. The Xerophytic Forest is similar to the desert in that its dominant plants are widely spaced, leaving much unoccupied ground. It is, again, similar to the desert and unlike the other forest areas in the small stature of its trees, which never exceed 50 feet and frequently attain less than 25 feet in height. The two types of tree which dominate the Xerophytic Forest are the nut pine (Pinus edulis, P. cembroides, P. parryana) and the juniper (Juniperus utahensis, J. californica, J. 44 THE VEGETATION OF THE UNITED STATES. occidentalis, J. pachyplea). Sometimes these two types are equally mingled, or more frequently one of the two is predominant. The species mentioned do not greatly overlap, but occupy different areas within the Xerophytic Forest. With these coniferous trees grow also certain evergreen broad-leaved oaks. In the Great Basin and in Colo- rado the role played by the oaks is a minor one, but in New Mexico it is more important, and in southern Arizona several arborescent species of evergreen oaks are frequently as common as the conifers, or more so. The Xerophytic Forest also contains numerous conspicuous shrubs of different types (Cercocarpus, Cowania, Artemisia, Ephedra, etc.), as well as such succulent and semisucculent plants as the yuccas and agaves, and conspicuous bunch-grasses and other perennials of inter- mittent or seasonal activity. Northwestern Hygrophytic Evergreen. Forest—This forest occupies the coastal region of Washington, Oregon, and extreme northern California, and an isolated portion of it lies on the western slopes of the Cascade Range in Oregon. This area exceeds any portions of the Mesophytic Evergreen Forest in density of stand and in the stature of the trees, which very frequently exceed 100 feet in height. The heavily shaded floor of the forest 1s covered with fallen trunks and limbs, overgrown with mosses and hepatics, and underlaid by a deep bed of humus. The deciduous trees are few and small, but a number of evergreen ericaceous shrubs are common on the floor of the forest, as are also ferns and large-leaved herbaceous plants. The density, tall stature, and vigorous activity of the Hygrophytic Forest give it a very distinctive physiognomy and betoken a set of environmental conditions unlike those of the Mesophytic Forest, in accordance with which it possesses a number of distinctive tree species. The tree which is of most general occurrence throughout the area is the Douglas fir (Pseudotsuga mucronata), which is also found far beyond the limits of this forest. It is accompanied in nearly equal admixture in many localities by the black hemlock (T’suga meriensiana). Other species common in this forest are the Sitka spruce (Picea sitchensis), white fir (Abies grandis), giant cedar (Thuja plicata), amabilis fir (Abies amabilis), noble fir (Abies nobilis), redwood (Sequoia semper- virens), and western white pine (Pinus monticola). The highest ocean- ward elevations of the Coast Range are similar to other subalpine areas in the coniferous forests, and are characterized by an open stand of symmetrical conifers, branching to the ground. Alpine Summits——The principal alpine summits are those of the Cascade, Sierra Nevada, and Rocky Mountains, although small areas occur elsewhere. Their vegetation is composed of such dwarfed or prostrate trees as may be able to exist above timber-line, together with low, matted, or polsterform perennial plants with large roots. Meadows or the margins of lakes above timber-line are the habitats of DISTRIBUTION OF VEGETATION IN UNITED STATES. 45 numerous herbaceous species, usually less highly specialized than those growing in rocky soil or crevices. On the highest mountains of the United States the vegetation is often limited to mosses and lichens or is locally absent. Swamps and Marshes.—These terms comprise an extremely varied series of communities, partially dominated by trees and partially by coarse grasses, sedges, or other palustrine plants. The words “swamp” and “‘marsh’’ are both somewhat objectionable for use in the present connection because of their intrinsic reference to the nature of the habitat. The distinction between swamp and marsh has so long been drawn in popular speech and scientific writing, however, that the words are used here as terms descriptive of the vegetation rather than designations that imply the feature of the environment which deter- mines the vegetation. The areas of swamp and marsh are so intri- cately interwoven that no effort has been made to separate them. The greatest development of swamps and marshes is to be found along the shores of the Atlantic Coastal Plain, although there are smaller areas of marsh on the Pacific Coast and scattered areas of swamp throughout the glaciated region. The saline marshes are dominated by nearly pure stands of halo- phytic grasses, while the fresh or brackish marshes are inhabited by very diverse populations of herbaceous perennials and annuals. The swamps of the Southeastern States are composed of a particularly rich assemblage of deciduous broad-leaved trees (Nyssa, Acer, Mag- nolia, and Quercus) or of nearly pure stands of the deciduous needle- leaved bald cypress (Taxodium distichum). Although the map of the vegetation of the United States which has just been described (plate 1) is not so detailed as might be possible or desirable, it was found, nevertheless, as has been noted, that many of its smallest areas and the sinuosities of many of its major boundaries would be meaningless when brought into comparison with the rela- tively small number of stations from which we were able to secure climatic data. We have therefore prepared a generalized map of the vegetation of the United States, shown as plate 2, which was executed with special reference to the number of stations represented in our accumulations of climatological data. The detailed map has been published and described for the sake of giving the basis upon which this more generalized map has been drawn. The number of areas has thus been reduced from 18 to 9 by a reduction of the four desert areas to one, by a consideration of the two semidesert areas as one, by the elimination of the transition areas from desert to grassland and from deciduous forest to the forest areas to the north and south of it, and by disregarding the alpine summits and swamps and marshes. We have chosen to separate our study of climatic correlations for the eastern and western portions of the Northern Mesophytic Evergreen Forest. Although these two areas are ecologically alike, it seemed es 46 THE VEGETATION OF THE UNITED STATES. desirable to give them separate study, in view of the fact that they are so widely separated, at least within the geographical limits of the United States. ' ‘The generalized map (plate 2)! is, therefore, a simplification of the detailed vegetation map, in addition to being a generalization from it in the sense that the lines between the plant formations have been smoothed, although their location has in no case been changed in such manner as to throw any of our leading climatological stations into vegetations other than those in which they actually belong. The areas represented on the generalized map of the vegetation have been designated as follows: . Desert. . Semidesert. . Grassland. . Grassland-Deciduous Forest Transition. . Deciduous Forest. . Northwestern Hygrophytic Evergreen Forest. . Western Section of the Northern Mesophytic Evergreen Forest. . Eastern Section of the Northern Mesophytic Evergreen Forest. . Southeastern Mesophytic Evergreen Forest. Cc CO NT > OTH CO DD Ill. DISTRIBUTIONAL AREAS OF CONFORMIC GROUPS OF PLANTS. Under this heading we desire to discuss briefly the groups of con- formic plants (plants of the same growth-form) which we have used in the correlations dealt with on the following pages. Four groups of such plants have been charted and are exhibited in plates 3, 4, and 5. It seems desirable to give here some of the detailed data upon which these maps have been based. CUMULATIVE DISTRIBUTION OF EVERGREEN BROAD-LEAVED TREES. The evergreen habit in broad-leaved trees is commonly regarded as one that has developed in moist, warm climates, and this view is confirmed by the predominance of trees of this type in the tropical rain-forests of both hemispheres. We have endeavored to define both the term ‘‘tree’”’ and the term “‘broad-leaf”’ as definitely as possible for securing the list that we have used. We have regarded as trees. only those woody plants which have a well-defined trunk and a height of 20 feet or more, and have regarded as evergreen all of those trees which retain some of their leaves throughout the year, at least holding the old ones until the time of appearance of the new leaves. The needle- leaved evergreen trees have not been included in this class. The trees of this group merge into shrubs and in such a manner that it is extremely difficult to draw a hard-and-fast line between them, and indeed some of the species which are arborescent in one portion of their 10n Plate 2, and also on plates 6, 7, 11, 34-37, 39, 42-72, the description “‘Southeastern meso- phytic forest’”’ should read ‘‘Southeastern mesophytic evergreen forest.’’ PLATE 2 ‘UOlVIOS XY SK) 1h N WS \N N = N oh oo ae ee ee 4 S ou} JO SUOISTAIDGHS JO SsodAq JesroUes oUTU BuLMOoUS ISTAL [ t I [ er S RRS ‘soyB)G popu) oy} Jo deur uoryeyosoa poZzipe.ouory) ( = 44 x A eS KAY JSV1IOJ UdIIBADAD usayyoN = 91 Aye SRSSSYS SNL YS ES > SS SSS > p p <)> J Eis -LOt (601 It (159M) GO1OY UBDIBIDAI 38910} u991819A9 oh Aydosshy ys910J snonpiseq SESS POS ORR LARGO KS RXR RS RRS " O97 Fo 96; fan S { re SS SR Pigs 5 KS SSS o Shed p . oll 310} Snonpisep DISTRIBUTION OF VEGETATION IN UNITED STATES. 47 range are shrubs in another. It is also well known that a number of trees which are evergreen in southern latitudes are somewhat decid- uous near the northern limits of their ranges. Evergreen broad-leaved trees are found in the United States only on the Pacific coast, in the mountains of the extreme Southwest, and in the southeastern portion of the United States, reaching their greatest abundance in peninsular Florida. ‘Those of the Pacific region are either confined to the Pacific coast of the United States or are found only in extreme northwestern Mexico. The evergreens of the south- western mountains are largely trees which have the major portion of their range in the Sierra Madre region of Mexico. Those of the south- eastern United States are partly peculiar to that region and partly trees of wide distribution in the West Indies, this being notably true of those found in extreme southern Florida. In the western states the greatest extension given the area of this growth-form, at least to the north, is due to the extended range of Arbutus menziesii. In the east the maximum extension of this type is due to the ranges of Ilex opaca and Magnolia glauca, which extend north in the Coastal Plain as far as Massachusetts. The member of the southeastern group which extends farthest west is Quercus virginiana, which is found in western _ Texas. The inclusion of the evergreen shrubs Rhododendron maximum and Kalmia latifolia would have extended the region of occurrence of this growth-form into the southern Alleghenies and farther into the Northeastern States. With the exception of these shrubs, the ever- green habit is rather poorly represented among the shrubs in the deciduous-forest region, although the evergreen broad-leaved habit again appears in the north as characteristic of numerous bog shrubs. In the construction of the map of cumulative occurrence of broad- leaved evergreens 129 species have been used. Of these species, 25 occur in California and the Southwestern States, 25 in the Eastern States exclusive of peninsular Florida, and 79 in the last-named region. The western and eastern groups do not overlap, except in so far as Quercus virginiana is sometimes found in western Texas in the same region with evergreen oaks characteristic of the Mexican Cordil- lera. Our eastern group of evergreens merges into the group for peninsular Florida in a manner which it is impossible to describe accu- rately on the basis of existing literature. Several of the evergreens of the Southeastern States do not range to the extreme southern end of Florida. Twelve of our 25 eastern species have been eliminated with certainty from the number credited to southern Florida. Out of the 79 species which we are listing for peninsular Florida, only 65 are found in the Everglade region exclusive of the keys, while 26 are confined to the keys and their adjacent shores. The complicated distribution of many of these trees in peninsular Florida has made it necessary for us to map that region in a somewhat conventional manner. 48 THE VEGETATION OF THE UNITED STATES. Following is given a list of the species of evergreen broad-leaved trees which have been used in the compilation shown on plate 3. In order to identify these with greater certainty, author names are given: EVERGREEN BRoAD-LEAVED TREES OF THE UNITED STATES. Western group: Southeastern group—continued: Arbutus arizonica (Gray) Sarg. Arbutus menziesii Pursh. Arbutus texana Buck. Castanopsis chrysophylla (Hook) A. DC. Ceanothus spinosus Nutt. Ceanothus thyrsiflorus Esch. Ehretia elliptica DC. Fremontodendron californicum (Torr.) Cov. Garrya elliptica Doug]. Myrica californica Cham. Prunus ilicifolia (Nutt.) Walp. Quercus agrifolia Nee. Quercus arizonica Sarg. Quercus chrysolepis Liebm. Quercus densiflora Hook. and Arn. Quercus emoryi Torr. Quercus engelmanni Greene. Quercus hypoleuca Engelm. Quercus oblongifolia Torr. Quercus reticulata Humb. and Bonpl. Quercus wislizeni A. DC. Rhus integrifolia (Nutt.) Benth. and Hook. Sophora secundiflora (Cav.) DC. Umbellularia californica (Hook. and Arn.) Nutt. Vauquelinia californica (Torr.) Sarg. Southeastern group: Bumelia angustifolia Nutt. Bumelia cassinifolia Small. Bumelia lanuginosa (Michx.) Pers. Bumelia lucida Small. Bumelia tenax (L.) Willd. Bumelia texana Buckl. Cliftonia monophylla (Lam.) Sarg. Cyrilla racemiflora L. Gordonia lasianthus (L.) Ellis. Ilex cassine Walt. Ilex myrtifolia Walt. Ilex opaca Ait. Magnolia glauca L. Magnolia grandiflora L. Osmanthus americanus (L.) B. and H. Persea borbonia (L.) Spreng. Persea pubescens (Pursh.) Sarg. Prunus caroliniana (Mill.) Ait. Quercus laurifolia Michx. Quercus nigra L. Quercus virginianas Ell. Sabal palmetto (Walt.) R. and S. Symplocos tinctoria (L.) L’Her. Vaccinium arboreum Marsh. Xanthoxylum fagara (L.) Sarg. Peninsular Florida group: Alvaradoa amorphoides Liebm. Amyris balsamifera L. Amyris maritima Jacq. Anamomis dicrana (Berg.) Britton. Anona glabra L. Avicennia nitida Jacq. Bourreria havanensis (R.andS8.) Miers. Bourreria virgata (Sw.) D. Don. Bucida buceras L. Bumelia angustifolia Nutt. Calyptranthes pallens (Poiret) Griseb. Canella winteriana (L.) Gaert. Capparis jamaicensis Jacq. Chrysobalanus icaco L. Chrysophyllum oliviforme L. Citharexylon cinereum L. Coccolobis laurifolia (Jaeq.) Sarg. Coccolobis uvifera (L.) Sarg. Colubrina reclinata (L’Her.) Brongn. Conocarpus erecta L. Cordia sebestina L. Crescentia cujete L. Crescentia cucurbitina L. Cupania glabra Sw. Dipholis salicifolia (L.) A. DC. Drypetes diversifolia Urb. Drypetes lateriflora (Sw.) Urb. Eugenia axillaris (Sw.) Willd. Eugenia buxifolia (Sw.) Willd. Eugenia confusa DC. Eugenia longipes Berg. Eugenia rhombea (Berg.) Krug and Urban. Exostema caribeeum (Jacq.) Griseb. Exotheca paniculata (Juss.) Radlk. Ficus aurea Nutt. Ficus brevifolia Nutt. Genipa clusiifolia (Jacq.) Griseb. Guaiacum sanctum L. Guettarda elliptica Sw. Guettarda scabra Vent. Gyminda latifolia (Sw.) Urban. Gymnanthes lucida Sw. Hippomane mancinella L. Hypelate trifolata Sw. Icacorea paniculata (Nutt.) Sudw. Ichthyomethia piscipula (L.) A. 8 Hitch. DISTRIBUTION OF VEGETATION IN UNITED STATES. 49 EVERGREEN BROAD-LEAVED TREES OF THE UN1V1ED STATES—continued. Peninsular Florida group—continued: Sapindus saponaria L. Schaefferia frutescens Jacq. Schoepfia chrysophylloides (A. Rich.) Planch. Sideroxylon fcetidissimum Jacq. Simaruba medicinalis Endl. Peninsular Florida group—continued: Ilex krugiana Loesn. Jacquinia keyensis Mez. Krugiodendron ferreum (Vahl.) Urb. Laguncularia racemosa (L.) Gaertn. f. Lysiloma bahamensis Benth. Mimusops parvifolia (Nutt.) Radlk. Ocotea catesbyana (Michx.) Sarg. Swietenia mahogoni Jacq. Oreodoxa regia H. B. K. Terebinthus simaruba (L.) W. F- Picramnia pentandra Sw. Wight. Pithecolobium guadalupense Chapm. Thrinax microcarpa Sarg. Prunus spherocarpa Sw. Thrinax parviflora Sw. Pseudophoenix sargenti1 Wend. Torrubia longifolia (Heimerl.) Britton. Psychotria undata Jacq. Trema floridana Britton. Rapanea guianensis Aubl. Xanthoxylum coriaceum A. Rich. Reynosia septentrionalis Urb. Xanthoxylum flavum Vahl. Rhacoma crossopetalum L. Ximenia americana lL. Rhizophora mangle L. Zygia unguis-cacti (L.) Sudw. Rhus metopium L. CUMULATIVE DISTRIBUTION OF MICROPHYLLOUS TREES. (PLATE 3.) This group comprises plants which are trees in form and reach a height of 15 feet or more, being characterized by leaves which are either simple and very small or have pinnate or bipinnate leaves with small leaflets. Several species have been comprised which have green stems and leaves which are of very short duration or wholly absent. The members of this group merge into the much larger class of shrubs in the southwestern United States which possess a similar character. Kight of the species which have been used are extremely common as shrubs, but frequently become trees within the limits of our definition. Microphyllous trees are most strongly represented in the United States in southern Texas and southern Arizona. The maximum north- ward extension of individuals of this group reaches northern Texas and the southern portion of Nevada, due to the range of Prosopis glandulosa. The cumulative distribution of this group, as well as of the group just considered, is shown in plate 3. The twenty-three species used in constructing this map are as follows: MicropHyLttous TREES OF THE UNITED STATES. Acacia farnesiana Willd. Acacia greggiiGray. Acacia wrightii Benth. Brayodendron texanum (Scheele) Small. Leucena pulverulenta (Schl.) Benth. Olneya tesota Gray. Parkinsonia aculeata L. Canotia holacantha Torr. Cercidium floridum Benth. Cercidium torreyanum (Wats.) Sarg. Condalia obovata Hook. Holacantha emoryi Gray. Keeberlinia spinosa Zuce. Leuczena glauca (L.) Benth. Leucena greggii Wats. Parkinsonia microphylla Torr. Parosela spinosa (Gray) Heller. Pithecolobium brevifolium Benth. Pithecolobium flexicaule Coulter. Porliera angustifolia (Engelm.) Gray. Prosopis glandolosa Torr. Prosopis pubescens Benth. Prosopis velutina Wooton. —— LK EE t) 4 ¥, gl o He | Lo leael f\ "a f) /; N \ ) ad ( gh — aK ee \ gy N | = ri Pees ew Rat ee Gs L9 69 ol8 cS d | GL Glico R288 as C7 \ Wee ey: TS i Sey Fo °o ° u ° ia | & rr TS op ake ve = n Oo od sreaKelee 53 i = By, S o e a « Ss i, 7 ARS i U Ci \ ¥ a — WA —| INN] tile a a cae ays A We AL" | J go] Aq LL Yh ol SMart: 16 66 6 0t6 68 ok 52 THE VEGETATION OF THE UNITED STATES. DECIDUOUS TREES OF THE SOUTHEASTERN UNITED STATES. (PLATE 4.) On the basis of the literature descriptive of the vegetation of the southeastern United States, a group of fifteen deciduous broad-leaved trees has been selected as representative of this vegetation form in that section of the country. The cumulative distribution of the fifteen trees which have been selected is shown in plate 4. These trees are of interest because they are extremely common in the Atlantic Coastal Plain and are nearly all either infrequent in the Piedmont and Allegheny regions or are absent there. These trees are, in short, representatives of the deciduous habit which have their maximum cumulative occurrence as well as their maximum abundance outside the deciduous forest area and in the heart of the Southeastern | Mesophytic Evergreen Forest. Five of the species used are palustrine and nearly all of them occupy other habitats than those in which the evergreen needle-leaved trees are dominant. The following is a list of the species which have been used in the construction of the map shown in plate 4: Acer drummondii Hook. and Arn. Quercus brevifolia (Lam.) Sarg. Fraxinus caroliniana Mill. Quercus catesbei Michx. Hicoria aquatica (Michx. f.) Britton. Quercus digitata (Marsh.) Sudw. Liquidambar styraciflua L. Quercus michauxii Nutt. Nyssa aquatica L. Quercus phellos L. Nyssa ogeche Marsh. Quercus texana Buckl. Planera aquatica (Walt.) Gmel. Ulmus alata Michx. Populus heterophylla L. CUMULATIVE. DISTRIBUTION OF THE COMMONEST EASTERN DECIDUOUS TREES, (PEATE 5)) A selection has been made of the thirteen deciduous trees which are commonest in the Deciduous Forest area and are most widely dis- tributed throughout it. These are all large forest trees which are wholly deciduous throughout their ranges and are commonly found in upland habitats. The maximum occurrence of this group is in the region extending from central New York to northern Alabama, com- prising the entire extent of the Allegheny Mountains. From this region, in which 18 of the species are found, the abundance of this group shades off to the east, south, and west, so that the area in which from 12 to 8 species are found covers the Coastal Plain of Virginia and Caro- lina, extends south to western Florida, and west as far as the eastern boundaries of Texas, Kansas, and Minnesota. The following is a list of the thirteen species that have been used in the preparation of this map, shown in plate 5: Acer saccharum Marsh. Juglans nigra L. Carpinus caroliniana Walt. Liriodendron tulipifera L. Castanea dentata (Marsh.) Borkh. Quercus alba L. Fagus atropunicea Ehrh. Quercus prinus L. Fraxinus americana h. Quercus velutina Lam. Hicoria glabra (Mill.) Britton. Ulmus americana L. Hicoria minima (Marsh.) Britton. DISTRIBUTION OF VEGETATION IN UNITED STATES. 53 THE COMMONEST EVERGREEN NEEDLE-LEAVED TREES OF THE SOUTHEASTERN UNITED STATES. (PLATE 6.) The four evergreen needle-leaved trees which are most widespread and most dominant in the Southeastern Mesophytic Forest are Pinus echinata, P. teda, P. palustris, and P. caribea. The ranges of these 4 pines have been superposed on a single map (plate 6). Pinus echinata possesses the most northerly range of this group, and it and Pinus teda exceed the distribution of the southeastern evergreen formation itself. The three most widely distributed species of this group reach their western limit at about the ninety-sixth meridian. The distribu- tion of P. palustris is closely coincident with that of the southeastern evergreen formation, while that of P. caribea lies entirely within that formation. ‘These four species are all found in southern Georgia and northern Florida and the extreme southern portions of Alabama and Mississippi. The region of maximum occurrence of this group lies, therefore, in the heart of the southeastern evergreen area. THE COMMONEST EVERGREEN NEEDLE-LEAVED TREES OF THE NORTHEASTERN ‘ UNITED STATES. (PLATE 7.). The ranges of the 4 evergreen needle-leaved trees which are most - generally dominant in the eastern section of the Northern Mesophytic Evergreen Forest are plotted together and are shown in plate 7. These trees are Pinus strobus, Tsuga canadensis, Abies balsamea, and Pinus dwaricata. The region of cumulative occurrence of these trees corresponds closely with the distribution of the evergreen forest formation. The southernmost extension of this group is found in the case of J'’suga and the northernmost in the case of Pinus divaricata. All four of these trees are found together in northern New England, northern New York, and in Michigan, Wisconsin, and Minnesota. The range of climatic conditions has been determined separately for each of these trees, owing to the fact that their regions of cumulative occurrence correspond so closely with the eastern section of the Northern Mesophytic Evergreen Forest. The same has been done with respect to the dominant trees of the Southeastern Evergreen Forest. THE ECOLOGICAL DISTRIBUTION OF PINUS TADA. (PLATE 8.) It is rarely that data are available on the relative abundance of a plant within its area of geographical distribution., Owing to the excel- lent work of Mohr,' we are able to use both the geographical and ecological distribution of the loblolly pine (Pinus teda). The map prepared by Mohr has been reproduced in plate 8 and shows three areas of varying abundance in addition to the region of scattered 1Mohr, Charles, Timber Pines of the southern United States, U. S. Dept. of Agric., Bur. For. 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Pr A NS eo ina yal Fia6 £8 of Ol .g0r .G0T 69 ws LOL ,60T III Cf 64 THE VEGETATION OF THE UNITED STATES. IV. DISTRIBUTIONAL AREAS OF SELECTED INDIVIDUAL SPECIES. A relatively large number of individual species have been so selected as to include a few of the dominant plants in each of the leading vege- tations. Many of the minor plants have distributional areas which coincide roughly with vegetational areas, as has already been shown for some of the northeastern and southeastern evergreen needle-leaved trees. Each of the dominant species that we have used for correlation with the climatic conditions is accompanied by numerous minor or subordinate species for which the same climatic controls must often be of importance. The trees are predominant in the list of species which we have used, partly because they are the dominant element in so many of our types of vegetation and partly because it is easier to secure full and accurate distributional data for them than for plants of any other type. The distribution of most of the flowering plants of the United States would seem to be fairly well known if a list of the known occurrences of these species were examined. When, however, the attempt is made to plot the distribution on a map, the very great gaps which exist in our knowledge become very evident. We have depended largely on the invaluable data of the United States Forest Service, as given in various publications, for our maps of the distribution of trees. The species which we have used fall into some 22 groups, which will now be enumerated. The distributional areas of. these plants have been arranged on the maps so that their limits will intersect as little as possible and so as to economize space. The plates on which these distributions are represented are given in each case. 1. NORTHWESTERN EVERGREEN NEEDLE-LEAVED TREES. (PLATE 13.) Tsuga heterophylla (Raf.) Sarg. Picea sitchensis (Bong.) Trautv. and Mayer. These two trees are taken as typical of the numerous evergreen needle-leaved forms found in the hygrophytic forest of the North- western States. J'suga ranges eastward to the Rocky Mountains of northern Idaho and northwestern Montana, but Picea is closely restricted in its range to the hygrophytic forest region itself. 2. WESTERN EVERGREEN NEEDLE-LEAVED TREES. (PuATES 14 AND 15.) Pseudotsuga mucronata (Raf.) Sudw. (=P. taxifolia (Lam.) Britton = P. doug- lasii Carr). Pinus ponderosa Laws. (including P. scopulorum (Engelm.) Lemmon). Pinus contorta Loud. (including P. murrayana Oreg. Com.) Pinus edulis Engelm. In this group are comprised four of the leading trees of the western portion of the Northern Mesophytic Evergreen Forest. It has been possible to map the occurrences of Pseudotsuga with considerable accuracy, in fact, in far more detail than our series of climatological figures would warrant. Pinus ponderosa is likewise widely distributed < / | Be | (} / | at 5 \ oP | — as : ; | IT77 Vv] | 7 P ) AN | ayy, / i7ae wi, . ; = J c al le ahha heh Bie Ne are 1-61 fi . \ LS h es an eae \ Ne Be eee oD 69 tt SL off tL 62 IS ol 6 ofOI 801 SOT 01 .60T III ,eIl SIT 21 & Let AL ie 7A, I £61 S81 221 621 ag 0 pee Ware ‘rca ) = 66 F op Oo = “© oS Co. _ ° 12 6 Oo Ww ok IT ob IT I ‘aa A et ep 4 Whe —_ S = 4 © for} i=) cond ‘ fi "D).L0JUOI SNULT PUB DsOlapuod snurg JO UOTYNAIIySICT 6 ° Cor Cnty f Np Pn aati cy, Eds at meses aie ba | i's By ~~ ANA vA W/4 py" vay / SS : Hy i = t 4 oN , \ \ ap i f B. 6Gq. 100 c0" COL, -20t cot a eee or Gh et el ae eet LJ rj if ama | Ate a puap nauDjsDD pwe ‘Dervundoyn snBog “unuDYooos LaoW JO TOTYNGISIC AN \ EV N re CN \ 4 Van ‘ olb a Xa h y \ 4 f N y a P_% he Ly Wa ee ‘4 \ { \ V7 NK ’ \ \ ; A = Raat CU Ea 20 flys sata! Pri As | {a J 3 of VE OL LL Soe Cee 8 6 .€6 ass AS) Gale ee > L8 = Eis ii el Pe > I i G6 46 66 Ol <€0t SOL LOK GO! IIT ert SII QZ GIT ter .e2) <9el ler eet a o6L (8 ‘ DISTRIBUTION OF VEGETATION IN UNITED STATES. 69 through the forested portions of the western United States from the Canadian boundary to Mexico. Pinus contorta is very nearly coin- cident in its range with the northern portion of the area occupied by Pinus ponderosa. Pinus edulis is used as an example of the type of evergreen needle-leaved trees which is dominant in the Western Xero- phytic Evergreen Forest. It has not been possible from any data which are at hand to represent the range of this tree in as great detail as we used for the other member’ of this group. 3. SOUTHEASTERN EVERGREEN NEEDLE-LEAVED TREES. (PLATE 6.) - Pinus palustris Mill. Pinus teda L. Pinus echinata Mill. (=P. mitis Michx.). y Pinus caribea Morelet (=P. heterophylla (Ell.) Sudw.). The range of the members of this group of characteristic evergreen needle-leaved trees of the Southeastern Mesophytic Forest has already been discussed on a previous page. 4, NORTHEASTERN EVERGREEN NEEDLE-LEAVED TREES. (PLATES 7 AND 13.) Pinus strobus L. Tsuga canadensis (L.) Carr. Pinus virginiana Mill. (=P. inops Ait.). Pinus divaricata (Ait.) DuMont. (=P. banksiana Lamb.). Abies balsamea (L.) Mill. The distribution of four of these species has also been discussed in showing the relation of their ranges to the range of the eastern portion of the Northern Mesophytic Evergreen Forest. Pinus virginiana has been used as an example of a type of distribution which is somewhat unusual among the evergreen needle-leaved trees, occupying an area between the northern and southern areas of evergreen needle-leaved forest and lying almost wholly in the deciduous region. 5. Eastern Decipuous Tress. (PLATES 16 AND 17.) Quercus alba L. Fagus atropunicea Ehrh. (=F. americana Sweet =F. ferruginea Ait.). Castanea dentata (Marsh.) Borkh. (=C. sativa var. americana Sarg.). Acer saccharum Marsh. (=A. saccharinum Wang.). This group comprises four of the commonest trees of the deciduous forest, all of which were used in the map of cumulative occurrence of trees of this type given in plate 6. Quercus alba is found practically throughout the eastern half of the United States, with the exception of peninsular Florida and northern Michigan and Minnesota. Fagus atropunicea is also found throughout the greater part of the eastern United States, although it is somewhat less restricted in range than Quercus alba. Castanea dentata is more strictly confined in its occur- rence to the Alleghenian region and its adjacent areas. Acer sac- charum is similar in its range to Quercus alba, but extends farther to the north and not quite so far to the south. 70 THE VEGETATION OF THE UNITED STATES. 6. SOUTHEASTERN Dercrpuous TREES. (PLATES 17 AND 18.) Quercus falcata Michx. (=Q. digitata Sudw.). Sapindus marginatus Willd. These trees have been used as typical of the southeastern distribu- tions, the former being very nearly coincident with the Atlantic Coastal Plain in its range, the latter occupying its largest area in Texas and Oklahoma, and extending eastward along the Gulf coast to Florida. 7. NORTHERN Decipuous TREES. (PLATES 17 AND 18.) Populus balsamifera L. (including P. hastata Dode). Quercus macrocarpa Michx. These trees have been selected because of their wide northern range, which is limited in the former to the eastern portion of the Northern Evergreen Needle-leaved Forest and to a small area in the northern Rocky Mountains, while the latter tree extends south to the inner edge of the Coastal Plain and is remarkable for its extreme western extension into the grassland region. 8. SOUTHEASTERN EVERGREEN Broap-LEAVED TREES. (PLATE 19.) Ilex opaca Ait. Magnolia grandiflora L. (=M. fcetida (L.) Sarg.). Ilex has been used as an example of an evergreen broad-leaved tree which is nearly coincident in its range with the extent of the Atlantic Coastal Plain, and Magnolia has been used as another tree of the same erowth-form which is confined to a more southern section of the Coastal Plain. 9. Patms. (PLATE 20.) Sabal palmetto (Walt.) R. and S. Serenoa serrulata (Michx.) Hook. Washingtonia filamentosa Wendl. (=Neowashingtonia filamentosa (Wendl.) Sudw.). The three palms which are most widely distributed in the United States have been used as the sole representatives of this type of plant and as groups which are confined to the warmest portions of the United States. Sabal and Serenoa are both confined to western Florida and the adjacent coasts, while Washingtonia is found only in the interior deserts of southern California. 10. PALUSTRINE SHRUBS. (PLATE 22.) Cephalanthus occidentalis L. Adelia acuminata Michx. (= Forestiera acuminata Poir.) Decodon verticillatus (L.) Ell Itea virginica L. EO songounbuou. snpuydog pure viefuunsog snyndog yo wornqiysiq a \ a ca, eye ‘= eh \ ey Kf \ => /\ oe wey fe Sa) ee £9 Seen weed aaa 14 HESS ARS 1G) 8 *p.Loyrpunib pyoubo py pus vondo xa77J JO UOTYNGIIYSICT 6 o Ol of Ol of01 LOI 01 ol Il All ol (aul Jo YyNOs) @ pal a ; 188 ee eee | | sOYIpuess eyjouseyy 4 9% ayinos) eaedp xa j red | Gz ead a KS is os 1 \ ° {0 aN Oo Sulien 3. cy) wee (¢ sr we pe oe ie oe a, (auty jo a] ; ln = ] ; i ( = Je) a ECCS eariehs (ROEEC AaHB SL aoe f [Hes eel oa ieee Scanwan ter ~ T4VAE9 | Ss aaeil f Nl A c~ Letts Pty nae, ave hy 2us a ae BS ! t iy / ? ay, — (Z - ~ “an: ee Nl a ra We i we SS Bak is hice oa PS i) A} 7 \ a K ral \ ry | WS cats cance ie tna Ae K I \ a ak | f ZL eo SLU OR seer ae i VASAT | Pere PSL my fee a a | oN eter iS A a CGcamaloes CLs OR hi GE* AG 3 68> BG. (18: 68s 16-06 cb: ke 86 ol 601 ofGI = LET 661 Be. Ate ars ama Tapes OT €01 GOT LOT AL Stk 3901. Lak = OlFasc Ih. eek —— = en ee open ———————— - “‘psojuamnpy prwojburysp Yj Pus ‘DIDIN.LLAasS DOUALAG ‘oad yoGQDY JO MOTYNGII4SIC] TT, z y, Q (Merce Bi), if ie anes | S74 ane \ \ Fee ES Bah Ld = ; ae > | — ) LA 5 i= PEE a D eC y, r 1 ! Ql \ D jaas ie \ vv 4 V y) > RY 4 \) y i ¢ re : Po ‘ | \) N C) ; "4 ated AY, we = ) agers ; | 5 an i bop | b | <] ol BH REL e0r tt QUIT QIt OTT LIL er ° a a ae = ° S =| VY <1 mss NS 6 Ol 80r ct rot aah stint eos Aw \ \ eis SS SN, w/a a ie Aye ie nh SY Seba Wi 4 7 ise f y, —ai - =~ lee 28 os ENE as = IC au can ’ PSs <_| |_§ BHR alee Z| Lae ) Boy : 14 \ Vf \ a el se COUR Pe eter = oA ” eaten ane A be rt hat ¥ eae 4 PAT A ORCS ii! ee eee LoS ae ae ee ee | uly ~~ GEL Ble IR GBR Rr gL 6B FG CB 400 LE: 466 ogPOE--g001 SOD LOT 2001 ain CIT 50 A OEE F-ROk 200-120 ~-,681 Ke) aay oil eevee &% a ; RX6 ees | OO et URE 2 PEA | Se. ee i | Ah ol, plo G Woe _< L bl 3 18 é “0 g ce 6 3&6 ol6 66 10 4 “SUDJUapIII0 snyzUD]DYday pues ‘snypynouuan uoposacy ‘nounB.na 09} 7 ‘oyownunao pyapy Jo uoNNqISsIG ee ee ° ™ f fe Gay io} for) Ba t i) a ' ol ae % . @ e a o vay 7) ise) vo oy ~ 3 jo) a ~— oO I 3 tel} US| eS (ys) vo P=] = ons oe ns ae ee ee oe oe (dooy ayy rym) eyeurunse elapy xX I | / “By \ vend Lk \\ wn te me aa me He LA q a 4 Y, an | Zi Lf gah A cif a eran as ket A ae. aps im Eide xa > iA i. aney aie att Sates SEES Umea aie BNE gaeeee hs a pate Vite an Ae Nt Sick aa i bal AK . 6/O Ee sn ov Ket eek ) We cae yeaa : 18 pias PSE {) ie iy ie RM ie Fel AS LTS 28 a4 9 eee) a6 =e SLOb 601 Ween SESS eae t eh aay ° ° noe) a60 a) Tele eo) toll, 0b ele es cue” alec eeas 6 OT GOL 201 ,60T IIT .gIl GIT 621 UAT “GIT weiat te Te DISTRIBUTION OF VEGETATION IN UNITED STATES. 79 The members of this group are all shrubs of swamp and palustrine habitat and have been selected for use in our work with a view to bringing out the features of climatic control for plants which exist under a practically uniform set of soil-moisture conditions. Adelia is confined to the central portion of the Atlantic Coastal Plain. Itea occupies a similar area, but extends throughout the Coastal Plain as far north as New Jersey. Decodon is found in palustrine situations throughout the eastern United States, and Cephalanthus occupies a similar area with a remarkable westward prolongation of its range into southern Arizona and the central valley of California. 11. MicropHyLLous Desert SHRuBS. (PLATE 21.) Artemisia tridentata Nutt. Covillea tridentata (DC.) Vail (including C. glutinosa (Engelm.) Rydb.). These shrubs have been used in view of the fact that they are the most abundant plants in two of the most important of the desert areas. Artemisia is found throughout the Great Basin Microphyll Desert and extends beyond its limits to the east and northeast into the higher portions of the Grassland area. Covillea is the leading plant throughout the California Microphyll Desert and the Arizona and Texas Succulent Deserts, extending eastward into the Texas Semi- desert. 12. Cacti. (PLATE 23.) Opuntia polyacantha Haw. (including closely related varieties). Carnegiea gigantea (Engelm.) Britton and Rose (=Cereus giganteus Engelm.) The species of cacti which have been used were taken as examples of this great group of stem-succulent plants, the former representing one of the most widely distributed of the species found in the United States, and the latter one of the most restricted of the species which is in any place an important element of the vegetation. Opuntia poly- acantha is found throughout the Grassland region, extending from southern New Mexico to the Canadian boundary and occurring in small areas in Washington. Carnegiea is limited to southwestern Arizona at elevations below 4,000 feet. 13. CHARACTERISTIC COMPOSITES OF THE GREAT PLAINS. (PLATE 24.) Silphium laciniatum L. Solidago missouriensis Nutt. Gutierrezia sarothrze (Pursh) B. and R. These suffrutescent perennials are found throughout the Grassland and Grassland-Deciduous areas and, in their range and relations to climate, may be taken as typical of a large number of similar plants. Stlphiwm occupies the most easterly range of this group of plants, 80 THE VEGETATION OF THE UNITED STATES. extending as far as Pennsylvania and Florida, with the suspicion of its having been introduced along its easternmost limit. Solidago is closely confined to the Grassland and Grassland-Deciduous Transition area, with a northwestward extension in regions of this type through southern Idaho and eastern Washington. Gutierrezia is found in the western portion of the Grassland and in the higher portions of all areas © in the extreme southwestern portion of the country. In addition to its natural habitats, this plant is an extremely common one in all areas in which the original cover of grasses has been disturbed by grazing or other unnatural conditions. 14. CHARACTERISTIC GRASSES OF THE GREAT PLAINS AND THE PRAIRIES. (PLATES 11 AND 25.) Bouteloua oligostachya (Nutt.) Torr. Bulbilis dactyloides (Nutt.) Raf. (=Buchlée dactyloides Nutt.). Keeleria cristata (L.) Pers. Agropyron spicatum (Pursh) Rydb. (=A. divergens Nees,=Festuca spicata Pursh. Not A. spicatum Scribn. and Smith). Hilaria jamesii (Torr.) Benth. Andropogon virginicus L. Bouteloua hirsuta Lag. Four of the members of this group of grasses characteristic of the Grassland and Grassland-Deciduous Forest Transition regions have already been used in constructing the map of cumulative occurrence of grasses (plate 12). Theranges of three other species are given in plate 25. Agropyron and its allies have been selected because of their importance in the formation of the Grassland of the northwestern States, Hilaria because of its importance in the southernmost exten- sion of the Grassland and the Desert-Grassland Transition, and Andro- pogon because of its importance in the easternmost portion of the prairies of the Grassland-Deciduous Forest Transition. 15. PALUSTRINE HERBACEOUS PLANTS. (PLATES 26 AND 27.) Sparganium americanum Nutt. (including §. americanum var. androcladum (Engelm.) Fern. and Eames). Dianthera americana L. Sium cicutefolium Gmel. These palustrine herbaceous plants are of interest for the same reason that has been mentioned in connection with palustrine shrubs. Spar- ganium is extensively distributed in the Eastern States, but its pre- cise range is not well known. Dvanthera is found in the eastern half of the United States south of Wisconsin and outside the eastern half of the Coastal Plain. Szuwm is found practically throughout the United States, with the exception of the continental desert areas, its occur- rence throughout a large part of this region being extremely infrequent. ‘snorub.ia uobodoipuy pur ‘vrsauol prop] “wunjyoonds uoiidosby jo aoyNnqi4siq BY ~ 12 & o J2 o S31W 009 i GBA) SNIIUIZINA UC ; 9] 94) UIYIIM) tssULE = <] a yisou) winjesids uoshde P \ 7 0 by ) via MAL l SiN To a Ke S v7 AT) a) Nw = Bs ee Z| [7 1 y | La | ime £ sy t i ila / a ol | T-Sh GLi__61E Sot + {> L» I 631 2 as ol reaiecny ee ae aS ma ra ? OL GOT (SOL ,2OF 601 ITI err | J is 5 | 1 i }

oS an Oa es LN EF [7 3 N ae ; Dose o. ey Co = ~-_ i : >; © cae -e- 3 ~ = YY aw tt / iS | : BY | | (\ — s OL .80E SOT ,LO 601 LIT LIL Il att 5 DISTRIBUTION OF VEGETATION IN UNITED STATES. 85 16. PALuSTRINE GRASSES AND SEDGES. (PLATES 26 AND 27.) Arundinaria tecta (Walt.) Muhl. Dulichium arundinaceum (L.) Britton. Spartina michauxiana Hitchk. (=S. cynosuroides (L.) Willd.). While not strictly a plant of palustrine habitat, Arundinaria is found in moist alluvial soil and is of interest as one of the largest grasses found in the United States. Dulichium is distributed over an area very similar to that occupied by Sparganium, while Spartina occurs in palustrine situations throughout the northeastern portion of the country from Georgia, Oklahoma, and Wyoming to Canada. 17. MisTLETOES. (PLATE 28.) Arceuthobium cryptopodum Engelm. (=Razoumofskya cryptopoda (Engelm.) Coville. Arceuthobium americanum Nutt. (=Razoumofskya americana (Nutt.) Kze.). Phoradendron flavescens (Pursh) Nutt. (including varieties). Phoradendron juniperinum Engelm. In view of the fact that the mistletoes are independent of the condi- tions which the ordinary terrestrial plant encounters in its relation to the substratum, a series of four of these plants has been selected for our correlational work. The moisture conditions of the substratum in which these plants grow are doubtless determined in large measure by the moisture conditions that exist for the hosts themselves. Phora- dendron flavescens, together with its varieties, possesses an extremely wide range from the Atlantic to the Pacific throughout the southern half of the United States. .The other species that have been used are western in their range, and we have been under the unfortunate necessity of representing their areas of distribution by smooth lines which surround the territory in which they are of scattered occur- rence, chiefly in the forested mountains. 18. PLants oF NORTHERN TRANSCONTINENTAL RANGE. (PLATE 29.) Arenaria lateriflora L. (= Mcehringia lateriflora (L.) Fenzl. Parietaria pennsylvanica Muhl. Cornus canadensis L. The two herbaceous plants and the single shrub which form this group extend entirely across the North American continent and range southward to different distances, the southernmost range being that of Parietaria. Cornus is the least southerly in its range in the Eastern States, but is the most southerly in California. Transcontinental ranges of this character are extremely abundant among plants of still more northerly distribution than these, a number of trees and shrubs being found almost continuously from Labrador to Alaska. We are 86 THE VEGETATION OF THE UNITED STATES. here concerned solely with the southern limits of distribution of these plants, all of which range northward into the forested belt of Canada. 19. PLANTS OF SOUTHERN TRANSCONTINENTAL RANGE. (PLATE 30.) Spermolepis echinata (Nutt.) Hell. Daucus pusillus Michx. Parietaria debilis Forst. (=P. floridana Nutt.) Similar ranges extending from the Atlantic to the Pacific are found in the case of a few herbaceous plants which grow and mature during the different portions of the year in different parts of their transcon- tinental ranges. Daucus extends from North Carolina through Louisiana, Texas, and California, and up the Pacific coast to Washing- ton, although it is relatively infrequent at the extremes of this range. All of these plants extend beyond the limits of the United States and we are able to investigate only the northern limits of their distributions. 20. HERBACEOUS PLANTS OF SOUTHWESTERN RANGE. (PLATE 31.) Kallstreemia grandiflora Torr. (=Tribulus grandiflorus Wats.). Cladothrix lanuginosa Nutt. Pectis papposa Harv. and Gray. Euphorbia serpyllifolia Pers. (=Chamesyce serpyllifolia (Pers.) Small. A small group of plants has here been selected as representing types of distribution applying to a very large number of plants in the south- western arid regions. Cladothrix, Kallstremia, and Pectis are all con- fined to the extremely warm regions of Texas, New Mexico, and Arizona. Euphorbia is found throughout the western half of the United States in varying abundance. 21. HERBACEOUS PLANTS OF CENTRAL DISTRIBUTION (NYCTAGINACEA). (PLATE 32.) Beerhaavia erecta L. Oxybaphus nyctagineus (Michx.) Sweet (=Allionia nyctaginea Michx.). Oxybaphus angustifolius (Nutt.) Sweet (=Allionia linearis Pursh). Oxybaphus floribundus Chois. (= Allionia floribunda (Chois.) Kze.). In view of the fact that we have been concerned in so many cases with only one of the two edges of distribution of plants, we have here selected a group of central occurrence so as to make it possible to investigate the conditions of their eastern and western limits. Mem- bers of the same family have been chosen in this case because of the desirability of working out the behavior of a group of plants which are closely related in growth- form as well as in taxonomic relationship. Boerhaavia is found in the extreme south from Georgia to Arizona, while the other species of this group have their main regions of occur- rence in the Grassland and Grassland-Deciduous Forest Transition. ‘SUSUIPDUDI SNULOO PUB, “DoUDAhsuUad DIUDjaLIDg ‘DLOYLIIID] DIUDUaLY JO UOTYNGII4SICT aa 7 °o Road % oe a re f\ &. | L Ea. Sal Sere, J ‘\ SEU 6 Sanit > ey | HEC “a r | 4 eel Ni i 4 Z L bh oe po jes gh : i“ St / x 7 a — LP : { (\ y—Z- cia, Or /\ A ce \\ 7 KK é > / cs A are ee = SoS : Ae ! d 2 rd 9 ol ee FOL C01 SOL LOI 601 ILI IL .6r Zl 1 681 LN av PV gd 19 - 69. fla g6l =) - 62. N83 6 oS ° e | > v > a is ; ~i an ° CY} t an Lo | = a f S ‘3 / D aa 1) ee 5 bs I CAEN wee. a \i tied ¥\ YM EX isa areal A} : (| AMON ae Ais eae La Sale Ale of ian. = Y / 1 IRE hi =n 7/65) <] sy A (Se ey . LTA, 6 SOT £0 1 Zor .60 ttl of 10 ery 41 0 ee t Le if 1 66 Dr RanWvL ees Cuore. LO Ge RS = ela Ole iS ( Sane i] rar) | y ol L 6 0&6 06 ° oO ° ° ° ° os) 1 ° ° J I of ° “pryofypiduas piquoydny pus ‘nsoddnd s1yj0aq ‘v.1oyrpunib vruaysyoy ‘psoubnun) xr11yj0pn),) JO DOTYNGLI4SICT Pe a | 4 man! $2 js acm ae = MT i AY Ae f| ee on eo ae <€/ RV 1 ji A = a Nort = <1 Trt A : Sint RQ WA L Y iN : ee Rey Rel atcecapeannuseess nasal: FCO SRANUIR Rass canna aa aah Ap \_s \\ eae ea Sa Loe ete Cee Sa ea ei si uO ol ele el od) 6) eG ee Gea 16 66 OT gO! of9 6 a) t ARe Sit en i ak — ae eee ee OEE PA 4 ne A At \ Ss acu a) ot al hese =a Dp I sL0I g E ra & wi), ie wis B 4 By KS K : LMC i ob hoes \ oo \ 7 { VA ARR ooh 7A \ Ws <1 gy ¥ a AAA \ iS cS [| we \ Yor ] pmlc | as ECD EG REO SPL Red ate ee LOT C01 GOL LOT 6Or III etl at eae {17 1 6a! NS DISTRIBUTION OF VEGETATION IN UNITED STATES. 91 22. PAIRED SPECIES OF HASTERN AND WESTERN RANGES, RESPECTIVELY. : (PLATE 33.) Flcerkea occidentalis Rydb. Floerkea proserpinacoides Willd. Trautvetteria grandis Nutt. Trautvetteria carolinensis (Walt.) Vail (=T. palmata Fisch. and Mey.). Cebatha diversifolia (DC.) Kze. (=Cocculus diversifolius DC.). Cebatha carolina (L.) Britton (=Cocculus carolinus (L.) DC.). There are a few cases in the flora of the United States in which a genus has two species, one of which is eastern and the other western in range. We have selected the paired species of each of the three genera, Flerkea, Trautvetterta, and Cebatha, with a view to investigating the climatic conditions characteristic of the present separated ranges of these pairs of closely related plants. There is some doubt in the case of the two species of Flerkia as to their specific distinctness. The two species of Cebatha apparently overlap in central Texas, whereas the other two species are widely separated. 92 “‘DUYosDI DYINGA,) Pus ‘pyofisuaarp DYIDGAY) ‘SLsUaUTO4D9 piUayaanDLy, ‘SypUDsb DLLa}}AANDA J, ‘sapioon ui S ee). : : ad ox So f= ° c So (eee aeeer wat See aa PEPTIDE Set Dee ae ces nme LOSE TR SUR RS eg oh a = ow, Bere: a is eel mK Heal NS : b I i ee y AE areca ea Ly Ae pi ae | or ee as Clic A ane zal ae Ol —4 . C BAS ay EL LOT Ly ete | WN caecaaseeatauaceaecan j RSet CU ere CEP ey 6 lOl e01 SOL LOT .601 ltl git git obll Pal Th Cee AO ec! cTGul= 66 ee PART II. ENVIRONMENTAL CONDITIONS, INTRODUCTION. The physiological point of view has been constantly held before us, as has been said, in planning and carrying out the complicated com- parisons and correlations with which the present publication deals. Part I shows how the numerous vegetation features employed by us were derived, emphasis being placed on the physiological character- istics of the plants considered. Part II deals with the principles and methods by which the climatic features that we have used were selected, and shows how the requisite numerical computations were made and how the maps were prepared. This selection had to be based, as has already been indicated, upon two different kinds of circumstances: the physiological importance of the climatic features (as these are known to influence plant activity in general) and the availability of climatic data suited to our purposes. These matters will be set forth under three general headings: (I) general influence of the environment on plant life; (II) chief environmental conditions and the general nature of their effects upon plants; and (III) climatic conditions of the United States. The first two of these sections are mainly physio- logical-ecological in nature and are general in their scope; the last is mainly climatological-ecological and deals with the actual climatic data employed in our researches. 95 GENERAL INFLUENCE OF THE ENVIRONMENT ON PLANT LE. I], EXTERNAL AND INTERNAL CONDITIONS AND PLANT ACTIVITY. The behavior of any plant is said to be controlled by the surround- ing conditions, variations in these being the stimuli, or causes, which produce in the internal, physiological complex of the organism various responses or effects. Such responses are, however, quite as dependent upon the nature of the responding organism as upon the nature of the stimuli. With the same set of environmental conditions different plants behave differently, merely because their internal conditions differ, and with unlike environmental complexes plants of the same form exhibit quite different behaviors. The behavior of plants in general thus depends upon two interacting sets of conditions, the one set being external and the other internal. The latter set of conditions makes up, of course, the nature of the plant and serves to define it physiologically. These internal factors determine the ability of the organism to respond to exposure to any given constant external condition, or to any given change in any condition, and they also determine the extent of such responses. A plant might be rigorously defined by means of these powers or capabilities to respond to stimuli, and it is some of these powers that are, indeed, unconsciously used by taxonomists in their descriptions; but, although certain groups of the bacteria are now described by conscious reference to their physiolog- ical properties, the physiological nature of the taxonomic description in botany may be said hardly to be generally recognized as yet. As a plant develops, its internal conditions pass through a series of more or less profound alterations, and the different developmental phases of the same plant often show greater divergency in response to the same environmental complex than do the corresponding phases of distinct plant-forms. Thus, environmental conditions that are favor- able to seed germination or to vegetative growth may be markedly unfavorable to the production of flowers or fruit. It follows that for the best growth and reproduction of many forms the external conditions must vary from phase to phase as growth proceeds. This is one of a number of considerations that make for great difficulty in the incep- tion of any satisfactory quantitative study of the relation of external conditions to the characters of individual plants and of vegetation in general. A second consideration that enormously complicates our problem is this, that the response, or effect of the external system upon the organism, is definitely dependent upon the duration of the component 97 98 ENVIRONMENTAL CONDITIONS. conditions that make up the environment. Considerable time is required for most responses, and a momentary alteration in the envi- ronment may often pass without apparent effect upon the plant. Thus, outside of the time factor, the necessary and sufficient conditions for the production of those changes in manner of growth that are termed etiolation are present every night, but these conditions are not effective over a long enough period of time to result in visible responses. In the study of any external factor or complex of factors it is logically necessary and inevitable that the time element enter seriously into consideration. Physiologists have found it advantageous to analyze the environ- ment into its component conditions or factors. While some factors have so far received but a minimum of attention, a large amount of reliable information is already at hand bearing upon the effects pro- duced by the action, over various time intervals, of different intensi- ties of heat, light, oxygen-supply, etc. The method of such deter- minations has been to hold all factors but one as nearly constant as possible, and to cause various selected intensities of this one factor to register their effects upon the plant, in the form of alterations in growth or other activity. But this study of the simple component factors of the environment is only the learning of the alphabet, and the task of really reading the book of plant phenomena in the light of cause and effect still rests with the future. We are already well aware, in a general way, that the responses brought about in the organism by a certain quality, intensity, and duration of any external factor are totally dependent upon the nature of the other concomitant factors which are comprised in the environmental system. For example, a given increase in the rate of water-supply may fail to produce any marked acceleration of growth in certain forms existing under excessive drought conditions, but if the increase in soil-moisture be accompanied by a decrease in the evaporating power of the air, growth response may be immediate and definite enough. Again, the agriculturist is well aware that with many soils an increase of the nitrate content is without full effect unless other salts are simultaneously added. In such cases the result of these several increases together is not generally a simple summation of the results obtained by the single additions separately. While a large amount of laboratory experimentation of the most refined physical sort will be required before we shall even approach an adequate knowledge of the influence of single conditions upon plants, the far more difficult study of the complex environmental system of which these single conditions are always components has already begun to attract attention. It seems safe to predict that the line of work thus started will rapidly gain in prominence, and it is 1Livingston, B. E., Evaporation and Plant Development, Plant World, 10: 269-276, 1907. INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 99 conceivable that plant physiology may eventually work out the principles whereby the behavior of plants may be one day explained, predicted, and controlled. This is, of course, the hope of ecology and of the developing science of plant-culture. It is our aim in the present chapter to present merely a tentative outline of the general and more superficial relations that apparently obtain between the plant and its environmental conditions. No attempt is here made to make our consideration logically complete, either from the standpoint of physical causation or from that of the plant kingdom in general; attention is mainly turned upon some of the most obvious physiological considera- tions and upon the behavior of ordinary vascular land-plants. II. THEORY OF PHYSIOLOGICAL LIMITS. In an etiological study of plant distribution, either natural or artificial, the conception of physiological limits must hold a very prom- inent place. We understand by this term the extremes of intensity, etc., in a given factor which a certain plant can withstand. Starting from the optimum intensity of heat for any plant, for example, we may reduce the temperature till death ensues, thus attaining the minimum temperature limit for life. If the temperature be increased sufficiently above the optimum, another death-point is reached, the temperature maximum. The plant is thus able to retain life only under temperature conditions that fall within these physiological limits. With some other factors a similar pair of limits can be deter- mined; with many, however, only a single limit exists. For example, a submerged aquatic possesses a definite minimum rate of water- supply, but it is impossible to produce death or injury by increasing this rate even to its physical limit, as by surrounding the entire plant with water. It is obvious that in such a case there exists no maximum limit for life. Cases where there is a well-marked maximum but no minimum are also frequent, most toxic substances furnishing examples of this. Plants live normally in utter absence of these substances; they also live normally in their presence, so long as the amount sup- plied does not surpass a fixed maximum limit. Life is able to proceed, then, in any particular plant, only so long as the external conditions do not surpass the physiological limits for ‘the life processes of the form considered. In different plants and in different developmental phases or stages of the same plant these limits may be very different, so that an environmental complex that inhibits life in one phase or form may allow healthy activity in another. It is mainly in accord with this generalization that distinct climatic areas are characterized by corresponding types of vegetation, and the principle is therefore probably of primary importance in the study of plant distribution. 100 ENVIRONMENTAL CONDITIONS. The generalization just mentioned is very greatly complicated, as has been indicated, by the variations and fluctuations in the internal physiological conditions as development proceeds. The limits for life are often very different in the various developmental phases of the same form. ‘Thus, mature seeds of many temperate and boreal annuals show temperature minima far below the freezing-point of water, while the vegetative phases of the same forms may succumb to the first frost. Winter buds of northern deciduous trees possess high powers of resistance to low temperatures, while summer buds of the same plants may not bear temperatures as low as the centigrade zero. Besides the variations in limits of growth and life in different phases of the same form, it must be remembered that, in any phase or at any time in the life of the organism, there are a number of different processes going on, such as photosynthesis, respiration, digestion, secretion, and the like, each of which has its physiological limits, and the limits for one process are frequently not at all the same as for another. In general, the pair of limits that characterize these simpler processes, which together make up the vegetative or reproductive activ- ities of a plant, are much less widely divergent than those for the mere retention of vitality itself. By retention of vitality we probably mean the occurrence of the life processes at their lowest intensity, an inten- sity that is just sufficient to maintain life, though this expression may be taken in a general way to denote simply the power of initiating the various more vigorous and obvious processes when conditions become right. Seeds retain their power to start the germination processes for long periods of time under conditions that preclude germination itself. Again, with increasing scarcity of water or lowering of temper- ature, the growth processes of all plants are sooner or later brought to a standstill, long before death ensues. Moisture conditions that are optimal for vegetative growth frequently prevent the production of fruit, so that gardeners make it a practice, with the coming of the flowering-time in many plants, to diminish the water-supply. That the factor of time enters into the determination of physio- logical limits is obvious. Many plants are able to survive a short period with the soil about their roots in a saturated condition, but succumb to a longer period of exposure to a saturated soil. Numerous forms retain their vitality through long periods of drought, when the soil is nearly air-dry, but if the dry period is sufficiently prolonged death is the inevitable result. As has been mentioned, general growth is not noticeably affected by the regularly recurring nocturnal period without illumination, but etiolation becomes marked, and various other pathological conditions are induced when ordinary plants are kept in continuous darkness for but a few days. In phys- ical terms this means merely that the effects of any set of external conditions upon the plant are always cumulative and are exaggerated, in one way or another, with the lapse of time. INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 101 A combination of the time factor and that of intensity is, frequently if not always, the effective condition which determines the success or failure of plants in nature. With a somewhat rapid alternation of favorable and unfavorable conditions, where the unfavorable factors for any short period do not in themselves at first produce death, the organism may generally lose its power of resistance and finally go to the ground. In regions where such rapid fluctuations in the intensity of external conditions occur, the natural vegetation must necessarily comprise only those forms which can bear this sort of fluctuation. Alpine plants are reputed to be especially resistant to the great daily ranges of temperature that occur in their habitats, and many plants, such as lichens and certain liverworts and club-mosses, exhibit a high power of resistance to repeated wetting and drying-out. The limits for life, growth, or reproductive activity (the latter a _ sort of growth) define the resisting power of an organism in respect to the particular condition considered, and, by maintaining the quality and intensity of the other environmental factors and causing the one in question to vary, the range between the limits for that one may be more or less approximately determined. But, with two or more factors varying at the same time, the problem of physiological limits becomes much more difficult. The study of the behavior of plants when several factors are simultaneously in a state of change has, as we have pointed out, only just begun. We may be sure, however, that the resisting power of a plant to any single condition will prove to be markedly influenced by other concomitant conditions. The antagonistic action of certain salts, such as those of calcium and magnesium, in the work of Loew, Osterhout, and others, is a case in point, as is also the well-known fact that, by a degree of desiccation that does not surpass the death-limit, the power of many organisms to withstand both high and low temperatures is markedly increased. The common experiment comparing the effect of high and low temper- atures upon dry and moist seeds is a clear illustration of the latter case; within limits, the less water a seed contains, the more freezing or heating it can bear without losing its vitality . III. RELATION OF PLANT DISTRIBUTION TO THE PHYSIOLOGICAL LIMITS OF THE VARIOUS DEVELOPMENTAL PHASES. Each plant-form, each developmental phase, and each physiological process exhibits a minimum or a maximum, or both, for each of ‘the environmental factors, these limits depending, of course, on the other conditions that prevail within and without the plant. Whenever an environmental factor falls below the minimum for life, in either quality, intensity, or duration, the annihilation of the organism of course ensues. A like result follows any increase above the life maximum. It is only with each of the environmental conditions falling between 102 ENVIRONMENTAL CONDITIONS. its respective life-limits, under the given set of relations between the other conditions, that a plant can exist at all. But the mere existence of a given plant-form, its mere retention of vitality, is not sufficient to give it a permanent place in the vegetation of a given region; each plant must pass through various developmental stages, must come to maturity, and must reproduce. Since the intensity lim- its for the retention of life do not approach each other so closely as do those for growth and reproduction, it is easy to understand that the duration of the different intensities or qualities of certain factors must determine whether or not a given form may come periodically to maturity in any region. Though the lower temperature limit for life in seeds, bulbs, rhizomes, and the like, and in resistant perennials, is not attained in the temperate and boreal winter, yet the temperature conditions for growth and the production of fruit obtain only in the summer season. Similarly, the moisture conditions in a desert fall, for the greater portion of the year, below the minimum for the growth of many desert shrubs, these producing new leaves and flowers only in and immediately following the rainy seasons. The same is true of root and bulb perennials and of those annuals which succeed in the desert. It is thus seen that, in regions characterized by an alterna- tion of seasons of plant activity and of dormancy, the lengths of the seasons of activity must determine whether or not the plant repro- duces adequately; and since adequate reproduction is essential to the maintenance of the form in the given region, this length of season must determine whether that form succeeds or fails. While a mature plant, or a portion thereof, may exist in a relatively inactive condition for a long period of time, in an environment whose factors lie without the limits for most forms of activity (but within those for the retention of life), the resisting power thus evidenced is usually of but a low order when compared with that exhibited by ripe seeds or spores. From a physiological point of view such bodies represent merely a certain phase in the development of the plant, a phase in which the life processes are even more in abeyance than during the dormant periods of the mature form. An annual may play a very important réle in the vegetation of a region, although during the greater 1It is of course to be borne in mind, in this connection, that an alteration in one environmental condition may result in death simply by causing one or more of the vital processes to be so greatly accelerated or retarded that the other given external conditions, although they have not been changed, become fatal. Thus, while a given rate of water-supply may be sufficient for life and growth under a low evaporating power of the air, an increase in the evaporation-rate, unaccompanied by a corresponding increase in the rate of supply, may result in death. Had the rate of water-supply been adequately increased as the transpiration-rate rose, such a plant might have survived. It is frequently said that in such a case death is due to a condition which was not altered. This simply means that internal conditions have been changed, so that an environ- mental factor heretofore favorable to life becomes unfavorable, without itself changing. It is in this connection that the “law of the minimum”’ of agriculturists has been developed. (See: for example, E. J. Russell, Soil conditions and plant growth, Third ed., London, 1917, chap. II. Also see: F. F. Blackman, Optima and limiting factors, Ann. Bot. 19: 281-295, 1905.) INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 103 portion of the year the environmental conditions surpass the limits for both growth and life in the plant itself; the conditions in their adverse period do not surpass the limits for the retention of life in the seed. During a comparatively short period the environment may allow germination, growth, and the production of more seeds, and this short growing-season, together with the bridging of the adverse period by dormant seeds, constitute the conditions that are necessary and essential in order that such a plant may maintain a permanent place in the vegetation of its region. External conditions frequently surpass even the life-limits of many seeds; in such cases it must, of course, follow that the plant can not become a permanent part of the natural vegetation. This is probably true of the majority of cultivated plants that do not volunteer in the second season. A tropical plant, such as the castor-bean, may make a luxuriant growth in the temperate summer, but its seeds must be pro- tected through the winter and sown each spring. In general, the natural plants of the temperate and frigid regions must necessarily experience a longer or shorter period, usually each year, with proper conditions for growth and reproduction, and they exist through the adverse periods in some dormant phase. Not only must the conditions of the active period lie within the limits for growth and reproduction, but the period itself must be of adequate length, otherwise the necessary amount of growth could not take place, and fruit would not be matured. The principle that a plant, to become a part of the permanent vegetation of a locality, must have an adequate growing-season and must not meet its death during the remainder of the year, must be regarded as fundamental to the study of all problems dealing with the study of plant behavior under natural conditions. This principle is commonly accepted, though perhaps seldom formu- lated. With regard to any geographical area or region, we may conceive that all plants may succeed therein, for which the physiological limits - for life and those for growth and reproduction do not approach each other more closely than do the extremes of the physical conditions in the respective seasons for the given region. This view has led to a form of analogy which may be termed the sieve conception of environ- ments. According to this, we may regard the physical conditions of the surroundings as resembling a sieve or screen, with meshes of a certain magnitude, through which, as we may imagine, will pass only those successful forms which withstand the most adverse conditions of the environment. The analogy is but roughly applicable; to make it more so we may suppose that the size of the meshes in our screen is continually changing throughout the year, while the size of the imaginary particles which are to be screened are also undergoing continuous change with the advance of the organism from phase to phase of its development. With the progress of the season the con- 104 ENVIRONMENTAL CONDITIONS. ditions change and the powers of resistance also vary. Thus modified, the sieve analogy becomes unwieldy and does not aid us very much in our thinking. Since the behavior of a plant is nothing but the summation of the behaviors of its active parts, and since all higher plants exhibit, at any given phase in their growth, various gradations in the activities of their different tissues, it follows that any adequate consideration of the physiological limits of plant activity as a whole must be ex- ceedingly difficult. It is therefore impossible, in the present state of our knowledge, to treat the question of complex limits quantitatively. The best that may be done in the discussions which follow is to attempt to bring together a series of confessedly incomplete and exceedingly inadequate treatments of the main environmental factors and their general mode of action upon ordinary autotrophic land-plants. IV. GENETIC CONTINUITY OF PROTOPLASM AND ITS CYCLIC ACTIVI- TIES, IN CONNECTION WITH PROBLEMS OF DISTRIBUTION. In the preceding sections of this chapter the general terms of the problem of plant distribution have been presented in the words of the present-day physiology of plant organs. There can be little doubt that the day of this organic physiology is about to pass. It has been, of necessity, mainly descriptive and has not concerned itself prima- rily with the details of the actual causes of plant response and their mode of action, but there is already a strong tendency to turn attention from the description of plant organs and their responses to the physical causation of these, a development of physiology which bids fair to place this branch of science on the same quantitative etiological basis as that upon which physics and chemistry are now working. From the current literature of plant distribution and of ecology in general it is suggested that many workers in this field have so far failed to realize the present status of the physiology which lies at the base of all ecological facts. Ecology, which was at first regarded as a purely descriptive study, a mere cataloging of relatively superficial descrip- tions of phenomena and a classification of these, was an outgrowth of taxonomy. But it has advanced with more rapidity, perhaps, than any other branch of science, and it has already accumulated enough descriptions so that a beginning at least in the study of cause and effect has been made. Such a study must, by the very nature of its subject- matter, take account of all the contributions so far made by physiology towards an etiology of plant phenomena in their broader aspects. For a long time the physiology of organs must be the basis of ecological considerations, and it is with this in mind that we have taken the principles of organic physiology as the basis of our discussions. We have consciously avoided such ideas as that of purposeful adaptation and other teleological conceptions, still too common in botanical writ- ing—with what success the reader will best beable to judge—and have - INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 105 aimed to place our treatment of plant distribution on a basis as free from anthropomorphic conceptions as is that of physiography, a science with which plant geography must always be closely related. But the modern trend of physiology, with its application of the methods and findings of physico-chemistry and its tendency to seek explanations of all phenomena in the properties of matter and energy, offers to the study of distribution at least one conception which goes far to simplify the logic of physiological limits and their modes of variation. The present section will deal with this conception. From the standpoint of general physiology, the reproductive activ- ities are to be regarded as a special form of growth. The protoplasm of any species is a continuously existing thing, to be likened, perhaps, to a river, in which the material particles are ever changing and of which the form, course, activities, etc., show a continuous variation. The channel of our river moves from place to place within the limits of its valley; the river accomplishes much work of excavation and the like at certain seasons of the year; at other seasons it is inactive and, in the arid regions, often disappears from sight completely, flowing only underground. In the latter condition we may perhaps speak of it as dormant. Following this analogy, the living substance of any species may be thought of as continually existent, but varying widely in situation, amount, activity, etc., with the ever-fluctuating physical conditions within and without its mass. Thus the conditions for the success or failure of any species in any region or habitat are that its protoplasm be indefinitely maintained in that area, and that the various cyclic phases of physiological activity follow one another in a certain order. By such a conception we are enabled to generalize without the complication incident to the special consideration of the reproductive activities. Serutinized in this manner, fhe individuals of a given plant-form are seen in somewhat the same light as are the buds of an indefinitely growing perennial, such asa tree. These buds are continuously dying and being formed, but the system of growing-points which make up the tree possesses form, size, etc., and maintains itself throughout years. Growth here consists partly in the approximate replacement of parts which have been destroyed by the action of adverse condi- tions, and partly in an actual increase in the number of growing-points comprised within the entire system. By this sort of generalization we may bring all plant-forms into the same broad category, as far as the general influence of external con- ditions is concerned. ‘The protoplasm of any species, in any region, passes through variously active and dormant phases with the march of the seasons, the success of a species requiring that there be, at least, no progressive and permanent decrease in the number of growing- points or individual groups of active cells. But there may occur, and usually do occur—outside the tropics at any rate—great periodic fluctuations in the number and activity of these biotic units. 106 ENVIRONMENTAL CONDITIONS. Plant protoplasm may be said to pass through alternating phases or stages of dzastole and of systole. In the condition of diastole it is very active, increasing rapidly in amount and extending and altering its configuration to a remarkable degree. These changes are due directly to numerous physico-chemical processes and energy transformations which, during the period of this phase, are quite violently active. In the condition of systole, on the other hand, the various characteristic life processes are at a low ebb, some of them being apparently alto- gether abated. ‘The mass and extent of the protoplasm falls off more or less markedly, in the death of many parts which were previously the seats of vigorous activity, and in many cases the whole organism practically fails to exhibit any form of life at all. This rhythmic pulsation is of course immediately due to internal conditions, but the latter are, in turn, to be causally related either to changes in the envi- ronment or to effects of a constant environment summed or integrated by the organism. While the point of view just suggested is not at all new, and has been of great service to some students of heredity, we are not aware that it has been resorted toin studies of the influence of external con- ditions upon the maintenance of plant population in a distributional sense. It seems to promise such utility as a logical tool that we venture, in the following paragraphs, to outline the behavior of some of the main plant types in terms of this conception. Attention may first be directed to the case of a perennial which propagates vegetatively, omitting for the present any question as to whether seeds are produced. An excellent example of this is seen in several forms of much-branched cylindrical opuntias, as the various ‘““cholla’’ cactus-forms of the North American Southwest. By the action of various agencies, such as wind and animals, short branches are easily broken off from these plants, and are widely distributed by the operation of the same agencies and by that of flood-water. Under favorable conditions these fragments possess the property of taking root and forming new plants. Such may be regarded as the simplest form of species maintenance, and it is of course the rule among the lowest forms of plants. We have here to do with the mature plant at all times, the only complication in vegetative phases lying in the fact that roots are produced and proceed with their characteristic activ- ities under the peculiar conditions offered by the dispersal of the joints. With the coming of each favorable season, mainly defined by condi- tions of moisture and temperature, growth in size occurs in numerous branches, some of the latter being portions of larger plants, while others lie singly upon the ground. By the action of adverse conditions many branches are destroyed, but enough survive apparently to maintain the status of the species in the vegetation of its area. During the vear great fluctuations occur in the quality and intensity of the environ- mental factors; periods of extreme drought and heat, periods of drought and cold, periods of abundant moisture and either high or low tem- INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 107 peratures, follow one another in unending succession. In certain periods foliage is produced and growth proceeds with rapidity; in others the leaves disappear and growth is retarded or checked; in still others nearly all activities cease and the branches remain dormant till the return of conditions favorable to growth. In a manner similar to the above, we may consider all perennial forms that maintain themselves or spread by vegetative propagation, as in the case of those with underground branches, rhizomes, stolons, divid- ing-bulbs, and the like. Ina form like Solomon’s seal (Polygonatum), vegetative propagation is very important; a single rhizome may give rise to numerous hew growing-points (by means of branching), which eventu- ally become separated from the parent rhizome with the decay of the connecting portions, so that, if time suffices, a considerable area may be occupied without other activity than this purely vegetative one. Of course bulbs, tubers, and the like are to be regarded as plant phases which are characterized by dormancy and highly resistant properties, for which the physiological limits are widely separated. There occur all gradations in stem and bud vitality between the bulb or tuber and the great deciduous or evergreen tree, all agreeing in the essential point that with the coming of adverse conditions they undergo a check in their activities. The deciduous forms lose a large proportion of all of their vegetative organs. All these forms remain alive but dormant till the return of the growing-season. A second example may be taken from those tropical forms which reproduce by seeds, but in which vivipary vaults the resting-period usually so characteristic of the seed. A history of the activities in the mangrove, for instance, might run somewhat as follows: In the mature phase of this plant there are manifested cell activities which result in the dormancy of many cells. Some of the dormant cells, the eggs, are capable of resuming growth in size under certain conditions, the main condition being the entrance of protoplasmic material from another cell; that is, the occurrence of fertilization. If fertilization takes place, and this is to be looked upon as merely one of the environ- mental changes which act upon the plant in its cycle of developmental phases, then the ovum develops into an embryo and continues growth without any marked pause or resting-stage, forming ultimately a new plant. External conditions must furnish stimuli by changing in quality or intensity at various times in this development, one of the most special of which is the falling of the germinated seed into the mud below. We see in such forms all the usual phenomena of production by seed, but the pronounced dormant phase of the majority of seeds is omitted. However, unless the embryo root reaches the mud of the substratum (which signifies pronounced environmental change) the cycle of growth is checked. A third example may be chosen from among the plants which reproduce through seeds, but in which parthenogenesis bridges the interruption which usually precedes the formation of the embryo 108 ENVIRONMENTAL CONDITIONS. from the mature egg. Here no external change is apparently required to induce the ovum to proceed to the embryonic phase, but the embryo finally reaches a resting-stage, where growth activities are checked. Other alterations in the internal conditions of the dormant phase which we term a seed often require a prolongation of the resting- period, but, in any event, before active growth in size is again manifest definite changes in the external complex are required; the seed must absorb water to a certain degree, the temperature and rate of oxygen- supply must fall within the limits for germination, and various other conditions must be fulfilled in order that the embryo may emerge from its dormant state. The dormant phase of the mature egg is omitted or very much reduced in parthenogenesis, that of the seed in vivipary. The periods of rest, or of internal conditions adverse to growth, often coincide with periods of adverse external conditions, and the dormant tissue usually possesses high powers of resistance to the latter. This is a consider- ation the importance of which, in general climatic behavior and distribution of plants, can hardly be overestimated. Our fourth and last example is taken from the great majority of plants, where fertilization is necessary and a more or less prolonged period of dormancy intervenes between the maturation of the seed and germination. ‘The annual plant perhaps illustrates this sort of rhyth- mic activity in its simplest form. Germination occurs in the spring, when temperature, moisture-supply, etc., are favorable for this kind of growth. Later, the various developmental phases follow each other with more or less pronounced alterations in the external conditions, and when seeds have been matured the parent plant dies. This final death may occur because of the action of internal conditions, perhaps connected with the ripening of the seed, or because of the action of external factors, such as drought or frost. But the dormant phase represented by the seeds is highly resistant, and these bodies carry the living protoplasm forward through the winter of adverse condi- tions to the beginning of a new cycle of activity. The general conception outlined above may be expressed briefly to the effect that each particular sort of plant protoplasm (form, species) is indefinitely perennial, ever passing through repeated cycles, ever changing in internal nature from one developmental phase to another, growing, fragmenting (as in reproduction of all sorts), resting in a dormant condition, and always again taking up the endlessly repeating series. Of course our conception of the repetition here involved must be broad enough to include such alterations from cycle to cycle (variation, mutation, etc.) as the study of evolution demands for the origin of new forms from old. This mode of contem- plating plant activities should be as valuable in physiology and ecology as has been the conception of the alternation of generations in the descriptions of the consecutive steps in plant phylogeny. CHIEF ENVIRONMENTAL CONDITIONS AND THE GENERAL NATURE OF THEIR EFFECTS UPON PLANTS. I. GENERAL CLASSIFICATION OF ENVIRONMENTAL FACTORS. The environmental conditions that are commonly most potent in the determination of plant development, and that therefore appear most important in distribution, may be classified under the following headings: (1) Moisture conditions; (2) temperature conditions; (3) light conditions; (4) chemical conditions; (5) mechanical conditions. The present section will be devoted to a brief summary of the nature and effects of these factors as they vary in quality, intensity, and dura- tion. No attempt is made to denote more by the order of items in the above list than a very general estimate of the relative importance of the various factors as they are usually operative in limiting plant distribution. There is, of course, nothing to be gained in a discussion of the relative importance of a number of factors, all of whith are necessary in order that a given phenomenon may occur. Such con- sideration were as bootless as a discussion of the relative importance of the hub, spokes, felloes, and tire of a wheel. The reader is there- fore requested to make nothing of our order of arrangement. Students of ecological plant distribution have usually classified these sets of conditions according to their origin or source, rather than according to their mode of physically affecting the plant. Thus, the literature contains many references to climatic and edaphic condi- tions, physical and biotic ones, and the like. Such groupings seem, however, not to have led much farther than to the mere description and arbitrary classification of distribution conditions, and, since by their very nature they point to the causes of the factors imme- diately involved rather than to the real nature of these factors or their effects upon the plant, they promise little for our present purpose. Thus, shade produced by a natural rock arch or overhanging cliff may be impossible of physical or physiological differentiation from that produced by a tree; yet the former is said to be a physical factor and the latter a biotic one. Again, the mechanical relation of the physical separation of plant and soil, together with the accompanying ruptures and lesions of the plant tissues, might arise equally well from the action of animals (a biotic factor) and from that of wind or torrential water (undoubtedly physical factors). In a study of the ultimate causes that bring the proximate, effective factors into being, such classification has its value, but in such studies we have assuredly left our field of plant distribution for the adjoining one of climatology, physiography, and the rest. In the beginning it appears more promis- 109 110 ENVIRONMENTAL CONDITIONS. ing, because simpler and logically more direct, to attend strictly to the various factors as they actually affect the plant, leaving the analysis of the sources of these factors to other studies, perhaps at a later day. We shall here consider only the proximate determining conditions in plant behavior and distribution, merely mentioning a few points bear- ing on the more remote determination of these controlling conditions, which are available from researches in climatology and other fields. Since every effect upon the plant must be supposed to be directly traceable to conditions that previously prevailed within and without the organism, and since we make no attempt here to analyze the various physiological processes that constitute the varied plant re- sponses, it has been deemed best in these considerations to regard as an external condition or factor any status of the processes of the ex- ternal world that directly influences changes within the plant. Many logical difficulties arise here, as is usual when any attempt is made to subdivide a continuous series into regions, and the only satisfactory method of procedure is to subdivide the series into arbitrary portions, being sure to define the limits chosen. Thus, for ecological purposes it seems quite as undesirable at the present time to enter into the exceedingly complex physiological considerations involved in a study of the details of plant activities as these are controlled by conditions as it is to take up in detail the more remote causes which bring the various effective conditions into existence. This logical difficulty arises, of course, from the fact that the plant is not an independent system, but is perfectly continuous with the universe about it; the classification, into external and internal, of the conditions determin- ing chemical and physical changes within the plant, is at best but a ‘subjective affair with the mind that classifies. Whether a given con- dition is to be taken as external or internal will always depend largely upon the previous experience and point of view of the observer, upon his internal conditions. For the present needs it seems desirable to base our arbitrary definition of the controlling factors upon the spatial limits of the plant-body as ordinarily considered. Thus we define as effective external conditions all phases of universal progress outside the plant-body which directly affect the latter in such a manner as to produce alterations in the chemical, physical, and physiological processes that occur within. An example may illustrate this. The passing of a given region of the earth’s surface from shadow into sunlight at dawn is not a condition immediately effective upon plant processes, nor is the influx of radiant energy to the surfaces of objects in the vicinity of the organism. The plant-body is first affected in this case when there occurs an increased rate of transmission of light or heat energy through the periphery (or a decreased loss of heat, which amounts to the same thing as an increased income), so that some substance actually a part of the plant-body becomes lighted or warmed. CHIEF ENVIRONMENTAL CONDITIONS. bit It is only by a logical short-cut, not always tenable, that we may say that the rising of the sun produces such responses as the opening of stomata, the eastward bending of flower-heads, the assumption of the day position by nyctitropic leaves, and the like. From the logical standpoint, attention is here to be confined to changes in the rate of inward or outward transfer of the various forms of matter and energy between the surroundings and the plant-body itself. It must be confessed that, while most existing types of vegetation have been rather carefully, and in some cases perhaps even somewhat quantitatively, described, yet there appears so far in the literature scarcely anything of a fundamental nature upon the external factors and their modes of action in determining plant distribution.! It is thus largely upon quantitative studies of the intensity, duration, etc., of the external conditions and upon the true physiological inter- pretation of these that the future conquests of this branch of ecology must depend. It therefore seems desirable, even at the risk of ap- pearing to ‘‘carry coals to Newcastle,’’ to venture the following physiological discussion before taking up such meager contributions as can be brought together in regard to the geographical distribution of the different environmental complexes of the United States, as these may be related to the distribution of the various vegetational types. The different categories of environmental conditions will be con- sidered in the order of the preceding list, and attention wil be turned briefly to the various modes in which these are effective to bring the different plant responses about. In the interest of clear presentation, it will now and again be advantageous to overstep our logical limits in the other direction, and to touch upon some of the relations of the more remote conditions that, in their turn, influence or control the proximate and immediately effective environmental conditions. IT. MOISTURE. 1. WATER REQUIREMENT WITHIN THE PLANT. The very complex moisture-relations to which plants are subjected are to be considered as of the utmost importance in the great majority of distributional problems. These may be physiologically best studied from two standpoints—that of the requirement for water and that of the water-supply—since these two factors determine by their inter- action the moisture conditions of the plant. They may be taken up in order. Since every active cell is filled with water, it follows that there must occur constantly, or with but brief interruptions, 2 movement of water 1Serious beginnings in the direction of physiologically experimental investigation of the relations holding between plant-growth in the open and the controlling conditions of the environ- ment have been made by a very few workers. In this connection, see McLean's studies of the control of seedling soy-beans by the conditions of the Maryland summer climate (McLean, F. T., A preliminary study of climatic conditions in Maryland, as related to the growth of soy- bean seedlings, Physiol. Res. 2: 129-208, 1917). References to earlier literature are there given. See also: Hildebrandt, F. M., A physiological study of the climatic conditions of Maryland, as related to plant growth. Physiol. Res. 2: 341—405, 1921. 142 ENVIRONMENTAL CONDITIONS. into all enlarging portions of the plant-body. This demand for water, due to growth, is usually quite insignificant in degree, but it is never- theless real, and the absence or inadequacy of the water-supply to growing cells must always act as a check upon enlargement. Also, since water is destroyed in the process of photosynthesis in green plants, there must be a continuous influx of moisture into all photosynthetizing cells. If this supply is cut off, the formation of carbohydrates must cease in a short time. With insufficient water- supply, growth ceases before photosynthesis, but both processes must soon be brought to a standstill. The water demand occasioned by photosynthesis is perhaps usually more pronounced than that for enlargement, yet the rate of influx thus brought about is far too small in amount to permit of measurement by simple methods. Also, water disappears when hydrolytic decompositions occur, so that such processes as the digestion of starch are essentially drying processes. On the whole, these water requirements may be safely assumed to be only of relatively slight importance in comparison with that of transpiration, which is next considered. The fact that all plant tissues contain water, and that no cuticular or other covering is absolutely impervious to this liquid—many leaf- cuticles, etc., being rather freely permeable to water—makes it logically follow that there must ever be a more or less pronounced evaporation of water from all plant surfaces that are exposed to the outer air. This superficial evaporation through externally exposed membranes makes up the so-called cuticular transpiration, . which varies in amount in different forms, depending upon structure, and is often of great importance in determining the need of the plant for water. The water lost by cuticular transpiration is replaced from more deeply-lying tissues, according to the principles of diffusion and of imbibition, and sooner or later there must occur an inward move- ment of water from some region without the plant-body, or else death must ensue. But, while cuticular transpiration is a very real and almost con- stant source of water requirement, it is of relatively little account in comparison with stomatal transpiration. The presence of mem- branes of high moisture-content within the leaves—the walls of the mesophyll, etc.—which are in direct connection with the external air through the stomata, makes continuous evaporation from these internal tissues an inevitable condition, unless, indeed, the foliar surface be covered with a film of water or of a solution of higher vapor- tension than that which occurs within the tissues. The internal atmosphere is maintained more or less nearly in moisture equilibrium with the wet membranes that bound it, and ordinary diffusion through the stomatal pores constantly removes water-vapor to the outer air. CHIEF ENVIRONMENTAL CONDITIONS. 113 This water-loss, constituting stomatal transpiration, usually occurs at a rate much higher than that evidenced by cuticular transpiration. The ubiquity of this form of water requirement and its generally sreat magnitude render it the dominating physiological moisture condition for most plant-forms growing in the open air. However it may be removed, the water-content of an active tissue that is being depleted is always replenished at a greater or less rate from other tissues in the vicinity or from without the body. If such renewal of the water-content fails for a considerable time, partial or complete loss of activity must result. In plants without storage- organs the usual transpiration-rate can continue but a short time without entrance of water from the outside. Where storage-tissues are present the external supply may, of course, be cut off for a longer time. Since transpiration is the most important factor in determining the need for an external water-supply to the plant, it will be necessary to consider here some of the conditions that influence this process. Its rate is dependent upon three conditions: (1) the structure and condi- tion of the leaves or other transpiring parts; (2) the evaporating power of the air; (3) the intensity and quality of illumination. As is well known, there occur in different plants, under identical external condi- tions, great differences in the rate of transpiration per unit of surface. Certain structures, such as waxy and hairy coverings, palisade tissue, and other features, make cuticular transpiration markedly less pro- nounced than it might otherwise be, and many stomatal characters similarly influence the rate of stomatal water-loss. Many anatomical characters are known to become permanently altered by age, of course with reference to the nature of the environmental complex, as where cuticular thickening may increase or fail to do so, according to the age and surroundings of the plant. Such physiological responses are apparently dependent upon the rate of movement of transpiration- water (Pfeffer-Ewart, Plant Physiology, 2: 121). In regions where the evaporating power of the air rises rapidly during the growing- season, plants with a highly developed cuticular response of the form just mentioned may be expected to survive longer than others with a less-marked response of this kind. Stomatal movements, of opening and closing, may also be of considerable importance in certain cases, though this whole question is sadly in need of a more thoroughgoing physical investigation than it has yet received.' 1 Concerning the quantitative aspect of differences in the power of plant leaves to retain water and thus retard water-loss, see the following papers: Livingston, B. E., The relation of desert plants to soil-moisture and to evaporation, Carnegie Inst. Wash. Pub. 50, 1906.— Idem, The resistance offered by leaves to transpirational water-loss, Plant World 16: 1-35, 1913.—Livingston, B. E., and A. H. Estabrook, Observations on the degree of stomatal movement in certain plants, Bull. Torr. Bot. Club 39: 15-22, 1912.—Bakke, A. L., Studies on the transpiring power of plants as indicated by the method of standardized hygrometric paper. Jour. Ecol. 2: 145-173, 1914. 114 ENVIRONMENTAL CONDITIONS. The amount of water in the transpiring organs appears also to be important in determining the rate of water-loss. Thus, transpiration is frequently checked in the daytime, with no apparent wilting and no closure of stomata, but with a marked fall in foliar water-content, while the evaporating power of the air is maintained or even increases in magnitude.! Second only to the nature and condition of the leaves, etc., the evaporating power of the air exerts an enormous controlling influence upon the rate of water-loss from plants. For any particular plant- form it appears to be by far the most potent of all the climatic factors affective above the soil-surface. The evaporating power of the air is 2 compound factor, dependent itself upon three other factors, as commonly considered—temperature, humidity, and wind velocity. Its resultant effects are the summation of the partial effects brought about through the influence of these three factors upon the vaporiza- tion of water and the removal of the water-vapor from the evaporat- ing surface. Evaporation, as a climatic factor, will be more thoroughly considered in another place. The intensity of the sunlight and its quality are also potent factors in the determination of transpiration from plants. While a certain small proportion of the energy of the solar rays is made potential and entrapped in the plant by the photosynthetic process, by far the greater portion of that which is neither reflected nor transmitted becomes potential in the water-vapor that escapes from the plant by transpiration. Thus, intense sunlight with a good proportion of the longer waves is markedly effective to increase the transpiration-rate of plant organs whereon it falls. The color and structure of plant organs have also to do with this, through the influence these exert on reflection and transmission. With a smaller proportion of the greater wave-lengths or with less intensity the effect is not so marked.” Ecologists have classified plants, as to their ability to withstand different degrees of light intensity, into those which thrive best in shade, in bright sunshine, etc., and have given to these groups Greek names, but inasmuch as there are all possible gradations in this power of withstanding sunlight, and since there is as yet so little information of a quantitative nature bearing upon these matters, it seems advisable here merely to emphasize the fact that one of the most important influences of sunlight on plants is upon the rate of water-loss, and, therefore, upon the water-requirement. Another form of water-loss from certain plants is the active excre- tion of liquid moisture from nectaries and other superficial glands, such as water-pores, etc. The process by which this is brought about 1 Livingston, B. E., and W. H. Brown, Relation of the daily march of transpiration to variations in the water-content of foliage leaves, Bot. Gaz., 53: 311-330, 1912.—Shreve, Edith B., The daily march of transpiration in a desert perennial, Carnegie Inst. Wash. Pub. No. 194, 1914. 2 Livingston, B. E., Light intensity and transpiration, Bot. Gaz., 52: 418-438, 1911. CHIEF ENVIRONMENTAL CONDITIONS. 145 is not at all understood, but we may be sure that the water-loss thus occasioned is of no great general importance in the distribution of plant-forms, especially since the greatest excretion of water, as in guttation, usually occurs at times when the transpiration-rate is low and the supply of water within the tissues is relatively great. In- deed, one of the common teleological conceptions bearing upon the so-called regulation of water-loss by plants is that these organisms actively and purposefully force water out of their tissues whenever ‘they have been compelled by external circumstances to absorb more of the liquid than they want. To summarize the preceding paragraphs, the entrance of water into the ordinary active plant is essential to its activity: (1) because it is necessary for the enlargement of water-saturated cells; (2) because it is destroyed in photosynthesis, etc.; (3) because it is continually being lost by cuticular and stomatal transpiration and by excretion. 2. SUPPLY OF WATER TO THE PLANT. As has been emphasized above, the transpiring tissues of a plant must receive water from elsewhere, otherwise they would soon become wilted and collapse, and other active tissues must likewise receive water, though frequently in much smaller amounts. There are several sources from which this water may come. Water-storage tissues and dying cells, or cells passing into a dormant stage, may furnish more or less water to other tissues, according to the form of plant considered and its phase of development. A relatively very small amount of water, fixed previously by photosynthesis, must be set free in the tissues by the activity of respiration, and this may become available for growing cells or may be again transformed by photosynthesis. Also, the reverse of hydrolytic decomposition (such as the synthesis of starch from glucose) results in the chemical formation of some water. For the transpiration of ordinary plants the latter sources are surely inadequate.’ During rains, and when the temperature of the foliage falls below the dew-point of the surrounding air, the external surfaces of the plant become wet, and a considerable amount of moisture may enter the plant-body through the cuticle and even through stomatal open- ings. This source of water is especially important only for certain forms, such as mosses, liverworts, and plants of similar water-rela- tions. With heavy cuticle, trichome coverings, etc., very little water 1VFitting suggests that respiration water may be important in this connection in certain desert tubers, ete. (See Fitting, Hans, Die Wasserversorgung und die osmostischen Druckverhiltnisse der Wiistenpflanzen, Zeitschr. Bot. 3: 209-275, 1911.—Livingston, B. E., The relation of the osmotic pressure of the cell-sap in plants to arid habitats, Plant World 14: 153-164, 1911.) The latter is in part a review of Fitting’s paper. An excellent discussion and the most valuable ex- perimental treatment yet available of the amount and importance of respiration water in plants and animals is the following: Babcock, 8S. M., Metabolic water: its production and réle in vital phenomena, Wisconsin Agric. Exp. Sta. Bull. 22, 1912. 116 ENVIRONMENTAL CONDITIONS. can find its way into the tissues by these channels, and it follows that those plants that transpire the least must exhibit the smallest amount of leaf absorption. The main source of water-supply to the majority of plants is of course the soil or other substratum in which the plant is rooted. We may consider in greater detail the first and the last of the sources just mentioned. In relatively large plants the diffusion of water from non-active to active parts is often of great importance. Thus, as a tissue dies its contained moisture may pass into other portions and there support growth and other activities. A familiar example of this is exhibited by bulbs, rhizomes, etc., that produce leaves, shoots, and even flowers and fruits without the influx of any water from without. Water from the bulb moves gradually into the more active portion and supplies the moisture for growth and transpiration; here the so-called storage- tissue plays the same réle of water source as does the moist sub- stratum in the case of ordinary rooted and absorbing plants. In many instances water-bearing tissues may lose much of their water during the growth period of the plant and may still retain vitality and the power to absorb, so that at another season, when the external water- supply is greater, such tissues may receive water in larger amounts from the substratum and so return to their original turgid condition. In many cacti, fleshy euphorbias, and the like, all of the water for transpiration—a relatively small but nevertheless important amount— and even for reproduction may be derived from the quiescent stem parenchyma for long periods of time. Many water-storage plants of the desert can retain vitality and maintain their reduced transpira- tion for several years after they have been removed from the soil and are thus able to absorb no water from without.! Such isolated plants often effect new growth and ripen fruits with the return of the proper season, the conditions that bring about re- newed activity in such cases boule probably mainly those of tempera- ture. Of course, these forms must eventually succumb to lack of water, as must any other form when deprived of a water-supply, but the interesting point here is simply that they may withstand the absolute lack of a water-supply from without for exceedingly long periods of time. To most plants, a root system or its analog is essential throughout the actively transpiring phases of its development. As has just been implied, such a system must likewise be present a part of the time, at long intervals perhaps, even in the most extreme water-storage forms. Through these water-absorbing organs the moisture of the substratum finds its way to the tissues of the plant. This water often traverses long distances of stem, etc., and it is thus seen that the rate at 1MacDougal, D. T., E. R. Long, and J. G. Brown, End results of desiccation and respira- tion in succulent plants, Physiol. Res., 1: 289-325, 1915. CHIEF ENVIRONMENTAL CONDITIONS. i LZ) which the transpiring portions of a non-storage plant may receive water depends upon several conditions: the rate at which water may move in through to the absorbing surfaces, the nature and condition of the roots, and the nature and condition of the water-conducting tissues. In most cases where growth ceases or wilting occurs, the inadequacy in the water-supply seems to arise, not from the attainment of the physiological maximum of absorption and transmission, but from a greater or less drying-out of the soil, whereby it fails to transfer water to the absorbing roots at.a rate adequate to supply the demand of absorption. Quantitative information bearing upon the relations between soil-moisture and plant absorption and transpiration is not yet available, and our consideration of this exceedingly ‘important subject must be very brief and very tentative.' It is certain that, with diminished supply of soil-moisture and with other conditions remaining unchanged, transpiration in any plant must be decreased in amount, also that this diminution in the trans- piration-rate does not progress parallel to the continuous drying of the soil, so that it ultimately comes about that the supply fails to equal the demand, transpiration becomes greater than absorption, the non- storage plant ceases to grow, and wilting or even partial or total death ensues. Such a decrease in the rate of movement of water to the roots does not necessarily mean any considerable fall in the average percentage of moisture present in the soil, but gives evidence merely of the fact that the movement of water through the soil-films and into the roots has become less rapid. Under such conditions the soil immediately surrounding the absorbing portions of a root-system becomes drier than that at a greater distance, and the movement of water into the drier layer is too slow to keep the surface of the root adequately moist. This matter of the possible rate of water transfer from soil to root, fundamental as it is, is greatly in need of thorough investiga- tion. The subject has been opened by Livingston and Hawkins and by Livingston and Pulling in the papers cited above. This should prove a wonderfully productive field, both for scientific ecology and for agriculture when serious attention is at length turned to it. Great differences in the water-relations of plants in different habitats are secondarily occasioned by the nature and exposure of the soil in which they are rooted. Surface drainage often conducts the water of precipitation away before it can penetrate the soil to an adequate degree, and underground drainage frequently depletes the moisture- supply of porous soils almost as fast as water enters from a shower. Evaporation removes water rapidly from some soils and but slowly from 1Jn this connection see Livingston, B. E., and Lon A. Hawkins, The water-relation between plant and soil, Carnegie Inst. Wash. Pub. No. 204: 3-48, 1915.—Pulling, H. E., and B. E. Liv- ingston, The water-supplying power of the soil as indicated by atmometers, Jbid. 204: 49-S4, 1915. Also see: Livingston, B. E., and Riichiro Koketsu, The water-supplying power of the soil as re- lated to the wilting of plants, Soil Science, 9: 469-485, 1920. 118 ENVIRONMENTAL CONDITIONS. others, and the supply remaining to a plant after a period of dry weather depends very largely upon this factor. Fine-grained soils resist both evaporation and subdrainage, but they also resist water- absorption by plants, while coarser ones give up their water more readily! so that in a region frequently visited by drought the upland vegetation is, in general, most highly developed on the heavier soils. As to the internal conditions that influence the rate of water-supply to the transpiring parts of the plant, there appears to be, for any plant at any time, a maximum rate at which water can enter the roots and pass through the vessels. This rate seems to depend upon the extent of the root-system and upon the condition of the absorbing portions of the roots as well'as upon that of the conducting tissues in general. It is probably never for very long periods that this maximum rate is attained in moist weather; most plants at such times do not appear to transpire at a rate that exceeds their maximum rate of ab- sorption and conduction. Evidence has been obtained in the arid regions, however, and this probably holds also for dry periods in humid areas, that this maximum rate may frequently be reached when the rate of transpiration is greatly increased through high evaporating power of the air.’ In such cases growth ceases even with an ample supply of soil- moisture and the plant remains quiescent, without other sign of in- jury, till a lower evaporation-rate allows absorption and transmission again to surpass the rate of water-loss. Thus, in the spring dry season at Tucson, Arizona, morning-glory plants attained a few leaves and then rested without growth until the higher humidity of the summer season arrived, although the soil in which they were rooted was kept continuously at or somewhat above its optimum water-content by irrigation. When the evaporation-rate had fallen markedly, with the coming of the cloudy and more humid summer rainy season, these plants resumed their growth in the usual manner.?® The ability of a plant to absorb and conduct water is, of course, an internal condition, which depends upon many things. Naturally, the more extensive is the absorbing surface of the roots the more 1 Of several soils with approximately the same chemical composition, but differing in the size of their particles, that with the finest particles gives ordinarily the most luxurious vegetation. The physical and physiological reasons for these phenomena have apparently not been taken up in detail. In this connection see Livingston, B. E., and G. H. Jensen, An experiment on the relation of soil physics to plant growth, Bot. Gaz., 38: 67-71, 1904. On the capillary move- ment of water in natural soils, see: Pulling H. E., The rate of water movement in aerated soils, Soil Science, 4: 239-268, 1917. 2 Livingston and Brown (1912): Brown, W. H., The relation of evaporation to the water- content of the soil at the time of wilting, Plant World, 15: 121-134, 1912.—Briggs, L. J., and H. L. Shantz, The wilting coefficient for different plants and its indirect determination, U.S. Dept. Agric., Bur. Plant Ind. Bull. 230, 1912. Other citations of this work are given in the two fol- lowing papers: Caldwell, J. S., The relation of environmental conditions to the phenomenon of permanent wilting in plants, Physiol. Res., 1: 1-56. 1913.—Shive, J. W., and B. E. Livingston, The relation of atmospheric evaporating power to soil-moisture content at permanent wilting in plants, Plant World, 17: 81-121, 1914. 3 Livin gston, 1907. a- CHIEF ENVIRONMENTAL CONDITIONS. 119 rapidly may moisture enter, providing, of course, that the maximum rate of supply of soil-moisture to this surface is not surpassed. Also, the rate of absorption must be markedly affected by the condition of the absorbing membranes and the cells adjacent to them. If these tissues are pathologically modified, as by the presence of poisons, even a large extent of root surface may fail to allow as much water entrance as might occur through a smaller root-system in a healthy condition. The condition of the vessels in the stem, etc., whether well or poorly developed, whether the lumina are large or small, and whether cross- walls are frequent or not, is an important factor in determining the maximum rate of water conduction with a given pressure gradient. It will be remembered in this connection that the primary deleterious effect of certain fungus growths within the vessels is due to a simple stopping of these passages. In such cases the plant might suffer from lack of water, although its roots possessed an adequate power of ab- sorption and were in a soil of adequate water-supplying power. Of course, the causes of the internal conditions above mentioned are to be sought in previously effective external and internal condi- tions, as the effects of which any present status of affairs must be considered; but this phase of environmental influence lies far beyond the matters with which we are here concerned. 3. RELATIONS BETWEEN WATER-REQUIREMENT AND WATER-SUPPLY. From the above consideration of the water-requirement and water- supply of plants it is clear that growth and other activities are not dependent upon either of these factors alone, but depend upon the relation that holds between them. It is this relation which gives the clue to all physiological and ecological problems concerning mois- ture. So long as water moves into any tissue as rapidly as it is re- moved, that tissue may maintain itself in a quiescent state; so long as the possible rate of influx surpasses the actual rate of loss, the tissue may increase in size and carry on any processes requiring the fixation or destruction of water; and whenever the supply falls below the de- mand (7. e., whenever the demand exceeds the supply), growth and many other activities must cease. If the latter condition continues long, partial or total death must follow, or at least the more or less complete entrance of the organism into a state of dormancy. The effect upon the plant is the same, whether the physiological lack of water be brought about through an increase in the demand, through a decrease in the supply, or through both of these acting together. 1 Livingston, B. E., Note on the relation between the growth of roots and of tops in wheat, Bot. Gaz., 41: 189-143, 1906.—Livingston, B. E., J. C. Britton, and F. E. Reid, Studies on the properties of an unproductive soil, U. S. Dept. Agric., Bur. Soils Bull. 28, 1905.—Livingston, B. E., Further studies on the properties of unproductive soils, U. S. Dept. Agric., Bur. Soils Bull. 36, 1907. 120 ENVIRONMENTAL CONDITIONS. Higher evaporation-rate or increased solar intensity may raise the rate of transpiration in any plant until it surpasses the possible rate of supply to the transpiring parts. On the other hand, the drying- out of the soil or a pathological condition of the absorbing or conduct- ing system of the plant may reduce the rate of entrance or transmis- sion of moisture until the transpiring tissues suffer from dryness. The effect of this physiological drought, however caused, is a gradual loss of water and hence of turgor, which results finally in plasmolysis and wilting. Under such conditions tissue enlargement must cease before plasmolysis is accomplished, and can not begin again until a certain amount of turgidity has been regained. As long as the ratio between the rate of possible water-supply and. the rate of water-demand in any tissue or organ is greater than unity, growth may occur. When this water ratio falis to unity growth must soon cease, though the organ may retain its form and vitality. When the water ratio becomes less than unity, incipient drying occurs and plasmolysis must soon follow if the ratio continues less than unity. Whether plasmolysis and wilting result in the death of the tissue in- volved depends upon the extent to which the ratio falls below unity and upon the length of the period during which this condition obtains.* Of course, it must be remembered that the matter here brought forward is very much complicated by the free interchange of water by various parts of the plant itself; the wilting of a certain tissue may not denote anything out of the ordinary in the plant as a whole, for the normal process of development often includes many reversals in growth. Thus, a tuber grows for a long time and then loses its water and other contents, while the entire plant of which such tuber is a part may be said to be continually advancing through its development phases. With the continuation of a drought period most plants die only by degrees; the lower and older leaves are apt to succumb first, and it is only after a somewhat protracted dry period that total death of an individual occurs. Even in such cases the existence of seeds usually carries the vital substance forward to the next favorable season. The withering and falling away of a few of the older leaves often acts as an automatic removal of the drought conditions, for such a decrease in the transpiring surface may so diminish the transpiration-rate as to prevent further wilting. The same result is frequently brought about by a temporary lowering of the evaporating power of the air or of the light intensity. The tendency to wilt, which is manifest in most plants on dry, sunny afternoons, though no actual wilting may occur, is regularly checked by the coming on of night with its conse- quent lowering of the evaporation-rate, and also, sometimes at least, through closure of the stomata. The water ratio of transpiring organs 1 Livingston, B. E., Incipient drying in plants, Science, n.s., 35: 394-395, 1912.—Caldwell 1\35- CHIEF ENVIRONMENTAL CONDITIONS. DAS thus falls during bright days and rises again at night. In the arid regions it appears that this night period of recovery is of very great importance. Many plants that are normally very resistant to drought conditions as they occur would probably succumb com- pletely on the second day if the night period of recovery of the water ratio were omitted. A shower of rain affects both terms of the water ratio; it increases soil-moisture and decreases evaporation, while incipient drying or partial plasmolysis may sometimes be almost immediately corrected through actual absorption of moisture through leaf surfaces wetted by rain. In the majority of ordinary plants the water of transpiration passes with comparative directness from the absorbing surfaces of the root- system to the transpiring surfaces of the foliage. Stored water is here of little general importance. Outside of the arid regions such plants appear to absorb and transmit moisture from a moist or wet soil with sufficiently great rapidity to prevent any serious wilting, even with the highest transpiration-rates; that is, the maximum possible rate of absorption is seldom inadequate. But, with a soil that is becoming dry, there comes a time when the actual rate of ab- sorption fails to keep the water ratio above unity, and in such cases wilting soon occurs. If a plant wilts for this cause it may be made to revive by mere addition of water to the soil about its roots. How- ever, if the maximum possible rate of conduction is at fault (which depends, as has been seen, upon the structure and condition of the roots, vessels, etc.), such treatment will fail to produce a complete return to the usual condition. (Caldwell 1913.) Before the problem of the quantitative aspects of wilting and of general plant behavior with regard to moisture may be seriously ap- proached, the study of soil physics and of water absorption, conduc- tion, and transpiration, must furnish us with means of determining with fair accuracy the terms of the water ratio. The study of soil transmission and plant absorption have been strangely neglected by students of plant physiology. That of transpiration and the condi- tions controlling it has progressed somewhat further, but much remains to be determined. No field of plant physiology promises greater conquests than this one of the water-relations, either from the stand- point of pure science or from that of a rational plant-culture. (Living- ston and Hawkins 1915; Pulling and Livingston 1915, also Pulling 1917. When a plant wilts from lack of soil-moisture it is well known that the soil about its roots is not dry, but always contains a considerable amount of water. This residual water, left after the roots have ceased to absorb, has been called ‘‘non-available.’’ Under a given set of con- ditions this moisture-content appears to be constant for any plant and for any soil, but the conditions upon which the magnitude of the resid- ual soil-moisture content depend are much more complex than has usually been thought (Shive and Livingston 1914). 122 ENVIRONMENTAL CONDITIONS. As the soil adjoining the absorbing membranes becomes drier, the surface tension of the capillary films about its particles increases until it finally equals or surpasses the imbibition attraction for moisture exerted by the exposed walls of the absorbing-cells. These capillary phenomena are the main factor in the attraction of the soil for water, and it is this capillary force against which the forces that produce water-entrance into plant roots must operate. It therefore appears that, at the time when absorption ceases, we may expect to find the vapor-tension of the exposed root-membranes just balanced by that of the soil solution. The amount of water remaining in different soils, with different plants, has been determined by various workers, and it has been taken to vary with the nature of the plant and with that of the soil. It is lower in sandy soils than in heavier ones, depending thus upon the specific attraction of the soil for water, a variable which depends largely upon the size of the soil particles. Non-available soil-moisture has often been treated briefly and summarily in texts and monographs as a soil constant. This it assuredly is not,? for with a given plant and a given soil, this factor may be made to vary within wide limits, according to the status of the other conditions. It depends, indeed, for any soil and any plant, upon the transpiration-rate for the period during which wilting occurs. The higher the rate of water-loss from a plant the more water will there be in the soil about its roots when permanent wilting occurs. Plants in a moist room remove more water from the soil in which they are potted before permanent wilting occurs than do other similar ones in a dry room or in the open. This state of affairs might have been inferred from the principles already brought out, that the drier the soil becomes the less rapidly will it conduct moisture to the roots of a plant, and that when the transpira- tion-rate surpasses that of intake, there must be a tendency toward wilting. The residual moisture content of a soil, with reference to a certain plant when wilting occurs, is simply the amount of water which that soil contains when the rate of water absorption and conduction to the foliage have been, for an adequate period, less than the rate of loss from the leaves. The length of the period of lag which elapses between the time when the rate of foliar water-supply first falls below that of transpiration and the time when permanent wilting ensues 1The best general treatise on soils and their relation to plants is, so far as we are aware, Mitscherlich, E. A., Bodenkunde fiir Land und Fortswirte, Berlin, 1913. The work can not be too highly commended as, in general, a logically and physically sound treatise on this, one of the most difficult of biological subjects. On the general phenomena of capillarity and the complex principles upon which these depend the reader may be referred to Freundlich, H. Kapillarchemie, Leipzig, 1909. 2 Livingston, B. E., Present problems of soil physics as related to plant activities, Amer. Nat., 46: 294-301, 1912.—-Briggs and Shantz 1912, Brown 1912, Caldwell 1913.—Shive and Livingston 1914. CHIEF ENVIRONMENTAL CONDITIONS. 123 must be a function of the internal water-conditions of the plant-body and of the difference between the rate of supply to the roots and the rate of transpiration. It will be seen at once that a statement of the residual water-content for any soil and plant is meaningless without a statement of the transpiration-rate at the time the determination was made, or, at least, the statement of some measure of the condi tions that determine transpiration. It is apparently quite possible to define these conditions with some precision by means of measure- ments of the evaporating power of the air. Aside from actual dryness of the soil, another condition produces the same effect upon the plant. This is included in what has been termed by Schimper physiological dryness. ‘This condition exists where a plant apparently suffers from drought and yet is rooted in a moist or even wet soil. The optimally moist soil of the experiment with morning-glory described on page 119, might be said to be physiologically dry for that plant under those conditions of transpira- tion. The term more commonly connotes those cases where the plant suffers from lack of water, due either to some pathological condition of the roots or conducting organs or to a too high physical concentration (osmotic pressure) of the soil solution. In either case the symptoms are those produced by a dry soil, but the actual amount of moisture present in the soil may still be relatively very high, or the soil may even be completely saturated. The best known cases of adverse osmotic conditions in the soil solution are those of the so-called ‘‘alkali’’ soils, where the salt-con- tent is usually high, although the component salts are not highly toxic. In such soils ordinary plants suffer from lack of water, ap- parently not because water movement into the roots is checked through increased external capillary resistance, as in a soil that is actually nearly dry, nor because of toxic effects, but merely because of the high osmotic pressure of the soil solution itself, which may result in plasmolysis of the superficial root-cells and the consequent derange- ment of the absorbing mechanism. Plants that are characterized by an unusually high osmotic pressure in their absorbing organs seem to succeed in such soils.! Those instances of physiological dryness which are produced by injury or by a pathological condition of the absorbing or conducting system need not here be treated in detail; it needs only to be re- marked that any condition leading to an inadequate power of absorp- tion or conduction may bring about a correspondingly inadequate water-supply and, in general, may result in the same symptoms as those produced by soils of low moisture-content or of low power of water delivery. 1 See in this regard Fitting, 1911, and the remarks on this paper by Livingston, 1911. 124 ENVIRONMENTAL CONDITIONS. The factor of duration is exceedingly important in the moisture- relations of plants. While cessation of enlargement must immediately ensue with incipient plasmolysis of a growing tissue, a partially plas- molyzed tissue may retain vitality for a long time and may imme- diately recover with the return of an adequate water-supply, provided that the process of desiccation has not progressed too far. Thus, many plants complete their growth in seasons and in regions where wilting occurs for several hours daily, this being corrected and positive growth being accomplished during the cooler or more moist hours of the day. For such forms a change in the rhythm of fluctuation of the water ratio might prevent maturation or reproduction, although the fraction of the total period of growth represented by the total period of wilting might remain unchanged. Also, the after-effect of adverse conditions being, as it seems, generally more pronounced than that of favorable ones, rapid fluctuations between adequate and inadequate water ratios frequently result in much less growth than would have occurred in a continuous period of favorable conditions, although the latter were of no greater duration than the total of all the short favorable periods really experienced by the plant in the first case. This factor of fluctuation or variation in the environment is especially difficult to consider at the present time; it is mentioned here only to throw emphasis on an important phase of the duration factor which will need careful investigation in the future. With regard to the quantitative aspect of the moisture limits which plants are able to withstand, very little information is available. Since the activities of the plant as a whole are the summation of the activities of its various parts, we must regard the primary moisture condition that is effective in the control of plant activity as simply the water ratio obtaining in the active tissues. But practically nothing has so far been done with this dynamic aspect of the water- relation. The determinations that are available bear simply upon the amount of desiccation which various forms or organs may bear. Many of the scattered observations on this point are presented in Ewart’s translation of Pfeffer’s Plant Physiology under the heading “Desiccation.’’ To obtain further information bearing upon the point in which we are at present interested, the whole viewpoint needs to be somewhat different from that heretofore employed. The moisture-contents will need to be uniformly calculated to comparable terms, such as to the basis of dry weight or natural volume, and the different regions of the bodies of higher plants will have to be separately considered. In connection with the foregoing discussion of the relation between the rates of entrance of water into the plant and those of its exit, Woodward’s! conception of the water requirement of plants should 1Woodward, J., Some thoughts and experiments concerning vegetation, Phil. Trans. Roy. Soc. London, 21: 193-227, 1699. CHIEF ENVIRONMENTAL CONDITIONS. 125 receive some attention. The water requirement, in this special sense, denotes the ratio of the total water-loss by transpiration to the yield of plant material for any given period of time, usually for the entire erowing-season. This conception has recently received renewed attention and very thorough study at the hands of Briggs and Shantz,’ who have employed it as a physiological criterion by which to compare the relative drought resistance of agricultural plants. If several different plant-forms be grown under the same set of climatic conditions, it is found that the different forms differ in their water requirements; the amount of water required to produce unit weight of crop is greater in one case than in another. In such a case the plant with the lower water requirement is the one giving the larger crop with the smaller amount of water, and it is obvious that this criterion must be very valuable in the study of agricultural con- ditions in arid and semiarid regions. It is also clear that such com- parisons between plant-forms are always made with reference to some given set of climatic conditions; if one form has a lower water re- quirement than another for one climate it does not follow that the same relation must hold for the same two forms in another climate. Thus, relative water requirements need always to be stated with reference to a particular environmental complex, which must be de- fined as precisely as is possible. Of course the water requirement of a given plant-form may also be employed as a criterion by which dif- ferent sets of environmental conditions may be compared, the physio- logical properties of this plant-form being the standard of measure- ment in such a case. This whole matter promises much for both agricultural science and the ecology of uncultivated plants, and it may be predicted that water requirement will assume greater impor- tance in discussions of plant water-relations, as this field becomes more thoroughly investigated. The foregoing general and incomplete treatment of the subject of the influence of water conditions upon plants may suffice for the present. It is to be hoped that the future may furnish well-collected and well-related data on these questions and that some of the experi- mentation to be carried out in the future may be more adequate to the purposes of ecology and agriculture than is much of the hap- hazard experimentation so far predominating in the literature. 1 Briggs, L. J., and H. L. Shantz, The water requirement of plants, II, A review of the literature, U. S. Dept. Agric., Bur. Plant Ind. Bull. 285, 1913. This is a very complete and valuable annotated bibliography of the subject and includes discussion of and references to the writers’ own work. In this connection see also Shive, J. W., A study of physiological balance in nutrient media, Physiol. Res., 1: 327-397, 1915. P. 379. 126 ENVIRONMENTAL CONDITIONS. Ill. TEMPERATURE. 1. TEMPERATURE REQUIREMENT WITHIN THE PLANT. One of the fundamental conditions that have to be fulfilled in order that life processes may go forward is that the body of the organism must possess a temperature lying between certain limits; the tem- perature of the living cells must be neither too high nor too low. If the temperature rises beyond the maximum temperature limit for life, or if it falls below the corresponding minimum, death must follow. In this consideration, which is one of the most clearly established principles of physiological science, it is to be borne in mind that the numerous processes, or material and energy transformations, that make up life are partly chemical in their nature and partly physical. All processes that result in an alteration in the kind of matter within the plant are chemical. Here belong photosynthesis in green plants, all the various kinds of chemosynthesis, and all processes of oxidation and reduction, of hydration and dehydration in the chemical sense, of polymerization and hydrolysis, etc. On the other hand, all proc- esses that result merely in a change of state of the matter within the plant-body are physical. These latter do not usually receive so much attention at the hands of physiologists as: do the others, and they are probably not as well known, but they are certainly no less important. As examples of such physical changes may be men- tioned such processes as coagulation or precipitation of substances out of solution or suspension, the various possible alterations in the viscosity of liquids, and even the transformations that may occur between the solid, liquid, and gaseous states of matter. It is fre- quently true of physiological phenomena that the chemical and physical processes are so closely related that it is impossible to relegate a material change to either category alone. In this connection it may be recalled how modern researches along the border-line between physics and chemistry are tending more and more to erase this line and to prove it to be quite an arbitrary demarcation. | All of the innumerable processes, physical and chemical, that occur in the living plant must be thought of as having their temperature limits, just as has the grand summation of these processes. In so far as physiological studies have gone in this connection, it appears that each component process possesses temperature limits more or less different from those of others, and also different from those of the grand summation. Thus, with falling temperature growth in size is checked when a certain minimum temperature is reached, at lower minima cell-division and photosynthesis are also checked, and at a still lower minimum respiration ceases and death ensues. It follows from this that general plant activity can not proceed at any tempera- CHIEF ENVIRONMENTAL CONDITIONS. 127 ture that might prevent the occurrence of any of the simpler physical and chemical changes essential tothe make-up of this general activity. According to the kinetic theory of matter an alteration in the tem- perature of any body is to be considered as a change in the rate of motion of its component particles and, consequently, as a gain or loss of kinetic energy by the latter. The degree to which this energy of motion is possessed by the molecules, etc., of a mixture—that is, its temperature—is to be regarded as the proximate condition determin- ing the nature of the transformations that occur therein. Therefore every temperature change must be regarded as affecting a more or less marked alteration in the velocity of each of the many physical and chemical processes that make up the life activity of a plant. It is possible, therefore, to proceed a step farther than we have gone in our generalization above. Not only is it true that the prime essential temperature condition for general vitality is that a tempera- ture must obtain under which all the necessary component processes may occur, but the temperature must be such that these component processes may go on with adequate velocities. They must not proceed with too high nor with too low rates; otherwise death must occur. Thus photosynthesis, for example, might occur in a plant at a certain temperature, but the rapidity of the formation of carbohydrates might at the same time not be great enough to make up for the loss entailed by respiration, growth, etc., at that temperature. As has been mentioned in another place, however, it is quite possible for an organism to survive a brief period of exposure to a condition to which it would succumb with a more prolonged exposure. It is clear, then, that the temperature limits usually given for plants are not definite and quantitative measures of the limiting conditions for vital activity unless they are taken in connection with the length of time during which the organism is subjected to these temperatures. The question of the duration of temperature conditions in connection with the establishment of physiological limits has received attention from Blackman,’ from Miss Matthaei,? and from Lehenbauer,’? and is worthy of still further study. From the foregoing paragraph we may formulate the following statement of a general and fundamental principle regarding the rela- tion between temperature and vital activity. The temperature of the living plant-body must not remain for more than a maximum time period at any temperature which, if longer continued, would cause any essential physical or chemical process of the general life activity to surpass the minimum or maximum limit of its velocity. 1 Blackman, (1905)—IJdem, The metabolism of the plant considered as a catalytic reaction, Science, n.s., 28: 628-636, 1908. 2 Matthaei, Gabrielle L. C., Experimental researches on vegetable assimilation and respiration. III. On the effect of temperature on carbon dioxide assimilation Phil. Trans. Roy. Soc. London, B. 197: 47-105, 1904. ’Lehenbauer, P. A., Growth of maize seedlings in relation to temperature, Physiol. Res., 1: 247-288, 1914. 128 ENVIRONMENTAL CONDITIONS. The temperature limits for vigorous activity, as these are usually given, are very different for different plants. The lowest minima are somewhat below 0° C., while the highest maxima are above 60° C. For the retention of life in dormant phases the range is, of course, much greater than for vigorous activity. Dry seeds can endure, for long periods, temperatures far below the freezing-point of water and far above the boiling-point. It needs to be emphasized that the water- content of a tissue is highly important in determining what may be its minimum and maximum temperature and the duration of such temperatures that it may survive. 2. RELATION OF TEMPERATURE WITHIN THE PLANT TO CONDITIONS OF THE ENVIRONMENT. Material changes, whether physical or chemical, generally result in the warming or cooling of the medium; some heat is generally produced or else disappears with each material alteration. Wher- ever material processes are going forward in the plant, heat must be continuously supplied, or else it must be as continuously removed; otherwise the temperature of the body must fall or rise and a cor- responding alteration in the processes themselves must ensue. In the case of a living plant the many physical and chemical processes of its life must, of course, influence one another, in velocity and direc- tion in various ways, among which the mutual effect of heat absorp- tion and liberation must be important. Thus the heat set free by respiration may be of primary importance in maintaining a possible temperature for cell growth, and the absorption of heat by transpira- tion is probably often the prime condition that prevents a too great rise in tissue temperature. If there were no outward or inward passage of heat through the periphery of the plant, it is obvious that life could be possible only so long as this complicated interplay of the heat effects of the various physiological processes were automatically so limited that no essential process might be too greatly altered by temperature change. But, just as the moisture conditions of the plant-body are usually much more influenced by water changes between it and its surroundings than by the generally insignificant destruction and formation of water within the tissues, so also the internal temperature conditions usually depend mainly upon heat exchanges with the exterior, and the internal absorption and liberation of heat which has just been considered are of prime importance only in relatively few cases, if they ever are at all in nature. The temperature of the plant tends closely to follow that of its environment; roots can seldom possess a temperature markedly dif- ferent from that of the surrounding soil, and stems and leaves are never very much warmer or cooler than the air that bathes them. If the vital processes result, at any time, in the liberation of heat, a CHIEF ENVIRONMENTAL CONDITIONS. 129 marked rise in temperature is prevented by outward conduction and radiation, and the body-temperature remains automatically at about the same point as that of the material surroundings. On the other hand, if the summed result of physiological changes be a disappearance of heat within the cells, then any considerable fall in tissue-temperature is automatically adjusted at an incipient stage by intake of heat from without. The only exceptions to this rule that are worthy of mention here are the cooling effect of transpiration, whereby the temperature of foliage is sometimes as much as a few centigrade degrees below that of the air, and the heating effect of sunshine, whereby leaves are some- times a few degrees warmer than their surroundings. From thermodynamics we may be sure that the outward and inward conduction of heat are automatically self-controlling, heat not being conducted from a cooler to a warmer body. Thus an atmosphere at a given temperature will never, by heat conduction, render a plant either warmer or cooler than the air itself. But it is possible for a plant, or other body, to receive heat by radiation from an imme- diate environment the temperature of which is much lower than its own. Conversely, for a time at least, it may radiate heat into an immediate environment having a higher temperature. The first case is very important in many instances, as in the absorption of sunlight by green leaves, which will be considered under the topic “ Light.” The second is of much less frequent occurrence, but may sometimes be important in the cooling of leaves on clear nights when radiation is rapid. As in the case of the entrance and exit of water, the nature and condition of the plant surfaces exert a considerable influence upon the possible rate of entrance or exit of heat, either by radiation or conduc- tion. The effect of a more or less thorough insulation of the plant- body would, of course, be the introduction of a correspondingly pro- nounced lag in the temperature changes of the plant, as far as these are due to radiation or to conduction to or from the exterior. Thus, after a temperature change in the surroundings, some time may elapse before uniform temperatures within and without again prevail. In the case of roots this feature is probably of but little importance, although the results of secondary growth often produce on old organs of this sort a layer of cork and other modified cells of sufficient thick- ness, so that a considerable retardation of heat conduction no doubt ensues. Heat radiation appears to be of little or no importance in subterranean organs. The aerial portions of the plant exhibit more considerable effects of the retardation of heat transmission. This is especially notable in many buds, in the stems of the larger plants, such as trees, and in densely hairy leaves. The bark of the cork oak is familiar to every- 130 ENVIRONMENTAL CONDITIONS. one as a substance with a low power of heat conduction, and the hairy buds and younger leaves of such forms as mullein (Verbascum thapsus) are known to assume the temperature of their surroundings, after a rapid temperature change in the latter, with a distinctly sensible lag. One of the main internal conditions affecting the rate of outward and inward heat conduction is that of moisture-content, which, as we have seen, is also of great importance in the determination of the rates of intake and outgo of water. The rate of absorption or elimination of radiant heat is affected also by the nature of the plant periphery; rough surfaces radiate and absorb a greater proportion of energy rays than do smooth ones; plaited and folded surfaces radiate and absorb much less than plain ones of equal area; the color of the tissue is highly important in this connection, and the exposure of the surfaces considered, with reference to the earth’s surface and to the sky, is also of primary importance. Most of the heat radiation and absorption by plants occurs in the direction toward and from the sky, and by far the greater portion of the radiant energy absorbed is from direct sunshine. This latter feature has been emphasized in our discussion of transpiration and will be touched upon again in connection with the treatment of light. Of course, it is to be remembered that the effect of heat radiation in producing a body-temperature higher or lower than that of the sur- roundings is soon limited by the increased rates of both radiation and conduction in the opposite direction, so that very great differences between outside and inside temperature are not to be expected. The heating effect of direct sunshine upon green, transpiring leaves is limited, not only by outward conduction and radiation, but also by the cooling effect of transpiration. Even in intense sunshine the temperature of turgid, rapidly transpiring leaves is frequently or usually below that of the surrounding air.! The main generalization in connection with the temperature rela- tion is simply that the temperature of the plant is never very different from that of its immediate surroundings. The important effect of the different rates of heat exchange between plant and environment is practically confined to the determination of the temperatures of leaves and other similarly exposed parts when under the direct rays of the sun, and to the production of a more or less pronounced lag in the tissue temperature changes brought about by great and rapid alteration in the environmental temperature. 1 Shreve, 1914. CHIEF ENVIRONMENTAL CONDITIONS. 131 3. THE DURATION ASPECT OF THE TEMPERATURE RELATION. The velocities of the many physical and chemical changes that compose vital activity as a whole, depend, as has been seen, upon the temperature. It follows that the outcome of each separate process, and that of the entire complex, is largely determined by the degree of temperature and by the length of the time period during which any temperature has obtained. The accomplishment of the entire plant, as measured by the amount of its growth, for example, might be the summation of the various accomplishments of the component processes during the given time period, which latter are simply the integrations of the various process velocities with respect to time. Since we are very far from being able satisfactorily to separate the component processes that go to make up the activity of any plant, it is necessary here only to call attention to the above proposition as representing a general principle the details of which must occupy many minds in the future. For the present the physiological ecologist can do nothing but consider the varying velocities of certain broad, complex processes such as growth, crop production, and the like. But our generaliza- tion is of use at least in this, that it enables us to lay out the field for future study, with a probability of satisfactory results that might otherwise be absent. We have seen that physical and chemical processes are intimately commingled in the intricate complex which we call life. To this con- ception may be appended the additional one that many of the physical properties, probably all of them in the final reckoning, depend upon chemical changes which have previously occurred. It is quite im- possible for a physical change to occur in the substance of a plant unless the various materials involved be present, and these may be assumed, in general, to have resulted from chemical changes. Since we know already that chemical action is exceedingly important in most plant phenomena, the last statement allows us tentatively to state that this action may probably be found to have the controlling in- fluence in general life activities. If this be true, the general activi- ties of the plant should follow more or less accurately the principles of chemical action. The relation of chemical processes to temperature have been much worked upon and the law of Van’t Hoff and Arrhenius has been developed in this connection. It states that for each rise in temperature over a range amounting to 10 centigrade degrees, there is a doubling or tripling of the reaction velocity. Often the coefficient is 2 or a little more or less (PH; =P+Hs, 1.2; C.H;0,. . C.H;+NaOH, 1.89)*. Usually it is between 2 and 3 (C,H;ONH, soles te pats Mar. 23 | Nov. 22 244 Cedarville (15)........... AGG) ain cates age Mar. 15 | Oct. 6 205 ERAICONCED) aise ie Gane so a BO oi NE ak aaah a, Mar. 27 | Dec. 6 254 SION CIA oo toes 6 sles DLAs i atic Spas Be Feb; 28: | Dee!) 2 277 Claremont (14)........... DDO os Uy ova 6 Mahone ake Mar. 17] Dec. 5 263 Cloverdale (14, 16)........ SAD ee a cece Mar. 41] Dec. 6 277 Colton (14) oe oe Se BGS he eis atom ae Jan. 22/]Dec. 4 316 Craftonville (14).......... be (is 2 Se | ABE Feb. 7 | Dec. 26 322 Crescent City (16)........ 15) 0 RE Raa NT May 10} Nov. 27 201 ia vasville’ CE) ico. secs ee it AR | Sea bee Feb. 26 | Dec. 7 284 5 Soa Sof el (12: ARG Ges ae EOIN Fodls, errata ch May 21] Nov. 27 209 Elsinore (14)...........0. De Baan sine Sa coast Mar. 23 | Nov. 26 248 mureks (16) 20s... dele os oe (oY: RRR | Heir Mar. 29 | Nov. 29 245 Ballbrook (LE) rion dhe oss 7.0 (0 eae | Aaa Feb. 20 | Dec. 7 290 ROK Dp TTC parce slats ‘aia ili otal cossanianayiiise at alte’ w are Grea eee Feb. 41] Dec. 8 307 Kort Ross (16) oe eode. sc. OS: ach sleet Feb. 14 | Dec. 29 318 MUEOSNG) CUA) ots 5 cate aee w ae aL! 8 “Tecate ie, aeties te Mar. 1] Nov. 14 258 Georgetown (15).......... 2 GOO) -\) Moses -..| Mar. 41] Nov. 29 270 RPO VRCRA) YG eeu ck eubsig wate 1 5 OR Rar ase Feb. 25 ] Nov. 5 253 CUI Ga CLA) ey calc miecs sol SOO Re ee: Mar. 14 | Nov. 30 261 lantord(U4) oven thy views v2 0 | Sen Mar. 16} Nov. 9 237 Healdsburg (16).......... Es Pe ck agree aa Apr. 8 | Nov. 16 222 rollaster CH) eve dk sae es ST SARS i Wee eer ee ee Mar. 16} Nov. 23 252 UND ME VER CULO) cere Ge arab a ste Mite cimratar'eahinecerelaille och w eomtaiar ee June 10] Sept. 8 90 Independence (H)......... hore: CAE ws ae tema Mar. 17] Oct. 25 222 Kernville (14)....... OS BGOOk, ces Sens 6 May 10 | Sept. 27 140 Bingsbure (14) cis. ska MURR Me IR ck ie etatete « Feb. 28 | Dec. 27 302 164 ENVIRONMENTAL CONDITIONS. TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. Average date of— Length of No. Of fn So ee ee ees Station. Altitude. years of ast toe | eee t frostless record. : ; ; season. 1m spring. |in autumn. California—Continued: feet. days. aPorte(15)cae2 oes ee 000) t. 22 ep oe May 30 | Oct. 9 132 Lemon Grove (14)........ GOO 9) 8...) as Feb: . (22) |, Deesa a0 291 Lick Observatory (14)..... ZAGAT 2 ean (ARP, G8 ae Mar: 28 j-Oct. 1 197 liivermoete (hs. sees LS aL Peper» Feb. 23 | Dee. 2 282 hed: GAY sae eee SF ee (Pe = Soaks. Mar. 12 | Nov. 16 249 Los Angeles (14).......... 70) 3 a | Mate oe Jan. . 27 1 Dec.227z 334 Los Gatos (14)........... 600 ist Mae Jan. 22'| Dee. a4 326 Manzana (14)). 82). Be. dae Fe! | amd, (emi B24. ese Mar. 25 | Oct. 16 205 Menlo Park (14)... .2....:. G4 PN Se ee Jan... 22 | Dee: 24 336 Merced (14) jyF. 82s seis Me Pie Neos coepeeee bara Apr: "7. | Dee: vais 240 Mills College (14)......... PAO: Lille. 5.) eee Jan. 30] Dec. 4 308 Milo (04)... ee eee GOO) 8 bs. 2 ee Feb. 16 | Nov. 29 286 Malton: (n) Ge. 4e<. x8 GEN. es eae Feb. 81] Nov. 29 294 Mokelumne (14).......... DAO Oo) [Rverece aes Mar. 21 | Dec. 15 269 MonwmentalgGigs) es bee see ee ale a ccda 6 oe SS SS May 30] Oct. 16 139 Mt. Tamalpais (16)....... PAY (5 na Olen ee Mar. 3 | Dec. 13 285 Napa; (iG): see ee BO SA aca Mar. 20 | Nov. 15 240 Nevada City (15)......... DSU) Adin ae wuda cet May 8] Oct. 19 164 Nes C14) 2. ack Aes Rs. SA eon tee ne Feb. 11 | Nov. 30 292 North Ontario (14)........ 1 Bar Ast 0 Cama eeaeegs i a er Mar. 14] Dec. 14 275 Oakland (Deck? oi sek SG:.0 P4t 3. See Jan. 7 | Dec. 20 347 Ontario"(n)- Gea eee SGOs 4 ess eee Mar. 7| Dec. 16 284 Orlearish('G) Beer ay oe! CMe ein clos, sie ndis.c ss SES Jan. 29 | Mar. 14 289 Palo Alto (lath: 4. 3. 2 ee 70 eas teens era ei Feb. 19! Dec. 25 309 Paso Robles (14). 2.2. . . Ac oi 0 ae Pee ee 2d Apr. 1 t Novin 5 218 Peachland (1G6)2% 8042 PQ 5 ee Apr. 14] Nov. 21 221 Placerville (14)-.......... 1 WAS | ies Pens Mar. 15 | Dee. 31 291 Portervalle (14)s: 6.22 es AGS OE oes Feb. 7] Dec. 10 306 Poway (14). 28. Sek caw AGO ee Cabs see ae oi: Jan. 26 | Dee: =3 311 Red Blatt (ta). 2332 8 (7 Age ee are ee Se Mar. 27 | Dec. 16 264 Reddine (penn) Se eee BRT Od cs Sa ee Feb. 20] Nov. 27 280 Redlands (H).22. 6288.4 Pea oo, ess eee Feb:, 19 | Dee: =2 296 Sacramento (15). ..2... 2c: (LE PAs bes Feb. 16] Nov. 15 272 Salinas (4). S200. 24S. Loe TS (areas "SCR Feb. 18 | Dec. 2 287 San Arde. (14) seks. 2a ae 731 (ates eee, 2) ae Mar... 3.|. Dee. 120 292 San Francisco (14)........ PO ce See ee Jan. 25] Dec. 10 319 san Jacinto (4)... 2 ee O80) ho Aicta hose oe Mar. 27 | Nov. 20 238 Sap Jose’ (14). cee Sin Re \ Seaiue Feb. 6 | Nov. 27 294 San Leandro (14)......... 5 LK | AIR ge Mar. 9 | Dec: 247s 274 San Luis Obispo (14)...... PA) Wao: ae ae Mar. 3] Nov. 18 260 San Miguel (14).......... GU ste. SURE oo Feb. 22] Nov. 13 264 Santa Barbara (14)....... TE (RU PSEA oR Jan... 19 | Dee.; 18 328 Santa Clara (14).........: 1 Nenana PSE Rin se omen ete Feb. 27 | Nov. 25 271 Santa Cruz (14)... cer 28: 7 | pamee: (ARR 55 Rene Mar. 10 | Dee. 9 274 Santa Margarita (14)...... N66 Api Moweees - Feb. 15 | Nov. 25 283 Santa Paula (14) .:.2-...4. 35) | ns PAPE; eee ee Jan. .23 } Dee: 2438 329 santa Resa (iG): .. Ae fe 12) a PM 5 ete Apr. 24] Dec. 10 230 Sisson (15)..... AE see SOD, eis a Aes Mar. 19: | Oct. 12 207 Soledads(14) ase ches: ee PSS 2 3) eleaa 2 Bebb, 79+) Deeievii 301 Storey: (14) ee Ase hae DR Kets, Lok ee a oa Feb. _23.| Dee. -.3 283 SIMNTATL GS) tee es ee BOTS Cea eerie Hep. 13: 4 Oct. 413 242 Susanville (15)........... AeA Gaal an May 10] Sept. 22 135 ®ehachapi (14)\) 9.25... ste Se) ie Se Po Mar. 17 | Nov. 28 256 Gracy (lA) Asecn. + she G4 On 2 eee oe Feb. 17 | Nov. 18 274 alae (44). seer? lite oe: PA: Sia? Ey SLs Ra Mar. 7 | Nov: 15 253 CLIMATIC CONDITIONS OF THE UNITED STATES. 165 TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of — Length of Station. Altitude. years of |———————_|_ 2Verage ‘ record. | Last frost | First frost frostless in spring. | in autumn. Rea California—Continued: feet. days. (ilcraty’ GG); Sree eich, ee G20) ie Wt: APRS ene Apr. -14, | Noy. (i 201 Upper Lake (16).......... Peay cll We, hatetoen Bis Mar. 30] Nov. 13 228 Upper Mattole (16)....... 2 2AM | ga: fa ae Mar. 71] Nov. 18 256 Valley Springs (14)........ (617/25) oman (esi aaee y= ae Apr. 12 | Dee. 17 249 arse (CA ages sata. sia eee 5151 Sen ane Mar. 13 | Nov. 27 259 Watsonville (14).......... PAB AA | COUR 3 RRR Mar. 8]! Nov. 3 240 Westpomt (4)... 0). ek pps 7 een a) Ee Apr. 16| Nov. 8 206 IMtlowSs Glo) es eee i Be PSO viv ees cies ss Jane "22. Dees) 12 323 Colorado: Jee Wh oCeMd 0) AG se See Di QO Dyke eos elle tele «ic Apr. 29] Oct. 11 165 Boulder i(S) 800% ooh. s BA 5,347 12 Apr 27.) Get.) 159 165 Ganon City. @)\..5. 0... 8a DiOZ9 hin sw leas eee os Apr. 29 | Oct. 5 159 @astle Rock (8)).i. 0... 05 2 6,220 15 May 28 | Sept. 19 114 Cedar Edge (9)........... 6,175 Ue May 20 | Sept. 23 126 Cheyenne Wells (38)...... 4,279 15 May 10] Sept. 22 135 Mollbrany(O) ees os bn LEN 6,000 8 May 26} Sept. 24 121 Colorado Springs (7)...... ES Ore a Aion vam May 31] Oct. 3 153 CAT TOTS! (GS) es 4,400 iit May 81] Sept. 30 145 STAC) ie eM eris se Wee see 4,965 13 May 16 | Sept. 25 132 MEPSMIVETICS) ions ole aim de ha 5,272 38 May 6 | Oct. 6 153 urango (9) ieee... . lS 6,534 12 May 28 | Sept. 26 121 Mort Collins (8): :.../: .. 63) 4,985 18 May 91] Sept. 24 138 Fort Morgan (8).......... 4,338 13 May 71 Sept. 28 143 Gien Byrie (7)ih..3 ooo. ied OOOO res sey a. May 12] Sept. 27 138 Grand Junction (9)....... 4,608 16 Apr. -18:|; Oet. 18 183 Grand Valley (9)......... 5,089 14. May 10] Sept. 29 142 RG ECCIEV NCS) iiet is Jalo%. ors 68 4,639 16 May 6} Oct. 1 148 PEPAIAS CH) siete sesese «ecole s DADO G mute tears teen tas May 17 | Sept. 24 130 HiGehnme! (7) vasa wees See SYNC) OR AEDS) CRONIES | Se aia May 20 | Oct. 2 135 TOM GE),o eee sd ses, 5 aie Dp SOO Ue Nails ee sneee oo 5s May 1 | Oct. 1 153 FTolyolkeu(S) Assia tte. oe A 3,745 9 May 9] Sept. 22 136 ERUSECU SCT). 10, sik e a 6 levels Gy SIGs can ts os May 15] Sept. 25 133 GATT AT GH) i, ra eet ct eehe « wele SOO NU esas Cmts aie Apr. 27 | Oct. 3 159 Las Animas (7)........... SSO OA cl tsro cae May 2 {| Oct. 2 153 AO) eras etal tia tee 2 Mkb 6,190 9 June 16 | Sept. 6 82 MEER GS (S)) Bare clog seeatleial ete 4 »380 16 May 2] Sept. 29 150 Long’s Peak (n) (8)....... 8,700 9 June 26 | Sept. 2 68 Mancos(9): 5025 6 e..s SRN 6,960 10 June 9 | Sept. 17 100 Mieckers(9) iiss ho. tae 6,183 14 June 12 | Sept. 12 92 Montrose (Qe iie oats 5,811 10 May 16 | Oct. 2 142 Moraine. (8) ethieacce shies ols 7,750 12 June 15 | Sept. 13 90 eae O a (OG) MwG use wee hie toe 6,500 13 June 12] Sept. 3 83 PRONE (CG) cele dc ees see hees 5,694 8 May 5 | Oct 3 151 Hee ble C7) ena Goa eek Bi Pas Villsie Heer age Apr. 27 | Oct ‘ 163 Rocky Ford: ()e.. scilas ek re 1 eae (aa. May 2 | Oct 3 154 pazuache (E)iny.. ee. ie Casa (2!) ns ea Lo = eae May 24 | Sept. 17 116 roe TUCS FAN A eee vg O50 RS ae 2 Sn May 31 | Sept. 20 112 Sen Darts: (Bee ds 0. re CG Pel uiemnciers June 9] Sept. 11 94 Santa: Clara.(7)...28.. 248 Seg ee ee lee June 3] Sept. 24 113 Et CG) thie c aitima cue me e tah 5,441 12 May 21 | Sept. 27 129 Stigar Moat (8) (Me ee Oa 9 July 9{| Aug. 17 39 Garnet (22)! so tcc eee 2,575 9 Apr. 17 | Oct. 20 186 Grangeville (Qi)... 2. 2s 3,500 @ May 19 | Sept. 25 129 Idaho Halls (22)... 23.25. 4,742 4 May 22] Sept. 12 113 ello gwar woe see ont 2,330 4 May 14 | Sept. 25 134 Wake (22) cee a, Seen ar cere 6,700 il June 25 | Aug. 20 56 Walkeviews: (2 )sie tee vcs ue 2,250 12 Apr. 29 | Oct. 9 163 ALANGOLE C22) sects cate neue 5,300 4 May 18] Aug. 16 90 Bewastonn(2 lysates. 27 202 Lost: River (22)2 6 oc... 20% 5,700 10 June 9/| Sept. 1 84 Miartini(22) cet tek teense 5,600 4 June 26 | Aug. 24 59 Wilmer (22) Os .. Wavcnie ae 4,097 5 May 19 | Oct 4 138 WroscowA Litera. eee «ate 2,748 16 May 8] Oct. 10 155 Vr ayo) ae etn. att 2,750 15 June 2 | Sept. 19 109 Bakley (22) se) oa oahe ca suet 4,191 15 May 31] Sept. 12 104 Da C22 ete Sa eee sb Me ae 3,100 9 May 25 | Oct 4 132 Orohno (21) Pees «meets oe 1,027 4 May 18] Oct. 12 147 Paris (22) omaha aickee cept 5,946 13 June 14] Sept. 3 81 Payette (22) sia. mace oe oe 2,159 15 May 11 | Sept. 29 141 Pocatello (22)i is. 25. cals 4,483 9 Apr. 20] Oct. 12 175 Pollock 1)e tes soit. wte oe 2,050 12 Apr. 26] Oct. 12 169 Porthill (2D) 6... 2. See 1,665 16 May 14 | Sept. 14 129 Priest River (1). .o.5. .2.% 2,078 6 May 29 | Sept. 22 116 Roosevelt (2h) eee cesar 208 7,250 6 June 29 | Aug. 21 53 . St: Maries (20) 2. os 2.5.8 2,263 12 May 8| Sept. 14 129 Salmon (21) cee sae on ee 4,040 3 May 26| Sept. 7 104 ; Soldier (22) -2ae2 on ec aes 5,140 11 June 27 | Aug. 19 53 Swan Valley (22)......... 5,434 8 June 28 | Aug. 15 48 Wiernom) (22) ay. b tice eH lyse aoc tales» 11 June 14 | Aug. 29 76 Wrarren’(2 1) ne sec etee se 5,350 4 June 12| July 23 41 Weston (22). ee) vce ais ee 4,610 11 June 2] Sept. 9 99 Illinois: . Albion (66) ie os ain tees sete 531 15 Apr. 14] Oct. 21 190 ‘Aledo (64). 3 fuio a ee ieee 738 8 Apr. 29] Oct. 13 167 Alexander (G5)'so 1 fo6 nee 670 15 Apr. 24 | Oct. 6 165 Antioch (64). 2. 202 33 oe. 861 7 May 4 | Oct. 5 154 | Ashton (G4) ore. . eos oer 830 14 Apr. 29 | Oct. 5 159 ; arora (G4) oats secre 687 22 May 6] Oct. 6 153 Benton (66)e lees js. vee 598 75 Apr. . 21 | Oct.- 21 183 ’ Bloomington (65)...... a 840 16 Apr. 27 | Oct. 9 165 2 Bushnell(65)i) 2.0. 5. sc 662 14 Apr. 25 | Octs- 14 172 7 Cairo: (66). Bhs hee ae 359 38 Mar. 30] Oct. 28 212 : Cambridge (64)........... 824. 14 Apr. 22] Oct. 10 171 4 Carlinville (G5). 20. 2... so 663 17 Apr. 22).| Oct) Ad 172 BE: Charleston (65)....2...... 720 16 Apr. 24 || Oct: 2216 165 b Ghicapo (64ye tn. 82 824 38 Apr. 16] Oct. 15 182 4 Woatsbure: (Gd)eie oo. 738 13 Apr. 24 | Oct. 14 173 Cobden«(66) sr.4. He. Sas 656 13 Apr. 12] Oct. 21 192 f Decaturi(Go):. s.cseees hes 685 15 Apr. 231 -Ott. .) 12 172 ; Dixon! (G4) oo sees. hows oe 725 17 Apr. 27 | Oct. 6 162 i Biquality (G6) ic, ben 2 oar A421 10 Apr. 14 | Oct. 22 191 4 eS ee he =~ CLIMATIC CONDITIONS OF THE UNITED STATES. 169 TasLe 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No.of Average date of— Length of Station. Altitude. years of average record. Last frost | First frost oe in spring. {in autumn. SEE: Ilinois—Continued: feet. days. Maarielay (GGO)isihe +) hn. rer 495 12 Apr. 16 | Oct. © 16 183 Bllloria(GO)iciclyeinte «eres «etn 495 16 Apr. 18 | Oct. 11 176 Gal a(G4)s tere wives s slckas 842 16 Apr. 29 | Oct. 10 164 Golconda (66)....... Boy tie 500 20 Apres 6.4 Oct. 26 203 Greenville (66)..........-- 635 21 Apr. 15 | Oct. 15 183 Griggsville (65)........... 650 19 Apr <2) 4. Oct? 9oke 179 laliweays (OO) ese. : se6- ee 569 11 Apr. 5 | Oct. 26 204 Wavana(Gd) 182.065 cee. els 475 15 Apr. (23). Oet. 114 174 IEVerinys (OA) hcrsiae om, sleges) shore 500 20 May 5 | Oct. 7h 155 itl spore (65) 0) x fy... ses 675 14 Apr +22 -) Get. 25 176 Tielke GD ae ee ne 541 15 Apr. 26| Oct. 9 166 Kishwaukee (64).......... 730 13 May 4 } Oct. 1 150 Kenoxvallle (GD) 06 bs. dive 6 is 775 14 Apr: - 25.\. Oets . 13 171 LaGrange (64)............ 657 16 May . Lh 1 Octat* it 163 Wa btarpe) (G5) ibis. sie. «ier 698 14 Apr. 24 | Oct. 5 164 Matic. (G4) sreleic ole soets scenes ~ 883 21 May 61] Oct. 1 148 asalle (G4) seek Shade: POS te Meo ey 4 Apr. 28 | Oct. 13 168 imcoln (G5) soe ew «oe 482 16 Apr) 2b te Octs (Alo 166 Martinsville (65).......... 630 EG Apr; 22 |-Oct,, it ti Martinton (65)........... 633 17 Apr. 29 | Sept. 30 154 Mascoutah (65)..........- 425 11 Apr. . 22. | Oct. 14 175 McLeansboro (66)........ 462 12 Apr: 17 iOcts)) 24 180 Miinonk (65) 3. ke. ae 745 13 Apr. 27 | Oct. 8 164 Monmouth (@A)....-..... 784 15 Apr. 28) |. Oct: 10 165 IMORTISOM: (Skye ss eckte ss ole) 685 14 May _1 |} Oct. 6 158 Mount Vernon (66)....... 511 14 Apr. 20 | Oct. 15 178 New Burnside (66)........ 556 14 Are. eo) Oet.. - 22 178 Olney (GG). cou son. Gee. wes A486 15 Apr. 21 |Oet, 16 178 Oitawa G4) sou oe Ses. oe 500 19 Apr. 26 | Oct. 8 165 Palestines(66) ie... ae). 2 oie 500 18 Apr. -18.| Oets >12 177 ama (BB isletrsice Siete! eo 692 13 Apr, - 22 |. Get. 7 a6 177 Mears (GO): sdse ea aela ie ental 600 16 Apr: 221 Oct. 419 180 GOYA (GD) etek oo Wis bee jedi 609 53 Apr. 15 | Oct. 18 186 PTO SCG)... ee es ah. siete wate 700 21 Apr. 28 | Sept. 30 155 Pontiac (Gd) se. wc ee es 546 6 May 11] Oct. 14 166 an touleiGS) adds von ee eis 768 17 Apr. 26 | Oct. 7 164 tush valle (G5))s «. c.c cheers 0s 670 17 Apr 23.1 Oe. Fe 172 Sue MONT CGB) eHe nd kiete a Oe 459 12 Ayr: 12 4 Oot.. iG 187 Springfield (65)........... 609 29 Apr: IS 4 Oct. iF 182 Sereabor (G4) ed's. ieee 616 16 Apr. 30 | Oct. 8 161 Sycamore (64)............ 855 16 May 41] Oct. 1 150 meileer (GG) Haws aialel a slate 500 16 Aor. 13.) Get: 44 184 Miskilwan (G4) a0. 6 Vow 6 elas 798 14 Apr. 28 | Oct. 14 169 Mernon (OG)iveves c2 ss 3 ek 515 8 Apr. 23 | Oct. 7 167 RYN el TaNati ne GA.) aes k siete, sats 717 16 Apr. 24.1 Oek 8 167 Winnebago (64)........... 900 20 May 2] Oct. 2 153 Indiana: AR CETSOD (GF) 24 biinleteee » wets 892 14 Apr. 25 | Oot. I! 169 Angola (G7) weds scdie’s 5 oes 1,052 15 Apr. 30 | Oct. 8 161 PMU COL eerncc ces © = sank 874 13 May 3 | Sept. 29 149 Bloomington (68)......... 800 12 Apr. 19 | Oct. 20 184 Blutiton (67 )ai ve wc Coc cle 835 13 May 7 | Oct. 2 148 Butlerville (68)........... 767 16 Anr. 25} Oet: = 11 169 Collegeville (67).......... 662 9 May 3 | Oct. 7 157 Columbus (68): ..<63.. 6.4% 632 16 Apr. 26 | Oct. 5 163 170 ENVIRONMENTAL CONDITIONS. TABLE 2.—Frost data and length of average frostless season for 1808 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. years of |————_-_-""——_ pb as record. | Last frost | First frost rostless in spring. jin autumn.| 5°S02- Indiana—Continued: feet. days. Connersville (H).......... po 7s Ee deeper nafs a apa Apt: 27. | Oct: a 159 Welphe (OV): ei). ere eee 668 16 May 31] Sept. 30 150 Evansville (68)........... 386 12 Apr. 7 1}.Oct. 27 203 Parmersbure (68) -2 26. s alka eee ee. os 6 Apres 22 ty Octs Ws 179 Farmland (67). ....-.-. 2: 1,101 16 Apr. 25] Oct. 10 168 Fort Wayne (67)....... sala 775 11 May 2 | Oct. 9 160 Greenfield (68)..........-- 905 6 Apr. 21] Oct. 16 178 Greensburg (68).........- 954 12 Apr. 22] Oct. 16 177 Hammond (67)........--- 598 16 Apr. 27 | Oct. 15 171 Huntington (67)..........- 741 15 May 4 | Oct. 7 156 Indianapolis (68)......... 822 30 Apr. 16] Oct. 19 186 Jeffersonville (68)......... 455 18 Apr. 16] Oct. 18 185 Kokomo (67)......-.-- bye 840 16 Apr. 26 | Oct. 1 158 iafayette) (67).....-'...-.- 617 18 Apr. 26 | Oct. 5 162 WaMorte (Ot) ro meres oie 810 12 May 1 | Oct. 5 157 Mogansport (67) 2.25..." 620 16 Apr. 24 | Oct. if 166 Marengo (68).........--- 363 16 Apr. 19] Oct. 11 175 Marion (Oe) 2 ice sconce eras 814 18 May 9/] Oct. 4 148 Wirawzy7 (G8) 6. ces Sei 6 sist 980 18 May 2] Oct. 4 155 Moore’s Hill (68)......... 918 7. May 2] Oct. 8 159 Mount Vernon (68)....... 410 16 Apr. 18] Oct. 20 185 Northfield (67)........... 900 13 May 3 | Oct. 2 152 IE Ola (GOS) isch eto oe Ml aya ie) scene 611 11 Apr. 18] Oct. 15 180 Princeton: (G8) 22% vio. «ea 481 16. Apr. 17- |) Octin var 183 Richmond (68)..........- 972 12 May 7 | Oct. 3 149 Rockville (68)...........- 722 16 Apr. 27 | Oct. 7 163 ome {(GS) = feiss. & dyehe cteans 370 6 Apr. 211] Oct. 13 175 Scottsburg (68)...........- 570 15 Apr. 16] Oct. 16 183 Seymour (68). ices 610 15 Apr. 19 | Oct. 13 177 South Bend (67).......... 726 15 May 51] Oct. 12 150 Terre Haute (68)......... 498 16 Apr. 191] Oct. 22 186 Veedersburg (67)......... 612 10 May 1} Oct. 5 157 Wevay) (G8) 2. ese 6G tes acs 525 1 Apr: 19!) (Oct. 24 188 Vincennes (68)..........- 431 15 Apr. 141] Oct. 20 189 Washington (68).......... 484 12 Apr. 16] Oct. 19 186 Worthington (68)......... 526 15 Apr. 22! Oct. 24 185 Iowa: Algoma; (4) ot 8 aki o 5 foe 1,500 16 Apr. 26 | Oct. 4 161 PARR (SEA Vag ce ce 1,440 16 May 9 | Sept. 28 142 mana Che). oei koh eek. as AGS hee | Params x Sac Apr. 23 | Oct. 5 165 ATlanitreNCH) eo. estes’ oe 1 WH 6: CN Area W-Saen ont caa May 11 | Sept. 19 131 Belle Plaine: CH)¢ 2.0%) 2). 2: SGA occas May 1 | Oct. 4 156 Bonaparte (H)........... AOOE Soil ec Sea Apr. 20 | Oct. a 170 Carroll)... bie ss tess ee A (PARR hae ee) Boe May 51] Sept. 22 140 Cedar Rapids (54)........ 733 16 Apr. 24 | Oct. 6 165 Charles City (54)......... 1,015 iLvA May 16 | Sept. 26 133 Olarindan(a4) eee sue 1,064 (H) 16 Apr. 26 | Oct. 5 162 Chinton CH): ci. eer. cane DIS cal eins 5 tou oes Apr. 28 | Oct. 2 157 Corning) seen 6 soe. sae 5 8 a Ca Peat td pty Apr. 26 | Oct. 2 159 » Corydon (54) cao gi cis eile 1,100 (H) 15 May 1 | Sept. 30 152 Davenport (54)........... 580 37 Apr. (22) Oct...) ts 174 Decorah (54)...:........- 975 15 May 101] Sept. 26 139 Des Moines (54).......... 861 31 Apr. 22 | Oct. 10 171 Dubuque (54)............ 639 36 Apr. 20 | Oct. 13 176 Plkadeér; GH) soe ee ee eae TPA (ga RAGS ce May 95 | Sept. 23 141 CLIMATIC CONDITIONS OF THE UNITED STATES. 171 TaBLE 2.—Frost data and length of average frostless season for 1803 stations in the (P late 34.)—Continued. United States. Station. Iowa—Continued: Fayette (H) Forest City (579 ES Or Sore ae Greenfield (H)............ Grundy Center (H)......-. Hampton; (64) 3.04.5.» oes Harlan (54) eoer ee ee ee ew oe Independence (H)......... Moxa City: CED) stays. site so ce Iowa Falls ( COA iets cts te lay oy Spat Weolewle(D4) 85 Hgts ones Larrabee (H)............- Mount Pleasant (54)...... Newton (H) Sac City (H Rares hecomfislie lets Altitude. EH NWECSANE reivailice: ay 6! cca veyeal ee aR sig) oi 0 yc sreourney, (54) 4.0 62.6) 65. BHOUx City (OS) eo. ders) os ou Washington Kansas: CED) aie tay otter Achilles (3S) occ bos se TSS OVEN OC BN (312) OE ey Atchison: (H) ...% 2s... 6 Clay Center (38).......... Colby (88). eeeoe ee ee we ww 8 Wold water: (39) os sk 46 oles Columbus (39) 2.5 25... Goncordia (38) 35. sist. «mee @oolidge; (S9)..si.60. 6. Cunningham (39)......... Dodge City 32) ee a MN wood, (39). 4 .2.ceie os ws mi POria, (OO) e eG. cape eo ese, Englewood (H)........... Eureka (39) Farnsworth (G2) ae Se ae Hort Scatt (9) oo. 6. .6 ad Frankfort (39)..........6. Garden City (39)......... Gove (88).. eee ee eee ee ee oe EE TETIOLA UGS) cicie aes eto! «5 aus Planover (G8) vais... srl. emis IVarmisow (38) .\ee. os See e waa Hays (388).. Horton (38) Hoxie (38). Hugoton (39) Hutchinson eee eee ee ee ew we CC CED) leo slahe ns: sis.caee Independence (89)........ PEDMOLO (SO) isis d's sahecerw's: wile Lakin (39). Larned (39) Tawrence (38)... 0... cea Lebo (39).. Macksville (89)........... Manhattan lege) (38) (Agric. Col- CC es ee No. of years of record. Average date of— Last frost | First frost in spring. jin autumn. Length of average frostless season. — | | CT “es eee se eoee a er ry o\ (a: ei ee) steve; 8: 6 ec ees ewe eee 00.8 6 alae es ee May 8 | Sept. 18 May 5 | Sept. 26 Apr. 29 | Oct. 9 May 31] Sept. 26 May 5| Sept. 30 May 6 | Sept. 27 May 41 Sept. 26 Apr. 23 | Oct. 8 May 91] Sept. 24 Apr 1 May 2 ‘ May 11] Oct. 12 May 6 | Oct. 16 Apr. 5] Oct. 24 Apr; 17 |, Oot 38 Apr. 28 | Oct. 10 > ss) 1 bo oO e) ° ot — Oo 172 ENVIRONMENTAL CONDITIONS. TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. years Of. > 3 ee Poni =. record. Last frost | First frost BRS in spring. |in autumn. : Kansas—Continued: feet. days. Marion. (69) 2 visi ¢- 2... 222 1,310 14 Apr. 18 | Oct. 17 182 McPherson (39).......... 1,495 16 Apr. 20] Oct. 19 182 Medicine Lodge (39)...... 1,475 11 Apr. 12 | Oct. 18 189 Minneapolis (38)......... 3 1,259 16 Apr. . 3041 Octi vas 164 Ness City Goys.<2 22. 2,260 13 Apr. 30 | Oct? 115 168 Osweso(39) Ses aS 899 17 Apr. 17 | Oct... 24 190 Ottawa: (9) 6s eke ee 926 13 Apr. 20 | Oct. 15 178 Piolo. G9). tee 865 8 Apr. 20] Oct. 14] 177 Phillipsburg (38).......... 1,939 14 May 3 | Oct. 10 160 Republic (28) .¢ 2.350.488 1,495 6 Apr. 30 | Oct. 17 170 Romei(S9)..22 72 22 3ae 2S 1,218 15 Apr. 16 | Oct. 20 187 Silinia (38). eee eee co 1,227 17 Apr. 27 | Oct. 12] 168 Scott City (S9).t 4-2. 2,971 5 Apr. 24 | Oct. 14 170 Sedan:(S9)2 00s). Pees soe 834 17 Apr. 10 | Oct. "27 200 Tepeles (38) cee aes ae 992 21 Apr. 9 | Oct. 15 189 Tribune (soy te Boe eh ee. 8 May 11] Oct. 6 158 Ulysses GO) fee) 3,027 15 Apr. 29 | Oct. 15 169 Valley Falls (38).......... 913 10 Apr. 24] Oct. 8 167 Varoquarts9)~ 2522425 2022 3,600 (H) 14 Apr. 47 |Get. 21 187 Wakeeney (38)..........- 2,456 16 May 3-} Oct. 2 152 Wallace 8) es 3,303 15 Apr. 22 | Oct. 2 163 Wachitae (39) ie Sessa 1,301 21 Apr. 8 | Oct. 19 194 Wintkeld (69) 20. a sr.3 2 1,124 14 Apr: 19: | Och aS 179 Wates Genter (39) /222...22 1,068 14 Apr: 17-|- Odi. a2 180 Kentucky: Aiphaiiayee este Ween ae eee gem geek 13 Apr AS [-Oct: 6 176 Bardstown (76)........... 637 12 Apr. 18 | Oct. (48 183 Beattyville (75)... 26... 650 5 Apr. 25 | Oct. 10 168 Berea (75)2. 2222 an Sen ees 1,070 8 Apr. 18 | Oct. 12 a7 Blandville (/6)2 2... 32 2 445 14 Apr. 15 | Oet. 20 188 Bowling Green (76)....... 500 16 Apr. 47) Oct-28 186 Canton tCadiz tip) co. steele ee oe ec se 13 Apr. 14 | Oct. 16 185 Harlinetoan (76)-4 .. fe. Ss" 370 16 Apr. 19 | Oct. 16 180 Hidmonten (HB). 235 2-5. .2F CU SL SS 0 tae Apr: 274; Octo tt 177 Bubankd@5)cie en fo. oe Lae 15 Apr. 28 | Oct. 8 163 Evansville (76)........... 434 12 Apr. < 4°Qete 27 203 Greensburg (76).......... 581 16 Apr. 20 | Oct. 6 169 Hopkinsville (76)......... 524 12 Apr. 11 | Oct. 20 192 irvaneton.(76) 224 3 SS Soe ne ees one 11 Apr: 47} Oct... i¥ 183 Gertchheld (76)... S35. 222 635 13 Apr. - 14 | Oct: * 46 185 Bexincton 5)". 2...3.. 989 26 Apr. 19 | Oct. 23 187 Loretto (76) 2225... 5s. . 681 11 Apr. 214 Oct: 6 168 Kauisville:(/6) 2 6.5% .34 ee 525 19 Apr. 9 | Oct. 22 196 Maysville (75)....... Syn eae 524 11 Apre - 23° 1- Oct.) 44 174 Middlesboro (75)......... 1,128 13 Apr. 19 | Oct. 14 178 Mount Sterling (75)....... 930 17 Apr. 23 -|.Oct: 33 173 Owensboro (76)........... 479 12 Apr: - 10 | Oct;* > 24 197 Paducah (/6)e>%... 22... +P 341 15 Mar. 29 | Oct. 26 211 Richmond (75)02 2 os « 928 15 Apr..- 415. | Oct. » 18 186 COLL Reais pete ay Bie TS oe eee 11 Apr. 21] Oct. 14 176 Shelby City (75).......... 1,087 14 Apr. 24 | Oct. 6 165 Shelbyville (76)........... 759 £7 Apr. 15 }.Och 15 183 Williamsburg (75)......... 939 12 Apr. 5 j-Oct. 20 198 Louisiana: Abbeville (45)............ 18 18 Mar. 41] Nov. 15 256 CLIMATIC CONDITIONS OF THE UNITED STATES. 173 TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. gone | ay ee record. Last frost | First frost 5 7 , season. In spring. |jin autumn. Louisiana——Continued: feet. days Alexandria (46)........... 77 19 Mar. §8| Nov. 10 247 mite: (G45) ok oR aed 130 18 Mar. 13 |} Nov. 10 242 Baton Rouge (45)......... 35 15 Mar. 11] Nov. 19 263 Burrwood (45) ............ 1 14 Feb... 8.| Dees «15 300 Malhoun(4G) es oe so saw 180 15 Mar. 15 | Nov. 9 239 Cameron)! (45) iie..). 24s. aes 6 15 Feb. 22 | Nov. 26 ce tf Cheneyville (45).......... 67 18 Mar. 1] Nov. 8 252 Chintam(Ad) eh ek. ssn 113 17 Mar. 12 | Nov. 9 242 Collinston (46)........... 65 8 Mar. 2, |) Novi, 10 253 Covington (45)........... 39 17 Mar. 3 | Nov. 18 260 Donaldsonville (45)....... 33 17 Feb. 25 | Nov. 21 269 Farmerville (46).......... 177 16 Mar. 19 | Nov. 5 231 Pranidin (45) 5.) bees oes 10 18 Feb. 20 | Nov. 25 278 Grand Cane (46).......... 302 13 Mar. 11 | Nov. 10 244 Hammond (45)........... 44 15 Mar. 7 | Nov. 17 255 ous) eu iol Oe ee eara once Bh at oe 18 Feb. 28 | Nov. 20 265 Jennings (45)ie)...68 He 30 13 Feb. : 22h\Nov.) -21 272 Lafayette (45)............ 36 20 Mar. 3 | Nov. 13 255 Lake Charles (45)......... 22 18 Feb. 24 | Nov. 25 274 Lake Providence (H) 1 UC Ai tare (ee a Mar. 14] Nov. 8 239 Meakeside (45 )ial ss es vee eee ek 8 Feb. 13 | Dec. 5 295 Lawrence (45)............ 6 17 Feb. 13 | Dec. 11 301 Liberty Hill (46)..........]. See. Rnaes 19 Mar. 22) Never. 227 Ntelvalle (45) ice se se bs oes 45 18 Mar. 8] Nov. 7 244 Minden (46) 25. 005. sas 194 20 Mar. 14 | Nov. 13 244 Nonroe: (46) 262. /e5...003 82 16 Mar. 14 | Nov. 12 243 New Iberia (45).......... 15 17 Feb. 20] Nov. 29 282 New Orleans (45)......... 8 37 Heb.) ca (ee: akG 310 Opelousas (45).0...62.. 04. 83 i beg Mar. 51] Nov. 17 257 ROTEL) yee seo dS autrefbolich e see 206 16 Mar. 95). Nova 12 248 Palo: Alto- Ga) us). 6ty..c- tee SUO) odhis eee ks Mar: 27 | Novem 222 Pearlington (80).......... 10 16 Mar. 1 | Nov. 24 268 iRontotoc- (9) eee: dase eee 475 18 Mar. 28 | Oct. 28 214 Vicksburg (SO)e%.2.2) ee. 247 38 Mar. 6: Noy 12 252 Water Valley (79)......... 300 ty, Mar: > 27 )-Oct. coat 218 Waynesboro (80)......... 191 17 Mar. 20 | Nov. 4 229 Woodville (80)........... 560 16 Mar. 12 | Nov. “14 247 Mazoo City (SO)... 288 sek 116 16 Mar. (28 | Neve- +2 219 Missouri: Appleton: (49) aa. esas cea ee ten ce 18 Apr. 20 | Oct. 19 182 YSTEN oy ole Gy) ee OEE AUS oo nines SU 12 Apr: 22 |-Octs jae 173 Bellei(5O) ity aheee a eee nee 1,000 8 Apr le | Octi4 ats 181 Bethanya(Ol) ree. cet «ee 881 16 Apr: 26+| Oct: 8 165 Baschiree, (50) ss. te ei aes 1,200 16 Apr. 17 |; @cte2 16 182 IBbrunswiek (ile... kha haus 652 20 Apr: 17 | Octo 14 185 , Caruthersville (50)........ 860 13 Apr 5) Oct: s24 199 Columbia (SB)... 6 eee ek 784 20 Apr: | WS :-Oct. pie 179 Darksville(Gil)ix. S4he. ¢ ser 826 17. Apr. 231. Oct 14: 174 Mea AO)... cones. 2 otek tees eis hi sere ater ots 10 Apr: , 16,4 Oct. 4 +13 180 WeSotos(sO)issens ee oe 498 ‘6 Apr 201, Ot: —2i2 174 Baarport. (Ol): oes oes 535 12 May 1 | Oct. 8 160 Ma Vettel icv. hent. .ebek 725 24 Apr 2M | Oetay pie 176 MuUltom KD) eee aks oe 818 14 Apr. (21). Oct: 8 170 Gallatwm(o Dea. 6.80 3 22 ® 803 17 Apr. 517.) ‘Octs7 219 185 Ganoi(5O) oe see OAR ek als oe es a 6 Apre. 2a.) Oct. «15 lags Conn) :...ded iz foe. sah 700 15 Apr. 29 | Oct. 9 164 Grant City.Coys yi. -cnsest. 1,130 12 Apr: 26 4-Oct;.413 170 Greenville, (GO). 5 .f2rs we talle B osaclhe «he sf 12 Apres 16:1 Oet: 9 176 CLIMATIC CONDITIONS OF THE UNITED STATES. 177 TaBLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. » Ae Average date of— Length of Station. Altitude. VEAPSHOL: |e oe ae Foye record. | Last frost | First frost | ““0°”©%S in spring. |in autumn. Breen, Missouri—Continued: feet. days. Hannibal (65)i253). 23 32288 534 17 Apr. 16 | Oct: 16 183 Harrisonville (49)......... 912 19 Apr. 19 | Oct. 26 190 EVOUStON (OO) eee als ale. sist olets 1,280 17 Apr. 25 | Oct. 9 167 Tronton (0) seas cee 925 21 Apr. 28 | Oct. 3 158 PACKSONCOO)ei ee) sus 6 se bi 458 Ly, Apres 22 Oeghe 4 L 172 Jefferson City (51)........ 628 16 Apr. 19 | Oct. 15 179 Joplin: (49) oe nce. ele) 979 7 Apr. 15 | Oct. 19 187 Wansasi City (51) oi) 2s 3 963 20 Apr; 10) | Oct..23 196 Koshkonong (50)......... 911 9 Apr, 15) | Och. 22 190 amar (AQ) eine yee vs 964 18 Apr 18 | Ot. 17 182 Lebanon (49).............- 1,265 18 Apr. 14] Oct. 17 186 eximpgton (5) 2. 2). 0).f seve. 813 16) apr. Ei Oct’ 7 183 Biberty (oles seok eos ks 864 18 Apr. 20 | Oct. 8 171 Mowusiana (51) 00.0 ye. se} 500° 11 Ann, 22 1 Oct... 12 173 1 ey erap ole Gp Sy Aone a Emaar 881 8 Apr. 20 | Octsn 16 179 Marble Hill (50).......... 420 16 Apr. 19] Oct. 13 V7 Marshall (49)............. 779 16 Apr 19 Oet eout 175 Maryville) (G1))i0 5) 023. se 1,160 15 Apr: 21) Get: 7 169 BT EXICONCD IL). icles c-alelie is oleveis 797 30 Apr. 16 | Oct. 16 183 iranian COL) ei ok. os 622 9 Apr. 21} Oct. 12 174 iMineralspring (49) 6.35006. we Le esa 12 Apr 14 |) Oct. 1216 185 Rrontireal (49) ead oe lmaew eh ook eae 10 Apr. 19 | Oct. 5 169 Mountain Grove (49)...... 1,490 8 Apr. 23 | Oct. 14 174 Mt. Vernon (49).......... 1,480 16 Apr. 25 | Oct. 8 166 MEeEOSNO), (49) eek ee eee: 1,023 17 Apr. 24] Oct. 15 174 Mevada (49). 0.6. ce ees ase 860 12 Apr. 19 | Oct. 14 178 New Madrid (50)......... 285 5 Apr. 241] Oct. 20 179 Wakheld (50)ien. sie se 793 Ve Apr. 16) |) Oct. 22 189 iene (50). seen se be Ss 1, 246 17 Apr. 16 f Oct. 18 185 reson (Glee ale es ee 1,113 19 Apr.) 25} Oct. - 14 172 Poplar Bluff (50)......... 344 9 pre et Oete (att 193 Princeton (S1)....020 660652 1,026 18 Apr: - 24. | Oct: 9 168 Richmond’ (51) ..0........ 824 ef Apres) 7) Ost (24 200 BolatGO) sus. at oe 1,092 13 Apr. 20] Oct. 15 178 St. doseph (Ol) css Sicee: 825 8 Apr: 24 1 Octe (27 176 She ours (66). fis pes 568 35 Apr. 3 |: Octi 27 207 Sedalia (49) ee op So 889 14 An. 19) Oete 29 183 SOVIMOUP (40) vices cece ih doles «ees cies 12 Apr. 19 | Oct. il 175 Shelbina Ol)ywcc.. cece ek ss 781 8 Apr. 24 | Oct. 10 169 Sikeston (50)..2....0....- 328 14 Apr. 10 Oct. 18 191 Springfield (49)........... 1,350 20 Apr. 14 | Oct. 18 187 Steffenville (51)........... 576 14 Apr. 24 | Oct. 10 169 SublettiGl) i585 4. Beek a 1,000 15 An 2 |) Oe”. °S 187 MTEnMCOM COL) ek ere wanes on 812 13 Apr. 20 | Oct. 9 172 Unionville (52)is... 2) $5... 1,072 15 Apr. 25 | Oct. 13 171 Warrensburg (49)......... 883 16 Apr. 18 | Oct. 17 182 Warrenton (51). .:.22. 0.0% 865 18 Apr. 21) Get; 15 177 Wheatland (49)........... 920 13 Apr. 18 | Oct. Ss 173 WW IRELSON (EO) tar rela comecalthew ia a chee aa. t 17 Apr: 2): ) Oct’. 18 180 Montana: 2:\ 0 CAN C24. D VSM TR nA a 5,200 10 June 25 | Aug. 24 60 Agricultural College (27)... 4,700 8 May 28 | Sept. 7 102 Anaconda (28)............ 5,300 8 June 13 | Sept. 4 83 Auaista, (29) oc a. Gas een 4,071 10 June 6 /'Aug. 25 80 PE ACO) cw tree tice ui crates 4,461 4 June 19 | Aug. 11 53 178 ENVIRONMENTAL CONDITIONS. TaBLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. Years OL als a a pbs record. | Last frost | First frost Seaeen on in spring. jin autumn. ; Montana—Continued: feet. days. PINS (ZO) Meeks cess Ore 3,115 10 May 7 | Sept. 16 132 Boulder(@7)i ce ok. ease sue 4,920 8 June 19 | Sept. 5 78 Busby (LO) ins a ts Mel hess ec. 6 June 3] Sept. 17 106 Butte.(27) vce eae eee 5,716 14 June 5 | Sept. 15 102 Canyon Ferry (27)........ 3,644 10 May 13 | Sept. 18 128 Cascade: (29)20 4. sous. wee 3,361 6 May 20 | Sept. 19 122 Chester (29) 5 4: Sots twee oe 3,140 6 May 23 | Sept. 13 113 Chinook (SO) oi oe8 ©. cela 2,502 10 May 13 | Sept. 11 121 Chouteau (29)...........- 3,810 11 May 30 | Sept. 6 99 Clear (Creek (9) 2) nee ee wee 8 4 May 30 | Sept. 26 119 Columbia Falls (28)....... 3,100 16 June 9] Aug. 22 74 Copper’) seek mos eels dca eiee ne 4 June 11] Aug. 3 53 Crow Agency (26)...... 3,041 27 May 15 | Sept. 26 134 Culbertson (30)........... 1,927 G May 30| Sept. 5 98 Cut, Bank (29) fice es 3,700 7 June 14 | Aug. 29 76 Davytont(28) oe. ee 2,800: 6 May 17 | Sept. 15 121 Decker (26). he es eee 3,400 5 May 23 | Sept. 7 107 Deer Lodge (28).......... 4,768. 8 June 16 | Sept. 6 82 Dillow Cl). ae Gee es 5,147 9 June 91] Sept. 1 84 East Anaconda (28)....... 5,500 4 June 1} Sept. 14 105 Pikalaica (26) 2. somes te Se eo: 7 May 22 | Sept. 22 123 Pallon G6) catocdoe ee oe 2,208 4 May 22 | Sept. 29 130 Morsy ti (26) oa tee we ce 2,514 3 May 9 | Sept. 29 143 Fort Benton (29)......... 2,630 g May 16 | Sept. 30 137 Fortine (28) :226. forsee 2,975 3 May 31 | Aug 6 67 Hert Wogan (20) os. oe 6,000 12 June 16] Aug. 30 75 Fort Shaw (29)... cee. 123% 3,500 2 May 10 | Sept. 16 129 Glassow 0) sis... ve. s eee 2,092 14 May 22 | Sept. 12 113 Glendive (G0) 2208 eee 2,069 16 May 12 | Sept. 22 133 Gold: Buttei@oyn os Peak deceit Gog 3 May 22 | Sept. 1 102 Great Walls (29). cc... ae 3,350 18 May 71] Sept. 16 132 Hamilton (28)24. 4.2255 ee 3,575 7 May 12 | Sept. 24 135 Harlowton (27) ..020222<65% 4,165 15 June 61] Sept. 4 90 Havre (29) oo). 2 oe i ee 2,505 11 May 15 | Sept. 14 122 Helena (27) 2450 oo9 5 eee 4,110 35 May 7 | Sept. 28 144 Ebuntley (26) 2s toe ee 3,014 2: May 5 | Sept. 29 147 DOLGAAMUCSO) nse Race ee OE came ates 4 May 10 | Sept. 13 126 Kalispell:(28) 220... 800855 2,965 2, May 13 | Sept. 30 140 Lewistown (29)........... 4,010 12 June’ 5 | Sept. 3 90 Ervineston. (27): 5.02. cee 4,488 8 May 20 | Sept. 17 120 Hodgesrass (26). 222.250 3,441 4 May 18 | Sept. 21 126 Wianhateam (27) oc ae 4,292 8 sume «4.6: | “Aue. “27 82 Marysvalle (27) 2.3.42 28 5,360 13 June 8] Sept. 11 95 Miles City (26) 52.252. 202 me Doub 18 May 7 | Sept. 24 140 Wiissoula C28)2". = os ee ee 3 2b 10 May 13 | Sept. 19 129 Ovando@s) e202 See ee 2,207 10 July. «4:) Anes 12 39 Philipsbure(28). 400 5,275 6 June 11] Aug. 15 65 Plains) (28) 6 ee een ee 2,475 10 May 29 | Sept. 19 Ps Pleasant Valley (28)....... 3,500 2 July LO | Aug 14 25 Polsoma(2S) ech e tate, cate: 2,920 2 May 10] Oct. 14 157 Foplar GO) we se Ne 2,020 16 May 16 | Sept. 11 118 ihaymond (29)he6 ta.) ae: 4,260 3 June 22 | Aug. 25 64 Red Lodge (26)........... 5,548 8 June 13 | Sept. 2 81 AEN OWA CAT ice Gee to x es 4,383 10 May 27 | Sept. 14 110 Ridgelawn (0)... 2. 7: 1,915 6 May 13 | Sept. 21 131 CLIMATIC CONDITIONS OF THE UNITED STATES. 179 TaBLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. Vears' OL i z sheet record. | Last frost | First frost : : : season. in spring. jin autumn. Montana—Continued: feet. days. St. Ignatius (28).......... 2,700 4 May 23 | Sept. 10 110 She al (BO) | Ochs )2 159 Geneva: (87). ie slo cs ae alors « 1,633 16 May 5 | Sept. 30 148 GEMMA COO) Ho. seme ete ees 1,584 33 May 31] Sept. 26 146 (CYSr ahaa (Ga) Se a eA Os 3,902 14 May 13 | Sept. 22 132 Grand Usland: (87) 6.2.0. 1,861 13 Apr. 26 | Oct. 5 162 Grant and Madrid (37).... { eee } 14 May 4.| Sept, -25.|. . 3:1) Nov... 2 213 Fayetteville (90).......... 170 13 Apr... 4.1) Nov... °2% 217 Goldsboro (90)........... 102 12 Aor. <, 6, Nove ie 210 Greensboro (90).......... 843 15 Apr... 27.1 Oct:. 25 201 Hatterast(Ol) 25: 2 ko oe 11 33 Feb. 28 | Nov. 11 256 Henderson (91)........... 490 15 Ape oe AO. ase 207 Highlands (Enc. 525. ote SOLE 6 lee a eee May. 5 | Oct. 7 155 Horse Cove (78).........- 2,800 17 Apr. 20.| Oct. , 22 185 Kinston (90) s2205: a sces os 46 8 Apr) jaf} Oct. 29 205 WEnOIr (39) ich Zee oe we 1,186 28 Apr: 18>) Oet. 18 183 Linnville(7S) ice jc hs co 3,800 13 May 3 | Sept. 30 150 Littleton (91) 62%. 238.2% 380 14 Apr: <8. Oct.2320 202 Louisburg (91)... 5. Yao. 375 17 Apr. 10] Oct. 29 202 CLIMATIC CONDITIONS OF THE UNITED STATES. 183 TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. VEStSsOE io eee bbe il record. | Last frost | First frost | “70°” in spring. jin autumn. cidhiarittl cg North Carolina—Continued: feet. days. Lumberton (90)........... 102 15 Apr. 6.| Oe. st 208 Planteon(Oh nse she cue sw anatd 12 33 Mar. 22 | Nov. 29 252 Marion (S89) sisdiae sie! die. o bis 1,425 17 Apr: 18 | Oet:. -\25 190 Mocksville (90)........... 651 10 Apr. ; 21 | Oct: St 203 Moncure (90)... ).....0.0' 145 13 Apr. 19 | Oct. 17 181 Monroe: (89) 250.565. 6 os 586 15 Apr, 21.) Oct.. .12 174 Morganton (89).......... 1,135 21 Apr. 18] Oct. 16 181 Wit. Agry (9O)ais8 0 bc). sods 1,048 19 Apr. 20: | Oct.. 15 178 Mt. Pleasant (89)......... 650 16 Apr.) 1 Oct,, 4s 189 Washville (91) 200.0604... 000 190 13 Ape. 8 Oetin.26 204 Newbern (91) .........6.. 12 25 Apr: 5. | Nove. oF 216 Oakridge (90):.........00 885 12 Apr. 10.; Oct. .25 196 Patterson (89)............ 1,200 10 Apr. 19 | Oct. 14 178 Pittsboro (90)............ 480 17 Apr. LL | Oct: 416 188 daleteii(90) sce). dae. 2 Xo 390 22 Apr. 41]{Nov. 3 213 amseur (QO)... 8s soe: 442 16 Apr. 16 | Oct. 17 184 Reidsville (90)............ 828 7 Apr, 15 °|Octs, 22 190 Rockingham (90)......... 210 15 ApEn: iS) OChia tak 206 oxboro, (90) i... 2.6. sales 600 10 Apr. 10] Oct. 24 197 Salem '(90) ...6.5..00.0 06% 1,000 15 Apr: -21 | Oct: 17 179 salisbury) (89)365 6.90. oes 760 23 Apr. 91] Oct. 21 195 SIAROMN(G()))csaeii0s aie aes: w/a Halle 900 16 Apr. 16} Oct. 16 183 eum (GO) ss be Sie SG cois 225 17 Apr « 3°) Nowe? 1 pA [SSE HELA Cok’) aes hea ee 700 13 Apr. 18] Oct. 22 187 S/O TCNK (2/8) GU Acai DM ae 50 15 Apr. 6: Noweg22 210 Soapstone Mountain (H).. OOO ec eee a Apri Ei! | Oet. ate 183 Southern Pines (90)....... 519 18 Apes. i Oets: 30 206 Southport (89)........... 18 29 Mar. 29 | Nov. 14 228 Statesville (91)........... 950 22 May 1 | Oct. 18 170 Marboran (OL) wy isle so es 50 23 Apr: 11 | Oets. 25 197 Washington (91).......... 25 13 Apr. 4{]Nov. 4 214 Waynesville (H).......... VARS 5) SIRI | A 0 a Apr. 20] Oct. 10 173 WreldoniQ@1) cs.0..0.3.. 005. 81 36 Apres. 12s) Océ.” (24 195 Wilmington (90).......... 78 38 Mar. 27 | Nov. 15 233 North Dakota: NTs 00 GY) A ae 954 13 May 18 | Sept. 18 123 PASNEW (82) ccd bas bbls cates 2,001 14 May 25 | Sept. 10 108 Berlin’ (EH): asides She we eis EL AIO)s less Sees June 2 | Sept. 12 102 Bismarck: (S)ais i. Yas wee 1,674 34 May 11 | Sept. 17 129 Church’s Ferry (H)....... DV SAGB ey) liens ds eeaeahe a « June 1 | Sept. 16 107 @oal Harbor Cl) .: ig... % 1,901 13 May 20] Sept. 12 115 Devil’s Lake (32)....... ie 1,482 4 May 27 | Sept. 25 121 Wickinson (Lee whos. bee 2,543 17 May 23] Sept. 9 109 BOTTA CBZ yas 3D vin Heke oan 1,249 17 May 21 | Sept. 16 118 PeenOrt: Vates (Sh). ecms «aes 2,576 17 - May 20] Sept. 19 122 aller ton(S2 yeaa cs ees ctvens 1,439 1l May 17 | Sept. 16 122 GCA EOM(S2 iiss cc Sole w chate 827 17 May 21 | Sept. 13 115 Jamestown (82)....c.c0.08 1,390 17 May 30 | Sept. 15 108 McKinney (81)........<0. 1,640 15 May 29] Aug. 3 94 IVE ea CED) sche sie shaders aueta POSE. leis Hees May 29 | Sept. 12 106 Napoleon: (S2) i. decks aes 1,955 17 May 26] Sept. 6 103 @akdale? (G1) snes ee ws ones 2,400 15 May 24 | Sept. 21 120 Mem bind (S2)Wakh sae acc arank 789 11 June 1 | Sept. 15 106 Orta Cah) sites eisaiel olen 1,954 15 May 28 | Sept. 13 108 OWE) Cole) oct ae wile’ ahata Cittate 1,020 Le May 29 | Sept. 14 | 108 184 ENVIRONMENTAL CONDITIONS. TaBLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. years of (—_|—_—_———_ paid record. | Last frost | First frost Tostless in spring. jin autumn. ease North Dakota—Continued: feet. days. University (G2) 0. aes e 830 17 May 20 | Sept. 14 117 Wahpeton GH). 6. 26. (21 eames Lege, INR. May 8| Sept. 15 130 Walhstom (sl)... aes 1,872 30 May 18 | Sept. 14 119 Willow City (81).......... 1,471 17 May 30 | Sept. 11 104 Ohio: Akroniy(69) os8 oo. etna 1,081 18 Apr. 27] Oct. 9 165 Bangorville (72).........: 1,380 22 May 6 | Oct. 3 150 Bellefontaine (70)......... 1,276 15 Apr. 28 | Oct. 7 162 Bowling Green (69)....... 670 17 May 10] Oct. 2 145 Bucyrus (69). ..........¢.. 1,000 15 May 9 | Oct. 3 147 Cambridge (2) ocean 803 16 May 5 | Sept. 28 146 Camp Dennison (70)...... 570 16 Apr; 25) 7 Ota 701k 169 Canal Dover (72)......... 884 15 May 8 | Oct. 2 147 Canton (69) ous cee wees 1,065 18 Apr. 27] Oct. 5 161 Cincinnati, (70): 22). 2. ee 628 of Apr. 141] Oct. 25 194 Circleville: (71). oe 694 14 Apr. 28] Oct. 5 160 Clarksville (70) 32502. se 1,010 16 Apr. 25 | Oct. ff 165 Cleveland! (69)..0:0.-524 0s 762 38 Apr. 16 |} Oct. 31 198 Coaltom) (i) 5 sce 718 14 May 3 | Oct. 4 154 Columbus (71)... 22.0223 918 31 Apr. 16] Oct. 17 184 Dayton O)ee: ones vol mee 790 15 Apr. 27 | Oct. 10 166 Dehance (69)¢ 23s. i eee 712 tors May 7 | Sept. 29 145 Delaware (71)............ 927 13 May 3 | Oct. SS 153 WDEMOS*CC2) oo Ue ae ee 1,325 18 May 3] Oct. 10 160 Bindlay (G9). soleus eee 776 18 May 3 |-Oct. 4 154 Garrettsville (69)......... 1,005 22 May 18 | Sept. 29 134 Granvalle (72). vse eee 960 20 Apr. 30] Oct. 5 158 Gratioti@oincc ocseien is oe 1,000 18 May 5] Oct. 5 153 GreeniGO)e ee: vase seis: 500 15 Apr. 21] Oct. 14 176 GreenhicrGs (He cae eo at Soeiersile Oe ace 12 Apr. 19 | Oct. 12 176 Green Hill (69)........... 1,135 17 May 16 | Sept. 28 131 Greenville (70))-3 s205. ae 1,060 16 Apr. 30] Oct. 10 161 Hedges (69) 00. het s nee 725 15 May 13 | Sept. 30 140 Hillhouse’ (69). ..0. 5.028 997 17 May 18 | Oct. 3 138 Hiram CH). oo: os messes BAO OS a ee lene maees be Apr. 28] Oct. 14 169 Hudson (69) oe otic cc ace oer 1,153 15 May 8 | Oct. 2 147 Ironton Gay oes se eee ee 575 17 Apres Ziel Octs sh hE 173 Jacksonburg (70)......... 975 18 May 2] Oct. 13 164 MCENTOM MC) 2 rd cto eo ee 1,015 16 May 9 | Oct. 5 149 Kallbackat? 2) stones 1,087 16 May 2 | Oct. 1 152 (hancaster (71). o.jecas « s 898 14 Apr. 24 | Oct. 3 162 IMarietiaid2)'< oc cl mace cree 627 25 Apr. 18] Oct. 20 185 Nlanion. Chl) ee canteens errs 980 17 May 7 | Oct. 1 147 McConnellsville (72)...... 710 24 Apr. 29 | Oct. 8 162 Medina (OO) ee ce ek 944 15 May 9 | Oct. 6 150 Nilfordton (72), oe) 5 oa 1,200 16 May 6 | Sept. 30 147 Milligan (72) eek wai ee 875 15 May 9 | Sept. 28 142 Whllport (C2) een wee os ses 1,145 16 May 9 | Oct. 3 147 Montpelier (69)........... 880 17 May 2 | Sept. 30 151 Napoleon): (69) ooo 602 oo. 680 21 May 4] Oct. 5 154 New Alexandria (72).:.... 1,050 24 May 2 | Oct. 5 156 New Waterford (69)....... 1,053 14 May 9 | Oct. 1 145 North Lewisburg (71)..... 1,095 21 May 4 | Oct. 8 157 North Royalton (69)...... 1,000 17 May 2] Oct. 11 162 Norwalk (69) 5.6 35.4.2. 719 16 May 10 | Oct. 5 148 SS ee CLIMATIC CONDITIONS OF THE UNITED STATES. TABLE 2.—Frost data and length of average frostless season for 1803 stations in the (Plate 34.)—Continued. United States. Station. Ohio—Continued: Operimn (69) foe he aces a ete Orangeville (69).......... Ottawa (G9) soutien « es Pataskala (71))0h2.3 008 3 3 seis Plattepure (70). aoe... cals Pomeroy, (71) ii ees oes Portsmouth (71).......... Rocky Ridge (69)......... Sandusky (69)............ Shenandoah (69).......... Bianey, (10) sive ic ctw ss see pemorman (71) oo. .le ds 0 a ees MBrirere, (GO) isis eis ees «ol 8 Moledo (G9). see ei Fee oe ais Upper Sandusky (69)...... MEAN A CAO) va. cieteg oeterele oes Wackery (69) 2085 Sisiecs's «oles Warren (69) .0)(o66'.e 6.6 cs Wauseon (69)............ WV AVCLLY OD ee we soi slelenss Waynesville (70).......... Wellington (69)........... Wooster (69)............. Oklahoma: Marapaho (41) 6005.0 0. 2a. reaver (aly sess. be bw oss Altitude. 1,500 (H) 2,500 (H) Len aiGHE op Fg 0 C210) a ele ae (a Wrranclers (40 er os ce NS oi. 5 ee eae releases: (AW) i ais e's bs. Ae cll eo oe apes lore’ lou Chet (4D) cose. ie Milo clei slate ete aes PAC OMAN CA Dye vetets 3 tcvelels disivs Jails, oe ie -suettlel eens MIT AMG CLO) ie se a cdel es allshiee cilia c tel ajahaballer etch ols PE aN CA) Src ete crdbe hee itele tes aire. o-cede Rew aad isirberrael CAO) a. ciets la. ejeta tell’ we, slates end PLOT ELC MO! (CEL) es alelviacd. cchov dhe Sta, wis tere abn dys Ort Srl (4D) ack od ol oi BGP ATIO AA Ary OL rae Hoe sie tebe caters Parcin stom (4b) se ea eh ws Ua cla eee Hartshorne GO) ie ie ahah ie Blake Salve Healdtonr(42) ee oes ead PHVENMESSY CED) Wisteria, Soe citallie wae ehd, hale ee oo OM ATC CAL eve ae eects o: erara ah auatohate eae carats oldenville (40) ese ee eis Celebs wees wetterson (41) sce as Penton Dene ea ais ealinle. em aietel sn a8 Mingfisher (41)).. 60 6s ob MSGS MGEL) sate lta eisieie ss venta Mangum (41) oe ole 1,046 (H) 594 1,585 (H) MVP EIONON CL Mate sees sland talianele cous atthe eheuaie TAT SHE ICES LS) al (0) A | eg Hu WPeKG) oF eo] ofah @2 4.) ¥ S0% Ee ar es REGOIOD CEO toes ceieicts Maree Sintec Caearoe as MIMISCOREE CAO) we sais warwles Sails cela alamitc aes UNG WINE CALI tA WR eles ciel a endrara a: wi BN OLERTELY CMD hiee hehe c el ehaied a uve el acUhdhete lalate No. of years of record. Average date of— Last frost | First frost in spring. |in autumn. Length of average frostless season. May 7 | Oct. 7 May 17 | Sept. 30 May 1) Oct. 3 Ei, hb hte * ined May 31 Sept. 30 Apr. 21-| Oct. 7 Apr. 20 | Oct. 14 May 6 | Oct. 6 Apr. 14 | Oct. 26 May 9} Oct. 3 May 3 | Oct. 4 Apr. 23 | Oct. 7 May 5 | Oct. 3 Apr. 24 | Oct. 15 May 4 | Oct. 4 Apr. 27 | Oct. 2, May 91] Oct 5 May 12 | Oct 2 May 12 | Sept. 27 Apr. 29 | Oct 8 May 7 | Oct 4 May 9 | Oct 7 May 7 | Oct 3 Apr LE |? Oet.. tee Apr: * 22‘ Oct.4 748 Apr) 15s |\Oet:*" 2k Apres 2 Oct. | 22 Apri ae 956 20 May .6 | Oct. 12 159 Happy Valley (18)........ 4,200 10 Possible throughout year. Eleppner Gi8) 23 o..c:ce. «sane 1,950 10 May 6 | Sept. 29 146 Joseph: GS) Pika. ae sa de 4,400 19 June 15] Sept. 7 84 Klamath Falls (17)........ BDO ip Screletoret a ae Possible throughout year. EaGrande (18)s.c. Je. + 4: 2,784 19 May 20] Sept. 22 | 125 hakeview (lS)... aces 4,825 25 Possible throughout year. fuone Roek (GD)... 8. se Siig ly Ee SANT Ferner Sree June 23 | Sept. 16 85 McKenzie Bridge (17)..... 1,400 7 June 11] Sept. 12 103 WIGRTOR LS)! Sera eee coe 350 12 Apr: 19 1 Nove a 196 INEwportiGh 7) i ne%.eisete ce coae 69 18 Mar. 19 | Dec. 22 278 Paisley Gls) od se elle Sake 4,500 5 May 25 | Sept. 24 122 Pendleton (1S) ice ootele ters -o 1,272 18 May 8 | Oct. 5 150 OHIPCIPUAT) ae cee see 3,879 14 All month s. PortlandsGyn ccs oak 57 37 Mar. 16 | Nov. 16 245 ort Orlord (Up sss eck 300 4 Very infre quent. Prineville:(8) pc clae es = ae 2,860 12 June 8 | Aug. 21 74 RIV ETSIC HLS) eas nthe ee oie 3,000 12 June 26 | Aug. 30 65 Fosebure® CL) .e5.veens ficce 510 18 Apr. -15. | Oct. 30 198 Salem: (UG) os ois ¢ ie oe 120 16 Apr. 10] Nov. 2 205 Silver Lake (17) 2. ic... 0-05 7 ir 0) enn Me ena ae All aaa a ee eae Se | ee ee CLIMATIC CONDITIONS OF THE UNITED STATES. 187 TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. Noi os Average date of— Length of Station. Altitude. years of |———_ |. 21 age record. | Last frost | First frost frostless in spring jin autumn. ta Oregon—Continued: feet. days. Barta, GES) icc 2) oe aus eo. 4,150 13 May 13 | Sept. 28 138 The Dalles (17) .....0005-3- 112 19 Apr. 10] Nov. 5 209 Wana tila (VS) sje lees ¥ aie ve 0,004 340 7 Apr. 14 | Oct. 22 191 “GIST 6 32) | einen a sn pe PR 3,047 17 May 30} Sept. 9 102 Warmspring (17)......... ' 1,600 7 May 24 | Sept. 25 124 MVESTOD CES) iiesyercie nie «= 4 nis 1,800 19 May 13 | Sept. 24 134 Pennsylvania: TUS of of (2 (6) Ie ene 1,135 Chae deeysvans | ea wer Os |) Oetes vi 151 Emporium. (97)... 26): ). = «+ pT Yay OS an ae | ER May) VE | Oct. 7 149 PETRI (I G)ie 5 cisialeictscs s whede is ayays ORANG We (a 2 ete nct ae Apr... 20 | Oct 3k 194 PV CTOHE COIL) sieves we ceases mcahe Pi OSOR 3 se aime os May 5 | Oct. 8 156 Branidin,¢Venango'Co.) (96)ilie. - 0). sam coe Ilene «e060 May, if | Oet, it 147 arrcbure (97)... + ves os AU] RAS Mal | Aen CTA MES Aor Oe Oeks. wa 196 tuntimedon (EH). ...:....... 6255 Cie iael | cer Meee eee May ~L- i Oet:, “15 167 Meanowms CE) ei. o'sus 35. 2 ry oem deere mene een Apre Zo. | Oct, 25 183 BE EVOY: Oil) siaistalers @skere es s0/s nB: 800 @ SD he oe Cee May 6 | Oct... 7 154 Mauch Chunk (98)....... Goer er eo Scie. aati May -- 3, }/Oct., “11 161 Philadelphia (98)......... Despre et ile oeecaene ee: Apr: 8. Get. 31 206 attsbure: (96)... see eo ey Biers t aaiedione ste Apr. 22} Oct. 18 179 Quakertown (H).......... 1S GSS el | Bean a muse RE Apr. 20] Oct. 20 183 Saegerstown (H).......... DRG lcs ecaystect ols May 14 | Sept. 24 133 Berea AIL CTEM Os cei a: 5 alerte eee Suc Bixe ousieiebaas oils et falets iuteve e's & Apr., 20.) Oat. S13 176 Selinsgrove (H)........... ABD Gite adsl cookaeede a, May 8 | Oct. 1 146 south Maton (H)....3....- GEOE oe ee Apr. 22 | Sept. 28 159 State College (97)......... 1 HS ity | RR Oe May 9] Oct. 2 146 Westchester (H).......... 460 Se eal oP AOE epee Olebet ak 186 Sere aa 0 A ie ee SSDs Ly wae Apr. 25 | Oct. 1 159 Rhode Island: Block Island (105)........ 26 21 Apr. 12]! Nov. 16 218 aS HOM CED) ccs e's oie » « is DOR |bct cscs es Apr. 26.) Oct. 17 174 Narragansett (H)......... S35 en Gaaeree ae Apr. 20} Nov. 11 205 Providence. (105)... 6066 «oe 182 24 Apr: 15. | Oct. 22 190 South Carolina: JE VEESS MEET 0 ION RE gna ea 565 18 Mar. 11 | Nov. 18 252 Allendale (86)............ 186 15 Mar. 24 | Nov. 20 241 Iacesbune (SC)iesies Se sce sisi 656 13 Mar. 24 | Nov. 2 223 IBEAUTOLG (88) \onsis es yes os oi 20 20 Mar. 91] Nov. 23 259 ilaekville: (SS); jcc. css eire 6 296 18 Mar. 19 | Nov. 16 242 Charleston (88)........... 48 38 Mar. 1] Dec 2 276 Wheraw (S88) os ieeea eee os oe 144 20 Apr Sol Now 4k 210 Clemson College (87)...... 850 13 Apr So | Oeti. si 209 Golumbidi Sl) oes. bus oss e 351 22 Mar. 22] Nov. 8 231 CWanwesyilSS) cies weiss wes 25 10 Mar. 26] Nov. 13 232 PNOTENCE! (SS) weiciec wiei eile ve oe 136 18 Mar. 31 | Nov... 7 221 Georgetown (88).......... 12 14 Mar. 19 | Nov. 13 239 Greenville (87)........... 989 14 Apr. a AS ae « 213 Greenwood (86).......... 671 20 Mar. 22] Nov. 4 227 INO WOEIEY: (ST) iwieis ce cstew oie 502 13 Apr. 11} Qos. 31 203 ISN EVI (SE Dicvs iahes a oeathlg onasske 512 15 Apr (3S | Oe... 26 206 Society Hill (H).......... PD i FERS Cae Mar. 18 | Nov. 15 242 Spartanburg (87)......... 875 14 Mar. 31] Nov. 6 220 Statebune (SB) ovr i's «aie 'ers sic 500 27 Ane.) FoianNow:- “9 221 Summerville (88)......... 75 10 Mar. . 20 | Nov. 17 242 SRREUTONV OST). vaierciarnters wa ee 620 15 Mar. 24] Nov. 12 233 METI COS ie ciaukisivnsieick. SICK bse ince 85 20 Apr. 4]Nov. 4 215 188 ENVIRONMENTAL CONDITIONS. TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. Vesa GL 3 ol pai record. | Last frost | First frost reste in spring. jin autumn. season. South Carolina—Continued: feet. days. Walhalla’ (86)5..00 Soe eee 1,061 14 Apr. 8) 1 Nov.i2 ot 207 Winthrop College (87)..... 690 9 Mar. 28 | Nov. 5 222 Yemassee (88) 2.0 c8.. 08 22 13 Mar. 25 | Nov. 11 231 South Dakota: Aberdeen. (34): .2. sn. <5 ore 1,300 18 May 21 | Sept. 18 120 ACACEHSY: (4) oe eee es oes hice oie ene 10 May 5 | Sept. 28 146 Alexandria ($4) : 25.20.05. 1,352 20 May 15 | Sept. 24 132 AWsherottlos) a sees 3,192 16 May 24 | Sept. 14 113 Bowdle(34) so. ase es 1,995 14 May 20 | Sept. 23 126 Brookings (64). 4. t2 ee ee 1,636 19 May 22 | Sept. 18 119 (Cherry: ACreclkc UE) a Acne c/s cee enre eee poe eee be May 25 | Sept. 20 118 CHAT (SA eee ermal le emis ware odes 13 May 25 | Sept. 24 122 Fort Meade (83).......... 3,624 24 May 7 | Sept. 23 139 Cary (Oo) oes CaO ee 1,484 12 May 19 | Sept. 25 128 GreenwoOud (a4 ht ee cerns sane sees 6s 14 Apr. 27 | Oct. 1 157 HMichmore (34) 2 4.2 cet 1,890 13 May 16] Sept. 24 131 Toten |Crhy CE ree eee cee cease cual bse e tae eaves May 16 | Sept. 20 127 uroni(34) ef ot0. se ee ee 1,306 27 May 12 | Sept. 20 131 Kennebee (64) <- 2 2 eee 1,689 16 May 13 | Sept. 25 135 Kimball (Heo: Soe ee APTS, eee ee May 6 | Sept. 27 144 Wiese: (GB) 5. cree coe teeta [evecare otaeel seas 10 May 18 | Sept. 21 126 TpLle mage (SS) esos Sellen welt ee bisa e 7 May 25 | Sept. 22 120 Menno (34) 2 eee eee 1,325 12 May 18 | Sept. 25 130 Nilbank-(G4) 0 soe ec e 1,148 17 May 14 | Sept. 23 132 Oclrichs (338) sce cee tae oe 3,339 18 May 10 | Sept. 23 136 PCIE (SS) 32% a ane ee 15572 17 Apr. 30 | Sept. 30 153 Rapid City (33)".5. 55. see 3,251 ot May 61] Sept. 26 143 Redheld: CH) 2..5..5 45 220e0 BOG ye) ile nic Sees 8 May 21 | Sept. 18 120 Rosebud (33) 7.05 eee 2,600 14 May 10 | Sept. 25 138 Sioux Falls (34)..62....02 1,400 18 May 12] Sept. 19 130 Spearfish (33)....... plate 3,647 18 May 9 | Sept. 27 141 Pyndall CB). Fo ce ee ome eS Lc aaa ee eee ee ae May 6] Sept. 23 140 Wanktonm (34) 223. hese cee 1,234 33 May -.2: |(Ociana 3s 154 Tennessee: Benton 7S). 2.3.58 see eee 880 15 Apr. 17 | Oct. 19 185 OVAL C07) ccc ekc hc teehee 450 14 Apr. - 2 | Oct. 28 209 Byrdstown Gh) =. i222. eeee A O2ZGT feces Settee ce Apr. .11-| Oct; 20 192 Carthaget(7). ak sss eee 500 13 Apr! 7 Get. 324 200 Chattanooga (78)......... 808 30 Apr. 2 | Oct. 26 207 Clarksville (77) 2. 3 een Se 520 15 Apr) 10) > Oct. 428 201 Wecatur((S)e wes eee 850 13 Apres) 177} Oct. 723 189 Elizabethton (H)......... gE ya aa Bee Apr. 22} Oct. 21 182 Brasmusi(?S) 2:2 hee oo are 1,850 12 Apr.: 21 \yOct” 715 177 Florence:(@ 7) ook eek. oe ee 560 10 Apr. 10 | Oct. 21 194 Greeneville (78)........... 1,581 14 Apr. 19 | Oct. 19 183 Hohenwald (77)... 640 8: 983 14 Apr. 19 | Oct. 9 173 JACKSON CIS inca ine Seer 450 10 Apr. 41] Oct. 30 209 Johnsonville (77)......... 364 13 Apr. 10] Oct. 20 193 Knoxville (7S) a... Siena 977 | 38 Apr. 31] Oct. 28 208 Tiynn ville (6a) ie ace eneee coe Ev aFO 10 Apr.) Si-O. (20 195 Memphis (77) 2062s 058 409 38 Mar. 21 | Oct. 31 224 Mountain City (78)....... 2,486 11 Apr.) 28:1 @6t. 15 170 Nashville (277) 35 .b650 ocees 573 38 Apr... 2} Oct. 26 207 Wewnort (Eye eee bi cee 1 28ON Ae oe ekg Apr: 12} Oats i730 201 Rogersville (78)........... 1,150 16 Apr. 17] Oct. 19 185 CLIMATIC CONDITIONS OF THE UNITED STATES. 189 TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. Mace Average date of— Length of Station. cinete peo: record. | Last frost | First frost ‘ pee in spring. jin autumn. ; Tennessee—Continued: feet. days. Bee Dy) (78) cass sees oie fa 1,410 16 Aor. 22 |-Oects, 3 174 Savannah (77) ai. ous 442 12 Apr. dt Wi Oets, 25 199 Springdale (78)........... 1,058 16 Apr.. 21 | Oct... 15 177 Springville (77)... cs. + 2.6 377 6 ‘Apr: 16: Oct... 1s 180 BPE MEOM CEs) iie hele oie. esate 345 ale Aor 5 | Oct i. 38 196 Mullahoma (77): sacs s's ve 1,075 13 Apr. 17 | Oct. 18 184 Texas: AitlenetG 2) iy we). lvse ee Bie 1,738 23 Mar. 15 | Nov. 15 245 PARA NAS) ile esl elslaid 1,429 13 Mar. 25 | Nov. 9 229 Amarillo (42). eee ia eh 3,676 18 Apr. 16] Nov. 1 199 PAIStIN (43) Oe Wie as 593 15 Mar. 12 | Nov. 18 yAsy | Ballinger (43)............ 1,637 5 Mar. 23 | Nov. 9 231 Beaumont (1)... 0.0028 29 Mp. Feb;: 24). Dee.) 2 281 eeville:()) icc. bee. ols 225 15 Feb. 14] Nov. 30 289 LEY TGS) ov aria ye C24) Rig ane ATs A MiMi as 6 Apr. 6 |. Nov... 7 215 Blanco (43) 300s oc eld ela ois 1,350 4 Mar. 22/3) Nove. 1.7 230 PBOCTHEK(T) ON. cavers dud 1,412 16 Mar. 1 | Nov. 24 268 Bonham (44)............. 566 7 Apr. 61] Nov. 13 221 Bowie (42) 0.68.6 ee 1,113 9 Mar. 16 | Nov. 10 239 Brady (43) oso sk lee ec eels 1,500 6 Mar. 29 | Nov. 7 223 Brenham (44)............ 350 19 Feb. 23 | Nov. 25 275 PST LOMn CL) Mee. 6 oes ss Sag 12 16 Feb. 10{ Dec. 9 302 Brownsville (1)........... 38 18 Feb. 61] Dec. 21 318 Brownwood (48).......... 1,342 13 Mar. 27 | Nov. 10 228 ohare C4 es ee ee 5 Apr. 25 | Oct. 18 176 Childress 42).....5..6.6. 1,869 OF fi) vAprs 2b) ONOve.y 62 211 JOUENB Ye (eh (C 999) aI ea 3,397 4 Apr. 21 | Oct. 29 191 Claytonville (43) ......... 2,100 11 Mar. 25 | Nov. 5 225 Coleman (43)...:......... 1,710 8 Mar. 18 | Nov. 17 244 College Station (44)....... 308 15 Mar. 4 | Nov. 21 262 Molorado (43) wie os ei. c esald 2,066 8 Apr. 11] Nov. 9 212 Columbia (se el. oe 34 16 Feb. 24 | Nov. 28 277 Corpus Christi (1)........ 20 24 Feb. 21 | Dec. 16 298 Corsicana (44)............ 445 19 Mar. 15 | Nov. 14 244 Mero; GL) ies i ee oa 177 17 Feb. 25 | Nov. 23 271 Wallas (44) iii. Ocoee 5 466 19 Mar. 19 | Nov. 13 239 Danevang (1)............ 145 14 Feb. 24 | Nov. 21 270 eT ION CL een el sp 952 5 Feb. 23 | Nov. 21 271 Dublin (4S) iis). Beers oaks 1,466 12 Mar. 17 | Nov. 14 242 Magle Pass (1) )fs.0....... 800 Lz Feb. 27 | Nov. 21 267 Pe Paso (2) iii ie hh) oy 3,702 (H) 29 Mar. 20] Nov. 11 236 Harland (43) wae ss ool 1,000 14 Mar. 16 | Nov. 20 249 Bort: Clark (ie okie. «ak 1,050 18 Feb. 24 | Nov. 23 272 Fort McIntosh (1)........ 460 18 Feb. 18 | Nov. 28 283 Fort Ringgold (1)......... 230 14 Feb. 12:1) Des, At 302 Bort, Worth G48). vies. cer 670 17 Mar. 8] Nov. 24 261 Fredericksburg (43)....... 1,742 18 Mar. 13 | Nov. 14 246 Gainesville (44)........... 738 77 Mar. 31] Nov. 7 221 Galveston (Ll) i666 eoec sees 69 39 Jan. 27 | Dec. 24 331 Gyre (42) ols s cise ele e 1,040 t Apr. 2] Nov. 10 222 Greenville (44)........... 550 8 Mar. 10] Nov. 18 253 PULSE en ter (4a). cate saialillvecale gc meee wee 2 11 Apr. Bap Oa .<80 211 Hallettsville (1)........... 235 17 Mar. 3] Nov. 21 263 PiBskel aD) ke oo 1,553 12 Ant: 9:4 | Nev. 32 222 Henristta (42) oi. eva ec can 915 12 Mar. 25 | Nov. 8 228 190 United States, Station. Altitude. Texas—Continued: feet. Hondo City) 262668 oe 901 Eouston Gl)tsc.. sie ae 138 Huntsville (44)........... 400 Kaufman (44). 5... 5 as et 448 Kerrville:G)6.o 05. c ek ee 1,650 Lampasas (44)............ 1,026 Milano 43) oes eee 6 oe 1,040 fongview (44) 2....05..0 0. 336 Pin eC ces vere eee eae 418 Menardville (48).......... 1,960 Winama (42) i ees cen eso eke 2,743 Mt. Blanco (42).......... 2,750 Nacogdoches (44)......... 271 TUBA Cy Cual C2 9 i ea A na 3 We A New Braunfels (1)........ 720 Palestine (44). 0.2.24... 510 BATS CRN cares taie testes ate 592 Port Lavaca’ ()\..c. 2 25.28 20 Guana 2). cesses sce 1,563 Rhineland. (42). 2.2.6 22% 1,200 Rockport (1) ¢ es s2 oes os 6 SanvAntonig Cl). 8 5.02. 701 San Marcos (48).......... 588 Sanmvoapar(4s) asc race Leite Seymour (42). 0. ones se eee 1,180 Sherman (44) \o 5. 50% soe 745 ponora (43) 6.5 us... oe oe oe 2,200 Spmarlangde (L) ca an. cs ces oe 79 Sulphur Springs (44)...... 530 aviori(As) <2. ase eck 583 temple (43)... cases ees cee 630 Meexinenae)e scene Jos tie 4,694 Mla AD) Cee esac te eee 3,501 Wictore (Hl) nee en. coe 187 NVacor G4) cra se eee oe 424 Waxahachie (44).......... 556 Weatherford (43)......... 864 Utah: AMELIE CLO) eile cee sk bo osc oe 4,800 Castle Dale (10).......... 5,500 ormme yt. ...0 8 s Sere 4,240 Hanery CO) 525.2 os. ee 6,260 Farmineton (11)... <2 4,267 Hilimere CH) 2.0. 5). saree 5,100 Fort Duchesne (10)....... 5,000 Government Creek (11).... 5,277 Grayson (10). 0.63.3. 02% 5,750 Green River (10)......... 4,080 Heber (10) oo. eek 5,606 PALO LCL ON. ees tc et ook 3,000 HManap (IO) soe ee cs 4,925 Welton (ii) ioe betes 7 4,230 | BTSs cpt G ke Be ay aan a 3 5,010 Powe: ace danke rae 7,000 Moran (Uy) eee wise. eee 4,507 ENVIRONMENTAL CONDITIONS. TasBLE 2.—Frost data and length of average frostless season for 1803 stations in the No. of years of record. (Plate 34.)—Continued. Average date of— Mar. Feb. Mar. Mar. Mar. Mar. Mar. Mar. Mar. Apr. Apr. Apr. Mar. Apr. Mar. Mar. Mar. Feb. Mar. Apr. Feb. Feb. Feb. Apr. Mar. Mar. Apr. Feb. Mar. Mar. Mar. Apr. Apr. Feb. Mar. Mar. Mar. Apr. June May June May May May May May Apr. June Apr. May May May June May 10 20 6 Zf 24 24 19 12 2 1 27 9 10 25 9 13 20 15 26 4 6 23 28 8 28 10 18 21 19 13 14 29 15 20 10 26 22 Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Oct. Oct. Nov. Oct. Nov. Nov. Nov. Dec. Nov. Nov. Dec. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Oct. Oct. Dec. Nov. Nov. Nov. Sept. Sept. Oct. Sept. Sept. Sept. Sept. Sept. Sept. Sept. Sept. Oct. Oct. Oct. Oct. Aug. Oct. Last frost | First frost in spring. |in autumn. Length of average frostless season. days. 254 278 258 254 230 228 243 249 262 222 180 205 247 169 261 245 240 295 229 214 323 276 261 211 223 256 198 272 239 254 246 AWE 194 293 250 230 236 158 107 141 111 132 127 130 129 122 148 80 200 139 152 140 72 151 CLIMATIC CONDITIONS OF THE UNITED STATES. 191 TasLeE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. Station. Utah—Continued: EW CUM C12 YON Ge Marysvale (11)........... RO (LO) [28 SA bie Shoo ehens Mrodenay(lh) co. 62.8. 6 ee Ocdem Gh) yoo wes ee. eee Parowan (Ub) oot.) ose. sete IBFOVO! (UL) 6 ue ss seek eae Hichtreld (11) 6.3. 4. sekees mt. George (11)... .0...5.. Salt Lake City (11)....... Snowville (H)............ Wernalh’ (nm): (lO). e 3%. oo Vermont: Burlington (105).......... @ormwalle (105) 0 re. Enosbury Falls (105)...... Jacksonville (105)......... Northfield (105).......... St. Johnsbury (105)....... RVs GOD) side ee le bs Woodstock (105).......... Virginia: Alexandria (94)........... ArVvVoOnia) (93)\c0 sis... c's Ashland (93) .:2....62 004% Barboursville (93)......... Bedford City (92)......... Big Stone Gap (74)....... Blacksburg (92)........... Bon Air (93) 226s. eos so wits Bristol) (F4)\ sis oo. bas Burkes Garden (74)....... @allaville(92)io5 0.6 oe. ee es Charlottesville (93)....... Columbia (93)............ Dale Enterprise (93)...... Moaswell\(93)iie.s ee ek Marmiyille' (92).:..6....0.3 Fortress Monroe (92)...... Fredericksburg (93)....... Hampton (92) 225.025. 02 . Hot Springs (93).......... BMexineton (98) wi. oes cds amcolin (94) sie) oe. Se Lynchburg (98) ........... Marron (64) neces whee hes Max Meadows (74)....... Newport News (92)....... Nokesville (94)........... INOrfolle (QE): iss ss cieie. «ice Petersburg (98)... 60s... Quantico (938) oo. s he cae Richmond (98).......... Roanoke(G2)yy ick ced Rocky Mount (92)........ Altitude. Average date of— Length of average frostless season. No. of years of record. Last frost | First frost in spring. jin autumn. 16 May 23 | Sept. 22 10 May 26 | Sept. 17 17 Apr. 21 | Oct. 3 9 May 18 | Sept. 25 14 Apr. 25° Oets (27 19 May 19} Sept. 21 14 May 12 | Oct. 3 14 May 28 | Sept. 15 16 Apr. 22 | Oct. 11 35 Apr. 19]! Oct. 18 BAe i eters June 18 | Sept. 26 13 May 12 | Oct. - 20 May 20 | Oct. 10 15 May 5.| Oct. 5 17 May 16] Sept. 20 23 May 19 | Sept. 18 22 May 13 | Sept. 16 15 May 16 |} Sept. 25 16 May 11 | Sept. 26 16 May 21 | Sept. 18 10 ADE. «S|: Oct. mot 13 Apr. 25] Oct. 14 15 Apr. 15: |-Oeti: SF 11 Apr. » 22) Oct: 18 13 Apr. 10] Oct. 29 7 Apr. 27 |, Oct: PM Ee Apr. 28 | Oct. 5 8 Apr +) 8 |/Oet. 20 14 Apr. )\ 23° 1) OGt h7 13 May 41] Sept. 29 14 Apr. 13 | Oct. 20 16 Apr. % | Oct 28 9 Apr. 2h |, Oct.) 18 17 Apr. 28 | Oct. 3 ¢ Apre- 21 | Oat. “22 9 Apr. 16 | Oct. 28 16 Mar. 26 | Nov. 14 16 Apr > T3: | ‘Oet- 920% 22 Mar. 20 | Nov. 14 17 May 1 | Oct. 4 18 Apr: 22"). Gets A328 8 Apr. 25 | Oct. 15 23 Apr. 14] Nov. 1 15 Apr. 26 | Oct. 8 14 May 1] Oct. 138 19 Mar. 26] Nov. 9 12 Aor. 17: } Qete “Si 23 Mar. 27 | Nov. 12 18 Apr. 11 | Oot 18 1l Ann. (19: } Gote* ‘21 12 Apr. 2.) Nov. 3 5 Apr: 21 | Oot. 19 12 Apr. -10 | Oct. 19 192 ENVIRONMENTAL CONDITIONS. TABLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. Ne Gf Average date of— Length of Station. Altitude. Years Of4. a sai ae record. Last frost | First frost dye in spring. {in autumn. SeaeOe Virginia—Continusd: feet. days. sirifeseru (PA are Sees oh em 1,000 9 Apr, 10: | Oct. vag 190 See OF) RR eainre, Rea i ean Ae 350 8 Apr. 14 Oet.1528 190 Shenandoah (93)........-- 937 3 Apr. 29 | Oct. 9 163 Spottsville (92)........--- 15 17 Apr. 17 | Oct. 16 182 Stanardsville (93)......... 670 12 Apr. 12 | Oct. 25 196 Staunton (93)/oe.2- Ge. Sa 1,380 iz Apr. 25 | Oct. 12 170 Stephens City (94)........ 710 14 Apr.) 20}. Oct. ert 176 SunbeaHn (92) 280 f.he sco e 60 6 Apr. Al-| Octs 238 203 Warsaw (93)........----- 200 16 Apr: 15.) Oct), 22 190 Wrest Brook (G3): «seeds Us, eek a 4 Apr. 15) | Oct 28 188 Williamsburg (93)......... 74 8 Apr. 9] Oct. 26 200 Woodstock (94)...:.....-- 927 11 Apr. 22 | Oct. 7 168 Wytheville (74)........... 2,293 15 Apr. 18 | Oct. 10 175 Washington: Aberdeen (19).........--.- 162 (H) 10 Apr. 27 |} Oct=,.22 178 Bellingham (lO) 5: eho. cer: a awe es 2) 10 Apr. 22. \Octae 21 182 Centralia (19) .ic.. . pes ee 212 (H) 9 May 6] Oct. 14 161 Clearwiter (19)4 26.6225 oasis oo okt. s: 9 Apr: 27°). Nove. wz 194 Cle Bhumi (Oa, oon). once 1,930 9 June 9 | Sept. 7 90 Coliax (20) eek. = Se) ae 2,300 13 May 25 | Sept. 10 108 Colyilled20) conc. sees eee 1,635 9 June 5] Sept. 7 94 Conconully (20); J 3: .,-'2 = (2: 2,300 9 May 18 | Sept. 21 126 Coupevalle (19) 425852 pee ae ete sa) < 9 Apr... 9 | New: 28 213 Crescéenis(20)io5.2 0.02 = see 2,250 9 May 23 | Sept. 22 122 Ellensburg (20)........... 1,571 15 May 23 | Sept. 21 121 Kennewick (20)..........- 367 76 Apr: 28 | Oct-seis 170 ier Center (19). 5 sas. weak ace ete as 10 Apr. -20 | Oct.a9 25 188 Eakesidej(20) ses ss -le owe 1,116 16 Apr. 10 | Oct. 19 192 ester (CEO) tee a tees bea een Ay ds 5 May 18 | Sept. 13 118 Pale (2Q)u 2 sack sec ne 600 16 Apr. 23 | Oct. 18 178 Noxee (20) 2a os kes. 3 eas 1,000 16 May 23 | Sept. 21 121 Worth Head (iQ) sf ae5< ase ait oe ee cies 6 Feb... 9 | Dee: 22 316 Ole (IO ee on ahe se ete 50 (H) 10 Mar. 27 | Nov. 21 239 Olympia (19) 43... Pie = oes 17 (H) 10 Apr... 28 1 Ney.) 2 188 Pomeroy. (Hos os ee eee PSOO AUT BaNiee 2 Apr. 26 | Sept. 28 155 Republic CO) ek Se 2 ee 2,628 8 June 15] Sept. 3 80 Bosaliac(20) Ae as oe 2 2,425 9 June 1]! Sept. 14 105 Seattle 19) 2s: 6 0 25e5s cee 46 (H) 18 May 21 | Nov. 22 246 Snohomish CHD). hes eee Se) \ Pilate eae acer Apr: 21) Oct: -24 183 Snoqualmie Malls: (19). 9 uo ah se. 8 May 9 | Oct. 24 168 Spokane (20) )...3,. o.ge2 444 1,943 28 Mar. 26 | Oct. 14 202 Sunnyside: (20). : 3.4 |\3 Oct. ©17 176 MEINIS: C73) \ Me iss ie 6 aes 1,940 10 May 18] Oct. 10 145 KGemville(73) ek sens crc te 738 16 Apr, 30: |.Oct, AS 166 raltOne (faye ra ose yoke 985 16 Apr. 30 | Oct. 74 160 LE Myouroy ely (72. 9 Malia gree ame Pcs 1,400 12 ‘Apr. Viti i- Get 2s 189 Huntington (74) 6.05.6. 510 15 Apr. 19 |. Oct. 13 ts Lewisburg (74)........... 2,200 10 May 10] Oct. 11 154 Moen (CCA ee ies acs ale a8 665 8 Apts 2hal, Cet) 12+ 186 Lost Creek (73)........... 1,033 14 May. -6.| Oeti ~- 5 152 Miarlinton (73) 0. <2 36/6). 2,169 10 May 2 | Oct. 1 152 Martinsburg (94)......... AISA en aires a RONEC hae ake Apr. 20]! Oct. 14 177 Moorefield (94)........... SOO Re is meh os Apr. 30 | Oct. 4 157 Morgantown (73)......... 1,250 fo SoMa. ea eOets sis 165 ‘New Martinsville (73)..... 634 16 Apr: 28 | Oct.) 14 169 Nuttallburg (74)... 660.0) 5 2,202 16 May 1 | Oct. 10 162 ‘Parkersburg (73).......... 638 20 Apr kon | Obs (il 179 ESOS CLS) sisi v diace (close 1,662 10 May 10 | Oct. z 150 J Es VET C) 0) tl GFE) ye cee 1,192 ia May 8 |} Oct. 9 154 iekens) C73) 20% 3c oe cies 2,785 16 May 91] Oct. 14 158 Point Pleasant (73)....... 553 16 Ary. 20 OCte. 20 183 Howellton (BH)... os. QO ey uliid saree AU, Apr. 23:1) Oct 12 L772 Mrerra Alta: (73). oeces oe eo: 3,207 10 May 11 | Oct. it 143 Wellsbure-CH) oi... 6s oes Dy ee eC a Ee May <3.) Oett) aS 165 Wheeling (96)............ 07 US it Rot | EC Apr. 15: Oct, 2a 193 Wisconsin: Amherst: (60) i... ce ee 1,200 18 May 22 | Sept. 27 128 Appleton (60)............ 795 11 May 6 | Oct. 1 148 PROTON (OS )ics vec cee ees SS 647 16 May 14 | Sept. 21 130 i Barrons) foes es.)escle a avatars ep a eens 18 May 22 | Sept. 15 116 Beloit: GO). sees. es 750 17 Apr. 16 | Oct. 18 185 ibrodhead (GOS. {0 ole 812 Tt Apr. 17 | Oct. 17 183 Butternut (58)... 2.0.2.0. 1,508 15 June 4] Sept. 9 97 Haltom GO) Vee. clos sates 860 15 May 8] Oct. 3 148 Grandom (60) Foe. coe fo 1,060 12 June 3] Sept. 14 103 Melavanr (GO)H es. 262 se 920 17 Apr: (20°4-Oete 16 179 Dodgeville (59)........... 1,116 10 Apr. 25 |-Oct: 8 166 Mowing (58) iso)... a 983 15 May 6} Sept. 24 141 Hau Claire (8)... 05). 030. 800 19 May 10 |} Oct. 1 144 HMlorence: (GO)e suas elke 1,293 18 June 2 | Sept. 13 103 Fond du Lac (60)......... 800 22 May § 5 | Oct. 2 150 Grand Rapids (59)....... e 1,021 a May 23 | Sept. 26 126 Grantsbure (68)%. bok w.ke 1,095 Re i: May 14 | Sept. 19 128 Green Bay (60)........... 617 Ze May 3 | Oct. 3 153 Elancock (G9) er. cate Heck 1,091 18 May 18 | Sept. 28 133 OTIC CEL) Me ee vise tee SOS this. le ee ee May 4 | Oct. 1 150 | ratheld (Oye oe dee f 973 12 May 20] Sept. 22 125 Eiayward (G8) ine oe We 1 , 197 19 May 26 | Sept. 12 109 inllsboro (SO) eles coe 1,000 19 May 13 | Sept. 24 134 | Boepemick (G9). ci ioe. 1,683 18 June 3.) Sept 17 106 WentOorpese (OO un. vues eeu 681 37 Apt. .30.) Oak 16 163 Lake Mills (60)........... 897 19 Apr. 23] Oct. 15 175 | Dancaster (G9)... cade. ee ok 1,070 18 Apr. 25 | Oct. 10 168 | Wiadisom (GO) vac ck cen 974 31 Apr. 22 | Oct. 18 179 Manitowoc (60)........... 616 47 May 9| Oct. 10] 154 | Mauston (59)............ 882 14 May 17 |} Sept. 24 130 | 194 ENVIRONMENTAL CONDITIONS. TaBLE 2.—Frost data and length of average frostless season for 1803 stations in the United States. (Plate 34.)—Continued. No. of Average date of— Length of Station. Altitude. years,orf4:|" "| Fae ne record. | Last frost | First frost | *TOSU¢S in spring. |in autumn. Seawol- Wisconsin—Continued: feet. days. Meadow Valley (59)......-. 974 19 May 21 | Sept. 23 125 Medford): (59) 4 visas elec) (eiens 1,420 19 June 3 | Sept. 12 101 Milwaukee (60)...........- 681 39 Apr. 28 | Oct. 7% 162 Neillsville (59)..........-- 996 21 May 23 | Sept. 20 120 New London (60).......-.- 762 14 May 14 | Sept. 27 136 Ocontoi(GO) Se6 2 see eee 590 19 May 10| Oct. 2 145 Osceola (GS) 2 see Pe 806 19 May 12 | Sept. 26 137 Oshkoshi(G0))42 ones sere 744 19 May | 7 | Sept. 30 146 Pine: Raver (GO). 3205. ae 900 15 May 13 | Sept. 28 138 Portace:(G9)i sees = hare 809 14 May 3] Oct. 41] + 154 Port Washington (60)..... 713 16 May 6| Oct. 12 159 Prairie du Chien (59)...... 690 22 Apr.- 27 | Oct: <2 168 Prentice (59) ays ase: 2o56 1,551 1l June 6 | Sept. 9 95 Racinex(GO)..23 356,185 joes 633 13 Apr. 28 | Oct; .13 168 Shawano (GO)ibe. 2.2. shee 796 13 May 14 | Sept. 26 135 Sheboygan (60).........-- 831 12 May 8| Oct. 11 156 Spooner (58) ies. diese 1,104 13 May 24 | Sept. 14 113 Stevens Point (59)........ 3 17 May 25 | Sept. 26 124 Valley Junction (59)...... 930 18 May 16 | Sept. 24 131 Viroqua 59) i Wee eUes. ais 1,412 19 Apr... » 30° /2Octs. 25 158 Washburn (H)............ G58) cease pete we May 16 | Oct. 12 149 Watertown (60).......... 824 18 Apr. {27} Gets yt 167 Waukesha (60)........... 864 14 Apr. 28} Oct. 12 167 Waupaca: (GO)2s.8 ou. ooo. 857 13 May 20 | Sept. 27 130 Weatisau(59) hiss ee: 1212 14 May 30 | Sept. 22 115 Weyerhauser (58)......... 1,297 a May 30 | Sept. 12 105 Whitehall: (58)i4 2.08.2 ot 675 17 May 6] Oct. 4 151 Wyoming: Alcova-Pathfinder (24).... 5,366 11 May 21 | Sept. 19 121 Basins) 2s. eee eee ec 17a (Pent ay ee ATED May 10 | Sept. 20 133 Buftalor 2b) sere Soe eee ASIOO) SAN ebget as May 28 | Sept. 21 116 Cheyenne (24) 3. 6.2k : Ss 6,088 38 May 21 | Sept. 17 119 Chuswater(24)).3-4...0on. 5,282 9 June. 1.) Sept: 106 Clarko(25) 29 ee Lae zs 4 en bergen oh ye May 4| Oct. 14 163 Eaton’s Ranch (25)...... AN GOO: 5 vaio Bee May 16 | Oct. 5 142 Fort Laramie (24)........ 4,270 15 May 15 | Sept. 20 128 Gilleiten(25) ist ek: eee AE GAG! sans eens May 23 | Oct. 4 134 Griggs! (25) ins ee eee A TOD: Aa sce May 31 | Sept. 8 100 EHyattsvalle: (25) 2 a2; Siew le ee oe Sec teeeree May 19 | Sept. 21 125 Kirtley (24).....0.00.000+ 5,000 6 May 29] Sept. 17| 111 handeri(Qa)kaccioshs 3k DENS 3 >; Sha are ee s May 26 | Sept. 11 108 Taramie (24) i205 ee 7,188 15 May 30 | Sept. 16 109 Ms hs eee 5,007 16 May 25 | Sept. 13 lil Moorcroft: (25) ose eee. Ae OA 5) teiseli2s bcs ako aha May 23 | Sept. 20 120 WTOOTEN(ZA) | cape iies eae 6,000 9 May 26 | Sept. 14 111 Neweastle (25)s.5 2 s..eue ARO WE TNs Reel May 22 | Sept. 20 121 Phillips: (24s a we ae 4,900 7 May 25 | Sept. 17 115 Ring Bhai (24 i eee 5,038 8 May 27 | Sept. 19 115 Rawlins (24) nF os ss. 2 kk. 6,744 6 June 3 | Sept. 13 102 Sheridan (25) eo gett s bose 5 72 | Aa Fee ates co May 21 | Sept. 24 126 Shoshone Dam (25)....... ps (od Ree ER Ee May 26 | Sept. 21 118 Thermopolis (25)......... 7a 5 lea | Vere Sieg 9s, ete May 8 | Sept. 13 128 Wheatland (24)........... 4,741 9 May 11 | Sept. 24 136 Wyncote Case. esos: 4,207 3 May 21 | Oct. 2. 134 CLIMATIC CONDITIONS OF THE UNITED STATES. 195 Most of the data of table 2 have been plotted on a map of the United States, to represent them in a graphic way. After the numerous stations had been located and the average length of their respective frostless seasons had been placed beside the points representing them on the map, lines were traced as accurately as possible through points having a common length of frostless season, a line for each increment of 20 days, beginning with 80. By this means the map was subdivided into 15 sorts of seasonal areas. The first sort has, according to our data, an average frostless season of less than 80 days, the second has a season of 80 to 100 days, and so on by steps of 20 days until the average frostless season for the fourteenth sort of areas is 320 to 340 days, and for the fifteenth, over 340 days. The only one of our stations that is unques- tionably without frost, thus having an average frostless season of 365 days, is Key West, Florida. In tracing the equiseasonal lines we have followed the data of table 2 as accurately as possible, making no attempt to smooth the lines. Topography has been allowed to exert a deciding influence in many cases where observational stations are too far apart satisfactorily to determine the positions of the lines. This is especially the case for that portion of the chart which lies west of the one hundred and fifth meridian of west longitude. In a very few cases the data of single stations have been ignored, where the length of season given in the table is obviously a marked exception for its region, thus suggesting the possibility of error or inadequacy in the data themselves. Wherever a small local area is indicated by the data from two or more stations, however, the area has been shown on the chart. It was found at once that the approximate equiseasonal lines for 20-day increments were altogether too crowded in the mountainous region of the West, when drawn upon a chart of any convenient size, and for this region all lines have been discarded in this region, excepting those for 80, 120, 180, 240, and 300 days. This method probably presents the details for this part of the country as accurately as is to be expected from the data now at hand. The omitted lines, all drawn for the East, have been abruptly terminated wherever they would enter the more generalized portion of our chart. Plate 34 is a repre- sentation of the chart just described. For the sake of clearness, the chart has been shaded so as to fall primarily into the five classes of areas. These areas denote regions with average lengths, in days, of frostless season of (1) less than 120, (2) 120 to 180, (3) 180 to 240, (4) 240 to 300, and (5) over 300. The other lines, representing greater detail, are shown in dotted form. A comparison of plate 34 with Day’s plate V (loc. cit.) shows, at first glance, a remarkable series of differences. Closer scrutiny brings it out, however, that the apparent discrepancies are mainly due to the fact that the lines of Day’s chart have been obviously subjected to a 196 ENVIRONMENTAL CONDITIONS. very strenuous smoothing process. Since a smoothed chart is thus already in existence, we have thought it best to let plate 34 represent as nearly as possible the present status of our climatic and physio- graphic information, and, as has been pointed out, we have made no attempt to smooth our equiseasonal lines. Professor Day informs us that some scattered data other than those available for our use were included in his study of the frostless season, and it seems probable that a few discrepancies between his chart and ours may be related to this fact. At any rate, for all practical purposes, and until such time as much more complete and reliable observational data may have been obtained, we may say that these two charts are in very good agreement. So far as we are aware, no attempt,other than Day’s and our own, to prepare a chart of the average length of frostless period for the United States has yet been made. The main generalization to be derived from plate 34 is that the areas of equal frostless seasons traverse the country, roughly, in a west-east direction, being displaced, however, to the northward in the vicinity of the Pacific and Atlantic coasts and to the southward in the regions of the western and eastern mountain systems. The coastal displace- ment is especially pronounced on the Pacific, where the 300-day season reaches as far north as Washington. Here the season of 180 days seems to extend even into British Columbia. On the eastern coast the last-named season extends as far northward as Massachusetts. The northward extension of the same season is seen to be limited in the central portion of the country, approximately by the southern boundary of Iowa, while the western mountains displace its northern limit, in southern New Mexico, to about latitude 33° north, and the Appalach- ians displace it, in northern Georgia, to about latitude 35° north. Again, the 120-day season is not represented at all on either coast, but extends as far southward as latitude 35° north, in Arizona and New Mexico. The Great Lakes exhibit a tendency, as far as our data extend, to lengthen the average frostless season in their vicinity. The chart shows also a frequent tendency toward an upstream extension of any given length of average frostless season in the vicinity of the larger rivers, even where this has no obvious relation to altitude. As has already been stated, the data for the average length of the frostless season have been made the basis for many of our studies of other climatic features, on the assumption that this time period may be taken as a rough approximation of the length of the season of active growth for a large number of plant-forms. It seems probable that it is proportional to the average growing season for most plants, at any rate. | CLIMATIC CONDITIONS OF THE UNITED STATES. 197 (C) LENGTH OF PERIOD OF AVERAGE FROST SEASON. By the frost season is here indicated the period of the year during which frost is apt to occur. In this season such plant-forms as are killed or thrown into the dormant state by the occurrence of freezing temperatures should not be active. While actual growth of such plants often occurs within this season of any year, in frostless periods of a few days, yet this growth is soon checked, and foliage, etc., thereby produced is usually destroyed by the recurrence of frost, so that the result of such short growing-periods is seldom to be considered as advancing the organism very much toward maturity or reproduction. It may thus be generally assumed that the average frost season for any region represents the average period of dormancy for a large number of plant forms. It is obvious that the average length of the frost season is the com- plement of the average length of the frostless period. Thus, from table 2, the mean length of the frost season may be obtained for any station by subtracting the number of days given for the frostless season from 365, the total number of days in the year. It is'also obvious that the chart of the mean duration of the frostless season is simultaneously a chart of the mean length of the frost season. Thus, on plate 34, the area represented as having a mean length of frostless season of less than 120 days is characterized by an average period of general plant dormancy of over 245 days, etc. It seems highly probable, though there is at hand no direct informa- tion in this connection, that many plant-forms are excluded from cer- tain areas in the United States, not by the lack of an adequately long growing-season nor by killing temperatures, but by too great a duration of the dormant period. It may thus be possible that, for a given plant, a certain locality might possess a growing-season quite adequate in every way for maturation and reproduction, and yet the length of the enforced period of dormancy might be so great that death from autolysis, respiration, and the like might ensue before the return of the conditions requisite for full activity. The question thus raised can not be answered until after the accumulation of a much more thorough knowledge of the limiting conditions of plant-life than is now available. Indeed, the first prerequisite for an attack upon such questions is some such laboratory for the study of environmental relations as has attracted our attention earlierin the present publication. (D) LENGTH OF PERIOD OF HIGH NORMAL DAILY MEAN TEMPERATURES. (TABLE 38, PLATE 85.) On the supposition that high temperature may, directly or indirectly, prevent the appearance of certain plants in certain areas, or that this may be the critical requisite for the complete development of certain 198 ENVIRONMENTAL CONDITIONS. forms, it follows that the duration of relatively high temperature may, in some cases, be a limiting vegetational condition. It has therefore seemed worth while to attempt a cartographical study of this feature. The temperature observations that have been carried out by the Signal Service and by the United States Weather Bureau have already resulted in an enormous mass of data. From our present point of view these data are very unsatisfactory in many respects. The distribution of the stations of observation is, as has been remarked previously, exceedingly unequal, and seems to have been the result of political rather than of scientific interests. Furthermore, the exposure of the thermometers at the various stations follows no general rule; some- times the instruments are placed on the tops of high buildings, some- times near the ground; they are seldom in the open country, and are almost always subjected to whatever peculiar conditions prevail in or over cities. Nevertheless, in spite of the many quite obvious funda- mental errors which a more rational guidance might have been able to avoid, the faithful labors of the observers and interpreters of the Bureau have resulted in a very valuable mass of statistical information upon temperature conditions, and it is from this alone that informa- tion such as we require may be obtained. Especially valuable to us is the Herculean work of Professor Frank H. Bigelow, who has done what was possible to bring order and meaning out of the chaos of existing observations. In the present instance, as also in the next following, we have drawn our fundamental statistics directly from Bulletin R of the United States Weather Bureau.’ In this bulletin Bigelow has presented the normal daily mean temperature for every day in the year for 177 sta- tions in the United States. Although the introductory statements of this work are none too clear as to the sources of the temperature data used in the computations, it is implied that these normal daily means are the direct outcome of a graphically mathematical treatment of the normal monthly mean temperatures as given in Bulletin 8 of the United States Weather Bureau.” Since, however, the list of the last- mentioned bulletin comprises but 123 stations, it is obvious that other data than these have been employed in the preparation of the daily normal means. It thus appears that the fundamental homogeneous reductions for at least 54 stations have never been published and that these have nevertheless been made use of in the preparation of the list of 177 stations which we are to employ. While there can be no rational doubt of the approximate reliability of all the data given in the first- mentioned of these two publications, it is to be regretted, where there 1 Bigelow, Frank Hagar, The daily normal temperature and the daily normal precipitation of the United States, U. S. Dept. Agric., Weather Bur. Bull. R, 1908. 2 Bigelow, Frank H., Report on the temperatures and vapor tensions of the United States, reduced to a homogeneous system of 24 hourly observationsf or the 33-year interval 1873- 1905, U. S. Dept. Agric., Weather Bur. Bull. S, 1909. CLIMATIC CONDITIONS OF THE UNITED STATES. 199 are so many mathematical steps between the actual observations and the finally resulting daily normal means, that so many of the funda- mental properties and characteristics of the data upon which the latter have been based still remain practically unattainable to the student of these important statistics. The enormous amount of work represented by the portion of Bulle- tin S that deals with the normal monthly mean temperatures resulted in the elimination, as far as this was possible, of the error-producing effects of variations and alterations in the hours of observation at the different stations throughout the long period of observations, as well - as in the reduction of the variously derived daily means to a homo- geneous system. For an account of the ingenious methods employed in this work the reader is referred to Chapter I of Bulletin §; for not nearly all of the stations are observations for the full 33 years available, and the possible approximate reductions of the means of short-record stations to a 33-year basis were not carried out in Bulletin 8, though a method for this sort of reduction is given on page 32. Whether these reductions have been carried out for the temperature data of Bulletin R we are not informed, but it may safely be supposed that the state- ment of the normal daily means of temperature for the 177 stations dealt with in Bulletin R, approach the truth as nearly as was possible, all circumstances being considered, at the time of the preparation of the bulletin. It is interesting and worthy of remark here that the letter of trans- mittal accompanying Bulletin 8, signed by Willis L. Moore, Chief, sounds a truly prophetic note in this sentence: These data, and the normals that have been deduced from them, will form the funda- mental basis for future studies on climatology and for the investigation of the relations between plant life and the thermal and hygrometric conditions that prevail in nature. We have chosen 68° F. (20° C.) as our critical normal daily mean temperature in the present connection, and have determined from the tables of Bulletin R the number of days in the year to which are ascribed normal daily means of 68° F. or above. These days are con- secutive in every case, owing to the smoothing process by which the normals have been derived. There are comparatively few stations in the United States without any such days, and for one station, Key West, Florida, this period of what most dwellers in temperate regions would probably term hot days is extended throughout the year. Scarcity of information has no doubt led us into more considerable errors in the western mountainous area than elsewhere. 200 ENVIRONMENTAL CONDITIONS. TaBLE 3.—Length of period with normal daily mean temperatures of 68° F. or above, and of period with similar means of 32° F. or below, within the year. Mean of | Mean of 68° F. or | 32° F. or below. Station. (Plates 35 and 36.) Mean of | Mean of 68°F. or | 32°F. or above. below. ——— eee Station. above. Alabama: days. AIT STON A ston oats eres 141 Birmingham)..2.).... 160 Wiabtlesrss ssc 2 kee 176 Montgomery......... WA Arizona: Plavetattes? 3.2 a aees 0 PROGRES. sii he are 186 GUC 017 aii aan Be Bet ee All| Arkansas: Pork omithoy-neee ce 149 latte Rack. s2u5es.e. 153 California: MIT Clea ee 65) eerie 0 IGESNOsS2he carer ainee oe 150 Independence........ 118 os: Anreles.Va...cnne 54 RedeBluitss 3. once 140 Sacramento.......... 110 San Dieror: . ae oe 50 San Francisco........ 0 San JOSext a Ge aaa 0 San Luis Obispo...... 0 Colorado: Wenvere.ssse0 dni s cist 74 1 DUST U Cec ee ene Man ea 38 Grand Junction...... 105 PUCHIO Myo Has Sei 89 Connecticut: artrorgeoi sj. s5 taste a 69 New Haven.......... 77 Florida: Jacksonville.......... 191 UD ICET oe er: 60s. wor 169 thomasvyille. 5.02.2 183 Idaho: POISE fs ee ae i WE WASLOM. hse cee 88 Rocateligns ae: see 64 Tlinois: SE ee aie ee 132 CiCheo cos: oes See 79 1 GSE Le ee i 90 IPCGTIAG Sei oss Gees ee 95 Sprinehield...... 4... 109 Indiana: Ewvansville........... 129 Indianapolis......... 108 Iowa: Charles City......... 81 Davenport. <.../..... 96 We) SIOUX OLY Ace. wore reels Kansas: Kentucky: Mexine ton. cise. sae Tonisvallesie hie as Louisiana: New Orleans......... Shreveport.) :i0......2- Maine: WaAStporgas.s.205 oe eee Portland sic. ccugse Cee Maryland: Baltimores.c2sdccueos Washington, D.C..... Massachusetts: Grand Haven........ Grand Rapids........ Houghton.) 2.25 s.oSse Marquette ..6 06's son Pert Uren. :22 hes Miendians. 5 Snes: Missouri: Dh LOWS. Sarl eke Sprmnehelds toe. Montana: ASS pelieec ervohe: aie slare CLIMATIC CONDITIONS OF THE UNITED STATES. 201 TABLE 3.—Length of period with normal daily mean temperatures of 68° F. or above, and of period with similar means of 32° F. or below, within the year. (Plates 35 and 36.) Mean of | Mean of Mean of | Mean of Station. 68° F. or | 32° F. or Station. 68°F. or | 32°F. or above. | below. above. | below. Nevada: days. days. South Dakota: days. days. HERON ON es Bieler: ches Web eteer gue 'e By 26 EVO Tg 5) 3.55) bee. a saz alo 67 140 Winnemucca......... 61 68 PACE A nite Siskei deka 85 129 New Hampshire: Rapid: Citys. o2. 2... 55 121 ON COTE 25 5 abs esos 44 113 WAM COMY, one ala ene 2 89 122 New Jersey: Tennessee: Atlantic City. oss sake « 91 Di Chattanooga......... 141 0 Cape May......5625. 101 0 Wn OxVaAll ei 3:50.54 ees oe 128 0 New Mexico: Wie mip niger. tele tee 153 0 HEVOSIVCL eich ia eis Geese 140 0 Nashville. fess. <5 141 0 Samba en. ose ss 57 76 Texas: New York: A DUEN GS as satel s ea 163 0 PMUIDARDY ore) h Bie eel oye css 76 107 ‘Amiariblonys Sec crane 114 0 pine haMmtom, 2. ..\s 56: 58 109 Corpus Christi.....:.. 218 0 DUT AIO eee sore as bee sr 64 104 EOIRPASO SCR Waitevae es cos 156 0 aA GOMe oe koe cies suonceale 47 129 Orca WiOLvmesaactecie: 173 0 LEGLMGY Os Waa tea aa ese 62 108 Galveston: ss. . cc eens 215 0 INE W MORK iia sack. 5 94 64 IPalestine!2.. ./a.s2.ne es 172 0 DEWEPOK 2s e)s cia cick +. 57 107 SanVANEOMIO.\2. 05 aa 197 0 IVOGMESEET 626 osc cis oc 84 63 109 SCA OT Soon eae aes 187 0 DYTACUSE. -. ec ka cee 67 108 Utah: North Carolina: Modenas ii 2s. .s25 o. 55 65 Asheville. 0. si ccs 90 0 Salt Lake City....... 87 63 @Wharlotte. <0. essh cis 138 0 Vermont: iatteras. oo seas eh 3% 148 0 Burkinaton)con ss vee 32 129 MUSLCIP os ae govern « « 137 0 INorthhieldly 0 e023. 0 137 Wilmington. .o.....:.- 147 0 Virginia: North Dakota: Cape Henry......... 128 0 MB ISIMATCK..'5)4.. co oe 3 os 4. 148 Dynehburecu. cs: ses 121 0 Devils Lake.......... 30 158 INOrfol ees Sis Os Be 132 0 Wallistom. 2's). 5,2 004.024 51 152 Richmonds,.,.i2 sas =< 133 0 Ohio: Wioythevilles: oo 2.0. 85 0 @memnaty: 0535s s5 a 121 25 Washington: Cleveland............ 83 92 North-Head . ..<..2:. 0 0 Columbus... 66.5.0 4. 102 68 Port Crescent........ 0 0 DAnGuUsky. 0.\0.e 6 se 6 as 90 89 DERULLO Nao cre srscnncank 0 0 MOlEdON sc ok PNG oo 88 92 SHOkKane secs ystete ek 45 78 Oklahoma: PREGNANT che a 5 Sk ae 0 0 Oklahoma........... 141 0 Tatoosh Island....... 0 0 _Oregon: Walla; Wallac 6 2.4%) 89 0 Bakker Oicyieis cas cass 0) 102 West Virginia: POMEL Gy ie. cis clave 0 al5 0 0 nS eu ok eK 63 66 IRONC DUES EY cis cick e's ais 0 00 Parkersburg 2c. vow cic 104 43 Pennsylvania: Wisconsin: 12a 2). ee ar A5) 93 Green Bay........... 50 135 Plarrisbure?. cc. a0 368’. 95 75 BacGrosse. ok . ce ewiawec 77 122 Philadelphia......... 107 44 MPSCISORS yoke Seek 71 123 IPVGUSbOUreN . is0 ss ce eee 102 56 Milwaukee........... 55 116 OMAN TOMS vcie-cis owe a 71 95 Wyoming: Rhode Island: Cheyenne. s 5 o.s sa: cs 28 110 Block Island. j....... 47 55 Thanclereees Sot Ve 32 134 PTGVIGENCO ts chicas 82 83 Yellowstone.......... 0 149 South Carolina: HATIOSTOMY csc a pees 168 0 Columbiai co.cc ica cs 159 0 om oe et dear SGT yO eeq OT = “0 : SORES vee SuSE NTNOSSEEETE EEO " ee jO O18 SJUOWIAIOUT “(Zz UUIN]OD ‘gE 9[qv} WO] BYEp) AAO 10 "WF ,89 JO SomnyvIoduIEY UveUI ATIep [eUIOU ysty YI porod jo (sep) syy3ue'y en a ee Cee 008 096 oh ob OF of 6 066 = LOT coll of IT Qseq) 38010} u901319A9 uoljIsuey — jsel0} uso1d19Ao o1.Aydor3 Ay 48010} snonpisep FPS | ondydosou uroypian —9F Wi91s9MqION c f 0 — zat p RIMS AAXRR fn ix i ai i 4 ae == ets = a } a It yy I Z i | S% x NS Ss a ‘i y yse10j Sy Aydosous ASo10y UI9}SedyINOS ie | \ \\ VA. y ® \\ Y) 4 17h SR BA trig o iy 477K % 5 S RRR ~A : Wooded \' 7 re e BONES RRR \ Y \ WN * ANY AY Va i 0 @ i M ele Nu i BERK RR / ae ‘4 uv DA \ Z PS Say nt RON Ler ecO hen GheameeL as M 202 5 | L\ PLATE 36 "% ojuyd st deur sty} Jo osvq OUT, “08 JO Orv SJUOTMOIOUT =*(g WUAINOd ‘e ofqQuy WIOLy VIVP) MOTO IO “WT TE JO Somnyvioduto} UBOUT ATIEp [BULLOU MOT TTA potsod jo (sheep) syysuoy] eek ooh ae: Is ROT a Rober .S20r =O ehh OEE SUEY ~ alee - pane | 7 are é (seq) (459M) uomsues | e- - jS010} U9a1T19A9 4SA10J U9AIBIDAD Wy wNAYdosout UraYIION SS ee 0 | 82 | cA -ROR : Apis MEQ = Sisoeouines” snp k \ UXy Nin lie, \Y Cy. KX IX AQ) 63 ANF 2 . 8% \\ YS OOM; Oe IN 7 gees Ni AS SS as ROS) | CORR RR ee 2 se é NO ae SN Z 77; WS see i OS es Li ji 4 ae eee A ‘MLAS NAN N77) Lh Bes = ‘ (es : S N SSN oy 2 me p <— \ Fin S| a a r Wii y E CY YA \ ae : eyohe mt NATTY Us fas f eo \ SS I h is } a _ y— aon i lllile: INSS WN a Se \ R a, ee o 4 "CAA A TW eae , » Rae ad we Hi As: —=s Se A . a aa “ ——p SSS an 4Y LAI % La eS ee ree 2 F : 4 ay 4 G, ,——— Fa Q —:- 2 ee ey J ia ct fs o\ (| p ~ a\ Pee ae | eq Se! Sa toes : pa er dee oo lf BO th ek ake eh AR hh” G8) AR GR IG oO 06 LB 00. LOL 204 ENVIRONMENTAL CONDITIONS. The numbers obtained by our study are given in table 3, and the chart formed with these is reproduced as plate 35, the locations of the stations used being denoted by small circles. The equiseasonal lines exhibit the data in a graphic manner. Increments of 30 days in the length of this hot season are represented. It is noticeable on plate 35 that our lines assume a generally east- and-west direction to the eastward of the one hundredth meridian of west longitude, and a north-and-south direction in the vicinity of the Pacific ocean. Both mountain systems exhibit a tendency to displace the various climatic belts to the southward, a tendency shown still more markedly by the Pacific Ocean, and the same tendency is exhibited to a relatively slight degree by the Great Lakes. The region thus normally without the hot period here considered embraces almost the entire Pacific coast, from the vicinity of San Luis Obispo to the Canadian boundary; also the northwestern part of Minnesota, the whole of the northern peninsula of Michigan, a small adjacent part of Wisconsin, the northern extremity of the southern peninsula of Michi- gan, and the extremely northern parts of New England. This entire region is generally in high repute for summer resorts. (E) LENGTH OF PERIOD OF LOW NORMAL DAILY MEAN TEMPERATURES. (TABLE 3, PLATE 36.) Just as the length of the hottest period may be supposed to influence the appearance or non-appearance of certain plants, so the mean length of the coldest period of the year may have its effect upon the distribution of the same or other forms. It seems improbable, how- ever, that a normally long period of very cold weather may be essential to the full development of any organism. This coldest season always finds the plant in a dormant condition, and it is hardly possible, on physiological grounds, that extreme cold should be directly advanta- geous to its survival, but it is to be realized that nothing is yet quanti- tatively known in this connection. On the other hand, it is quite clear, in general at least, that cold weather tends to exclude many plant- forms from the vegetation of any region where such weather may occur. Numerous plants that readily survive a single frost are com- pletely annihilated by the occurrence of several days of freezing weather. The question here raised refers mainly to the power of dormant plants to retain life under more or less persistent conditions of temperature below that of frost. As a critical normal daily temperature mean we here take 32° F. (0° C.) For each station included in the temperature tables of Bulle- tin R of the U. 8. Weather Bureau, it has been determined how many days in the year possess a normal daily mean of 32° F. or below. Owing to the averaging and smoothing process by which the daily normals have been derived, these data exhibit a regular annual march, and all = CLIMATIC CONDITIONS OF THE UNITED STATES. 205 dates accredited with normals of 32° or below occur consecutively. Thus the period so characterized may be termed the normal season of cold weather. Our method of procedure in the present case brings out the fact that nearly one-half of the United States is without such normal periods of cold weather as are here considered. The longest period encountered is of 158 days. The numbers obtained from this study are shown in table 3, and the chart of plate 36 exhibits the equiseasonal lines derived therefrom, this chart thus exhibiting graphically the extent of the areas having different lengths of cold season as here characterized. The station locations are again indicated by small circles on the chart. Increments of 30 days have again been employed, as in the charting of the periods of hot days (plate 35). From plate 36 it is seen that the area indicated as without cold season occupies the entire country south of a line passing, approximately, from Cape May, New Jersey, to Tucson, Arizona, and is extended westward and northward to embrace approximately the southern third of California, the western two-thirds of the remainder of that State, and the western half of Oregon and of Washington. It is in this area that the most highly reputed winter resorts occur. The area characterized by 150 or more days of normal daily means of 32° F. or below occupies only the northern third of Minnesota, the northern half of North Dakota, and a little of northeastern Montana. The eastern mountains and the Great Lakes appear to have little tendency to extend the areas of cold winter weather southward, but such an effect is noticeable in the case of the western mountains. The influence of the Pacific Ocean is conspicuous, crowding the area of cold season far back from the coast, even north of the Canadian boundary. 2. INTENSITY OF TEMPERATURE CONDITIONS. (A) PRELIMINARY CONSIDERATIONS. The physical conception of life phenomena allows us to regard the organism as a spatial system, in which a complex series of chemical and physical changes are ever in progress; during life, material and energy are always entering the system and are as unceasingly leaving it. The accomplishment of growth, maturation, reproduction, etc., of a plant is thus to be regarded, at any moment in its history, as the summation of the effects produced by the innumerable physical and chemical changes which have thus far occurred. Since all energy and material transformations are influenced to a greater or less extent by temperature, and since this influence is usually very important, it follows that, if other conditions were but constant, or if they always varied in the same manner, the state of a plant at any moment might be treated almost as a direct function of the various aerial temperature conditions to which it has been subjected in the past. Of course the 206 ENVIRONMENTAL CONDITIONS. other conditions do not always vary in the same way and they are never constant, not even as related to criteria without the plant-body. Even though they were constant for any plant, progressive alteration within the organism would assuredly produce great variations in the relations of the external world to internal conditions as criteria. It is therefore quite hopeless to contemplate an accurate causal interpretation of plant states merely on the basis of integrations of temperature effects. Nevertheless, the same incubus of hopelessness overshadows similar attempts along lines of approach based upon other external factors, and since we are sure that no single criterion alone will lead very defi- nitely toward the solution of our problem, progress may be sought only by treating the different factors separately and studying the results, after which artificial and natural combinations of factors may be attacked. Furthermore, the study of the temperature conditions of plant environments appears promising in this particular, namely, that temperature not only directly influences plant activities, but also influences all of the other effective environmental conditions to a greater or less degree. There appear to bé, in general, two possible criteria for comparing the temperature intensities of several different localities. By one of these the comparison is made of the extremes, merely, of the yearly maximal and minimal temperatures for the several stations. Thus the duration factor is completely left out of account. It is, however, possible to consider and compare maxima and minima, not for the entire year, but for shorter seasons, and these seasons may be of different length at the different stations. The difference between the maximum and minimum temperatures may then be obtained, giving the range of normal temperature for each particular season and place to be considered. The last-named function of the temperature condi- tions does take some account of the duration factor (since the season is described in each case), and may, in certain instances, have an impor- tant relation to plant activities. By the second general criterion the intensity conditions are summed or integrated, in some manner, through a given length of time, and the duration factor is thus seen to play a direct and important part in this procedure. Mean temperatures for long periods of time are not apt to be of value in studies of the relations between plant activities and the environ- ment; seasonal or yearly means, which comprise such an important part of the usual meteorological reports, seem never to have given any real promise in this direction. Such means do not take account of the duration factor; the summed daily means are divided by the number of days considered, so that either this number of days must be the same for all localities compared, or else the numbers obtained can bear no relation to the corresponding extent of plant growth and other activities. Thus, a long growing-season with a given mean tempera- CLIMATIC CONDITIONS OF THE UNITED STATES. 207 ture is not at all the same, as far as vegetation is concerned, as a short season with the same mean. In studies regarding the relations between temperature intensity and plant development it is necessary to measure and compare the relative effectiveness of the temperature conditions at one station with that of the conditions at another; it is not the temperature of the atmos- phere or of the plant that primarily interests us, but it is the possible effect which the various degrees of temperature may have in controlling plant activity. ‘To make the following subsection clear we shall digress at this point to explain the various concepts and the terminology which will here be employed, thus presenting a tentative discussion of the various sorts of temperature indices that may be used in vegetational or other dynamically applied climatology. The word ‘‘temperature”’ is used with a variety of different mean- ings, some of which are very vague. Temperature and heat-content are frequently confused, but the heat-content of a body is only one of the conditions that determine its temperature; the heat capacity or specific heat of the matter in question and the amount (mass) of matter considered being also influential in determining the temperature. The definition of temperature involves difficulties unless based on the kinetic theory of matter, in which case the temperature of a body is considered as a measure of the mean kinetic energy of its particles. Temperature is often said to be the relative measure of the sensible heat of the body in question, of its hotness or coldness, this conception being based on the heat-sense of human beings. The latter definition must assume that the matter considered does not change its state (as solid, liquid, or gas) when the human sense-organ is applied to it as a measuring instrument, but the heat-conductivity of the material is important in this connection. Thus, a block of steel and a similar one of wood seem to have different temperatures by the criterion of sense, although they may be of quite the same temperature as determined by a thermometer. The commonest way of measuring temperature is to state it in terms of the relative volume assumed by a given mass of some standard substance (such as air, mercury, alcohol, etc.) when that mass of substance is in heat equilibrium with the body whose tempera- ture is to be determined, this equilibrium being attained when heat does not migrate in either direction between the standard mass and the body under consideration. Thus air-temperature is measured in terms of the relative volume assumed by the liquid in a thermometer when this liquid neither gives heat to the air nor receives heat from the air. In short, the thermometer liquid is allowed to come to the Same temperature as the air and then this temperature is stated in terms of the volume occupied by this liquid under these conditions. Since the mass of the thermometer liquid is constant for any instru- ment, the different volumes assumed at various temperatures may be 208 ENVIRONMENTAL CONDITIONS. indicated as a temperature scale on the thermometer-tube, and these volumetric graduations may be of any convenient magnitude. Thus, centigrade, Fahrenheit, etc., degrees are the respective increments in the volume of the thermometer liquid corresponding to equal incre- ments in temperature rise. The term ‘‘temperature” often means temperature reading (on some thermometer scale), and it is also used in a self-evident adjectival - sense, Meaning pertaining to temperature. In order to apply construc- tive reasoning to temperature conditions it is necessary to be somewhat more explicit than is usually the case, so that the terms we shall use require definition. Temperature readings or measurements are simply numbers that represent comparative temperatures, and they may therefore be con- sidered as conventional indices of temperature. The numbers of the Fahrenheit and centigrade scales are merely these indices expressed in two different kinds of units. Thus, the normal daily means of Bulletin R of the United States Weather Bureau are to be regarded as averages of a number of means for the given date, these means themselves being averages of a series of temperature indices representing the different temperatures encountered in the air throughout the day. According to this terminology, all climatological studies of temperature conditions thus start with temperature indices. These indices tell nothing about the possible effects of the temperatures represented, as these may accelerate or retard any process; they have reference only to the state of molecular motion of the particular body whose temperature is considered. For the problems before us, as has been mentioned, the various degrees of temperature effectiveness upon plant activities must be measured and compared, rather than temperatures themselves, and it thus follows that we require indices of temperature efficiency. These are to be derived from the indices of temperature, with due regard to the nature of the process to be studied, and various attempts have been made to obtain from temperature indices these other indices that are to be measures of the plant-producing power, etc., of given atmos- pheric temperatures. We shall deal below with the various methods that have been tried. The relative applicability of these methods is to be determined only empirically, but certain a priort considerations need to enter into the critical discussion of this relatively new and very important subject. According to the way in which indices of tempera- ture efficiency are derived from temperature indices, we may have four distinct classes of the former, which will now be taken up separately. (1) Drrecr Inpices OF TEMPERATURE EFFICIENCY FOR PLANT GROWTH. Direct efficiency indices are obtained directly from the corresponding temperature indices, the numerical values being the same in both cases CLIMATIC CONDITIONS OF THE UNITED STATES. 209 This method of derivation assumes that the rate of plant growth varies proportionally to the environmental temperature. Any thermometer scale may be used and a set of efficiency indices thus obtained may be transferred from one scale to another by arithmetical treatment. The assumption here is exemplified as follows. If a plant grows 2 units per time period at 2° C. it should grow 10 units per time period at 10° C., 25 units at 25° C., etc. While direct indices of temperature efficiency (on the absolute thermometer scale) are of great value in studying simple physical processes, such as the expansion of gases, they do not promise much in connection with the study of physiological processes, and need not be seriously considered in our practical applications. (2) REMAINDER INDICES oF TEMPERATURE EFFICIENCY FOR PLANT GROWTrH. The derivation of what we shall here term remainder indices of tem- perature efficiency is but little more complicated than that of direct indices. A constant difference between the temperature indices and the corresponding efficiency indices is assumed (or derived from experi- ment), and this difference is subtracted from every temperature index, thus giving the required efficiency indices. It will be seen that this method virtually does nothing but alter the position of the zero of the thermometer scale, after which alteration it employs direct efficiency indices as these have been defined above. ‘Thus, the rate of plant growth at 40° F. may be considered as unity and it may be assumed that this rate becomes 2 at 41°, 10 at 49°, 50 at 89°, ete., the constant difference above mentioned being here 39. In the phenological studies that have employed this sort of efficiency indices it has been assumed that if the plant does not attain the particular growth-rate that is taken as unity, it does not grow at all; that is, with a temperature of 39.5°, for example, no growth is supposed to occur, when unit rate of growth would be obtained with a temperature of 40°. It is clear that the method of direct indices of efficiency is a special case of that of remainder indices, the constant difference being reduced to zero in the case of direct derivation. The integration of temperature data by these remainder indices has received the attention of workers in phenology for many years and a large amount of literature bears upon this subject. For a review and citations of the earlier phenological studies, the reader is referred to Abbe’s Relations between Climates and Crops, already mentioned. Because of their close relation to our special field of study, Merriam’s researches upon the zonation of temperature conditions in the United States must be considered here. The conclusions arrived at by this author have been largely adopted by plant and animal geographers in this country, and Merriam’s zonal terminology has come into very general use, despite the exceedingly tentative nature of the data on which this is based. 210 ENVIRONMENTAL CONDITIONS. Merriam’s work! and that of his colleagues of the Bureau of Biologi- cal Survey of the U. 8S. Department of Agriculture constitute by far the most thorough study that has yet been brought forth of the rela- tions of plant and animal distribution to temperature conditions in the United States, and Merriam’s temperature integrations have furnished, for two decades, practically the only available information in this regard. In his most complete account of this arduous work of integra- tion, Merriam writes: Several years ago I endeavored to show that the distribution of terrestrial animals and plants is governed by the temperature of the period of growth and reproductive activity, not by the temperature of the whole year; but how to measure the temperature concerned was not then worked out. * * * At one time I believed that the mean temperature of the actual period of reproductive activity in each locality was the factor needed, but such means are almost impossible to obtain, and subsequent study has convinced me that the real temperature control may be better expressed by other data. * * * If it is true that the same stage of vegetation is attained in different years when the sum of the mean daily temperature reaches the same value, it is obvious that the physiological constant of a species must be the total quantity of heat or sum of positive temperatures required by that species to complete its cycle of development and reproduction. * * * Iam not aware that an attempt has been made to correlate the facts thus obtained with the boundaries of the life zone. * * * If the computation can be transferred from the species to the zone it inhabits—if a zone constant can be substituted for a species constant—the problem will be well nigh solved. This I have attempted to do. In conformity with the usage of botanists, a minimum temperature of 6° C. (438° F. [42.8° F., see footnote, p. 231])? has been assumed as marking the inception of the period of physiological activity in plants and of reproductive activity in animals. The effective temperature or degrees of normal mean daily heat in excess of this minimum has been added together for each station, beginning when the normal mean daily temperature rises higher than 6° C. in spring and continuing until it falls to the same point at the end of the season. The sums thus obtained have been platted on a large scale map of the United States, and isotherms have been run which are found to con- form in a most gratifying manner to the northern boundaries of the several life zones. * * * While the available data are not so numerous as might be desired, the stations in many 1 Merriam (1894.) A very much abbreviated statement of the results embodied in the above paper was published as Part III of the same author’s Life Zones and Crop Zones of the United States, U.S. Dept. Agric., Div. Biol. Survey. Bull. 10, 1898. - This latter involves but two pages (54, 55) and does not include the climatic map. Nothing approaching an adequate presentation of the data upon which these important studies are based has, as far as we are aware, ever appeared. It can not be too strongly emphasized that work of this sort is deprived of by far the greater part of its possible usefulness in building up our knowledge whenever a derived chart is published without the station data upon which it is based. It appears that most writers who have dealt with climatic charts have considered these as an end rather than as a means. Such charts are simply broad and necessarily very general presentations of the facts or observations upon which they are constructed, and can accomplish little more for the student of plant distribution or of agriculture than to inform him where in the given region to look for stations with certain climatic characteristics. As soon, however, as his interest is thus aroused he requires the station data, and if these are not at hand, further quantitative studies therewith are effectually precluded. We will not suppose that this common suppression of basic data is to be related at all to any desire on the part of writers to veil the exact methods of their procedure in the preparation of charts; we suppose rather that the suppression here in view has usually arisen from lack of facilities for publication or from lack of time and energy requisite for the preparation of tables or for the placing of the numerical data upon the published charts. It is hardly conceivable that a writer who has derived important generalization from a mass of figures should not appreciate the probability that the same figures may be utilized, in the same or in different ways, by other students of the subject. Had Merriam’s publications included a list of stations each with its numerical climatic indices, the latter might have been put to many other uses than the mere preparation of the simple charts. 2 As the chart was published, however, the minimum here referred to was 0° C. (32° F.). See Merriam’s note, Science, n.s., 9: 116, 1899. CLIMATIC CONDITIONS OF THE UNITED STATES. 211 instances being too far apart, still enough are at hand to justify the belief that animals and plants are restricted in northward distribution by the total quantity of heat during the season of growth and reproduction. Merriam’s chart (1894, plate 12) of the summations just described is here reproduced in its essentials, as our plate 37, for purposes of com- parison, and because of its pioneer nature and present scarcity. From this map it is seen that the warmest zone of the United States, as here indicated, is characterized by a summation temperature of 26,000 on the Fahrenheit scale (14,500 on the centigrade scale), and that this zone is restricted to the lower Colorado Valley, the extreme southern portion of Texas, and the southern half of the Florida peninsula. The zone characterized by temperature summations below 10,000, F. (5,500 C.) occupies, in general, the highest portion of the Cascade and Sierra Nevada Mountains, the Rocky Mountains, northern Minnesota, a little of northern Wisconsin, the northern half of Michigan, and the northern half of Maine. The isoclimatic lines for 11,500 F. (6,400 C.), and 18,000 F. (10,000 C.) are seen to have a west-east trend, but are more or less markedly displaced southward by the western and eastern mountains and northward by the Pacific and Atlantic oceans. Our own work with remainder indices will be presented farther on. (3) EXPONENTIAL INDICES OF TEMPERATURE EFFICIENCY FOR PLANT GROWTH. As has been stated in our earlier discussions, it appears that some possibility of advance lies in studying climatic temperature conditions with reference to the chemical principle of Van’t Hoff and Arrhenius, and a first attempt in this direction has been made by Livingston and Livingston in the paper already cited. This principle states that chemical reaction velocity usually about doubles (or somewhat more than doubles) for each rise in temperature of 10° C., or of 18° F. Itis to be understood that the principle of Van’t Hoff and Arrhenius is applicable, even in purely chemical problems, only within certain temperature limits, and it is sufficiently clear that the same general sort of limitation must influence its applicability in physiology and ecology. Weare primarily interested here in growth processes and their rates, and, obviously, there may occur natural temperatures either above the maximum or below the minimum for growth, so that here are unquestionable limits for the application of the principle just stated. Furthermore, the principle itself supposes that the process considered increases its velocity with each rise of temperature between the limits of applicability, and we are well aware that increasing tem- perature is not accompanied by increased growth-rate throughout the range from the minimum to the maximum for growth in plants. An optimum temperature can always be found above which the pre- viously increasing growth-rate begins to decrease. Thus the applica- bility of the Van’t Hoff-Arrhenius principle to organic growth phe- IH ps ENVIRONMENTAL CONDITIONS. nomena as a whole can not be maintained beyond the limits set by the minimum and optimum temperatures for growth. However, these physiological constants are not the same for different plant-forms, and they may also be assumed to vary with other conditions within and without the plant. It therefore seemed desirable, in an attempt to apply this law of temperature coefficients to the climatological delimit- ation of geographical areas, to choose such limiting temperatures as should give promise of merely approximating the physiological limits for a large number of plant-forms. In this we follow Livingston and Livingston, who give a more complete discussion of this whole question than is required here. The authors just mentioned calculated their indices of temperature efficiency on the basis of the supposition that general plant activity occurs at unity rate when the daily mean temperature is 40° F., and that this rate is doubled with each rise of 18° F. in the daily mean. Thus, with a daily mean temperature of 58° F. the rate becomes 2.0, with a mean of 76° F. it becomes 4.0, etc. It thus becomes clear that the relation here assumed between any index of temperature efficiency and the corresponding index of temperature itself is an exponential one, expressed by the equation I =e where I is the index of efficiency and t is the corresponding index of temperature. From this equation, by substituting the various values of ¢, Livingston and Livingston prepared a table of the efficiency index values corresponding to the temperature indices from 40° to 99° F. This table is reproduced as our table 4. Of course, constants other than 2, 18, and 40 might be employed, thus giving other values to the indices of efficiency; these indices, as has been stated, are based on the supposition that plant TaBLE 4.—Exponential indices of temperature efficiency for plant growth, based on a coeffi- cient of 2.0 for each rise in temperature of 18° above 40° F., for each temperature from 41° to 100° FF. ro) H © 2 © 2 © a ga = on = = | ae re =] bas oS 2 = Sif OS Bille See Be. ol BoB el Boo de 2 ey Ie lee aS “8 9 Sy x Se S ys “se S ya wes S44 wa 8 Q O85 © oO Ons ® oO o 8 8 o oO = 2-2 5 oO Oo Hg Be PON'S oes QSPRS eee Oye dl org 2 © a,S Q°5 a3 | 325 Biers g 2°5 q 8 gq 2S q 8 ge 25 a8 Gee g 8 a Gus © me Be Piha KEE ane BH Se eS Pal © on HES = oO), Maes | So | a = B = a ie a PH: oR: SH 4] 1.0393 53 1.6493 65 2.6192 Tal AL Pace 89 6.5972 42 1.0802 54 Al? 66 par Pel by 78 4.3206 90 6.8566 43 A226 55 1.7815 67 2.8284 79 4.4902 91 7.1258 44 1.1666 56 esos 68 2.9391 80 4.6662 92 7.4048 45 IL GALS: 57 1.9240 69 3.0545 81 4.8490 93 7.6960 46 1.2599 58 2.0000 70 3.1748 82 5.0396 94 8.0000 47 1.3096 59 2.0786 ral 3.2986 83 5.2384 95 8.3144 48 1.3603 60 2.1603 72 3.4283 84 5.4424 96 8.6412 49 1.4142 61 2 PHA 73 3.5629 85 5.6568 97 8.9804 50 1.4696 62 Faj SPe 74 3.7024 86 5.8782 98 9.3329 51 Tea2io 63 2.4245 75 3.8480 87 6.1090 99 9.6980 52 1.5874 64 2.5198 76 4.0000 88 6.3496 100 {10.0792 1The temperature efficiency index is here assumed to be doubled for each rise of 10°C. (18° F.) above 40° F., at which temperature the index of efficiency is taken to be unity. 3 CLIMATIC CONDITIONS OF THE UNITED STATES. 213 activity in general doubles with each rise in temperature above 40° F., at which temperature the rate of development is considered as unity. (4) PuoysioLocicaL InpIcES OF TEMPERATURE EFFICIENCY FOR PLANT GROWTH. All three methods so far considered for deriving temperature effi- ciency indices from temperature indices assume that the rates of plant activity increase continuously as the temperature rises. If these various series of efficiency index values be plotted as ordinates on graphs whose abscissas are the temperature indices, then the graphs for direct and remainder indices both take the form of straight lines with an upward slope of 45°. The graph for exponential indices, on the other hand, has the form of a curved line slightly concave upward, which much more nearly approaches being horizontal in the region of climatic temperatures than do the other graphs. In other words, within the range of temperature indices encountered in climatology, the calculated efficiency index increases much more rapidly with rise in temperature for the direct and remainder methods of calculation than it does for the exponential method, as adopted by Livingston and Livingston. None of these graphs, however, shows a maximum, and we know that the true graph of temperature efficiency for plant growth must possess two points where the ordinate is zero and must have a maximum somewhere between these points. This maximum of the graph has a relatively large ordinate and its abscissa is the index of the optimum temperature for growth. It thus follows that none of the methods so far discussed can possibly furnish true indices of tem- perature efficiency for plant activities, excepting, as has been empha- sized, within certain limits of temperature range. If a perfectly satis- factory method of calculating efficiency indices from temperature indices is to be devised, it must be of such nature that both low and high temperature values will give efficiency indices of zero, and inter- mediate temperature values must give indices whose graph shows a well-defined maximum. Livingston! has attempted to obtain efficiency indices from the variations in plant growth-rate experimentally determined for different temperatures. As has been said, the best study of the actual relations between temperature and growth is that of Lehenbauer, and Liv- ingston has employed the results of that writer in this connection. He considered the average hourly growth-rates of shoots of maize seed- lings exposed to the same temperature for a 12-hour period, the tem- peratures included in Lehenbauer’s study ranging, by increments of one degree, from 12° to 48° C. lLehenbauer’s curve, plotted with growth-rates as ordinates and temperature indices as abscissas, was first smoothed by the use of a flexible spline, so as to give a generalized _' Livingston, B. E., Physiological temperature indices for the study of plant growth in relation to climatic conditions, Physiol. Res. 1: 399-420, 1916. 214 ENVIRONMENTAL CONDITIONS. curve, which was continued at either end to cut the axis of abscissas at 2° and 48° C. The ordinates corresponding to the various abscissal temperature values were then actually measured. Finally, all the new ordinates thus derived were expressed in terms of the ordinates for 40° F. considered as unity. The resulting series of values are Liv- ingston’s physiological indices of temperature efficiency. He presents a table showing these values for each single degree of temperature from 36° to 118° F., and that table is here reproduced as our table 5. TaBLe 5.—Physiological indices of temperature efficiency for growth, based on Lehenbauer’s 12-hour exposures with maize seedlings. Centigrade scale. Fahrenheit scale. Fahrenheit scale. Degrees. Index. Degrees. Index. Degrees. Index. 3 0.333 36 0.111 82 106.889 4 0.667 37 0.222 83 110.778 4.5 1.000 38 0.342 84 115.000 5 1.333 39 0.667 85 118.111 6 1.889 40 1.000 86 120.000 7 2.778 41 133e5 87 121 292 8 3.667 42 1.667 88 122.000 9 4.889 43 2.000 89 122336 10 6.333 44 2.344 90 121.667 at 8.000 45 3.000 91 117.667 12 9.889 46 3.500 92 113.444 13 nfs a 47 4.000 93 108.333 14 14.778 48 4.778 94 103.333 15 Ii 425 49 5.500 95 96.000 16 21.556 50 6.333 96 91.444 17 26.000 on (ew) Ua We | 97 85.000 18 31.333 52 8.167 98 79.444 19 38.000 53 9.222 99 Watt 20 46.000 54 10.333 100 66.667 21 54.778 55 11.667 101 60.000 22 63.444 56 12.778 102 52.667 23 fA AL 57 14,444 103 44 444 24 79.111 58 16.111 104 36.000 25 86.556 59 17.778 105 28 .667 26 94.000 60 19.883 106 21.889 27 101.222 61 22.000 107 16.778 28 108 .444 62 24 .333 108 12.556 29 115.778 63 2h WEL 109 9.444 30 120.000 64 30.000 110 7.000 31 121.889 65 33.333 111 5.222 32 122.333 66 SY ara 112 3.778 33 116.111 67 41.333 113 2.778 34 107.333 68 46.000 114 2.000 35 96.000 69 50.833 115 1.444 36 86.556 70 56.000 116 1.000 37 75.667 71 60.333 117 0.500 38 64.333 72 65.333 118 0.111 39 50.667 73 69.000 40 36.000 74 73.667 41 cnebees 75 78.111 42 14.000 76 82.333 43 8.333 rid 86.556 44 4.889 78 90.667 45 2.778 79 95.000 46 1.667 80 98 .667 47 0.667 81 103.000 CLIMATIC CONDITIONS OF THE UNITED STATES. 215 This physiological method of deriving temperature efficiency indices is of course empirical, but it is not more so than either the direct or the remainder method, and it has what seems to be a better experimental foundation than has either of these.. Furthermore, Livingston’s physiological indices appear to be much more in accord with what is actually observed in the case of growing plants than are the exponen- tial indices of Livingston and Livingston, and it may be said that we have at last obtained a method for estimating temperature efficiency that is applicable throughout the entire range of possible temperatures, the graph of these indices showing approximately the same form as Lehenbauer’s graph of actual growth-rates. Of course it is desirable that this set of relations be eventually broadened so as to include other plants than maize and other developmental phases than that of the seedling, and when this is accomplished the efficiency index values for general use will probably need to be altered; it would be surprising if indices for seedling maize plants should prove to be representative for plants in general. Enough data are now at hand, however, for a some- what rational beginning, and we regard these physiological indices of Livingston as the most promising of all the different kinds of indices of temperature efficiency that have been proposed. We turn now to the employment of these four different kinds of temperature efficiency indices in our study of the climatic conditions of the United States. In the application of temperature efficiency indices to climatological study we have followed phenological workers in summing these indices throughout a certain period, the resulting summation being supposed to represent, in the form of a single number, the efficiency value of that period, and for the station in question, as far as temperature is concerned. We have used Bigelow’s normal daily mean temperatures (Bulletin R of the United States Weather Bureau) as our daily temperature indices, with which all our computa- tions begin. For the time-period we have here again used the period of the average frostless season. The procedure has been (1) to find the efficiency index corresponding to the temperature index for each day of the average frostless season, at each station, and (2) to add these daily efficiency indices all together to give the seasonal efficiency index for the station in question. This method allows the length of the average frostless season, as well as the values of the daily efficiency indices throughout that season, to take part in the control of the final value which represents the seasonal temperature efficiency for growth. Thus, a long season with relatively low temperatures may give a higher summation index than does a shorter season with higher daily mean temperatures. The use of Bigelow’s normal daily means of tempera- ture as original data should give to these studies an exceedingly broad and general character, and may be supposed to produce some approxi- mation to the average conditions of temperature for many years. 216 ENVIRONMENTAL CONDITIONS. (B) SUMMATIONS OF DIRECT INDICES OF TEMPERATURE EFFICIENCY FOR PERIOD OF AVERAGE FROSTLESS SEASON. As has been said, direct indices of temperature efficiency offer little promise for our present purpose. We therefore present here only the numerical values (in the third column of table 6, summations above 0° F.) and do not reproduce the climatic chart based upon these values. This chart shows practically the same climatic zonation as is shown by Merriam’s chart (our plate 37) and by our charts based on the remain- der indices, the numerical values given to the various isoclimatic lines being of course different in each case. (C) SUMMATIONS OF REMAINDER INDICES OF TEMPERATURE EFFICIENCY FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 6, PLATE 38.) Remainder indices of temperature efficiency have been derived in the present study by the use of three different values for the constant difference, 32, 39 and 50. It will be remembered that the efficiency index is here taken to be equal to the corresponding temperature index minus the constant difference. Thus we have subtracted 32, 39, or 50, as the case might be, from each of the daily normal means given in Bulletin R, for the period of the average frostless season, and have then summed the daily normal mean efficiency indices thus obtained for each station considered. Columns 4, 5, and 6 of table 6 present the results of these three kinds of summations, above 32°, above 39°, and above 50° F. The method here followed is the same as that employed by Livingston and Livingston, in their summations above 39° F., and our final results for that series of summations are the same as those presented on their chart of ‘‘direct summations,” figure 1 in the paper already cited. Our summations above 32° F. are derived by the method actually employed by Merriam, but his failure to publish the data used in making his chart (our plate 37) make detailed comparison impossible. CLIMATIC CONDITIONS OF THE UNITED STATES. 217 TaBLE 6.—Summations of normal daily mean remainder indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plate 38.) [The daily indices are derived by subtracting 0, 32, 39, or 50 from the values of the normal daily mean temperature on the Fahrenheit scale.] Direct summation of normal daily mean temperatures for period of average Length of frostless season Station. frostless : season. Above Above Above Above Oe: O27 ie 39° F. 50° F. Alabama: days PACTS UOT cise) vis si so cco ie. 8 kav eh ens 201 14,882 8,450 7,043 5,033 PUCIMMIM OAM. 66 kok 5 a hele « ale's 231 16,660 9 , 268 7,651 5,341 OTs ALLS ala ayallow ta sial'as v store sty athales 279 19,756 10,828 8,875 6,085 IMIONtZOMETY 656 6 bs eee ee ee 243 17,618 9,842 8,141 5,711 Arizona: PENS battin sie bls lalid wise a elena: erect 105 6,492 3, 1e2 2,397 1,347 OSM ea SL ig ate a 283 21,108 12,052 10,071 7,241 Arkansas: PIG EG OMT UI otis ies ac bieens ed Secs 230 16,254 8,894 7 , 284 4,984 METELIEVEROCK .\e'o sick seco eb soe Zon 16,749 9,165 7,506 5,136 California: PEO eek rests is ro! os eso Vales or ten'ovreeso Sb 245 13,056 5,216 3,501 1,051 Re STTG e etc gehen wissen hits 258 17 ,974 9,718 7,912 5,332 Independence............... 222 15,003 7,899 6,345 4,125 Los Angeles................ 334 20,381 9,693 7,355 | 4,015 SURE re aie eS ath indies 264 17 ,944 9,496 7,648 5,008 SACTAIMECNGO. «46, o/s ok e's ghee ee e's 22 17,368 8 , 664 6,760 4,040 AIT BAMCISCO: o 55 sss os owe as 319 17,819 461% 5,378 2,188 SHEN IOS Se Reta ee aE OP A 294 17,745 8,337 6,279 3,339 San Luis Obispo............ 260 15,367 7,047 5,227 2,627 Colorado: MBFETIVICES Giotore selec koa see Bie e's 153 10,060 5,164 4,093 2,563 AOAP ATION ics) < (ake se bods dapat olla: allots 121 7,775 3,903 3,056 1,846 Grand Junction............. 183 12,554 6,698 5,417 3,587 MCE U air eeh a 5a! chore cots ee hile ele 163 10,950 5,734 4,593 2,963 Connecticut: PPT ETORON GS 33) foe's 6S avaiavspe.w ayes 165 10,660 5,380 4,225 2,575 PNET ELAVCI wl ee ccaa ne ey 180 11,560 5,800 4,540 2,740 Florida: ; Jacksonville. ok ees eee es 293 20,765 11,389 9,338 6,408 STUTSUCOT PrP aie ho eicle elena ond Gaal 318 23,721 13,545 11,319 8,139 Key West......... ERR it errs 365 28,757 17,077 14,522 10,872 MCTISEICOLA a oie airs cele oo ov euspeliaies ad 285 20,519 11,399 9,404 6,554 PRAT AN eile cine. aie lara Ginv dim wihte el 335 23 , 909 13,189 10,844 7,494 Georgia: PAU LMT Gee tevin yn tay cain tiuvaurai citi a 225 15,731 Syoor 6,956 4,706 PAMUPIIS EA cress Sle. (kiss & ocuere Ss 228 16,436 9,140 7,544 5,264 MVIEUC OM strane lcs ors Gh enone’ s eaten 238 16,831 95215 7,549 5,169 PSPUUAEUELTU GUNN cs che oh crickaele idl ee) eteus oe 263 19,288 10,258 8,417 5,787 MEMOMASVILE: sie cot ais he eidieves 257 18,748 10,524 8,725 6,155 Idaho: 15 LOVES CMS, EL ANSP REN RE TRA he, Nad 177 11,457 5,793 4,554 2,784 PENIS COM slce ues a allohs Weasel ales 202 13,030 6,566 5,152 oS, lon LEON CHE i=1U Ce ae A i PO 175 10,980 5,380 4,155 2,405 Illinois: POEUN atta. Nice 4 Wi Giiaiarsi ak aedicetids 212 14,750 7,966 6,482 4,362 CLAN CRIS C0 1G IRN Be 182 11,671 5,847 4,573 2,753 Waselle. ces els as WORE a ame ar 168 11,309 5,933 4,757 3,077 OATS Met alico ss wits a al ages eric waa say car's 186 12,356 6,404 5,102 3,242 AS) oF Tas.) Ro IAA ROR Ra AME Sa 182 12,442 6,618 5,344 3,524 Indiana: I WEVIEIULLG a civics cats are 0.4 cugemints 203 14,196 7,700 6,279 4,249 IMAAMENOHS visa ke ws anues 186 12,595 6,643 5,341 3,481 218 ENVIRONMENTAL CONDITIONS. TABLE 6.—Summations of normal daily mean remainder indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plate 38.)—Continued. Direct summation of normal daily mean temperatures for period of average Length of Fr aee Station. frostless OS eS See season. Above Above Above Above O° F. O27 he 39° F. 50° F. Iowa: days. Charles: @ity< Sos see e ee 133 9,095 4,839 3,908 2,578 Davenpobiits tie see 174 11,755 6,187 4,969 3,229 DesiVMlomess.. 0) custo seeiceseee 171 11,594 6,122 4,925 3,215 Dubuquene ose ee 176 11,688 6 ,056 4,824 3,064 Keokuks sap ae oh pe ie eee 197 13,215 6,911 5,532 3,562 Sioux? CiLY cise sas Oe ee 146 10,041 5,396 4,347 2,887 Kansas: Concordiawincse cs erie ee 173 12 EL 6,635 5,424 3,694 WOdPCL tac.c ee Sole Cea 181 12,612 6,820 5,553 3,743 FE OPEKA = ache; oie eee Fis SS 189 13,086 7,038 5,715 3,825 Wichita’ ces ge eee oe 194 13 ,660 7,452 6,094 4,154 Kentucky: MORIN COM owe co aes eee 187 12,880 6,896 5,587 3,717 Bows villes ce epee eaees > 196 13,791 7,519 6,147 4,187 Louisiana: New Orleanisw= 2 55 coe 53 fos 5) 310 21971 1251 9,881 6,781 Shrev Gponcens seictsi cs eee ee 252 18,228 10,164 8,400 5,880 Maine: Biastport ace 1551, 2s pe oe 167 2,119 a,4tD 2,606 936 Portland see cee is eee ae 157 2,699 4,675 3,576 2,006 Maryland: Baltimore... eee Pe es os 213 14,281 6,816 5,974 3,844 Washineton: 1.662.582 sce. 197 13,385 7,081 5,702 3, (a2 Massachusetts: BOSton: 2 spss! iecielces a ee 185 11,630 5,710 4,415 2,565 Nantuek Ctiscciess 5's coe ae 209 12,411 5,723 4,260 2,170 Michigan: ASG) Seas 6 cee pas 137 8,330 3,946 2,987 Lor? Detroit. giteck aces 164 10,738 5,490 4,342 2,702 Hscanabars: oo. dec come oe. 140 8,536 4,056 3,076 1,676 GrandsHawen o/c 15 ee eo 167 10,481 5,137 3,968 2,298 Grand Rapids... 40 sa95- Ses 164 10,745 5,497 4,349 2,709 Hourhtonies. 3.6. eee 152 8,979 4,115 3,051 1,531 Marquette sé '4s..o.0 eae 140 8,367 3,887 2,907 1,507 Port Hurons. sae eves eee 155 SETHE 4,817 3,732 2,182 Sault Ste. Marie... o.:...::- 138 7,959 3,543 2,577 1,197 Minnesota: DUI S ie ve <5 eee 152 8,973 4,109 3,045 Pi 525 NOOTnEAGS aces oh cba eee 132 8,499 4,275 3,;a0L 2,031 Sts Paw eek cc eist he 159 10,342 5,254 4,141 2,551 Mississippi: INPeriGia th ie cio re eee eer 230 16,424 9,064 7,454 5,154 Vicksburg. 5 cece cee eee 252 18,032 9,968 8, 204 5 , 684 Missouri: Coltim bide. ig... 4 os 6s geese 179 12,487 6,759 5,506 3,716 (Emniball 27s kere tec are 183 12,701 6,845 5,564 3,734 Kansas: Cityia cacao © ieee s 196 13,562 6,090 5,718 3,158 Sb plsOUIS cee eine ee ees ee 207 14,395 Cat ipl 6,322 4,252 SpE eel diss occ ).0 oaekeae cae. = 187 12,907 6,923 5,614 3,744 Montana: Elawhe. 2.5 Sik Seach ete oS 122 C51) 3,907 3,053 1,833 Hidlenat:. 2. cn cn heres 144 8,785 FW (4 3,169 1,729 Walispellss coos, chs ti seetere sored 140 8,283 3,803 2 ,823 1,423 Wislen Gils esse ay he: 140 9,337 4,857 3,877 2,477 CLIMATIC CONDITIONS OF THE UNITED STATES. 219 TaBLE 6.—Summations of normal daily mean remainder indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plate 38.)—Continued. Direct summation of normal daily mean lenge ot temperatures for period of average frostless season. Station. frostless season. Above Above Above Above OfaE: Bon be 39° F. 50° F. Nebraska: days. METHICONAE Perle 4's Yio ekooe mie eid 174 11,912 6,344 5,126 3,386 Morth Platte: oo ec ee Pike a 151 10,195 5,363 4,306 2,796 (STIS) a Es Os pea ene cree MP 170 11,723 6 , 283 5,093 3,393 PLOT UIC ere. Gis ae he eee «as 132 8,971 4,747 3,823 2,503 Nevada: TE SOVC ER GED SOO SMe oh GaSe ae 138 8,649 4,233 3, 267 1,887 WVOMMEMUCEA Cees. ee. 3. 131 8,641 4,449 3,532 2,222 New Hampshire @oncord woes ks Bae i des 146 9,280 4,608 3,586 2,126 New Jersey: Atlantic City.....-........- 207 13,348 6,724 5,275 3,205 SS aPe WAY eke. ci ees oa ob 186 12,362 6,410 5,108 3, 248 New Mexico: Bea ele Wego Sek ea 195 14,064 7,824 6,459 4,509 rSvEH On. CEC RE ok Se DM a mem Gr Ura ges 187 11,510 5,526 4,217 2,347 New York: JU SE) ON Si a ace a 177 11,382 5,918 4,479 2,709 mI WAM tO. 2. = es dese ba) 158 10,088 5,032 3,926 2,346 1 BSELAU CO AR Bis he eg a i 173 10,907 5,3/1 4,160 2,430 CEST ChIIG Ras hae a Re aaa eae 139 8,933 4,485 3,512 Fjes g Mew Mork. 6 4-5... 068 Le. 210 13,422 6,702 5,232 3,132 0 SV EO CES AB oe eee an ee ea 175 10,950 5,350 4,125 Z7ato EPOCMESUET on see ss) ais sacs oi ars 0° 171 10,864 5,392 4,195 2,485 ENEACUSS eh ss = sicisidvniy oo o4 «le 171 10,918 5,446 4,249 2,539 North Carolina: ANSTEY i aa em a rer 176 11,693 6,061 4,829 3,069 Chics ve Gk Meee pena ee 220 15,316 8,276 6,736 4,536 igi erie: i. eek. 256 17,650 9,460 7,668 5,108 ANOLON hs eso cave Sia See's ne 213 14,485 8,069 6,578 4,448 Malmingtone (2. 3. .S aces ss 233 16,359 8,903 7,262 4,942 North Dakota: PES OSTNU ATC Keer ay sic ccs. sajna, washes. che 129 7,932 3,804 2,901 1, orl Meals Lakers.) bea... 121 7,658 3,786 2,939 1,729 WVMUNISTOM tees 8/ ss Cm be aes 119 7,785 3,977 3,144 1,954 Ohio: ( COVAYS) C0 OE 6 WR ae 194 13 ,416 7,208 5,850 3,910 Rlevelandi tole.) e woul BS 198 12,546 6,210 4,824 2,844 Gminmbus ek ee 184 12,373 6,485 5,197 3,357 AN CUSK ie tds sin Sele woes 195 12,491 6,251 4,886 2,936 “LPOG Cy Ta Sa as 174 11,494 5,926 4,708 2,968 Oklahoma: GIA OMG ohio. Gide Cale ee ile 214 15,137 8,289 6,781 4,641 Oregon: BiAGeY CL acdc ecstatic Mase s 127 7,767 3,703 2,814 1,544 Beta alte. on 245 14,172 6,332 4,617 2,167 PRGRE DURE Cea 6 ois lew aera s 198 11,848 5,512 4,126 2,146 Pennsylvania: BLES ec aR ae cta ailaias ase eu ee are as 194 12,232 6,024 4,666 2,726 PP ANTISOUN SS Ci ate' lary acct acdavelci gta. © 196 12,882 6,610 5,238 3,278 VIS GELDIIGN Cs )eniccctemeee as 206 13,629 7,037 5,595 3,535 PUGS EMOTE ice nlerwia’ sis. 's, cle ersch-wie's 179 12,102 6,374 5,121 3,331 POMEL CONI ta teikbe wate caveibi selects 176 11,304 5,672 4,440 2,680 Rhode Island: BOOK USION Gi en alenre scsi 218 12,946 5,970 4,444 2,264 OW OMGGnieice.: Nia ahs x nresin's 190 12,164 6,084 4,754 2,854 220 | ENVIRONMENTAL CONDITIONS. TABLE 6.—Summations of normal daily mean remainder indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plate 38.)—Continued. Direct summation of normal daily mean temperatures for period of average Length of frostless seas Station. frostless aor. season. Above Above Above Above 0° F. Se Dp Soo ne 50°? South Carolina: days. Charleston. (ses sscneee ae. ae 276 19,470 10,638 8,706 5,946 Coliwloiate ck oe Sas ae nea 231 16,593 9,201 7, 584 5,274 South Dakota: EURO I Ny siairute ko oe nes Wem. 131 8,788 4,596 3,631 2,321 PICTLe pss b,c Uk BAe ee ee 153 10,387 5,491 4,420 2,890 AIG CUGY see sate wee. ct 143 9,149 4,573 3,572 2,142 Wankton dawkins goatee ore 154. 10,470 5,542 4,464 2,924 Tennessee: Chattanooga... 4.22.2 ee oe 207 14,602 7,978 6,529 4,459 Karoxvalle cin eee ee a: 208 14,229 Coe 6,117 4,037 Memphisisstents. geeks ool ce 224 155 c12 8,544 6,976 4,736 INashvaillenes ie clas et es 207 14,700 8,076 6,627 4,557 Texas Abilene. ih see 7 Cone het 245 175,536 9,696 7,981 5,531 Amarillo ees see mere: 199 13,542 7,174 5,781 3,791 Corpus Christi. tio. Aes ee ek 298 21,898 12,362 10,276 7,296 Pasa ii cde! ee a ae SS 236 16,819 9 , 267 7,615 5,255 Bort: Worth cc... 49 ces 261 18,816 10,464 8 , 637 6,027 Galveston .kcecloeeen ss 331 23,538 12,946 10,629 7,319 Palestinesaeaari ao eee hee 245 17,690 9,850 8,135 5,685 San Antonio 2% «4. 0es aeons 276 20,119 L287 9,355 6,595 PAV LOT eS Tats eee ok ee ele Rel 254 18,656 10,528 8,750 6,210 Utah: WTOCEH APR ish oo bo ee ee lt 130 8,451 4,291 3,391 2,091 Salt Make City adie eae use ces 182 12,078 - 6,254 4,980 3,160 Vermont: Burhne tones oe 3). acc ae elon 6 143 9,000 4,424 3,423 1,993 Northield Wes <8: ote RO. 126 7,812 3,780 2 898 1,638 Virginia: Taymeh burgess cee 24). eB G23 201 13,759 honk 5,920 3,910 INGrfo lice ae sxe aoe heist 230 15,691 8,331 6,721 4,421 BACH MONG ses ve tee ee aes 215 14,942 8,062 6,557 4,407 Wi thevilless 26, Saar 2 Re. s 175 11,544 5,944 4,719 2,969 Washington: North Head sc... 282 Agee 316 16,180 6,068 3, 856 696 ro] StEH A (SOP ie ene AL pea 246 13,770 5,898 4,176 1,716 Spokane. fon. Wi. beets ous 202 11,992 5,528 4,114 2,094 Tatooshvisland® |. 2 ..cerreet- 1% 271 13 ,623 4,951 3,054 344 Walla W alla.g.. 22. 256s os 216 13,819 6,907 5,395 3,235 West Virginia: PETS ses beater eteroke 145 9,521 4,881 3,866 2,416 Parkersburg) oii ache tee ee 179 12,195 6,467 5,214 3,424 Wisconsin: Green ‘Bayes .ks «os eees 153 9,663 4,767 3,696 2,166 BaCrosses. (ike. balk Sete ne ae 163 10,707 5,491 4,350 2,720 Madison (002 b).!d in peee ae 8 179 11,370 5,642 4,389 2,599 WMalwaukee 2). 028 Ws ee ee eee 162 10,191 5,007 3,873 2,253 Wyoming: CheyenneGse! 2245 cae ae 119 7,528 3,720 2,887 1,697 Die heks (2) Mas oo genes Pape (eH RUE see 108 6,911 3,455 2,699 1,619 221 PLATE 37 ‘z, oyu] st osvq oy, ‘sporipuny quosordor SON[VA [VOLIOWNN ‘WBE 194je “v9 OY} JOJ (WY -ZE PAOGK) AOUOIONYO oInyedoduIS, JO SedIpPUl JOpUleUIOI Jo suOIyeuIUING m0) ad0b GL 9601 lll fll Ph 8 | oLIt Slt off om ° ° of o- Oo Cu) ro at (seq) (389M) 18910} U991B19A9 uoljisues 48910J U991F19VAI }8910} U991d19A9 79910} Snonpisep ——™\ onAydosow ussyyoN =: 91] Aydosaut usz9y}I0N -purlseri5 1 eae OD Z) S3TIW 009 00€ 001 0 oe | SES y isisisigisis 9% See ever me hme PAN - oe | aX WSS 48010} 21Aydosow 489103 AW anys =) we 0URet (ities SN \ \ \ Vo iy CO Ne QS NZ Y - CLACLL VLA BN | SS \ ‘ aSt S i NX ly Na’, « N , /) Co TN Soe / ag N N SoH aN 8 i => o> ~ oD SUE vil Es 1 Le — EZ N Ve NY, xt \\ Ze a SS \\ \ . SN \\ aa i 4 GLU, Att 44, Lf, GEE nde ts : eaten f Me S 4 Eee = anaes y, v7 A we aa itl 9 ee ae if Dn ei Tifa i thy tha a al Ws \ll = UU ll xX x A LE} s Ys i LAD e mil A dalg aise | Sees \F ae LES AER geo s =s \ 8 ¢ oO, SE creel / : Sa A, L ~ ES \ S & masa oC Vee eh ee yee / A, 4 o6L 18 88 G8 of8 68 16 €6 86 L6 66 JOT COT GOI LOE 601 UII SIE SIE LIL GI IGE .€00 GI Ql2l 621 PLATE 38 222 aunerceen a a se "z, ayer st aseq OUT, ‘spuvsnoyy yuosordos sonyea yeorroumn Ny “(9 9148} WIOIJ B}BP) UOSBES SSO[}SOAy ODVIOAG JO porsod IO}J (“WT 6 2AOG’) AOUOTOYJO o1nyeredurEY Jo sooIput IOpUIvONd. JO SUOT}BUIUING (Seq) ‘4Sai10j Ud013 19A9 S371W 009 C00 it eth Oth. eIt eit. (Sa ) 4sar0} udeaB10A0 uojisues} 4S9I0J udaasI0A9 oy Aydoss Ay 4010} snonpioap SAydosour usoyON © FA Ydosow usdyyAON UJO}SaMYIAON -purysseiy = HEE DSSS OOS etatatrorete’ x 4So20J oy Aydosour jso.10y + SF (Se Z Ss ‘ fy NY Ai VY ‘@ SAY A \ \ WMI]. 4 \ b NO Sa \ . oe a (\y usajsvayjnos snonpidoad \\ oT Aes ee ee Se ome Eas | SHON 100) mmele Ete burs UR 5 BOG: COR Che ue Ge Rye etm ceo) OG) meLO PX: Sime (0) me 0) Gu 10) SPY X0) ANCSZ0) QI GO PLATE 39 223 ‘% oFR|d sStosvq oY, ‘spoipuny yuosoidol sanyea pwowounyy = *(z WUIN]OO ‘7 91q'%B} WIOIy BYBP) UOSvOS SS9]}SOIJ OSVIOAV JO poltod IoJ (AQTUN Jo onpvA XopUT SuLAvY sv powunsse ‘J OP) Aousroyyo o1nye1odu10, Jo soolpur [BIyUOUOdxe Jo suoTyeUIUING (iseq) (1S9M) 38910} Ua01B19A9 uoljisuesy 3Ss910} Udd.KI.I9A9 3S910J Ud9IBIDAD ay AydoisAy S910} SNonpiosp oyjAydosaur uszayy10N on Aydosaus us19yION Ul9|Ssamy ION ~purlsse15 a eae . ; TE ry = Le Pe —— Pee sta WY, ysaloy o1]Aydosour ysaloy U1a}seayyNos. snonpioeq SSTIW 009 SN INS: VS LV \ ~ Wit LPs SAY, Z RSE QS \K SS SY, PAN Ad x SS WS NS PAY - ie WY aye Ww NN ats . INS ¥ oe A Uk SN \ SSN NN \ COM ot = === KES , Uys ; ENA ss Si is 2S Fp CLAS, YAKS ) 2 S= a i [p= PG SSS SS SE SSSETY, a Ol --6. ate == =—_ “ od le dy | fe > Ze oS 7S = J \ _ nM NWA SX . \ N Ly fe add Ki a uk | ( ) N YS l gil fs ia ict p_/ OOO a WupLeane aati das 09 oA9 OU eles oy AAR ey a hee ce ee eR! ght ons oS £6 , 68 SG o 66 8646 66 JOL Or . D4 | PLATE 40 erage frost- es sant Behe , \) f) lat SAS APS . iy 7 No RON ae | 2? WWI RAK Ph -7SNS RC : an (ESS i ts | Y MS 3 } Oe ln, ARS YAR D.C ety Sy y by G 4 V Gy SX aN SSN ; ae 7 Z/W0\““e- Vi eM NE : WEE. G.GFUGOr NN “Ge nl 1 mS N' ~< yy CH; Y Go Real Vee at | abe ane t my —— ee a MOY/D SIN NWN NS .\. GG, wes Y 5 ee LON YY. RN Z 7 iY Yy Ke SS GZ: GAtrn- li. WS \SSGueKevw7 8 VED y MT | o o o °o in : rw 2 4 j __ less season (data from table 7, column 4). Numerical values represent thousands. Narrow full lines divide map into five differently | Summations of physiological indices of temperature efficiency (49° F. assumed as having index value of unity) for period of av Yyyy, bz ES SG wo, Lass = IW Ass = i TG SS" on = / 47 45 CLIMATIC CONDITIONS OF THE UNITED STATES. jap er, Charts were made for each of these four series of seasonal efficiency indices, but they all agree in the general delineation of the climatic zones and only the one for summations above 39° F. is here presented, in plate 38'. This chart differs from the corresponding one of Living- ston in a few details, but the two are practically identical. The increments of seasonal temperature efficiency indices shown on the chart of plate 38 are each 1,000 in the East, and the numbers placed upon the isoclimatic lines denote thousands. These values may be reduced to the corresponding ones based on the centigrade thermometer scale by the use of the familiar factor 5/9, the starting-point for our summations being 39° F., or 3.9° C. The lines of this chart are seen to have a generally west-east direction east of the Rocky Mountains, several of them being southwardly displaced by the Appalachians. The western mountains produce a very great southward displacement, and another considerable dis- placement of some lines, in the same direction, appears due to the immediate vicinity of the Pacific Ocean. It is interesting to note that the area having an index of 7,000 or less extends southward on the California coast nearly to the parallel of latitude 33° north, while the same area on the Atlantic coast extends southward only to about 35° north latitude. Most of the country appears to be characterized by these seasonal - indices of temperature efficiency having values between 3,000 and 10,000. The region where these indices are less than 3,000 seems to occupy northern New England, northeastern Michigan, northern Minnesota and North Dakota, western Montana, central Wyoming, and the Rocky Mountain system. The region having indices above 10,000 appears to occupy the valleys of the Gila and lower Colorado Rivers, a narrow strip of the Gulf coast of Texas, and the southern half of the peninsula of Florida. A closed area with indices between 4,000 and 6,000 is shown on this chart as occupying a region extending from the Columbia River to Great Salt Lake. (D) SUMMATION OF EXPONENTIAL INDICES OF TEMPERATURE EFFICIENCY FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 7, PLATE 39.) In applying the exponential method of deriving temperature eff- ciency indices from normal daily mean temperature indices as given in Bulletin R, we have followed Livingston and Livingston. The efficiency index corresponding to each normal daily mean within the period of the average frostless season, for each station considered, was first obtained from table 5, and then all these indices were summed to give the seasonal index in each case. The results of these summa- tions, which are the data given on the chart of Livingston and Living- ston’s figure 2, are presented in the second column of table 7. 1The chart derived from these summations of normal daily means above 32° F. has been presented by Livingston. See Livingston, 1913a. 226 ENVIRONMENTAL CONDITIONS. TaBLE 7.—Summation of normal daily indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plates 39 and 40.) [The mean daily efficiency indices are derived from the corresponding temperature indices, (1) by the exponential equation of chemical reaction velocities and (2) by the empirical growth- rate coefficients for maize seedlings as found by Lehenbauer for a 12-hour exposure to maintained temperature. The temperature efficiency for 40° F. is taken as unity in both cases. | “Ta SBS 2as sel cates 16.8 ag&s nee ae oe = 3 S28 52 8 ES x cS 6 & Soe lee ng ey BSox aes dea a © Axe oe an % ES 2 gs Ez ss ga Station. eae g.62% ray el a As as ao Ao, | Bee. | eeee | eee (ees oe2 |szude| 2458 | Sgie | eHe Cas odo so | 2B He oPEg | omae Hae She ee) Se oe Seas SAas & ae Ay an ont Alabama: Anniston. 5.0/0.6). 681.8 10.33 12,326 1.75 18.1 Birmingham...... 816.7 9.37 15,025 1.96 18.4 Mobile. 20-24% 228 963.7 9.21 17,340 1.95 18.0 Montgomery..... 886.0 9.19 16,511 2.03 18.6 Arizona: aes taih cacao vos 245 /2 9.78 2052 1 Des I | 10.8 PHOSHIX O22 50 oe 1,183.6 8.51 20 , 640 2.05 17.4 Arkansas: Fort Smiths. 2 oe 789.5 9.23 14,168 1.95 18.0 Little Rock....... 811.7 9.25 14,567 1.94 3 California: ee ai sis os eo 410.1 8.54 2,388 0.68 5.8 Hresno {20 50) 82s 862.9 9.17 15,007 1.90 17.5 Independence..... 677.6 9.36 1228 1.77 16.6 Los Angeles...... 764.8 9.62 8,451 1.15 11.0 Red Bluffs... 25. 844.9 9.05 14,339 1.88 17.0 Sacramento...... 706.1 9.57 9 , 884 1.46 14.0 San Francisco.... 586.4 9.17 4,122 0.77 7:0 Dal Osen. eee ke 657.9 9.54 7,000 1-12 10.6 San Luis Obispo. . 500,5 10.44 4,963 0.95 9:9 Colorado: Denverees ise 422.0 9.70 6,271 1.53 14.9 Darango ds e ee 311.5 9.81 4,077 1.33 Biejey | Grand Junction... 581.9 9.31 9,921 1.83 17-4 PueMlOs wisi s 6 see 477.1 9.63 7,604 1.66 15.9 Connecticut: eamtiord 23.) at 436.8 9.67 6,181 1.46 14.2 New Haven...... 473.3 9.59 6,703 1.48 14.2 Florida: Jacksonville...... 1,033.1 9.04 18,791 2.01 18.2 JAIPIGER i iiesvae Bee 1,260.0 8.98 24,872 2.20 19-7. Key West:....... 1,541.8 9.42 31,063 2.14 20.1 Pensacola. .)77455 1,028.4 9.14 18,914 2.01 18.4 AWE) CY 6: Sate yee 1,175.4 9.23 21,420 1.98 18.2 Georgia: WANA ect ees 737.3 9.43 13,019 1.87 ia Mw AU SEA oo.) ast 816.8 9.24 15,134 2.01 18.5 Macon ys 651. 810.3 9.32 14,564 1.93 18.0 Savannah........ 909.8 9.25 16 ,407 1.95 18.0 Thomasville...... 953.8 9.15 17 ,858 2.05 18.7 Idaho: Bowe iF. a aaron 467.7 9.74 6,716 1.47 14.3 Lewiston ,. ../.ci2.- 544.5 9.46 8,065 1.57 14.8 Pocatello: eee: . 437.4 9.50 5,893 1.42 13.4 a CLIMATIC CONDITIONS OF THE UNITED STATES. 227 TaBLeE 7.—Summation of normal daily indices of temperature efficiency for plant growth, (Plates 39 and 40.)—Continued. for the period of the average frostless season. oO = ENE § pu : ai Station. Tens oy ag p. 8 we ca) | Illinois: MBIT ON cee aves wicleia's 691 CHiCaALO 0s sss : 479. La Salle....... 496 JE{slolg (ya a ee 535 Springfield....... 562. Indiana: Evansville........ 672. Indianapolis...... 567. Iowa: Charles City...... 403 Davenport....... 519 Des Moines...... 514. Dubuque......... 503. Keokuk... 0.0... 588. Sioux City....... 450. Kansas: Concordia........ 575. 1D fo (0 (2 hee 589 PP OBER ASS os seb 56s 607 Wichita.......... 650 Kentucky: Lexington........ 588. Louisville........ 651. Louisiana: New Orleans...... 1,077. Shreveport....... 921. Maine: Hastport......... 299. ortland : . 2.6)... 371. Maryland: Baltimore........ 635. Washington, D.C. 602. Massachusetts: WSGSCOTE: iss see wis 462 Nantucket....... 459 Michigan: PASO 6 bos oo) sires pts 310. 1B I-\1i¢0y (no 448 Escanaba........ 319 Grand Haven..... 412 Grand Rapids.... 450 Houghton....... i 323 Marquette....... 304. Port Huron...... 385. Sault Ste. Marie. . 276. Minnesota: (Oc a 325 Moorhead........ 338 th PAW ce des 428. average frostless season: On OO AW OW WHY WARM NHAWAH 0 W0W 00 MOND RWYoOe “10 0 Ratio of summation of re- mainder indices (above 39° F., table 6) to sum- owoeo meomoOnnonooowo so voRe) © Oo © 00 © © © moooo OOOO OO co Ooo Oo OO OF 54 .58 .52 .50 34 41 69 .56 .08 .58 40 65 42 42 41 36 50 .43 17 .12 ag .63 .39 .46 .55 .28 .63 .68 .62 .62 .66 .42 54 .69 .33 .35 .84 .66 mation of exponential indices. seedlings) summed for period of average frost- Physiological indices(maize less season. Ratio of summation of a — a! a ~ ge ete ae physiological indices to tt et fest pt pet ek = © n= one ee summation of remainder indices (table 6). summation of exponen- physiological indices to tial indices. Ratio of summation of _ [o>) CO Os] CO wm OH O&O for | CO ee > ON —" —" ePOONwDDOW™M ow Oo co =) (J) ew) CO _ Oo — 228 ENVIRONMENTAL CONDITIONS. TaBLE 7.—Summation of normal daily indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plates 39 and 40.)—Continued. T me 5 1 >) — o ' eal Lond t Bee | 2650 diese 4 See ee Sow eer 8 & Subs | ee mone BSSx ES Ba HO Sey. aS gg o” Bas Egos fae Station. ee 8 a fox a8 a 2 p2ag Bes a SEs $ LESS "a.2 8 2 2S Visto | | a ayes 3S 8 a saad of Co gk.o § ioe oe gee ges a ele oS OSS = a ca} ai Ay aa ee) Mississippi: Mendian!...2e525 800.6 © 9.31 14,565 1.95 18.2 Wicksbute: sods ee 892.6 9.19 16,194 1.97 18.1 Missouri: Columbia. 32 4254 583.8 9.43 10,241 1.86 17.6 Hannibal). ..260 585.4 9.50 10,189 1.83 17.4 Kansas City...... 612.8 9.33 10,368 1.81 16.9 StsOmisies5 sere 677.6 9.33 11,868 1.88 1735 Springfield....... 588.8 9.53 10,031 1.79 by eae Montana: Havre. oc tee le SIS 9.79 4,036 1.32 12.9 Helena. eres 331.0 9.57 3,710 ss ir Tie Kalispell) 3 2 ch 297.2 9.50 2,820 1.00 9.5 Miles City....... 402.2 9.64 6 , 253 1.61 15.6 Nebraska: ibincoln= 47s. ie 538.9 9.51 9 ,062 17 ¥. 16.8 North Platte... .. 446.7 9.64 7,192 1.67 16.1 Mma hayes ccd ctae ce 534.7 9.52 9,087 1.78 17.0 Valentine. ..:622..0 394.5 9.69 6,393 1.67 16.2 Nevada: FRCRO MSO Ae a. eee 338.5 9.65 4,134 Peay 12:2 Winnemucca..... 364.7 9.68 5 ,463 1.55 15:8 New Hampshire: Concord! ii jis 368.0 9.74 4,724 1.32 1255 New Jersey: Atlantic City..... 544.2 9.69 7,878 1.50 14.5 Cape May....... 533.5 9.57 8,417 1265 15.8 New Mexico: FROswellisaris; few 678.4 9.52 12,448 1.93 18.4 Santa Fe. 442.5 9.53 5,350 1.30 12.0 New York: Alipay § 2555 tee 466.3 9.61 6,633 1.49 14.3 Binghamton...... 404.4 Nea 5,399 1.38 13.3 Builaloy Se 3 62.27 433.8 9.59 5,761 1.39 13e3 Canton e2 ee ae 358.5 9.80 4,713 1.34 13.1 New York...,054 2. 554.4 9.44 8,104 sys) 14.6 OSWES0ciniziois sake 430.3 9.59 5,524 1.34 12.8 Rochester........ 434.6 9.65 5.807 1.38 13.3 Syracuse, — Act 440.4 9.65 6,022 1.43 yar North Carolina: Asheville......... 495.4 O25 7,504 155 line | Charlotte..5 25% WAgeo 9.39 12 ,554 1.86 17.5 Hatteras). eu: 804.9 9.52 13,771 1.80 ITA Balerohe £625. eens 700.3 9.39 12,329 1.88 17.6 Wilmington...... 769.0 9.46 13,561 1.87 17.6 North Dakota: Bismarck. sis: oss 342.4 8.47 4,792 1:65 14.0 Devils Lake...... 301.2 9.76 3,754 128 12°5 Walhistonk 2)... 250: 320.5 9.81 4,508 1.46 14.1 CLIMATIC CONDITIONS OF THE UNITED STATES. 229 TasLe 7.—Summation of normal daily indices of temperature efficiency for plant growth, (Plates 39 and 40.)—Continued. for the pertod of the average frostless season. Station. Ohio: MOVE ON Ss Oklahoma: Oklahoma........ Oregon: Baker City....... Borland. 3) a. Roseburg......... Pennsylvania: MM RrisbUre. 6: . Philadelphia...... Partsbure .. 2. s. scranton..:...... Rhode Island: Block Island...... mapid City: >... .. h(ehroll Et 50) 0 eae Tennessee: Chattanooga..... Knoxville...) ... Memphis......... Nashville........ Texas: ME PASO. ave, vic a ies Fort Worth....... Galveston........ Salt Lake City.... Vermont: Burlington....... Northfield........ Exponential indices summed for period of average frostless season. Ratio of summation of re- mainder indices (above 39 F., table 6) to sum- mation of exponential indices. period of average frost- seedlings) summed for less season. Physiologicalindices (maize of Ratio of summation physiological indices to summation of remainder indices (table 6). of Ratio of summation physiological indices to summation of exponen- tial indices. | ff a wor © Mnmoon WO MNHDNODDOR OCODM RHDO WR ON WONAYD Oe co © © Ke) wooowo © ooo © Oo O Nekie) OOOO O oo © oO oOomoOOoOMDOOO SO © 00 © © Noe a — be Re WwW RR RH be bo 09 GO bo mt Oo OwOowN BRAN © on co i 00 HOHOO PROBL CONNOR NHADL Tol Te) 230 ENVIRONMENTAL CONDITIONS. TaBLe 7.—Summation of normal daily indices of temperature efficiency for plant growth, for the period of the average frostless season. (Plates 39 and 40.)—Continued. Bea | sees S3 S28 S24 Bee | Ss2e | aus ae gee ee keene alee eead | 2x8 Boe eee, lee ae q-se | fas DR an -_ 2 La sehen 82 | 22935 |g 8a.) 2288 |e Se 2 BU, oo | CHU CO Otaie O:.8 “ang cE 8 Oho 25 Gass ob Es oe nes |SeSee | 22928 0) S228 ee fa ea A a oa Virginia: Lynchburg....... 626.2 9.45 10,631 1.80 170 INortolkice, ise 718.0 9.36 12,194 1.81 17.0 Richmond........ 702.8 9.33 12,305 1.88 17.5 Wytheville....... 487.0 9.69 (oils: 1.55 15.0 Washington: North Head...... 496.3 ThE 2,693 0.70 5.4 Seattle, wists 462.2 9.04 3,692 0.88 8.0 Spokane jsic5 ea 8 446.3 9.22 5,059 1A23 bins Tatoosh Island... 407.8 7.49 1,947 0.65 4.8 Walla Walla...... 573.3 9.41 8,378 1.55 14.6 West Virginia: 1 EN DSS TFs tea aps hse 395.2 9.78 5,685 Ne Yi 14.3 Parkersburg...... 543.9 9.59 9,009 1.73 16.6 Wisconsin: Green Bay....... 382.2 9.67 4,942 1.34 12.9 LaCrosse......... 449.9 9.67 6,705 1.54 14.9 Madison......... 460.9 9.52 6,434 1.47 14.0 Milwaukee....... 403 .2 9.61 5,261 1.36 13.1 Wyoming: Cheyenne........ 295.3 9.78 3,640 1.26 12.3 Wander. Geek s's 2 FAH a a 9.80 3,548 1.31 12.9 It is seen at once that the values given in the first column of table 7 are much smaller than are the corresponding ones of table 6. Living- ston and Livingston made a study of the ratios obtained by dividing each exponential seasonal index by the corresponding remainder index, derived by using the constant difference of 39, and the resulting ratio values are here reproduced in the third column of table 7. The chart of our plate 39 presents the climatic zonation exhibited by the summations of efficiency indices derived by the application of the exponential method (Van’t Hoff-Arrhenius principle of chemical reaction velocity), and it is essentially the same as the second chart (fig. 2) of Livingston and Livingston. In a general way, the two charts of plates 38 and 39 agree in the positions and directions of the isoclimatic lines, but they differ in a number of details. A somewhat thorough comparison of these two charts has been made by Livingston and Livingston, using the ratio of the value of one index to that of the other (column 3 of our table 7), . and they present a chart of these ratios as their third figure, which we do not here reproduce. As has been pointed out, these authors con- CLIMATIC CONDITIONS OF THE UNITED STATES, 231 clude from their study of these two methods of estimating temperature effectiveness that the method that derives efficiency indices by sub- tracting 39 from each daily mean temperature index gives, ‘‘in a broadly general way, and for most of the area of the United States, nearly the same climatic zones”’ (loc. cit., p. 375) as those given by summations of temperature efficiencies based on the chemical coeffi- cient of 2.0. Nevertheless, these authors point out that ‘the similarity between the results derived by these two methods of temperature integration is, however, only superficial and roughly approximate. The ratios of direct summation (above 39° F.) to chemical efficiency summation, range in magnitude, for the mean frostless season in the United States, from a minimum of 7.49 to a maximum of 10.44.” Their chart (fig. 3) shows clearly that these ratio values (column 3 of our table 7) are to be considered as some sort of climatic measure. The marginal regions of the United States are frequently characterized by low ratio values and the two main mountain systems seem to have high ratio values. For most of the area of the country the ratio of the summation index derived by the method of subtraction, to the index derived from the chemical coefficient, has a value of about 9.5, and the assumption of this as a constant ratio between the two indices does not introduce very large errors for most of the area with which we are dealing. The feature of these chemical efficiency indices that should attract our attention, however, is their relative values; according to the funda- mental assumptions upon which these efficiency indices are based, these values should be proportional to the amounts of plant accom- plishment within the frostless season, at the corresponding localities. Thus, referring to plate 40, if plant production in the region of East- port, Maine, has a value of 300 for the average frostless season at that station, that in the vicinity of Jacksonville, Florida, should have a value of 1,000 for the frostless season there. The extreme range of this seasonal temperature efficiency, as shown by the chart of plate 39 and by table 7, column 2, is from 276 (Sault Ste. Marie, Michigan) to 1,538 (Key West, Florida), or from unity to about 5.6. By the remainder indices (plate 38, table 6), the corresponding range is from 3,543 to 17,077, or from unity to about 4.8. It is thus brought out that, while one method of deriving efficiency indices would lead us to expect only 4.8 times as much plant activity at Key West as at Sault Ste. Marie, the other would lead us to expect this ratio to have the value 5.6. Since the physiological indices of temperature efficiency promise to be much more valuable in climatological study than either of the kinds of indices so far applied in our study, we need not here enter further into this comparison. DoL ENVIRONMENTAL CONDITIONS. (E) SUMMATIONS OF PHYSIOLOGICAL INDICES OF TEMPERATURE EFFI- CIENCY FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 7, PLATE 40.) The physiological indices here employed, as indeed the summations themselves, are reproduced from Livingston’s paper (1916, 1) already cited. For each normal daily mean within the period of the average frostless season the corresponding physiological index was obtained from Livingston’s tabulation (our table 5, Fahrenheit scale), and all | the indices thus obtained were summed for each station considered. The seasonal physiological indices of temperature efficiency thus obtained are reproduced in column 4 of our table 7. In the same table are also given the ratios of the physiological seasonal index to the corresponding remainder index (above 39° F.; column 5) and to the exponential seasonal index (column 6). The geographical distribution of the seasonal indices of temperature efficiency, physiologically derived, are shown on the chart of our plate 40, the lines of which are reproduced from Livingston’s paper (1916, 1). As that writer states, the general delineation of climatic zones is here © much the same as in the case of the other two kinds of summations. The lines again show a general west-east trend, and are again displaced southward in the vicinity of the oceans (especially on the west) and of the mountain systems. A cursory glance at these three charts of tem- perature efficiency summations for the period of the average frostless season (plates 38, 39, and 40) shows them to be so generally similar that one might almost serve for either of the other two, as far as the forms of the various climatic zones is concerned. Which method of derivation of the efficiency indices is used seems not to be of great importance in the general seasonal result. As far as present knowledge goes, then, one method appears to be as satisfactory as either of the others in this respect. The authors of these methods have discussed some of the main features wherein these three charts differ in detail, and we do not need to enter deeply into this matter here; but the following points may receive brief mention. The actual values are much lower in the case of the exponential indices (plate 39) than in either of the other cases (plates 40 and 41). Furthermore, the values obtained by the remainder method are generally, but not always, somewhat smaller than those derived from the Lehenbauer measurements for maize growth. It is not possible, however, to reduce the values of one of these three series to those of another, by employing any constant ratio, as is shown by the variations in each of the three sets of ratio values given in table 7. For convenience, we may represent the summation by the remainder or difference method (above 39° F.) by D, that by the exponential or chemical method by C, and that by the physiological method (based on growth of maize seedlings) by G. We find (table 7) that the aver- CLIMATIC CONDITIONS OF THE UNITED STATES. Dae age value of D/C is 9.44 and that this value ranges from 7.49 to 10.44. Similarly, the average value of G/D is 1.60, the range being from 0.65 to 2.20, and the average value of G/C is 15.0, the range being from 4.8 to 20.0. While the first ratio value D/C shows a geographic varia- tion that is not apparently related to temperature conditions (Living- ston and Livingston, 1913), both of the other ratio values, G/D and G/C, exhibit a variation that is obviously related to temperature, and the charts of these values (not here reproduced) appear very much alike and also very similar to the charts of the summations themselves, as far as the direction of zonation is concerned. The main differences between these three summation charts, that require attention at the present time, have to do with the relative magnitudes of the summation or seasonal efficiencies indicated for the various stations. By the remainder method (table 6, plate 38) the seasonal temperature efficiency of southern Florida is about four times as great as that of middle New England. By the exponential method this ratio appears to be about 3.7 (table 7, plate 39), and by the physiological method it is 6.1 (table 7, plate 40). Which of these three ratios most nearly expresses the actual relation between the seasonal temperature efficiency for middle New England and that for southern Florida can not be determined without much more knowledge than is at present available. The ratios just given show clearly that the physio- logical method indicates a much greater range of seasonal temperature efficiency throughout the country than is indicated by either of the other methods, but whether this greater range is also represented by corresponding differences in plant growth must be left an open question for the present. As has been stated, we follow Livingston in deeming it highly probable, for various theoretical reasons, some of which have . been expressed above, that the physiological method of obtaining efficiency summations for temperature will prove of more service than either of the others. Attention should finally be called to the fact that the chart of our plate 40 brings out five zones or provinces of temperature efficiency for plant growth. These zones are somewhat similar to those shown on plate 34, but the present chart is of course much less detailed. (F) ABSOLUTE TEMPERATURE MAXIMA. The absolute maximum temperatures as given in the Summary by Sections were placed upon a chart and isotherms were drawn for 100° and 110° F. Most of the area of the United States was thus shown to lie between these two lines. It is a remarkable fact, and one that emphasizes the importance of the duration factor in climatology, that there is, on the whole, so little variation between the highest tempera- tures on record throughout the country. The following list of stations and their highest observed temperatures (according to the Summary) are given here merely as an illustration of the fact just mentioned: 234 ENVIRONMENTAL CONDITIONS. ae os ma di Houghton; Mieh. 22.32.72. 103 Vicksburg, Miss.......... 101 Ishpeming, Mich.......... 98 Natchez,’ Miss... 232.05.) 2. 105 Escanaba, Mich.......... 100 New: Orleans: Last. o.ek 102 Bilimes, Monts: coc oe oo: 112 Galveston, Vex.enoy sn 03 98 Havre Mont. c22)50ee 108 Silver City, IN; Miex. 2.4): 103 Chicaso. Ui sie verte cya ss 103 Pampa tae sire sere 100 Wacol eee cece s 106 Mina, Aaa ek le ey aos 96 The area characterized by maxima of less than 100° F. comprises northwestern Washington and coastal points on the Pacific north of about the fortieth parallel of north latitude, central Idaho, western Montana and Wyoming, northern Minnesota, northwestern Wis- consin, and the entire northern peninsula of Michigan, some of the western and not so much of the eastern margin of the southern penin- sula of the last-named State, eastern Ohio, the northern half of Pennsyl- vania, the Appalachian area south of about the thirty-eighth parallel, all of New York, the western half of New England, Atlantic coastal stations from southern Maine to North Carolina, the southern third of Florida, and a few coastal stations on the Gulf of Mexico. Besides the area thus described, there are several restricted areas of maxima below 100°, the main ones of which occupy the regions of the Sierra Nevada and of the Rocky Mountains. It is thus clear that only a very small portion of the United States has been characterized, during the periods of record, by maxima below 100° F. The area characterized by maxima of 110° or above comprises local- ized sections, the main ones of which are as follows: (1) the southern third of California, the great Sacramento-San Joaquin Valley, and Arizona south of the great plateau; (2) western Texas and the Rio Grande region; (3) southwestern North Dakota, northwestern and southeastern South Dakota; (4) western Kansas, south central Ne- braska and northwestern Oklahoma; (5) northeastern Arkansas, south- . eastern Missouri, southwestern Illinois, and a little of northeastern Missouri, and southeastern Iowa. It seems clear that the variation in absolute maxima throughout the country is so slight that this criterion can be of no practical use for our present purpose. Of course, it is patent that the lengths of the periods of observation are very unequal for the different stations, and it seems probable that, ‘with much longer periods, the absolute maxima will approach about 110° F. for approximately the whole country. (G) ABSOLUTE TEMPERATURE MINIMA. (PLATES 41 AND 42.) A chart of the absolute minima of temperature (as these are given in the Summary by Sections) was prepared in the same manner as was that of the absolute maxima. This chart brings out some rather definite climatic relations, and appears to be valuable for our purpose; it is therefore here reproduced as plate 41. The Fahrenheit intervals have been so chosen in the making of this chart that they correspond atl PLATE 41 Lae : ON Wy es > ZN > ZN WX. SS SSS Caw a oe. Ar ( KZ os li aN ae x ee aw Vs WAR WE Ae VZES RO NA AGS oe NW A Sg % Gs ae TS W327) os » ne 83° sr o a) ano 73 ° at : \ S ee Narrow lines divide the map into five differently Broad lines are the vegetational boundaries of plate 2. y. 0 * SW Lo yf ae es A S\ oo By. \ Y UI SS) a Ise ce ee 2 ‘Se Ye \ RY WsYe Le ore / GY a OS y Ay "2 TN \ LLL} YN a) iy y - : ae oa See gp SS ws 5 OG N =\) 07 ‘: Ss AN Yi oN SA oS Noi NN as ee Siz ivy ny ‘an \ ; Gp Yi4X LR ro IL dy le a), gS: ° 87° | 85° y 91 89 A 95° 93° Wan KES oe oe wy SN N ae Mrs < | Y SX Mae \WS \N GG al Vl x ; SAS i 119° 117° 115° 113° ie 109° 107° 105° 103° ae or ae \ S RRS — qe Sud ..cev- Jan. 16to Feb. 4 Philadelphia...... Jan. 15 to Jan. 28 IPAteo mural ayes ss in) 5 Jan. 20 to Feb. 4 SCEAMLOM) 2/5/5020 e00 Jan. 15 to Feb. 4 Rhode Island: Block Island...... Jan. 26 to Feb. 8 Providence....... Jan. 6toFeb. 3 S. Carolina: Charleston........ Jan. 7 to Jan. 27 Columbia......... Dec. 30 to Jan. 27 South Dakota: irony yes oho Jan. 11 to Jan. 26 i Gg fe) mee OME A Jan. 4toFeb. 3 Rapid City....... Jan. 12 to Jan. 27 VWanktomiii sens Jan. 16 to Jan. 29 Tennessee: Chattanooga...... Jan. 1to Jan. 14 Knoxville......... Jan. 2 to Jan. 19 Memphis......... Jan. 4 to Jan. 25 Nashville......... Jan. 8 to Jan. 21 Texas: Aibilenee2s 2 6 aan Jan. 6 to Jan. 20 Amarillo.......... Jan. 7 to Jan. 20 Corpus Christi....| Jan. 3 to Jan. 19 HliRaso yee ee Dec. 29 to Jan. 12 Fort Worth....... Jan) 2 to Jan. 24 Galveston........ Jan. 10 to Jan. 23 Palestine......... Dec. 31 to Jan. 20 San Antonio...... Dec. 28 to Jan. 27 Mallorca see Jans toa. 2 Utah: Modena.......... Jan. 3 to Jan. 20 Salt Lake City....| Jan. 4 to Jan. 17 Vermont: Burlington........ Jan. 9to Feb. 6 INorthieldiys 2... o. Jan. 7toFeb. 4 Virginia: Cape Henry....... Jan. 8toFeb. 9 Ibynchbure?.......- Jan. 10 to Jan. 23 INontolk, cites « Jan. 18 to Feb. 2 Richmond! i...) - Jan. ltoFeb. 3 Wytheville........ Dec. 29 to Feb 3 Washington: North Head...... Jan. 1 to Feb. 24 Port Crescent..... Dec. 31 to Feb. 5 SOOEE NES cud es ace Jan. 5 to Jan. 25 WPOKAHE cle! ae aie Jan. 10 to Jan. 23 PACORIAG Sens ore Jan. 1 to Jan. 28 Tatoosh Island....| Jan. 11 to Feb. 27 Walla Walla...... Jan. 1 to Jan. 25 West Virginia: HUIRINS Re wis ee Jan. 2 to Jan. 31 Parkersburg...... Jan. 7 to Jan. 27 Wisconsin: Green Bay........ Jan. 13 to Jan. 26 La Crosse........ Jan. 7to Feb. 1 IMACISOM. ce ooo Jan. 9 to Jan. 26 Milwaukee....... Jan. 13 to Jan. 26 Wyoming: Cheyenne......... Jan. 14 to Feb. 9 TOMUCE ts ok was Ga Dec. 26 to Jan. 20 PLATE 43 240 ell Sil (4SPq) (as2M\) yses0j u9e13190A0 uonisuey 4sor0y uda1319A9 JSo1OJ ude1519A9 o1yAydo. IZAY 3se.10} snonpiosp dAydosow ursyZION ©: 91GAYdosauw U1SYIION, I -purjssei5 S371W 009 ysor0y d14yAydosour yso10y UJ9]SBIYINOS snonpiseq < is q) SS \ CA p 7 SSAA <> ses cae 2 ‘> S S BERS O as ha 3 WSO xe OX RQ AS =I J a) ss 6 SS = ) et a <> ESAS sce “S o : es fx > at $ s Bosse LAN rs W777 "A y <2 4 > ee Ss %% > a N Samual ( BOSONS X " " SRO RSS ch a SSIES SRP & = OK Oy oer Bk LTA iterate CRI PAA Cy Pa CT RAE) a IG I oLIL GIL TOE 83 Get Let .6at *z, oyurd St oseq OY, ‘\[ Soo1dOp ore SoNyBA [BOTIOUIN , 9 8 3 aa ge m2 : \ \ y 3 y. ‘ AO RES =. ‘ =a N WY : \; ACNE x \“ . PLATE 44 NN AY tl it =o ULM A NM pene iy band ob L ‘a puna Ata ‘(UIBIIIOJA] 109J*) 1v9a4 OY} JO SYOOM XIS 4S09}OY 9} 10) Sounyvsodu1o} [euIIOU Wed] oSII P49 § (189M) ys910J UdaIBIAAA uorjyisuen 9910} SNONpisep -puelseriy) Wd purjssessy (seq) JSA1OJ UDIITIDAD \SP10J U9AIBIDAD c mi l oa EN EEN a we 4 \ Win OS LAY AIS \Y \ NY \\ \\\ yseI0j D4 Aydosew UWJ9}seay NOS SS S ‘ill > | iG \ SZ ‘ KEE DCD, Ss WV SRS WAS HNN Be NK k . 63 LEE SE 2 FEL SWARARAAAS ARN CS A, WS’ NS S aS he ih | VN ALN EOS } i f : : ‘i i i Ree SEH Bistdivinioutcan Sh Qgree es l LOSS RS ane =a N ig lia ty x x S. "I y J Hal HES .. , 4 ma aay. =, Ly, [2 Se De bd ) IBIS rr Dn 2 I8 f8 G8 28 68 1A6 <6 , 242 ENVIRONMENTAL CONDITIONS. (I) MERRIAM’S MEAN NORMAL TEMPERATURE FOR HOTTEST SIX WEEKS OF YEAR. (PLATE 44.) In the same paper (1894) from which we have already made extracts, ferriam calls attention to the fact that, while his summation indices (our plate 37) appear to furnish satisfactory criteria for relating tem- perature conditions to the northward limits of species distribution, yet these do not seem at all satisfactory in connection with the southward extension of northern forms. This author writes (1894, p. 233): It is evident * * * that the southward range of Boreal species * * * is regulated by some cause other than the total quantity of heat [7. e., his summation indices]. This cause was believed to be the mean temperature of the hottest part of the year, for it is reasonable to suppose that Boreal species in ranging southward will encounter, sooner or later, a degree of heat they are unable to endure. * * * For experimental purposes, and without attempting unnecessary refinement, the mean normal temperature of the 6 hottest consecu- tive weeks of summer was arbitrarily chosen and platted on a large contour map of the United States, as in the case of the total quantity of heat. We here reproduce in its essentials, as our plate 44, the chart thus obtained—Merriam’s (1894) plate 13— because of its scarcity and of its interest in connection with our own studies. The marked differences between this chart and that of our plate 37 (also reproduced from Merriam) are practically confined to the Pacific Slope. East of the Sierra Nevada, Cascade, and San Bernardino Ranges the zone with a normal for the hottest 6 weeks of above 79° F. (26° C.) corresponds well with that of the Merriam summation above 18,000 (F.) or 10,000 (C.); the zone characterized by a 6-weeks normal of from 72° F. (22° C.) to 79° F. (26° C.) corresponds with that having a summation of from 11,500 (F.) or 6,300 (C.) to 18,000 (F.) or 10,000 (C.); the zone with a 6-weeks normal of from 64° F. (18° C.) to 72° F. (22° C.) corre- sponds to that with a summation from 10,000 (F.) or 5,500 (C.), to 11,500 (F.) or 6,400 (C.); and a similar correspondence is noted between the zone having a 6-weeks normal below 64° F. (18° C.) and that with a summation of less than 10,000 (F.) or 5,500 (C.). On the Pacific Slope, however, no such series of comparisons can be instituted. While the coldest zone of the summation chart does not appear at all on the Pacific Slope of the United States, the zone of the 6-weeks normals, which corresponds to this elsewhere, occupies the whole coast as far south as Los Angeles. Furthermore, the next to the coldest zone of normals extends much farther westward and southward in the region under discussion than does the corresponding zone of summations; the former occupies the coastal area west of the San Bernardino and San Jacinto Mountains, south of Los Angeles. Merriam has drawn im- portant conclusions from these differences, bearing upon the delimitation of his life-zones, a matter which will receive some attention in Part III of the present publication. (J) NORMAL MEAN ANNUAL TEMPERATURE. (PLATE 45.) The normal mean annual temperature is commonly employed by climatologists for comparing climatic temperature intensities, and it *Z o7uId St osuq OY, ‘yf Soo1dOp o1v sonyVA [voLOUIN ‘(NvaING 10Y7B9M\ “GS ‘(f) 109J8) sounyviodui9, [enuue UvoUT [BUIION = bh. 4 cK off =. 68 6 oL6 ‘ Se ee : BO. £ “9 ‘ F e B RRR ee eee ms i ee es ae a Od) }S910] U99IBIDAD uotjisuesy f — JO} UIIITIIAD ary AydosBh 78910} Snonpisg) N q J \\ dnAydosou wray{z10Ny deatcice ; a S ~ iaieet| by 5) ees, . Wraryl iS i, We EN : JON -pur[ssess) ft \ == . 5 OO Sisidisiminidinia: CANS ; 48010} 2 Aydosau w19}seayjN0G snonpioaq \ NZ oy. y INN \\ \\ \ h Ws WW AN Vie A S WING oe RA . ‘ Wi \Sy SN; we \ NS 7 —Y ‘ < aN WN T° v yy ; NS F GY Z' g 4 PI ATE 45 y= bs ESA ANY \ SK es Q b Pune age? = " WA > LY rey be “> NS SN N N BS NR LAGS : SSS ENN see thas WE Ua Ss ae Lapeer) 1 Ne = N ed SS. SSS styl i a f) Bi { CT U ill ry] | t wif lll | ih aij Ae Sy ANS Nd Bi UT Won [ ¥, 8, OL <— 3 ie L ret S— “al = Aas =\= S h = j | To Vi AL WAF Lee AA 3 Eel = bu ol 06 Al ° ° i . in. SY tt Sram rm Simiis i ke mee e Eaiseaieibign ae —— 8 68 § .&8 a4 IL. GI. <2 6th. 1el 00k. G28 — LOL - 628 244 ENVIRONMENTAL CONDITIONS. is added to our list of temperature features for this reason more than for any other. Our chart for this (plate 45) is reproduced from that of the United States Weather Bureau.’ It requires no special comment, excepting that we have represented four of the lines as full, so as to bring out the general temperature zonation according to this criterion. 3. CONCLUSIONS FROM THE STUDY OF TEMPERATURE CONDITIONS. The most obvious generalization to be drawn from our temperature studies, as represented by plates 34 to 45, is patent to everyone, namely, that the temperature zonation of the United States has a pre- dominantly west-east direction. Latitude is of course the controlling geographical feature that brings this about, and the values of the various forms of temperature indices increase toward the south and decrease toward the north. Modifying features are the mountain systems and the oceans. The isoclimatic lines bend northward near the Atlantic and Pacific coasts. Also, they generally bend southward on either side of each of the three main mountain systems. On plate 34 the different patterns represent the country as divided into 5 climatic zones or provinces, accoiding to temperature conditions, and Merriam’s chart for summation indices above 32° F. (our plate 37) shows a similar convention. Of course, any number of zones might be considered, but it is perhaps most useful to follow Merriam in this matter if a few definite zones are required. These 5 temperature provinces do not, however, need to be given names of the sort used by the author just mentioned, and if special names were requisite they should be climatically descriptive; they should of course not be named after geographic areas. We therefore suggest, in this connection, that a 5-zonal arrangement for temperature conditions will probably prove satisfactory, these being subdivisions of the larger temperate zone of geographers, and that these 5 temperature provinces of the United States may be termed simply and directly: very warm, warm, medium, cool, and very cool. It might be as well for scientific purposes to number these provinces serially, but such a procedure would not be satisfactory in non-technical discussions. The simple, descriptive terminology here suggested is clearly understood by everyone, while such terms as upper and lower Austral (Merriam) apparently fail to be understood by many who actually employ them. It should also be noted that the area of the United States does not include all of the north temperate zone, and our suggested terms leave opportunity for other subdivisions lying north and south of our group of 5. Thus, south of the very warm temperate temperature province may be one called hot and still another called very hot, while north of the very cool temperate province may be two more temperate subdivisions, the cold and the very cold. 1U. S. Weather Bureau, Chart of normal annual temperature. (To and including 1914.— Letter from Professor C. F. Marvin.) CLIMATIC CONDITIONS OF THE UNITED STATES. 245 Probably the most generally useful of our charts of the temperature conditions is the one for the length of the period of the average frostless season, and the five temperature provinces just mentioned are indicated on that chart (plate 34). In terms of that particular temperature index, the relation between our simple names and the index values is shown in table 9. For other temperature indices the values would TABLE 9. Length of period of average frostless season. Temperature prov- inces of temperate zone in United States. days. Below 120 120 to 180 180 to 240 240 to 300 Above 300 of course be entirely different, but the general zonation for these other indices may be generally comparable to that of plate 34, if proper limiting values are chosen. In the case of the temperature summation indices obtained by the physiological method (plate 40 and fig. 1), for example, the zones noted in table 10, roughly comparable to those / Fia. 1.—Temperature zonation, according to physiological summations for period of average frostless season. Temperature efficiency provinces: very warm, more than 20; warm, 12.5 to 20; medium, 7.5 to 12.5; cool, 2.5 to 7.5; uery cool, less than 2.5. Numerical values represent thousands. (See also plate 40.) 246 ENVIRONMENTAL CONDITIONS. shown on plate 34, may be distinguished. These temperature prov- inces are shown on figure 1, reproduced from plate 40, for ready reference here. TABLE 10. Physiological Temperature prov- summation in- inces of temperate dices of tem- zone in United perature effi- States. ciency for plant growth. thousands. Of course, it is not expected that any two charts, based upon different forms of climatic indices, will agree as to details. Thus, the Pacific coastal region is seen to be mostly included in the cool province on plate 40, or figure 1, while it lies mostly within the medium province on plate 34. What particular form of temperature index, or what com- bination of such indices, will be found most valuable in distinguishing the climatic zones for studies of dynamic plant geography remains to be determined, but it may be safely predicted that no single form of index will be sufficient for the purpose of ecological and agricultural climatology. It is unfortunate that Merriam’s zones (our plate 37) and the unsatisfactory terminology that goes with them should have been allowed to become stereotyped; climatic temperature conditions have many dimensions and the useful comparison of climates requires the employment of many more than a single one of these. Ill. MOISTURE CONDITIONS. 1. INTRODUCTORY. As has been emphasized earlier in the present part (page 120), the moisture condition immediately effective to control plant activity is the water-content of the particular cells and tissues involved, and if it were possible to study the duration and intensity aspects of this condi- tion such a study ought to be fundamental for the ecological relations with which we have to deal. Asin the case of the temperature relation, however, it is impossible to make any progress at present by attacking the problem in this ideally logical manner; here also it is necessary to consider less immediate conditions and to pass to what is considered as the external environment, without even attempting at present to inquire, in more than a very superficial way, concerning the nature of the internal water-relations which directly determine plant phenomena. Our analysis of the matter before us proceeds somewhat as follows: CLIMATIC CONDITIONS OF THE UNITED STATES. 247 Vital activity is influenced by internal moisture-conditions that mainly remain to be studied by physiological science. We are sure that these internal conditions are largely dependent upon external water-relations, and our task is to find ways of measuring and defining the latter as they exist in nature, in such a way as to render our description of the moisture conditions of the environment valuable to those interested in geographical distribution. It has been already noted that such a procedure is rather simple in the case of the tempera- ture-relation, for the immediate and internal temperature conditions effective in the control of plant activity are closely paralleled at all times by the more remote conditions of the environmental temperature; there is usually no great lag between the march of the external, or ecological, and that of the internal, or physiological, temperature con- ditions. This is, of course, simple because heat migrates with com- parative readiness either into or away from the plant and hence equilib- rium in this regard, between plants and their surroundings, is seldom very far from being attained. Similarly, the environmental moisture conditions are also effective to control the immediate, internal moisture conditions, through the relative rates of the entrance and exit of water. In this case we have to deal with material instead of energy, but the general relations are the same. Therefore, it is with those conditions of the environment that may influence the rates of entrance and exit of water that the present section has to deal. A plant may suffer from lack of water, (1) because of too slow a rate of entrance of this sub- stance into its body during some previous time period, (2) because of too rapid a rate of exit, or (3) because these two conditions have been simultaneously effective. The environmental conditions to be here considered for the area of the United States will be presented under the two captions, the supply of water to the plant, and the removal of water from the plant. 2. SUPPLY OF WATER TO PLANT. (A) PRELIMINARY CONSIDERATIONS. A discussion of the power of the surroundings to supply water to plants should begin (for ordinary plants) with the power of the soil to supply moisture to roots; it makes no difference, for this primary in- quiry, what conditions may determine this power, for the only thing directly affecting the plant in this connection is this power itself.) Since, however, ways and means for comparing the water-supplying power of the soil at various times and places are still to be perfected, 1 Livingston has emphasized the crying need for methods of measuring and comparing the powers of soil to supply moisture to unit absorbing surface, and he and his co-workers have suggested three methods for the quantitative measurement of this power, all of which appear promising in this direction, but little has yet been done of a positive character. See, in this connection, the following papers: Livingston, 1906, 6.—IJdem, 1909.—IJdem, 1912, b.—Living- ston and Hawkins, 1915.—Pulling and Livingston, 1915. 248 ENVIRONMENTAL CONDITIONS. it is obviously impossible to deal here with this fundamental factor. We turn, therefore, to the conditions next in order of remoteness from the plant itself, and recognize at once that the water-supplying power of the soil is determined by its water-content and its physical make-up. Charts can not yet be made, however, to represent the mean water- content of the soil throughout any considerable area, and the charts now in existence,' of physical soil properties, can be of no quantitative value in such discussions as the present, until the corresponding mois- ture-contents (with their seasonal fluctuations) may be similarly represented. Our inquiry is thus forced back once more to a considera- tion of the factors determining the soil-moisture content. These factors are (1) precipitation, (2) superficial supply by overflow, superficial drainage, and subterranean supply and run-off, and (8) removal of water from the soil by plant-absorption and by direct evaporation. In the first of these tertiary conditions influencing the supply of moisture to vegetation we have, finally, a well-recognized climatic factor that has been measured and recorded, in a way, for many years throughout the area of the United States. It is impossible at the present time, however, to make any quantitatively comparative use of what little information is at hand regarding the second set of factors just mentioned;? this information is still far too general and qualitative to be of service in an inquiry such as the present. With the third set of conditions above mentioned (plant absorption and direct evaporation) we shall have to deal in the following subsection, for the same environ- mental conditions that control the removal of water from the plant are effective to determine plant absorption—in a great measure, at least—and loss of soil-moisture by evaporation into the air. While precipitation is thus clearly seen to be in no sense a direct or immediate condition influencing water-supply to plants, it is very frequently a condition that may be roughly related to plant activity, as is well recognized by everyone; the mean annual rainfall of a given area has long been regarded as of great value in estimating the possi- bility of plant growth in such an area.°® As in the case of temperature, precipitation and evaporation should be considered as they affect plants, rather than as they affect any given 1 See, in this connection, the numerous soil surveys of the Bureau of Soils of the U. S. Depart- ment of Agriculture. 2 The reader interested in underground waters will find numerous bits of still unrelated informa- tion in the series of Water Supply and Irrigation Papers published by the U. S. Geological Survey. Especially interesting is also the following paper: McGee, W J, Wells and subsoil water, U.S. Dept. Agric., Bur. Soils Bull. 92, 1913. 3 Of course it is obvious enough that this proposition holds only with certain restrictions, as, for example, where the subterranean water-table is considerably below the soil surface. Thus, the cat-tail (Typha) or tule swamps in the vicinity of springs in the Salton Basin of California have the same ecological aspect as have similar marshes near the Atlantic seaboard, though a comparison of the precipitation data for these two regions utterly fails to show any reasons for expecting such similarity. The sand-dunes of the Salton Basin and those of the Lake Michigan shores, on the other hand, show differences in vegetational aspect which may clearly be related to differences in rainfall between these portions of the continent. CLIMATIC CONDITIONS OF THE UNITED STATES. 249 rain-gage or atmometer tank, but these conditions have just begun to attract attention in connection with the quantitatively dynamic aspect of the study of plant activities, and we are not able to go nearly so far with their treatment as is possible with temperature. Work such as that of Képpen and of Lehenbauer for temperature influence upon plants is greatly needed for the corresponding influence of the moisture conditions, but this sort of work has not yet been attempted, even if it may have occurred to anyone. When such work is accom- plished (which will be possible only with good equipment for the general control of environmental conditions), then it will be time to consider efficiency indices of the moisture conditions in somewhat the same way as we have attempted to deal with the suggested indices of temperature efficiency. (B) PRECIPITATION. (1) InrRopuUcTORY. Since rainfall is so remote from being the immediate environmental condition controlling the water-supply to plants in nature, the measure- ment of this climatic condition must not be expected to show very definite relations to plant activity or distribution. As has been indi- cated, we employ rainfall data not because they are desirable, but because they are the nearest approach to what is desirable that the present state of our knowledge affords. In this case, as in that of tem- perature, we usually employ the length of the average frostless season as our duration factor. Since the effect of precipitation is markedly cumulative, we have also tentatively established a second annual period, which may prove to be more satisfactory for this condition than is the length of the average frostless season. This period is obtained by adding to the average frostless season, at its beginning, a period of 30 days. By this scheme the rain falling during the last 30 days of the frost season is considered as pertaining to the following frostless season. Thus the snow and rain of March is frequently very influential in determining the kind of plant growth that can occur in the following month, especially if the latter is comparatively without precipitation. The length of this added period is taken as 30 days quite gratuitously; perhaps it should be longer or shorter and it prob- ably should have different lengths, according to other climatic condi- tions, for different localities. At any rate, it has seemed desirable to make test of this modification. In the discussions that follow we shall let P represent the normal total precipitation for the period of the average frostless season, while 7 will represent the corresponding nor- mal total precipitation for the longer period just described. It is obviously not to the point at all to employ the summed pre- cipitation for a portion of the year as a measure of the water-supplying power of the environment available for plant growth during that period. Rather is it requisite to study the average water-supplying 250 ENVIRONMENTAL CONDITIONS. power of the surroundings throughout the period in question. A usable index of this is obtained by dividing the quantity P orm by the number of days in the average frostless season. This procedure is logically no better here than the average temperature for the frostless season would be in the case of temperature relations, but, as has been said, lack of knowledge prevents as logical a treatment of the moisture- relation as is now possible in this aspect of the other case. Rainfall is universally measured in terms of depth units, which denote volume or weight units per unit of horizontal surface. The position of the horizontal surface of reference is assumed to be at the level of the soil surface. Raising this surface a few meters above the soil has no considerable influence upon the readings in most regions, though it would be undesirable to place the rain-gage funnels at any very great distance above the ground in an arid country. In such a country a considerable amount of rain might frequently be recorded on a gage supported a few hundred meters above the ground, while a gage directly beneath, at the ground-level, might remain quite dry; the rain-drops often evaporate as they descend. Of course, the opposite is sometimes true in a very moist region, where the drops may increase in size as they fall. Our precipitation data are in terms of inches of depth, since inches are still employed in the tables of the United States Weather Bureau publications, from which we derive our original values. All such data may of course be readily converted into metric values, where more universally comparable numbers are desired. As a basis for our computations we have again had recourse to Bige- low’s tables of normal daily values (Bulletin R of the U. S. Weather Bureau). These tables present the results of an elaborate treatment of the observation data in the United States, resulting in a precipita- tion value for each day in the year for each station considered. Thus the normal precipitation is given for each day of the year and for each station in the list. If a ‘‘normal”’ year, in this sense, ever occurred, then the actual precipitation for each day in the year, for any station, would be the value given in Bigelow’s table. We have treated these normal daily precipitation values in somewhat the same manner as was followed in handling the normal daily means of temperature given by Bigelow in the same publication. By the use of these tables it is possible to study the comparative lengths of what may be called normal drought periods and normal rainy periods, as will be brought out below. All of our computations involve both duration and intensity factors, as will also appear in the discussions that follow. (2) Norman Mran Daity PreciPrraTION FOR PerRiop oF AVERAGE FROSTLESS SEASON (=). (TABLE 11, PLATE 46, anv Fie. 2.) The mean daily rainfall for the period of the frostless season should be a general measure of aridity in a certain sense, and we have obtained 251 PLATE 46 = /\ 2" Die Sete ee ‘z oyuyd st osvq oy, ‘soourAoid uoryeqIdio01d oAY OVUT dvul oy} OpPIAIp sour] [Mw “SOYOUI UI ov VYVpP [wOTIOUINNY *(g WUINjOO ‘TT o[qe} WOT BYVP) UOSvOS Ssop}SO1J OBBIOAB JO porsiod 10} suoryeyIdioosd [euLioU Alred : ie. as eG RE ce cde CERO ad (0) OS Se | AR} SR a CY RRS alae | Sect Sele Se ee eee (seq) (35944) 18910} u991B19A9 uonsuesy Sai : *'s °Oz a qso10J Ude1T19A9 48910} u9918.19A9 oy AydosB Ay 38910} snonpisep Be am \ RAG Q on Aydosaut ulayy0ON W191S9MYIION + puelseeisy e —— WN ~ 00 001 0 O82 ee alee 9% § ; tt 6 \ YS = = Oo! oN Pee tf Ozh WSS ogi | OF! LAAN SS qseroy 21 Aydosour “y8910} Axe XC, a: Ns: ® Usa seayINoS snonpioeq ad S INS (| \ if Ne N bg x $ Wy, . “yy “pe RSS \N \ NN 22 GZ) “W277 MNVY é Uae Cos {XS 4 5 yy VARS BES | a : N Z ‘ : i \ Re f V ie 8 oe d fixe 7S ; Z ieee LL Mie. OA. oY Wy Ge h ae eo sO 55 oO % oe <> 2S Fags SS \ NY \ SS =N PSO wail 3 Mt Un i] : an ie x oO we eee Lats eRe: SOL ‘ ~ y a. i. Ss *, D : % %< e SS a? s ’ DS ~~, ae 2 S j > “a a wee elithy } Drache Wl jee « on < WSN \\\\ WN Ie Y Sy oy ee IR IN SN <\ Stems A 57- rr a5 Sey : imam OY 4 ny ) | W : ne o Ta O © S op os Oa. $38 | $39 & = inches anches Vas de) O.130)| 186) | 4 ae 41.90 C2 O75 0.90 36.74 0.236 OO27 0.29 78.91 0.330 0.13 0.14 "99.72 | 0.297] 0.25 | 0.27 37.01 0.161 0.76 0.85 39.63 0.167 0.77 0.89 ash ham AN Ta aay seas. eed “eae "56.87 | 0.220| 0.08 | 0.10. 69.55 0.349 0.04 0.06 34.81 0.104 Oar 0.45 70.75 0.268 O17 0.22 46.38 0.171 0.21 0.29 32.49 0.102 0.48 0.61 30.48 0.199 0.33 0.39 | 38 .92 0.254 0.19 0.25 SCR) 0.262 0.10 0.13 Se wLe) 6). 8 clieie Shen 6 .e =) ee 8 e 6s eile @ @ Um @ Las | 20.08 | 0.18 b ig ese | 20.40 0.108 1.03 | ees Se 39.67, | 0.185] 1.16 1.25 | 61.60 | 0.141. (0.75 | 0.75 1 The values of S are given in tables 1 and 6, number of days frostless season. 2 Approximated from: Russell’s data for 1887-88. in the period of the average 3 Numbers with S in parentheses after the station name refer to the section number, in the Summary by Sections, under which the given station appears. 254 ENVIRONMENTAL CONDITIONS. TaBLE 11.—Precipitation and evaporation data for the period of the average frostless season. (Plates 46, 57, and 58.)—Continued. 8 NOD [cee Bese) ee are. ie ae 2 aa yh ; An as aS som hoes Moisture ratios a a th =i aera res for period of i) — mn ~_ n 3 Fa = = = SR Sa5 = ae average frostless gGe oh ens a > Be P/E Aa aS ES - = season, : = 5 265 i] ro) mn uD 2 2a oF SP eS a3 S ka eos = om) So = as qi 3 = 2 pros Station. 23 > & > fo 3 Sm Sm Deel oP | ae eae 38 £3 HO 25 =O Wl ——— as Qe os oS if a ae re ete aes 59 o£ a) Se SR a5 as Ea | &s E'S 3 th ete P/E | x/E os | Sue | ave OSS | eee oR eo) ae aires ad. | 28a | 232 gee | ge= 2S Sa | oad = an | $a ~ = = = = Florida—Continued: ; inches. | inches | inches inches inches inches noe ae "17]} 45.34 | 0,146 | 4g.52| 0.156 | 38.51 | 0.124 ig | 1.26 Penssen les 2 2 cee ee 45.01 0.158 49.51 0.174 41.59 0.146 08 1.19 tee eee } 50.13 | 0.150] 53.13 | 0.159 | 46.35 | 0.138] 1.08 | 1.15 Georgia: PR EBREY in 82 cS cr a 27.48 0.122 32 .67 0.145 36.95 0.164 0.74 0.88 PUPIEG IN Ae oe oS cae eee 29 .97 0.131 34.40 0.151 30.21 0.154 0.85 0.98 IVE Pa The fo hol BOS Cte 27.44 0.115 So a7 0.136. ].....20.)....--- a, See eee Soe ST 1 Seen i aes 39.63 0.151 42.98 0.163 oF Fe: 0.135 1.1% pe Thomasville. -. 2s... . 36.22 0.141 41.00 0.160 |........|...<...<],. oo eee eee Idaho: ESSA sss eke = hie ee 3.90 0.022 5.14 0.029 43.80 0.247 0.09 0.12 Ee ciane oe a 5.91| 0.029] 7.20] 0.036 [eee ce reels so ++oen| eee Paenielie so. 5 Jes bc 6.49 | 0.037 8:17.| 0.047 |.....2..|-.....02) Tilinois: Core ees Oe ee 23 .07 0.109 26.98 OnI27 35.85 0.169 0.64 0.75 GE 0. os 2 3 ese 19.18 0.105 21.96 Oot 25.94 0.143 0.74 0.85 Per pale foe eee 18.63 0.111 21.70 ES b+! Sl a ne Coa Peart a2.) tei 21.09 0.113 24.19 0.430) ) 2.55. |s22.... ee eee Sprint eel... 6 ..-2-sice ae 20.99 0.115 2A .21 0.133 28.26 0.155 0.74 0.86 Indiana: | Evansville............ 22.15 0.112 26.99 0.133. |....u...|.<.---..-|..2 eee Indianapolis.......... 22.09 0.119 25.94 0.139 34.95 0.188 0.63 0.74 Iowa: Gharlen'Grty.- = eo: 17.04 0.128 20.95 QO.158 |. .......]..-.-...]... se oe Davenport. 23522 222.28 20.52 0.118 | 23.38 0.134 Pay eed (FE 0.160 0.74 0.84 Wes Moamies 2. 22 sere 21.93 0.498. 4. 24.51 0.143 24.75 0.145 0.89 0.99. DehWwates... 3:6 ccees 22, AS 0.126 | 24.80 0.141 REST 0.132 0.95 1.06 ROG aT ss oo 2 Pate eye 24 44 0.124 26.76 0.136 32.70 0.166 0.75 0.82 | Sioux City... 022.220. 16.60]. 0.114 | 19.64] 0.135 |........|.......4.. 2 Kansas: (CONCOTI So CE bie = 20.07 0.116 Para ee | 0.129 28.79 0.166 0.70 0.77 Wade Gaty 2). ose be 15.93 0.088 17.36 0.096 | 36.69 0.203 0.43 0.47 Twepekas+.ne <2. oo ee hs 25.60 0.135 28.09 0.149 25.45 0.135 1.01 1.10 Wiehe 3) 35. a6 Sees 23.02 0.119 25.39 Es hl ns en Kentucky: TGexen ei oi oo ce fn 20.93 Oo ito 24.92 0.133 |: 3. 2c): cs esse cos de eee Demise. ooo. dhe oe Peek 0.114 26.59 0.136 39.19 0.200 0.57 0.68 Louisiana: New Orleans... 3... =. 49.15 0.159 Sead 0.173 40.61 0.131 1221 is Shreveport............ 30.11 0.119 33.93 0.135 36.96 0.147 0.82 0.92 CLIMATIC CONDITIONS OF THE UNITED STATES. 299 TaBLeE 11.—Precipitation and evaporation data for the period of the average frostless season. (Plates 46, 57, and 58.)—Continued. = 00 Snes (ee Bee 3 aS a a 3B 85 Moisture ratios ils yt We ss 4. = 2 52 for period of Se 52 a oe te average frostles a & ik el B os season, P/E. om 8 iS) ro) AS) . ty n . 3 oO o © cake 33 aa ae 7 Hoe Sunk wm oo oa 2 Ps SRO 1 Ze eat Station. 2S > & as 2 ie ae By Sane (ates Slee | ee Se ey eens BE | 23 pape: a) —_— OCD Oo oO o ° So ee os op 2. Sa Seas FEA ga 2 P/E a/E Bk Sy era Mercy S| © &0 "Sop Sie FS awe ies 3 OS. as oH | AR ®D SO ; a ie ia ae a Sey) 2 e— oe) We inl Seas Sav | sak BH = A H = Maine: inches. | inches. | inches. inch. inches. | inches. PPABEDOLE. ois s.c.0 soe 8s 18.26 0.109 Zee 0.127 13.97 0.084 Leak 1.52 OTGHAMG oi. cnc cs 8 17.79 0.113 20.95 0.133 17.13 0.109 1.04 £222 Maryland: IBANUEMOFE sob os oe ews 26.42 0.124 30.16 0.142 34.78 0.163 0.76 0.87 Washington, D. C.....| 24.96 0.127 28.71 0.146 30.26 0.154 0.83 0.95 Massachusetts: LEY SIS|ICNC Un en 2 i2 0.114 24.84 0.134 PTS 0.123 0.93 1.09 INantHeket.)5 i)... .o0 4. 18.99 0.091 22.74 0.109 18.40 0.088 £03 1.24 Michigan: 4 BIG RUT HUE) eg ab alg 14.97 0.109 NEG TEE 0.128 14.85 0.108 1.01 1.20 IEEEOUb icles asc 6 vo aie ene''e 16.82 0.103 19.15 0.117 24.39 0.149 0.69 0.82 scamndbae oso i.k. 16.15 0.115 18.93 OS id | ces eae aie ha ee enesciooeh ollie aucirete vetote]| hononabel lene 'a Grand Haven......... 15.28 0.091 Mid 0.106 19.28 0.115 0.79 0.92 Grand Rapids......... 15.19 0.093 17.64 OSUOS I ie tears ote crates co oe trv tavec apebamie? a. 2 EGU GOM ei. ok} t 16.25 0.107 18.57 ORDA cca Reem es eee os eect a, Maas 2 Wansmer(H) os. csc i... 14.02 0.089 16.51 0.104 17.59 0.111 0.80 0.94 Marquette... .......54. 14.94 0.107 17.59 0.126 14.48 0.103 kos heat len ehbiwo)) a 14.73 0.095 16.98 0.110 18.85 OFN22 0.78 0.90 Sault Ste. Marie....... 14.07 0.102 16.48 COAT GH heat Sie a secure es aoc oiauetyc la ana are te ee ol eecun es tale Minnesota: IDV eUE Tray) AAS ee 18.66 0.123 20.97 0.138 15.138 0.100 1.23 1.39 Minneapolis.......... 20.00 0.124 PPT (OW 043 YN CAR ce Pe Se eb ed Ae Pe (Sen OL Moorhead ;..).../.ca cs 14.59 0.111 17.03 0.129 15.46 Oot 0.94 1 4p RETARD eevee Sse abietens 18.91 0.119 21.09 0.133 18.33 Osits 1.03 aed gS Sie Wiin(e(s00 (et a 9.54 0.093 12.05 0.117 10.39 0.101 0.92 1.16 Mississippi: IMIG@RICIAMG 5h. 5 15 eis wae 30.63 0.133 35.73 CERN ea tans aie eee ayers whe s «| ow iks & Soe apd aerate ne WOO S) ov 0h ol a 34.87 0.138 39.83 0.158 37 .34 0.148 0.93 1.07 Missouri: (Oto) ihr] on fe Ral ee PAUSE 0.120 24.80 Cases Oe cdeters ual ture? o eect nas WG-8: Was Soo cea Minne Hannibal. Baa, bd Rive 2 22.02 0.120 24.88 Oa eiliye o eeeieatclieseraie Wis crcitaueiw'w a wtquafs Sane ate 6. ee Kans). |f 25-89 | 0.182 | 28.94] 0.148 | 30.26 | 0.154) 0.86 | 0.96 amar (S49) ..0..<6.... 26.58 0.146 30.20 0.166 25.83 0.142 1.03 1 ae yg SEMPIG@UIS sles, « do oS ace 22.59 OSE 25.83 0.129 39.29 0.195 0.58 0.66 Sprmeneld ook... 6.. fe 27.54 0.147 Sy Ee 0.166 24.96 0.1338 1.00 1.25 Montana: aa cae ate 7.08 053 | 8.96] 0.067 | 31.30| 0.234] 0.23 | 0.29 ee ata dine). |? 7-78 | 0.064} 9.45 | 0.077 | 20.86 | 0.171 |, 0.37 | 0.45 TRGIOM A. Sake dissc'wa Maas ol 6.48 0.045 7.82 0.054 29.70 0.206 0.22 0.62 256 ENVIRONMENTAL CONDITIONS. TaBLeE 11.—Precipitation and evaporation data for the period of the average frostless season. Station. Montana—Continued: Meglrapell (eo. Oe oe Lewistown (S29)...... (Fort Maginnis)....... Wales NCAT Y 5.5/0 2 2 Poplar (S30) . 35-553 2 (Poplar River) Nebraska: a}! oars ele He SSOUCORE. Sat. 2. 23 ee ss (Manchester) New Jersey: Adlantie City. .2.26o. 2: Cape Way) iso 00 es: New Mexico: Fort Stanton...... Muay hes oo Beep i ee Hubale ee Yo oe es SYTACHSE. Crs ee ee Walaimrten. 2. eee North Dakota: Hismarek. 22) ec oe) ie¥) B ct 18] bef oO Total normal precipitation for period a Nene a nut N m (Plates 46, 57, and 58.)—Continued. of average frostless season (P). 8 oa S Mean normal daily precipitation for = o 99999 S59999999 95 oS period of average frostless season Total normal precipitation for period of average frostless season preceding 30 days (7). plus oO FS) ry period of evaporation for Total ros o |! : ob Moisture ratios a for period of Fs 4 average frostless 26 season, P/E. as oe = — a3 SD = a P/E a/E S i <<} zo. SSS ona = inches Ov 0.45 0.62 0.174 0.34 0.41 0.142 0.90 1.01 BE eae re PS Hees es ; donee : 0.159 0.82 0.92 O172 0.60 OTS 4) Bere ee ee : ge — 0.122 | 0.94 | 1.09 | — 0.084 1230 1.50 0.290 0.23 0.27 0.293 0.18 0.20 0.134 0.84 0.94 ES tee: ee : ae ae Rates eter en 9s Aer ee ace : 0.114 0.87 0.98 0.133 0.71" 0.81 SHEL oes Oe Bee ; oe , a 0.096 1.76 1.96 0.123 22 137 0.117 1.35 1.47 0.147 0.55 0.66 average frostless season, 1887-88 CLIMATIC CONDITIONS OF THE UNITED STATES. pay | TABLE 11.—Precipitation and evaporation data for the period of the average frostless season. (Plates 46, 57, and 58.)—Continued. are. (es 3g | 3% 5 a § 3 es 3B 3 oD Moisture ratios Seo pene » & Sd oo for period of ae s 2B eae Cee is 5 averaze frostless aa | 2s a 2 8 o8 season, P/E. aS) e = 4 2 4 me ae See eget oy Sa | 2 8 ion. we 2 AB o ey n oS Stati ee 2s E : 5 S 23 Bg aut Wane ee ee e2 | 23 Tren iai). \eean ance o 4 ® = ge@ | Es gs ef Sea ti P/E | «/E 68 5 Soe ofa o® ie a oR G3 oe a os a® |stalace aes | 282 Ba ov wo) Sey 8 Baw a i) 5 0° oo 5°08 =) os H = A = = North Dakota—Cont’d: inches. | inches. | inches. inch. inches. | inches. meee 11 57 C1006") Mageezil OLS i. 16.3811 0.127.) 0.75. | 6.89 co ge g.22| 0.009; 9.96| 0.084] 20.31| 0.171| 0.40 | 0.49 Ohio: Gmemmati). . 65. e 19.13 0.099 22.38 0.115 37.20 0.192 0.51 0.60 @leveland. 6) 663.0 20.66 0.104 23.22 0.117 26.35 0.133 0.78 0.88 Columbus. .i......5.. 19.34 0.105 22.36 0.122 33.29 0.181 0.58 0.67 S246 | 01s) a ee 20.35 0.104 22.99 0.118 27.36 0.140 0.74 0.84 TNSHGS 0 hy eo 16.60 0.095 18.93 0.109 26.84 0.154 0.62 0.71 Oklahoma: Horiieile(S41)... 5... .!. 93749) OTIO I) 2bO4 (Oo 117 |) 933281) 0.158 |) 0270 0.74 Oklahoma... 0552 0.- 23.03 0.108 Zoek OE 1 LRG tg Stan a OR | ee ie nae reall ie Se Oregon: PS POTUL icten2 cic 5 ge ib s 41.25 0.152 51.09 0.189 Piet) Zp 0.080 1.90 As 1" J Bsa wits) at Cah 1 qo Be 0.025 4.73 OPO Callie Se sc wanes Ma tus ee cet ge ee Bon ee col oat POG HANG cs woe ee ahc 19.43 0.079 25.08 0.102 29 .42 0.120 0.66 0.85 FROSCIUN ES oss oec cc os be 8.33 0.042 11.59 0.059 28.35 0.143 0.29 0.41 Pennsylvania: LEAS A i ne D2HOe 0.116 25.07 0.129 25.10 0.129 0.90 1.00 arrisbuee 65.0.2. 0s 21.91 0.112 24.92 CORMAN ees Alpe hel. aac el [Re 1 Seen Bea Ric, ad & Philadelphia.......... Daou 0.116 DATE NST 0.133 32.13 0.156 0.75 0.85 PUGS OUT 6 oo. el oe 19.45 0.109 2220 0.124 29.69 0.166 0.66 0.75 SIG.SE) 18 0) 0 as te ee 19.88 0.113 2250 ORES Owe eis tewehlneuer eo aia ee oo top abel fe cebarnhe, eos) = Rhode Island: Block Island.......... Pfs OT 0.112 28 .66 0.131 17.56 0.081 1.39 1.63 Providence........... 21.63 0.114 25.56 GUNES Rags when tahets staaieies SHINee Bayt OTT gee ofa 6 South Carolina: @harleston :.......%.- 42.15 0.153 45.78 0.166 36.25 0.131 Lo 1.26 Wolumibtd. i.e. 06). . 31.16 0.135 34.74 0.150 31.81 0.138 0.98 1.09 South Dakota: UOT eres ea! dig 12.49 0.095 HSI 0.117 19.00 0.145 0.66 0.81 eae ‘ hae 10.68 | 0.070] 11.98 | 0.078 | 27.60| 0.180] 0.39 | 0.43 Levzh esto i Oy hh dea ee 11.70 0.082 14.30 ORM OO a holo cee Soenche tec ened Meas, ate thre wm POAIMICGON 2 5 cf dics Sain wa Le ead UF 0.111 20.11 OSE 18.79 0.122 0.91 1.07 Tennessee: Chattanocoga.......... 25.13 OMT Syl eee OaloE 31.00 0.150 0.81 1.01 inoxville sy. 6.0. yoo ek 25.28 0.122 30.71 0.148 30.70 0.148 0.82 1.00 MYER TOT MUS citys ite kare 27.87 0.124 32.91 0.147 37.00 0.165 0.75 0.89 INUSED WIIG. © cls eta valence o's, « 25.41 Onl23 30.69 0.148 36.66 0.177 0.69 0.84 258 ENVIRONMENTAL CONDITIONS. TaBLE 11.—Precipitation and evaporation data for the period of the average frostless season. (Plates 46, 57, and 58.)—Continued. Station. Texas: Abilene tO 5. a ah NTA i A ee fetta (Bort Whob)).. ce saat eee Fort Brown (H)....... (Brownsville)......... Corpus Christi... /.2).: Pascoe wt5~ .¢ Gaye Fort Ringgold (S1).... (Rio Grande City)..... Penh Worth. 6 oo. Galveston 43. jot = Salt Lake City. 725.2). Vermont: Barlineton st. 3. 6 WNorphnelds 9 o35.0 5.5 : Virginia: Eynchbure 2028s. WNorletlahed ose is aa Wytheville 2205) 4.53. Washington: North Head’ 32... 222... (Fort Canby) 2.234..255 Olympia (S19)........ 312 1 Te Rea pekanes £36 2h) SSR wy Tatoosh Island..... Pele Walla Walla 2 West Virginia: Bika hee) oS Ae: Parkersbure. . och> Ja: Wisconsin: Green (Bayes) See Iba Rirosses 25 89 WAG isomer: ss 2 Se Wyoming: Cheyenne oo oy. ost Dian Creer nity i ae Si Total normal precipitation for period — FF SC OS | | —o—o—onroSoSS S ee eee eee of average frostless season (P). Mean normal daily precipitation for period of average frostless season (P/S), Total normal precipitation for period of average frostless season plus preceding 30 days (7). period of evaporation for Total frostless season, 1887-88 average (Hf). Mean daily evaporation for period of average frostless season, 1887-88 Moisture ratios for period of average frostless season, P/E. P/E | x/E anches. 0.188 0.44 0.47 0.201 0.44 0.47 0.102 0.77 0.81 0.118 0.65 0.72 0.273 0.12 0.13 0.155 0.34 0.35 DUAR y: BENE Bh sae “regen pat 0.148 0.79 0.89 0.158 0.51 0.54 FP tee SI oa | Co By Hersey pity |e o'097' | 1 aoe 0.143 0.87 0.99 0.119 eo 1.39 see ee ee ele reese ee ete eer eee este eeeeeene sere cee ele eee eee ets eree ses se etseeeeesee oecawwraneerfteceecce = © efa ws ce = 6 1e Oih eee eocecrececestooe veces efoeoeeeeeefeeeeee © © eee es ee ste tran ae sc wef a ese 6 8 6) 2h ee se eee pee se cele l ss © « 6 oe oe 6] se a © 6 wie Ss sh 6s ee eee see «se © © | « © 2 © 0) « =e) c= <6 0 « © he ieee ee CLIMATIC CONDITIONS OF THE UNITED STATES. 259 The daily normals of precipitation for the period of the average frostless season are shown graphically by the chart of plate 46, where the isoclimatic lines represent increments of 20 thousandths of an inch. The values are seen to be high for the southeast (the maximum being 170, for Cape Hatteras, North Carolina). The lowest values occur in the arid region as this term is commonly understood (the minimum being 9, for Reno, Nevada). On this chart the lines for index values 60, 100, and 140 are represented as broader than the others, since these lines are useful in delimiting the main precipitation zones or provinces of the country. The line for value 60 extends northward from about Cape Mendocino, roughly parallelling the Pacific coast and passing into Canada near the western margin of the Rocky Mountains system. This same line reenters the United States near the eastern margin of the same mountain system, passes southward and somewhat eastward, so as to lie just east of the Rocky Mountains proper, and enters Mexico near the mouth of the Rio Grande. This line includes, within the loop thus formed, all of the region commonly called arid, and some- what more. Northwest from the area thus demarked as arid the values increase, and the lines for values 100 and 140 lie just within the United States, in the neighborhood of Tatoosh Island, Washington (which station has the value 199). East of the arid region as above defined the values of these daily normals increase slowly, and the line for value 100 passes from north to south through the eastern plains or western prairies, approximating a line drawn from Corpus Christi, Texas, to Winnipeg, Manitoba. At its northern end, however, this line bends eastward, apparently passing somewhere north of the upper Great Lakes, and then bends southward so as to reenter the United States north of Port Huron, Michigan. It crosses Michigan from east to west, bends southwest- ward to Grand Haven, Michigan, and reaches Cincinnati, Ohio. From this point it passes northward to Detroit and then follows the valley of the lower Great Lakes and St. Lawrence River, to pass again into Canada near the northern end of Lake Champlain. It apparently again bends southward and touches the Atlantic coast once more near Nantucket, Massachusetts. Between the arid region and the north- south portion of this line, and north of the portion about the Great Lakes, lies a region that may be called semiarid, the values lying between 60 and 100. The line for value 140 delimits what may be called the southeastern rainy region, which here includes southeastern Louisiana, southern Mississippi, Alabama, and Georgia, all of Florida, and the Atlantic coastal region north as far as the entrance to Chesapeake Bay. Key West, Florida, lies outside of this rainy zone. The region lying between the line for value 100 and that for value 140, including most of the eastern half of the country, may be con- 260 ENVIRONMENTAL CONDITIONS. sidered here as a semirainy region. There are thus four precipitation zones or provinces roughly marked out on this chart, which may be defined as in table 12. TABLE 12. Normal daily pre- cipitation for the Province. period of average frostless season. thousandths anch. Dry. provanee . 4 inj.. 5 sos Below 60 Semidry province........ 60 to 100 Semirainy province...... 100 to 140 Rainy provanee. - i.e 4/2 Above 140 The four provinces thus indicated will be repeatedly referred to in our further discussion of moisture conditions. (3) Tora, NorMAL PRECIPITATION FOR PERIOD OF AVERAGE FROSTLESS SEASON PLUS PRECEDING 30 Days, DivipEpD By NUMBER OF Days IN AVERAGE FROSTLESS Season (7/S). (Table 11.) This rather artificial index of precipitation intensity is based, as has been mentioned, upon the consideration that some of the precipita- tion occurring just before the opening of the frostless season is still effective in the early part of that season. In many places the first few weeks of the average frostless season are normally more or less dry, and yet plants may be able to begin their activities with the advent of frostless weather, on account of soil-moisture left over from the latter part of the preceding frost season. The length of the additional period of 30 days was chosen quite arbitrarily, in an attempt to bring these considerations into the index, which we term 7. Bigelow’s precipita- tion normals (Bulletin R) were againused. The values obtained are given in column 4 of table 11, and these totals divided, in each case, by the corresponding number of days in the period of the average frost- less season (7/S) are given in column 5 of the same table. The chart obtained from these averages (7/S) shows no pronounced differences from that presented in plate 46, and it is not reproduced here. This chart is mentioned, since the method by which it was obtained is new and may be of value in the future, for special studies of certain regions. The values of 7 will be otherwise employed below. (4) NumBer or NorMatty Rainy Days IN PERIOD OF AVERAGE FROSTLESS SEASON. (Table 13, Plate 47.) This kind of index of precipitation intensity is frequently employed by climatologists, though for other duration factors than the one here PLATE 47 ‘% VU] BI OSsuq OY, ‘seourAoid UO wyIdIO9AId OAY OVNI deur oy} oprarp sour [ny “(Zz WUINTOO "ET IG’I Woy BIBP) WOsvas Sso]}SO1J OFVAOAT OY} JO potsod oy Ut *‘(OUl [°( UBY4y 910UT JO woreytdioesd [BUIIOU YIM SABD Jo s19quin Ny (seq) (89M 38910} u901819A9 uonisuen 38910} u991319A9 38910} 99013199 on AydosB ky 16910} Snonpizap SnAydosow woyyoN — 21}4ydosaw usayyi0oN U191S9MYLION ~purlssess) EKO LLP) e OK, J] ¢ ‘o, OK 4810} 31)Aydosew UJaISeaYyINOS puelsse15 q fe) \\ : ANG \ NYS ieee yj ze a: AN 2004 NE UN ee N Ss Ly ur ARC Y b iy NN = 4 \\ SK NSN YSN : SY ~ { \ So g AY es £2 Ud SZ Ze 4 %, Vp: Lx SY ‘ SN e, S SS Sy lay} ie) EZ, Ke ON rx, 4 \ 1) RS EO “A iN hy y yy WSN SS NN MO. 76 WW am Y WS \ NS eo) 2 x 4 SSS SO iS x SOS BEN WS 4, Se EN S NAS NS xy 4 LCS ee SY Bs N Rey any INNS f fs RiaN x EE Oe 68 16 66 86. pond fer) hor) z ayeid staseq oy], ‘seoutaosd woryeytdroosd oy oyu deur oy} oprarp sour [nT ‘(g WuIN[Od “ET 9[qB} WIOIJ BYEP) MOSES SsoT}SOIJ OBLIOAG OY} JO POrtod oY} Ut ‘sSoy 10 YOUT T'Q JO UOT}eyIdiooId peuNIOU YIM SXep Jo sroquin\y + Ol G01 LOT 601 ol IT SIT of IT oAll SIT (seq) (1894) 4so10y U9dIB19A9 uol}Isuedy {S910} ud91TIDAI a AydossAy se10j snonpisep oy Aydosour UsoY}4ION U1d}SOMYIION >pue|sseip Fane ee 4s010J S4yAydosour Usayseay}NOS PLATE 48 ; ‘ S\t /\ <\ | X bok ry are ; = ies | (ENE ea hCee ee Ny olN 0. [Sears (iia me 069) kL oh 8G, oh GL i 5 ee ALE SMCs AIS y Coe lone Sane oy AO) oy ee A ete ChE Ma A ISI fat 262 PLATE 49 ‘% o9ud stoseq oy, ‘soouraoid aoryeyidrooid oay oyut deur oy} oprArp soul] [NE (“p UUINIOD ‘eT a1q74 WOT} VIVP) “Ssso] 10 Your TO Jo uoryeyIdioord euas0U YIM SAup Arp Aq poyuosordos oe 4BY UOSvOS 889[}801j 0dB1NAR JO potsod Jo sodeyu9010g (seq) (189A, 18910} u991B819A9 uolisuen S910} UQ0IB IDA 18910} Uu991819A9 on Aydoss Ay 189103 snonpisep dn AYydosaw uray ION ww AYydosaw WiayyION i - purlsszi5y S371W 009 ers, — sisi Hf / bs itppiageet f | \ “ COIL Ul u Ol Oo aN . 2 S ae i 4se10} 91;A4ydosew UW19}Se94jNOG purisseiy LZ cx) t SSNS, vert! S) SANS, N NS NS WS SS Sil NS NY SQV yasaq-1WI9G = . \ ASIN RDO ; & nd . AGRAS WY, ANS Ne b WAtz SZ 7s WAZGGF \ SN \\ IARI ES ROR AY VIG €§ : S\ xt a iS : rN \ a WN WwW | ~~ ~ ee \ y q x q 4 3 b , § ‘ YS . . q y \ P DoS a ee 3 se s 2 2 . g > A NS) J Rae. SS st ih wes", > \ 3 , zeN » ’ Res x >: is * oa b WG LA a SEU RSA ) sid hs SS — eit tl \ 25 %% SSSI HUNT Pose) UT xs a. hyp “ab. eRe, my aa i DOSS ee i ROO oar ee 4. x > YS “gn 8" NS LN eS > S See ies Ch a Sia wtf WS BS > > 1 al 1 ink Cy i", N Pt . I> 2 1 r N 6 5 \ K pia We aN Se SY SQN ROMs ~~ RN SOON ~ | Le TANS NS x SSS 9 SASK Nj MS Wet ST RSs % ~ Sete 3 FN Su Mbss t | | re SN S AS J SQ Ly IV QV AX ey Se RS t a ( Pith ete Pris: IN os Uy, N | | NT ] it j NYS Y se <> SSS S599 .o. $35 YH p 6 il °S o, muh. Es IN ell IN if SW SOX, S aes “s 2 5 <2 $508 iil (1) ype, nthe HY ) < r h SoS oo 9 f es = \ an 324 264 ENVIRONMENTAL CONDITIONS. used. Normally rainy days are here considered (arbitrarily) as those with normal daily means (Bigelow’s table, Bull. R) of over 0.10 inch. The days are counted without reference to when they occur in the period, so that we do not touch here upon the question of rainy periods. These data are given in column 2 of table 13. TaBLE 13.—Number of days in the period of the average frostless season with normal precipita- tion of more than 0.10 inch and with normal precipitation of 0.10 inch or less, the latter also expressed as percentage of the number of days in the average frostless season. (Plates 47, 48, and 49.) ga |e |x aa | a | apg Bon ea en SS | 88 | ea Pee ee se | oo ee | ze | 34 | 2354 BE | 2; | S258 Station. So Sa ane Station. = 2 a cease a 6 he COS g Gs "as Te Cos eH | go | agus d2 | 25 | ese ss cs | SaaS 63 53 | so@e ave Aig Boe S Sle A a2 85 Se | EN Scam 49 | Soh eae Rare) =) a fash {=| (2) R=1 SS a fs oa 0 = = Ay = = Ay Alabama: days. days p. ct Idaho: days. days p. ct. Ami StOms |: cee oa 145 56 28 Boise ieee oes 00 As 100 Birmingham....... 166 65 28 Re wistonican 00 202 100 Migbiler oe. koe 248 S. 11 Pocatellos estas. 4. 00 175 100 Montgomery....... ILA7é 66 27 Tllinois: Arizona: CAO A nya eee 122 90 42 POEMS? aie cena 00 283 100 Chicago saver se 89 93 51 Arkansas: Thay Salle tie See 103 65 39 Hort, omith sss. 3: 159 71 30 Peon Workin ee 97 89 48 Wattle Rocko... 182 55 23 Sprmeneldes 5.5.4.5 95 87 48 California: Indiana: Bure keane ane nk 55 190 78 Hivansvalle: 9.4, 2 120 83 41 Rresnor eerie oa 00 258 100 Indianapolis. ...... 133 53 29 Independence...... 00 199 100 Towa: Los Angeles........ 40 294 88 Charles City....... 80 53 40 Red Blut est ec oe 33 231 BSiie Day enportiiec. 25: 117, 57 33 Sacramento........ 13 259 95 Des Moines........ 134 oll 22 San Francisco...... 62 257 81 DUbugueswe..0 6. 141 35 20 San JOse. Sasdioaud 43 251 85 ieolcule i hen, 152 45 23 San Luis Obispo... 25 235 90 SIOuUxHCIby. wees 97 49 34 Colorado: Kansas: IDONIVER Ve eee occ! 00 153 100 @oneordia ten 2.5. 89 84 49 Pireblonisce peewee ne 00 163 100 Dodvre City... ..4..- 48 133 74 Connecticut: y Ro) of 2) <7 Ws aa ae eae 141 48 25 Earironds secre tee. 128 ot 22 Wichita see eae Gee 111 83 43 New Haven........ 148 32 18 Kentucky: fs Florida: Rexineton es. 2... .. 103 84 45 Jacksonville........ 198 95 32 Louisville.......... 128 68 35 DUPLECR ee ose eae tke (234 84. 26 Louisiana: Key West... oc... 161 204 56 New Orleans....... 284. 26 8 Pensacola. s)he: 226 59 21 SHTEVEPOFt. 5... 0. 166 86 34 Pani Aaee cs felis 165 170 51 Maine: Georgia: IUASHPORE G6 ese cues. 103 64 38 Atha Ge Ne oui celina oe 155 70 31 IPOreland aii ts i: 100 57 36 AU OUSEAI co. uae. sts 160 68 30 Maryland: NaGon h.-..5. So 2e oe 144 94 40 Baltimore... i. 2... 163 50 24 Savannah. 3.2.... 175 88 34 Washington, D. C.. 154 43 22 Thomasville....... 229 28 ity CLIMATIC CONDITIONS OF THE UNITED STATES. 265 TaB Le 13.—Number of days in the period of the average frostless season with normal precipita- tion of more than 0.10 inch and with normal precipitation of 0.10 inch or less, the latter also expressed as percentage of the number of days in the average frostless season. (Plates 47, 48, and 49.)—Continued. DS See (ds) AS ae o2 | Ae Q fey on ad Dh ts wi oo Station. is © ae ay eet Station. ic 2 ic 2 is 2B = a g a |) oie ag re Me cs g a go oe Om ag i) oa So Ate By iG Ta oe ca 2 6 Ae oune) (2) ©) > et ome) faye) SA aa Ag Ag aa Bs Aig Aig en = ro do > & Ox, a Oo a, © 0 WMO, ses oe Hoa = 6 aS (atl ah S E Ay = Ee = Massachusetts: days. days. p. ct New York: days days. p. ct. BOStOM ll I e. sk. 110 75 Al INN ATTY a sient ea, 110 67 38 Nantucketi);:...5.... 55 154 74 Binghamton. 3.06). 95 63 40 Michigan: BtialOpre aie se ee 80 93 54 Plpenete sos ks ks 8 92 45 33 Canton Vote 43 96 69 WWSTONGE wis faa 8 66 98 60 Wa aieay cars 4) Sereda 2) 97 63 39 SCAMAWA SG acs. ss 105 35 25 New York......... 143 67 32 Grand Haven...... 51 116 70 Oswerorn. Saw, fos 55 120 69 Grand Rapids...... 46 118 72 Rochester.......... 35 136 80 Houghton... 0.0.0... 84 68 45 Sy Ra CUsel) is sl. 98 73 43 Marquette......... 71 69 49 North Carolina: Fortaauron........ 26 129 83 Asheville. 54). 2. 142 34 19 Sault Ste. Marie.... 64 74. 54 @harlotte) Aka scone 175 45 21 Minnesota: Flatterasi ices. «cs 256 00 00 1D oll Tiel ols eee a 124 28 18 dE vfe¥l CG) edo WAI wR nee 180 33 16 Minneapolis....... 120 41 26 Wilmington........ 189 44 19 Moorhead......... 67 65 49 North Dakota: roltbs J E-alert naa 106 53 33 Bismareleim soca: Pa 108 84 Mississippi: Devils Lake....... 53 68 56 MerigtaM Ns. os... 185 45 20 Wallistom wees 2... 24 98 82 NWieksbure 04/00... 207 45 18 Ohio: Missouri: @incinnaty.. <2. 101 93 48 Columbiae 22.52... 98 81 45 Cleveland......... 95 103 52 Ptammiball.: sock. ce 0 « 127 57 Si Columbus. 22 6 os52 106 78 42 Kansas City....... 151 45 23 HM GUSK Ye cele vic, cist: 89 106 54 SL MOUIS ea . 115 86 43 al Bo) Fe% (6) at he i Se 49 125 72 Sprimeteld) i... 161 26 14 Oklahoma: Montana: Oklahoma......... 90 124 58 NPV MO aoa s tl alcie cs is. 5 11 111 91 Oregon: HPeleMa ck eee se 00 144 100 Baker City. os... 00 127 100 ialasmelle ies... es. 00 140 100 Portland aes. 73 172 70 MUMS CTY. oe woo 3 134 98 Hosebure. dec. 5 o<. 1 197 100 Nebraska: Pennsylvania: MEIN C OMS a) Seni Ove, 3 131 43 25 ORIG teu hi eac cit oe ctl 130 64 33 North Platte....... 29 122 81 HMarrisbure sc 2k 2 wn 113 83 42 (000121 oe re 138 32 19 Philadelphia....... 114 92 45 Valentine.......... 72 60 46 Pittsburehe. vk eee 91 88 49 Nevada WOLAMGUIEG scien oe 102 74 42 1 SGOT SO Re a 00 138 100 Rhode Island: Winnemucca....... 00 131 100 Block Island’: .....< 142 76 35 New Hampshire Providence. ....... lll 79 42 GONCORds wesce cscs 104. 42 28 South Carolina: New Jersey: Charleston........ 206 70 25 Atlantic City...... 108 99 48 Coltimbia wes... 154 77 33 POETS UIVEA vices erases 91 95 51 South Dakota: New Mexico: PRUEOD cis, «acre ee Ex 47 S4 64 MEMUA EG. ora cee ka 8 179 96 PROLIG Gale c Ce es es 13 140 92 266 ENVIRONMENTAL CONDITIONS. TaBLeE 13.—Number of days in the period of the average frostless season with normal precipita- tion of more than 0.10 inch and with normal precipitation of 0.10 inch or less, the latter also expressed as percentage of the number of days in the average frostless season. (Plates 47, 48, and 49.)—Continued. es | 3 B28 ag g 226 so | g2 | a8 2S!) 32a ee ‘ a aa Feros ad Qe ik 2 as ie Se Doe: >an 2 le eats Sa2a Stati Figedid MEMS Ts cam a. | ee Station. 3° —— ae Ea Station. Se s = es 2 2 = mee 27 COS @q a Cos : pei. so (| ee d5 | poe Boao) | seas Bs | So. eee Davi. sia |e oS Sa!) Se ees sf | 28 | 888¢ a8 | 22 | ees. = = Ay = = AY S. Dakota—Cont’d: days. days. p. ct. Virginia: days. days. p. ct. Rapid City s.2 <<. 28 115 81 Lynehbure wi 2. 232 166 35 17 Mankdont sae eee 99 55 36 Neartolke c2atie: 28 202 28 12 Tennessee: Richmond os 5.0, 2-86 160 55 26 Chattanooga....... 143 64 31 Wytheville........ 156 19 zt Kmoxville. iii 2: 147 61 29 Washington: Memphis... 30%... 32 161 63 28 North Head. 2. =. 150 166 53 Washville. 334 205 fee 158 49 24 Seniie.seo tae ee 46 200 81 Texas: Spokane s: tia ode 00 202 100 ANH eM Gh as6 Ser) cals ots 53 192 78 Tatoosh Island..... 199 72 27 Amaro. 23.052... 4: yf 142 71 Walla Walla....... 00 216 100 Corpus Christi..... 39 259 87 West Virginia: HR AS ec Ser tes 2 234 99 Welkansh A pay.) 2 ae 11/3 32 22 Hert Worthe.. . 3.52 58 203 79 Parkersburg....... 120 59 33 Galveston. ......:. 257 74. 22 Wisconsin: Palestme. 2 oo... 3 153 92 38 Green Bay 24s. 628 3 85 68 44 San Antonio....... 65 Pel ti 77 HaMerOSSek cen ae 135 28 17 d Ms COT el age ike ae oe 85 169 67 Niadison so7 seen a3 108 71 40 Utah: Milwaukee. .:...... 72 90 55 Modena. 32.5 2 s 00 130 100 Wyoming: Salt Lake City..... 00 182 100 (Cheyenne. 2<'c os Se 00 118 100 Vermont: anderse. 32. pes sor 4 104 95 Bartineton 2). 2.5: 108 35 25 Northfield oa» 2..2 < % 86 40 32 The values representing the number of normally rainy days in the period of the average frostless season were plotted in the regular way and the resulting chart is given as plate 47. This chart shows isocli- matic lines at intervals of 25 days; the total range for the country is from 284 days (New Orleans, Louisiana) to none at all (various sta- tions in the arid region). The general zonation is seen to be very similar to that shown in plate 46. The heavy lines show the four provinces above described. (5) Numper or NormMatty Dry Days IN Periop of AVERAGE FROSTLESS SHASON. (Taste 13, Puate 48.) This index is the complement of the preceding one, and is derived by subtracting that from the number of days in the period, in each case. A dry day is thus one that has a normal daily mean precipitation (Bigelow, Bull. R) of 0.10 inch or less. If the former be considered as CLIMATIC CONDITIONS OF THE UNITED STATES. 267 an index of raininess, this may be taken as an index of dryness or aridity. The values are given in column 3 of table 13 and are shown graphically on plate 48. This chart shows a total range for the country _of from 294 days (Los Angeles, California) to no days (Cape Hatteras, North Carolina). The isoclimatic lines here again represent incre- ments of 25 days each, full lines being shown for the values 50, 100, and 200. In a general way, the climatic zonation of the country is similar to that of plates 46 and 47, but this chart is markedly different from the others in certain details, and of course the actual values are different. Some of these differences will be:considered below. (6) PercenraceE oF Days IN PERIOD OF AVERAGE FROSTLESS SEASON THAT ARE Dry Days (wirnh NorMAu PrecipiraTION oF 0.10 INcH or Less). (TABLE 13, PLatTz 49.) This index of precipitation intensity is obtained simply by expressing as percentage each value of the third column of table 13, in terms of the corresponding length of the period of the average frostless season. These percentages are given in column 4 of table 13. They express the relative frequency of dry days in the period. These values are shown graphically by the chart of plate 49. The total range for the country is from nil (Cape Hatteras, North Caro- lina) to 100 per cent (various stations in the arid region). The lines of the chart are drawn at intervals of 10 per cent, those for 20, 50, and 100 being full lines, and the zonation is once more similar to that of the other precipitation charts already mentioned. (7) LenerH or Loneest NorMALLY Rainy PeRIoD IN PERIOD OF AVERAGE FROSTLESS Smason. (Tasie 14, Puate 50.) In many regions the duration factor for the favorable range of moisture conditions is not as great as that for the corresponding range of temperature conditions, and the former thus becomes the main duration factor influencing plant activities. In such cases only a portion of the period of the average frostless season is suitable for active plant growth. In southern Arizona, for example, the normal frostless season is very long (241 days at Tucson, from March 26 to November 22), but all of this period is practically without rain, excepting only a portion of the summer. The summer rainy period at Tucson extends from about July 1 to about September 15, but there is also a spring period of general plant activity, extending from the cessation of frost to about May 1. The latter period is nearly rainless, but the soil-moisture content is high, due to the residual effects of the winter precipitation. Thus there are here two periods of general plant activity within the period of the average frostless season, one from about March 26 to about May 1 (at which time the winter moisture is about dried out of the soil) and the other from about July 1 to about October 15 (when the summer moisture has largely disappeared). It 268 ENVIRONMENTAL CONDITIONS. is thus possible to consider two different periods of plant growth in this region, both of which lie within the limits set by the average frostless season, but neither of which is as long as that season. In some other regions there is but one period of general plant growth, but this is not as long as that of the average frostless season. When moisture condi- tions have been more thoroughly studied it may become possible to consider both the frostless season and that with moist soil, in deriving the duration factor for plant growth in general, but we have not found it expedient to attempt this at the present time; the relations encoun- tered are too complicated and information is too meager. Nevertheless, we have been able to derive two duration factors for precipitation, which may be superimposed upon the temperature duration factor here generally employed. These two new factors are the lengths of the longest rainy period and of the longest dry period within the period of the average frostless season. The first of these is considered here and the other will receive attention under the next- following heading. In attempting to derive an index of the normal duration of moist conditions, we have again begun our computations with the data of normal daily precipitation given by Bigelow (Bulletin R). Our pro- cedure has been quite arbitrary. In the case of each station the series of daily normals given by Bigelow has been considered as separated into a series of overlapping groups of 5 days each. Numbering the days of the period of the average frostless season consecutively, days 1 to 5 constitute the first group, days 2 to 6 constitute the second group, days 3 to 7 constitute the third, etc. The 5 daily normals for each group are averaged to give the mean daily normal precipitation for that group, and these means are set down to form a new series. Beginning with the first (in the period of the average frostless season) of these new group means, the groups are marked as rainy or dry, accordingly as the value of their means are or are not greater than 0.10 inch. Thus, a 5-day group is called rainy if its group-mean is over 0.10 inch, dry if this mean is 0.10 inch or less. If we designate the succes- sive 5-day groups throughout the normal frostless season by the alpha- bet letters, and if we follow each letter by an R or D, to denote ‘‘rainy”’ or ‘‘dry,” as the case may be, we obtain a series more or less similar to the following: AR, BR, CR, DR, ED, FD, GR, HD, ID, JR, KR, LD, MR, NR, ete. In this example the first four groups (A to D) are seen to be “‘rainy.”’ Then follow two ‘‘dry” groups (E, F), after which is a single ‘‘rainy’’ group (G), which in turn is followed by two “‘dry” groups (H, I), etc. Now, the last day of each ‘‘rainy” group is con- sidered as occurring in a normally ‘‘rainy’’ period, and the last day of each “‘dry’’ group is considered as within a normally ‘‘dry”’ period, and it thus becomes possible to determine the extents of the various ‘“‘rainy’’ and ‘‘dry”’ periods thus established. If, for example, group CLIMATIC CONDITIONS OF THE UNITED STATES. 269 A includes April 1 to 5, group B April 2 to 6, group C April 3 to 7, etc., _ it follows that the period April 1 to 8 (inclusive) is a ‘‘rainy”’ one; the period April 9 to 10 is “‘dry”’; that of April 11 (a single day) is “‘rainy’’; that of April 12 to 13 is “‘dry,”’ etc. The dates of beginning and ending of each normally “‘rainy’’ and normally ‘‘dry”’ period of the normal frostless season having been thus obtained for each station, the length of each period is noted, in days, and the lengths of the longest normally rainy period and of the longest normally dry period become the two indices desired for the station in question. The beginning and ending and the length of each normally dry period in the period of the average frostless season are given in the second column of table 14, and the corresponding dates and length of the longest normally rainy period are given in the third column. Roman numerals refer to months, the arabic numerals not in parentheses represent the days of the month, and these data are followed, in each case, by the length of the period, in parentheses. Thus, the longest normally rainy period in the period of the average frostless season for Anniston, Alabama, extends from May 18 to September 8 and includes 114 days. As has been remarked, this method of treatment is quite arbitrary, but it seems to furnish indices of normal raininess and droughtiness that may be valuable. At least, these indices are worthy of a test, and may be employed till more satisfactory ones may be devised. It should be noted that the smoothing process applied to the precipita- tion data by Bigelow (in deriving the daily normals) is here overlaid by another very efficient smoothing process of our own (the use of 5-day averages), so that the natural irregularity of precipitation is very largely obliterated, which is to be desired when normals are requisite. It may also be mentioned that the indices here set forth might have a still greater value for such work as this if the constant 0.10 inch were made somewhat smaller. Such an alteration would of course render the normally rainy periods longer and the normally dry periods shorter. The testing of such modifications may, however, be left to a later time, and to other workers, if they will take up this important phase of the climatology of precipitation. PLATE 50 270 en ON ta 'Z 990] stosuq oy, ‘soourAosd uoryeyidioodd oAY 0VUI deur olf} OPIAIp Soul ][Ny. “gE UUIN]Oo “Py o[qv4 ULOIy BYEp ¢ MOsteS Sso]}SO.1] Jo portod ut (7X09 008) porzod Aurea ySoduo] AT[euL10U jo (sXep) sqyduo'] olIt fll oS IT 6 §6t0 (seq) (a59M) 38910} U90I1319A9 UOITISUBT} We — 48910} UddIT19A9 }SO1OJ UddITIBAD a1 AqdoisAy 48910} snonpioep = S1yAydosou usoyitoN 9} Aydosaur usayy10Ky U19}SOMYyIAON -puejsseiy S37W 009 Oo€ 1 a HAHA HA . =a fn XQ, mlaia\nieial etal NN WX 3 HI HE HELE LZ SI = IS : ¥ : SS Sf > hx Mi Meri rongnearad nla o 5? RSIS nH | WN j | Ss NX xRIG SS A SOS iS BSS <5 5 roses <2 oP, Sp = =“ SS SoS SOS > = ae. x. 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Ss SY <9 wi RS, 5 SS BS 272 ENVIRONMENTAL CONDITIONS. TasBLe 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period within the period of the average frostless season. (Plates 50 and 51.) A normally ‘“‘dry period”’ begins on the last day of the first 5-day period whose average normal daily precipitation is not over 0.10 inch; a normally ‘‘rainy period”’ begins on the last day of the first 5-day period whose average normal daily precipitation is greater tham 0.10 inch. Months are represented by Roman and days of the month by Arabic numerals; numbers in parentheses are the duration of the respective periods, in days, these-being in full-face type for the longest dry period in each case. Station. Dry periods. Longest rainy period. Alabama: ‘ JATINISTOR = 6 sce LV,.29 to V, 17 (19): TX, 9 to 10, @); |. V, 18 to EX, 8S Grae IX, 27 to 28 (2); IX, 30 to X, 20 (21). Birmingham..... IV, 29 to W, 18 (20); [X, 27 to X, 5 (40)..| V, 19 to IX, 26 (131). Mobile: 32-2 c er V, 13 to 17 (5); X; 10 to 26: AT); XI, 172 V, 18: to X98 Gas to 20 (4). Montgomery...... TX, £to 97(9)s TX, 18-to Ke 246) 22. I]t, 11 to VEEL, 3h Arizona: Phoenix 709). Se: Ty 245to aL SAS a ver clk nee are etn No rainy periods. Arkansas: Fort Smith. ..... IV, 2 to 10 (9); VII, 16 to 25 (10); VIII, | IV, 11 to VII, 15 (96). 26:10 2X 612) Xe 25 to2ir (3). Little Reck. VI, 9 to 10 (@); IX, 2 to 8 (7); X, 1 to | IH, 20 to VIL, 8 G42). 29 (29). California: Hurekas.. 2a Web tone ORS) re cee tc ahh ee III, 30 to V, 4 (36). Mresnoy 2c Pibrelisig Ole TAL (25S ee en a No rainy periods. Independence. . 5 1ie 10 Gore, 24n CISD eee eke er ee Do. Los Angeles...... Th oO tore Penlagy (2o oct boy fo oe ee 1; 28 to TE 2tae ay - Bed Blutas es. VSO DSIa 1S AsO) i coke Rhee XI, 19 to XII, 16 (28). Sacramento...... 1D25 to L116 (10) 111, 19 to XT, 19 (242) :) Til, 7 to 18 (ey: Sam Hrancisce. .-.|- Lis 17 to Xa. 18247) XE 101) 2. oe. I, 26 to III, 16 (50). San Jose... oe PT tose SAAD ye ke eee TEE ee Il, 7. to TH, 16 (8s): Sam, Lams Obispoy:i OV tntowels BS (Zan) ear Mi ee lil, 4 to 3b (2s); Colorado: Denver ones. sce Wasiisbo me Gi GPa ee ie ees eo ae No rainy periods. FE ebony ee oes EVO 2Sr tok GS) ot ea eee Ee Do. Connecticut: : (Hartiords.)5. 8 V, 13 G); VI, 16 to 26 1); VIII, 31 to | VI, 27 to VITE, 30 G5)- LX 5: (6) EX, 27-40-X) 3). New Haven...... V, 21. to 22 (2): Vi, 15 to 23 @); VIII,-|. Vi, 24 te VI, soa SL AtOMEe2 1B) ex, 27, tox 17): Florida: Jacksonville...... 1G oe 1114 to 7 @): xX, 29 to X1il, | Ill, 8 to X, 284225). 4 (87). Spite. te eee MM, 15 to 17-(@); IIb, 8 to 2144: Iv, | V, 20 to XT; 105g 1 to 19 (19); IV, 21 to 28 (8); V, 18 to LO%(2)s TT) to27 (Ck) > Ma 15 "to 29 (15). Key: West. ..:... XE, 11:to.V; 10: G82); VI, 28 to VIl;:| VII, 22:to Xi, tetas 25) Vile 185 2144). Pensacola........ IV; 23° to: V, 25 G3); 1X; 20 to, 21-2): | V; 26 to EX, 1s:amae 10 to. 16-(7) > Xi, 14 to 22.9): Tanipa 2.08 os oe Hi; 9°to- 13°) 11, 240.1645): Til, 29° |) V..26 to X, 9am to IV; 25 (58)2"X. 10 to 43-4): X; 16 to 18 (3); X, 24 to I, 9 (78). Georgia: Addantacin pees LV; 29° to V5. £7019): 1X, 9 to 10 @yeiaV,.18 to 1X sate IX, 27 to 28 (2): TX, 30,to XI, 3 (35). ANIPUISEAS. csi: IV, 28 to 29 @)iV,6 to: 17 (12)2a X36 |. V, 18 to LS Cee to 9 (4); IX, 29 to XI, 7 (40). Macon}. ©2552 oe LV 27): IV 27 to V, 1872) Ex 28 VV, 19 to EX, 20- ee to XI, 13 (47). CLIMATIC CONDITIONS OF THE UNITED STATES. VAP: TABLE 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period within the period of the average frostless season. (Plates 50 and 51.)—Continued. Station. Dry periods. Georgia—Cont’d: Savannah........ IV, 9 to 11 (3); IV, 18 to 30 (13); V, 8 to 27 (20); X, 19 to 23 (5); X, 26 to XI, 27 (33) Thomasville..... DOA Bs ronnie, Gi UMA NES 74 |e al Hans a i le a Idaho AGISE ee eas DV29) GOR 22) ase ee ahaa hae Lewiston........ DHE OT oy, Gh ar Ga ((7A |) Ue I a a Rn Pocatello........ 1 BANA Ibe Bro, Esa 8G A 5) Te a OL ee Illinois: (Creo) a eae oe VII, 20 to 26 (7); VIII, 8 to IX, 26 (50); X, 4 to 15 (12); X, 20 to 28 (9). Chieago 0 ys... IV, 18 to V, 2 (15); V, 16 to 24 (9); VII, 15 to 22 (8); VIII, 5 to 9 (15); VIII, 31 to IX, 6 (7); IX, 18 to X, 15 (28). Maisalle. jf 605 6: VII, 15 to 27 (13); VIII, 5 to 20 (16); VIII, 29 to IX, 9 (12); IX, 19 (1); X, 6 to 13 (8). MCORIAG he eis es IV, 16 (1); VII, 8 to VIII, 14 (38); VIII, 22 to LX, 19 (29); X, 8 to 18 (11). Springfield....... VII, 6 to 13 (8); VII, 17 to VIII, 15 (80); VIdt, 20 to: Ee 13\(25): TX 19 Cl) xX, 8 to 17 (10). Indiana: Evansville....... IV, 29 to V, 3 (5); V, 14 to 24 (11); VIII, 5 to 9 (5); VIII, 27 to LX, 25 (30); X, 6 to 14 (9); X, 20 to 23 (A). Indianapolis. .... VIII, 12 to 17 (6); VIII, 29 to IX, 7 (10); IX, 17 to 26 (10); X, 8 to 19 (12). Iowa: Charles City..... VII, 27 to VIII, 8 (13); VIII, 26 to IX, 26 (32). Davenport....... IV, 23 to 29 (7); VII, 24 to 30 (7); VIII, 6 to 7 (2); IX, 3 to 6 (4); IX, 23 to X, 13 (21). Des Moines...... VIII, 5 to 10 (6); VIII, 30 to IX, 10 (12); TX6.17 (1) Xe 1 tors (8). Dubuque........ IV, 23 to 28 (6); VIII, 8 to 22 (15); IX, 19 to 21 (8); X, 5 to 9 (5). Keokuk . 0002 0c). LV; 2) to. 8 (Ow Was tele. ()s ViLLis 9 to 12 (4); VIII, 24 to IX, 3 (11); X, 7 to 15 (9). Sioux City....... VI, 12 to 14 (3); VIII, 6 to 16 (11); VIII, 28 to IX, 11 (15); IX, 20 to 27 (8). Kansas: Concordia....... IV, 25 to VI, 5 (11); VII, 9 to 16 (8); VIII, 4 to IX, 5 (3); LX, 16 to X, 14 (29). Dodge City. i... 21 PV) 18 to VV, 14 \(22)* V1, 27 to: VIE, 7 (42); VIII, 9 to X, 15 (68). EL Roy 3): a ne TV, 10 ta. 21) (U2): TV,26-t0' 3015); VELT, Sito) DXe GiGe yaks, 23) t6- 24s 3 to 15 (13). Wiehitia). occa IV, 9 to 27 (19); VII, 21 to 28 (8); VIII, i @ todd (S)> VERE, 25 >to EX, 5: (12) 3. TX, 23: to, 19 (27): Kentucky: Lexington....... [V.,.28 to VV; 8 Abs VI, 7 to 8 (2); VEIL, 29 to X, 23) (66). Longest rainy period. | V, 28 to X, 18 (144). | III, 7 to X, 25 (233). | No rainy periods. Do. Do. | i | | i III, 31 to VII, 19 (111). V, 25 to VII, 14 (51). IV, 29 to VII, 14 (77). IV, 17 to VII, 7 (82). EV; 19 to VITnS (78). V, 25 to VIII, 4 (72). IV; 17 to VELL Pha t7). V, 17 to VII, 26 (71). IV, 30 to VII, 23 (85). IV, 23 to VIII, 4 (104). IV, 29 to VIII, 7 (99). IV, 9 to VII, 12 (95). VI, 15 to VIII, 5 (53). V, 6 to VII, 8 (64). V, 15 to VI, 26 (43). VI, 1 to VIII, 30 (91). IV, 28 to VII, 20 (84). VI, 9 to VIIT, 28 (81). 274 ENVIRONMENTAL CONDITIONS. TaBLE 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period within the period of the average frostless season, (Plates 50 and 51.)—Continued. Station. Dry periods. Longest rainy period. Kentucky—Cont’d: Louisville... . .- V, 13 to 18 (6); VIII, 30 to IX, 26 (28); | V, 19 to VIII, 29 (103). xX, 4 to 22 (19). Louisiana: New Orleans.....| V, 10 to 17 (8); IX, 8 to 25 (18); XI, 1 (1).| V, 18 to IX, 7 (143). Shreveport....... VI, 19 to 22 (4); VII, 10 to 17 (8); VIII, | III, 5 to VI, 18 (106). 3 to: 1X, 5 (4): IX, 2040 23 Gye 28 to X, 17 (20). Maine: Masport... cee se V, 9 to 12 (4); VI, 10 to 19 (10); VII, | VI, 20 to VII, 30 (41). 31 tor Vid, 8-()* Vil 27-to Es as (18) ; IX, 26 to X, 5 (10). Portland. as-8 VI, 26 to VII, 21-@6); VIII, 30 to TX; | V, 15 to VI, 25563) 12 GAY Xia to 3 eS): Maryland: Baltimore....... IV, 16 to:23.(8); VI, 1 (1); TX, 27 to X, | VI, 2 to TX, 26:0: Pir(Zo)e ed. toro). Washington, D.C.| IV, 18 to 23 (6); IX, 3 to 8 (6); IX, | IV, 24 to IX, 2 (132). 26 to X, 19 (24). Massachusetts: BOStORLES fe ee IV, 21 to 22 (2); V, 13 @); V, 31 @:'{ VU, 20 to Vilie=serse Vi, 15 to: Vi; 1935): Vili, ‘31 to BY, t0:.Ct). Nantucket....... IV; 17 t0V, 23.30; Vi, 4 to: 20: U7): || Vill; 516 21 Game Vi, 22 to VINE, 4 (44): Vill, 22" to EX, 18%@s)- EX 20: to Ne ot (12) Xe 19 to 24 (6); XI, 2 to 5 (4). Michigan DNS Crs 02 at ee V, 25 to 28 (4); VII, 9 to 16 (8); VII, | VIII, 7 to IX, 28 (53). 22 to VIEL, 6 G6). DCLrotin eas «oe V, 1 to'6 (6); V, 11 to 21°11): VEIL, 2.1: V, 22 to VIEL wae to 18 (17); VIII, 25 to X, 11 (48). Eseanaba......... VII, 10 to 19 (10); VIII, 20 to 31 (12)...| V, 17 to VII, 9 (54). Grand; Haven... .2|-TVy 29 to: V, 6-(8); Vz 29 to: Vi,-f @): + V, 7 to 28 C2): VI, 9 to VII, 2 (24); VII, 4 to 28 (25); Vite to 2t Gb): VET, 26° to X's (4) ex te 12°02) Grand Rapids....| V, 2 to 7 (6); VI, 1 to VII, 28 (58); VIII, | V, 8 to 31 (24). (tO EX 363) 2G 1 tot 2-2); Houghton. 2.22 =. Ve e2ond a. Vid. Sto. Vil, SIvGayss0 es, ae V, 26 to VII, 7 (48). Marquette.......| VII, 8 to 19 (12); VII, 29 to VIII, 31 (84).| V, 16 to VII, 7 (53). Port Huron... = V; 19 to 23 (); VI, 14 to IX, 12 OD: | V, 24 to VI, 13 Cre IX, 19 to X, 9 (21). Sault Ste. Marie.| V, 15 (1); VI, 9 to 26 (18); VII, 8 to 30 | V, 16 to VI, 8 (24). (23); VIII, 12 to 27 (16); IX, 21 to 29 (9). Minnesota: Dalen. nes eee V, 5 (1); VII, 17 to 27 (11); VIII, 28 to | V, 6 to VII, 16 (72). a1 (4): Minneapolis..... VII, 12 to 24 (18); VIII, 15 to 18 (4); | IV, 30 to VII, 11 (73). 1X, 26 to -X, 1 (6). Moorhead....... V, 14 to 16° (@); V,. 25 to 31°@); Vil, | VI, 1 to Vil, 22:62 23 to: Vili, 13: (22)") VIEL, 28 to LX 22 (26). Ste Paul 25253 Ue: IV, 28 to V, 8 (11); VII, 12 to 25 (14); | V, 9 to VII, 11 (64). VIII, 18 to 26 (9); TX, 23 te X, 3. (11). Mississippi: Meridian........ V, 18 to 19 (2); VIIL, 20 to 28 (9); X, | V, 20 to VIIE, 19 G2). 4 to 27 (24). CLIMATIC CONDITIONS OF THE UNITED STATES. 275 Taste 14.—Beginning, ea and duration of each normally dry period and of longest normally rainy period wit and 51.)—Continued. an the period of the average frostless season. (Plates 50 Station. Mississippi—Cont’d: Vicksburg....... Missouri: Columbia........ Hannibal: 6... Springfield....... Montana: Kalispell......... co ee Miles City...... Nebraska: Wimcoln 6 wos. 8. North Platte eecee Winnemucca..... New Hampshire: Concord..... New Jersey: epee Atlantic City.... Cape May...... New Mexico: Santa Fe.... New York: J\Noveh oh} @ eee eee eee ee ee Dry periods. V, 14 to 16 (3); VIII, 20 to 27 (8);I X, 6 to 12 (7); X, 3 to 21 (19). VII, 18 to 21 (4); VII, 28 to VIII, 17 (21); VIII, 28 to X, 14 (48). IV, 15 to 20 (6); VI, 9 to 18 (10); VII, 12 to 15 (4); VIII, 24 to IX, 5 (13); IX, 30 to X, 15 (16). PV, 14°); IV, 16 to 17 (2): 2X ft to. 3 Q)o Ie 27 to we, 23) (202 VII, 13 to 19 (7); VIII, 5 to IX, 24 (51) ; X, 4 to 18 (15); X, 20 to 24 (5). XO AY COS UCL) ean Gare eset he ae V, 16 to VI, 6 (22); VI, 20 to IX, 14 (87). We'S) Go; Tome 28) (UAA) er, Bi tees ee V4 to EX 30) GAO) i er V, 8 to VI, 6 (29); VI, 13 to IX, 24 (104). IV, 20 to 22 (3); VIII, 26 to IX, 10 (16); IX, 20 to X, 10 (21). V, 2 to 19 (18); VI, 9 to 10 (2); VI, 25 to VII, 23 (29); VII, 29 to IX, 29 (63). TEX A 60302 (2) NEXG LO tO exe oS (25) V, 10 to 15 (6); VII, 14 to 17 (4); VII, 20 (1); VIII, 12 to IX, 18 (38). Vide to x Sle CSS )ira ese he ee Vi, LGHOM Xe 28" CSD tess eas lee Vi 8 to 14 (es Vi, 28, @)2 VIL. 31 to IX, 13 (14); IX, 28 to 30 (8). IV, 13 to 24 (12); V, 3 to 13 (11); V, 23 to VI, 8 (17); VI, 19 to 28 (10). IV, 18 to 25 (8); V, 3 to 14 (12); V, 24 to VI, 8 (16); VI, 19 to 28 (10); VII, 9 to 12 (4); VIII, 30 to IX, 8 (10); IX, 23 to X, 6 (14); X, 15 to 20 (6). IV, 16 to VII, 15 (91); VII, 26 to IX, 19 (86). IV, 24 to V, 21 (28); IX, 5 to 9 (5); IX, 24 to X, 7 (14); X, 13 to 17 (5). V; 3 to 15 (18); VIL, 10: to 14 (5); VILLI, 12 to 18.7) Teo to 2X6) (G2). [V, 2% to Vy, 17 (1): VI, 5 to 18 (14): VIII, 31 to IX, 11 (12). V, 10 to 25 (16); V, 28 to 30 (8); VII, 12 to 23 (12); VII, 30 to VIII, 27 (29); IX, 3 to 14 (12); TX, 19 to 25 (7). V, 5 to 13 (9); VIII, 11 to 18 (8); VIII, Si toy, b()s EX, 3. toc ls: (11): EX, 16 to X, 7 (22). LV, 16 to. 23 (8);.V, 16 to 23 (8): IX, 1 to 8 (8); IX, 26 to X, 4 (9). Longest rainy period. V, 17 to VIII, 19 (95). IV, 19 to VII, 17 (90). IV, 21 to VI, 8 (49). EV; 18 to, VEEL, 31 (136). Wo VIB, 12: (97). EV, 15 to. X, 3172). Vi 7 10:19 (13); No rainy periods. Do. Vi; 7 to 12); EV: 23'to VIET: 25 (£25). V., 20'to VE; S.@0): IV: 27: toi Viti Si) C27). V, 16 to: VEL, 13° (59). No rainy periods. Do. VI, 29 to VIII, 30 (63). VII, 14 to VIII, 29 (47). VII, 13 to VIII, 29 (48). VII, 16 to 25 (10). V, 22 to IX, 4 (106). V, 16 to VII, 9 (55). VI, 19 to VIII, 30 (73). V, 31 to VII, 11 (42). V, 14 to VIII, 10 (89). V, 24 to VIII, 31 (100). 276 ENVIRONMENTAL CONDITIONS. TaBLE 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period wtihin the period of the average frosiless season. lates 50 and 51.)—Continued. Station. New York—Conit'd: Oswere 2). 2 24 Rochester Syracuse... North Carolina: Wilmington..... North Dakota: pean. = Oregon: Portland... Roseburg... Pennsylvania: Erie Dry periods. IV, 28 to V, 25 (28); V, 28 to 30 (3); VII, 12 to 23 (12); VII, 30 to VIII, 27 (29); TX, 3 to 14 (12): EX, 19 to AZ Ga: V, 2 to 18 (17); V, 23 to 24 (2); V, 30 (4) =-VIE, <5 te 1814) NIE 1S oe SS (42): Vit. 2S to: VERE, it (15): Vit. 18 to 26 (9); VIII, 31 to X, 19 (50). 29 to VI, 13 (15); VIII, 12 to 20 (9); Wilt, Sl to X, 7 GS): X. 15.01). M Ex 7 16:10 (4): TX, 33 to X, 1 ety IV, 28 to V, 1 (4); IX, 23 to X, 17 (25); XI, 1 to 4 (4). No drought periods iV; 25 ie V, 5 (1): TX, 8 to 12'G): xX 2 to 7 (6). IV, 5 to 27 (23); XI, 1 to 15 (15) V, 12 to 29 (18); VI, We V, 19 to 31 (13); VI, 28 to IX, 14 (79). ... 22 to IX, 17 (88)... EV; 19:40 28 ©): IV. 27 ta, Sey. 18 to 23 (6); VIII, 10 to 14 (5); VIII, 31 to IX, 25 (56). IV, 17 to V, 16 (30); VI, 17 to 22 (6); VIII, 4 to 15 (12); VIII, 23 to 27 (5); IX, 21 to X, 1 (11). IV, 17 to 22 (6); V, 3 to 7 (5); VI, 6 to 11 (6); VII, 4 (1); VIII, 26 to IX, 27 (33); X, 5 to 17 (13). IV, 15 to V, 8 (24); V, 14 to 24 (11); VIII, 9 to 16 (8); IX, 6 to X, 26 (1). IV, 25 to V, 6 (12); V, 19 (1); VI, 14 to 20 (7); VII, 4 to 14 (11); VII, 29 to VIII, 28 (31); TX, 2 to X, 15 (44). IV, 3 to 22 (20): VI, 16 to VII, 4 (19); VII, 29 to VIII, 6 (9); VIII, 21 to IX, 6 (17); IX, 16 to X, 2 (48). V, 25 to IX, 28 (127) IV, 16 to X, 30 (198) SPR jy Be a pa oe ee ran (ee! emcee oe Com ee ar oe), wwe abe ate as Sans ent Sens etm so, pmo Gide pen pe IV, 21 to V, 13 (23); VII, 10 to 20 (11); VIII, 4 to 8 (5); VIII, 27 to IX, 7 (12). IV, 15 to V, 12 (28); VII, 12 to 20 (9); IX, 1 to 8 (8); TX, 20 to X, 6 (17); X, 19 to 23 (5). IV, 15 to V, 16 (32); V, 30 to VI, 3 (5); VI, 12 to 17 (6); VIII, 30 to IX, 9 (11); IX, 12 to 21 (10); IX, 27 to X, 7 (11). IV, 29 to V, 9 (11); V, 14 to 16 (3); Vill, 6 to 11 @); VIII, 29 to IX, 18 (51). IV, 21 to V, 15 (25); VII, 12 to 21 (10); TX, 1 to 8 (8); IX, 20 to X, 9 (20). a) OO ee es ew 28 to VI, 7 (11); VIII, 3 to IX, 25 (54). Longest rainy period. V, 31 to VII, 11 (42). VI, 19 to VII, 11 (23). V, 14 to VIII, 11 (90). IV, 21 to IX, 6 (139). V, 2to IX, 22 (144). II, 29 to XI, 11 (256). V, 6 to IX, 7 (125). IV, 28 to X, 31 (187). V, 30 to VI, 21 (23). VI, 8 to VIII, 2 (56). Vi, 1 to 27 (27). V, 24 to VIII, 9 (78). VI, 23 to VIII, 3 (42). VII, 5 to VIII, 25 (52). V, 25 to VIII, 8 (76). V, 20 to VI, 13 (25). IV, 23 to VI, 15 (54). No rainy periods. xX, 4 to XI, 16 (44). No rainy periods. V, 14 to VII, 9 (57). VY, 13 to VII, 11 (60). VI, 18 to VIII, 29 (79). V, 17 to VIII, 5 (81). V, 16 to VII, 11 (57). CLIMATIC CONDITIONS OF THE UNITED STATES. ZAE TaBLE 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period within the period of the average frostless season. (Plates 50 and 51.)—Continued. Station. Rhode Island: Block Island..... Providence...... South Carolina: Dry periods. IV, 21 to 27 (7); VI, 15 to 28 (14); VII, 17 to 28 (12); VIII, 27 to IX, 6 (11); IX, 19 to X, 7 (19). IV, 21 to 23 (3); V, 13 (1); V, 31 (1); VI, 15 to VII, 19 (35); VIII, 31 to IX, 10 (11); IX, 26 to X, 3 (8). Longest rainy period. IV, 28 to VI, 14 (48). VII, 20'to VIII, 30 (42). Charleston....... DE 3! tod () V2 toi6 (5) LV, 20; to, |) V, 21 to 2a1i, 2 (is6)- V, 6 (17); V, 14 to 20 (7). . Columbia........ IV; 5 to. 15 (11); TV, 25 to V, 17 (3) V, 18 to TX, 23 (129). South Dakota: BX 24 to X17 (4) 2x 11 tol 23 G3); XI, 1 to 8 (8). 25 (0; (0). 0 ee ee V, 13 to 186); V, 23 to VI, 3 (12); VII, | VI, 4 to VII, 8 (35). 9 to VIII, 2 (25); VIII, 15 to IX, 20 (37). MIORTO kaa elas V, 3 to VI, 2 (1); VI, 7 to 20 (14); VII, | VI, 21 to VII, 4 (14). 5 to LX, 30 (88). Rapid City...... V, 7 to 30 (24); VII, 1 to IX, 26 (88)....| V, 31 to VI, 30 (31). Manktom.. 2). 5h). VII, 17 (1); VIII, 16 to IX, 17 (33); TX, | V, 3 to VII, 16 (75). 22 to X, 3 (12). Tennessee: Chattanooga.....| V, 2 to 17 (16); VIII, 10 to 17 (8); IX, | V, 18 to VIII, 9 (84). 2° to 22021): Knoxville........ V, 12 to 17 (6); IX, 5 to 14 (10); TX, 23 | V, 18 to IX, 4 (110). to X, 28 (36). Memphis........ VII, 14 to 21 (8); VIII, 10 to 11 (2); VIII, | III, 22 to VII, 13 (114). 25:60 EXG) 12) (19) xe) 4 to 201) is ae. 27 to 30 (4) Nashville........ V, 9 to 20 (12); VIII, 17 (1); X, 3 to | V, 21 to VIII, 16 (87). 26 (24). Texas: Abilene.......... TL, 16 to IV; 22 (88): 1V,:28: to. V,. 4.1. V, 23 to VI, 16 (5). EV TS ite 22) sib aly to Mex, 7 (83). Amarillo. 3.0.5.8. IV, 17- te. V;:6,20) 2 V,20 (); Vi, 16.40.) V,; 21 to: VI, 15 @6). Galveston....... Palestine........ VII, 15 (80); VII, 27 to VIII, 4 (9); VIII, 15 to IX, 6 (23); IX, 12 to XI, 1 (51). TE 22) t0.. Vewl 262) Vi.) 20) to. Vie 16 (28) VI, 270 tov kx, 1) .(67) 3) 2k, 2 to XI, 3 (33); XI, 8 to XII, 16 (39). DET, 21 ton Van. 22) (ba) VIL. 25" to XI, 11 (110). III, 9 to IV, 24 (47); VI, 11 to 27 (17); WIL, 5. to 21.7) * VILy 2¢ to IX, 18 (54); IX, 30 to XI, 24 (56). 28) to: DE, 3) C0) s Lb) oto. LG: (12)- Wi, 10 to 23 (14); VII, 6 to 8 (3); XII, 13 to 15 (3). IIT, 28 to IV; 8 (2); VI, 17 to 20 ©); VEL Sito eX, 8..(68)s TX 2002) s cx 1 to 9 (9). IT, 24 to IV, 17 (53); V, 18 to VI, 13 (17); Vivilo to 225 (bs) VEL, LO: to. VILE, 23 (45); TX, 5 to 11,- (7); IX, 18 to 23 (6); IX, 29 to XI, 26 (59). IX, 2 to X, 1 (30). VII, 23 to 24 (2). IV, 25 to VI, 10 (47). VII, 9 to XII, 12 (157). IV, 9 to VI, 16 (69). IV, 18 to V, 17 (80). 278 ENVIRONMENTAL CONDITIONS. TABLE 14.—Beginning, ending, and duration of each normally dry period and of longest normally rainy period within the period of the average frostless season. (Plates 50 and 51.)—Continued. Station. Dry periods. Longest rainy period. Texas—Continued: WPaslonc tice tae III, 14: to IV, 11 (29); V, 27 to 29°(S); || IV, 12:to VE, 26 Gar VI, 16 to 23 (8); VII, 10 to VIII, 29 (51)> TX, 1 to 10°(10): EX, 19 to 23 (5) 3281 to-Xt,- 22 G3). Utah: Modena... 522. - Veto taux 25s (a0) ad ene ee ee No rainy periods. Salt dake: City slivercO to xo (lS 2) or. a Sas Do. Vermont: Burlington....... V, 30 to VI, 4 (6); IX, 8 to 13 (6); X, | VI, 5 to IX, 7 (95). | 2 to 10 (9). i| Northfield... V, 14 to 21. (8): Vi, 12 to 15° @s-Vil, | VIL 17 to ES ee: | 13 to 16 (4); IX, 2 to 15 (14). Virginia: | Lynchburg....... IV, 16 to 24 @); TX, 3 to 9 (7); X, 12 to |_IV, 25 to TX, 2 Gare 209) Xa 1G). INoriolic. je ae Ki tO. 186) ck: 90) 124) ee ae III, 28 to X, 13 (200). Richmond....... IV,-23 to: V, 4, @2)s 1X,'S to: 8 (); EX | V, 5:to EX, 2 Gz 30 to -X, 18:9): XI, 2 to 3°): Wytheville....... Xs (6 40:94) 19 Xow to OMA) ae ee IV, 19 to IX, 5 (140). Washington: North Head..... TV 524 to OX. (S2GS) 2 ee ae en X, 4 to XII, 22 (80). Seattle 2s cce2 os PEE 22 (2). EV, 10 to =X, 13.4087); Xx, | 2X, 2 to 22 71h: 24 to XI, 1 (9). Spokane. sc. ac: DE Ot toke WAR DO 2) aio lee ie tin No rainy periods. Tatooshicland....\) V,\15 to 21 (Hs Ville Sito. DX: 1.60) =. IX, 2 to XII, 9 (99). Walla Walla..... TV 52 to er (21G) eee eas No rainy periods. West Virginia: 1] Fe Brie ee pean VIII, 8 to 9 (2); VIII, 28 to IX, 6 (10); | V, 19 to VIII, 7 (81). IX, 17 to X, 10 (24). Parkersburg..... IV, 20 to V, 9 (20); VIII, 28 to. EX, 4 | V; 10 to VIN, 2716): (8)5 EX, 87 to Xe 1125). Wisconsin: Green Bay....... WE, TE); Vij-24 to 27, 4)> Vig 13 to |v, 4:to VE LOGae 26 (14); VIII, 15 to TX, 4 CD; IX, 23 tou, 3 C1). La Crosse.......- V, 1 to 4 G); VII, 13 to 24 (2): X, 2 | V, 5 to VIII, 124160): to 10 (9). Madison. 226 22% TV; 23:to V, 2/0); V;19-to 21. @); VIL, | V, 22 to VIL, 286sie 29 to VIII, 17 (20); IX, 16 to 23 (8); xe 2 to: 1s Ghz): Milwaukee...... IV, 29:te. V,-2 4): V, 23 to 29 (7); VII, | V, to 30 VIL, 12°43: 13 to VIII, 21 (40); VIII, 31 to IX, 7 (S) EX, 15 to. 25: Gil) XG 1 te:7 G4). Wyoming: Cheyenne 2)! 2. !: VES OMe ie CPE) oe ee ede ere a No rainy periods. ; . Mandenk eat fae pV Geos we cee OD aa Ii bgt (1: U8 Bee ee a ee oo V, 27 to Vi, 2 Gee 4 The lengths of the longest normally rainy periods in the period of q the average frostless season, as given in the third column of table 14, 4 are shown graphically on the chart of plate 50, in which the isoclimatie | lines represent increments of 25 days. The total range for the country i is from nil to 256 (Cape Hatteras, North Carolina). All of the region west of about the one-hundred-and-first meridian has exceedingly low values, most of them being zero, excepting the strip of country border- CLIMATIC CONDITIONS OF THE UNITED STATES. 279 ing the Pacific. The droughtiness of the intermountain area is here relatively exaggerated, on account of the choice of 0.10 inch as our constant in deriving these indices; the stations here characterized as having no normally rainy periods are not to be considered as really all alike in this particular. For the detailed study of the arid regions there seems to be no doubt that a lower value than 0.10 inch will be required. The precipitation provinces of the country, as indicated by the full lines of plate 51, are similar to those shown on plates 46, 47, and 49. (8) LenetH or Loncest NorMautty Dry PERIOD IN PERIOD OF AVERAGE FROSTLESS SEASON. (TaBLE 14, Puate 51.) These indices for droughtiness, corresponding to those for raininess just discussed, are given in the third column of table 14, and the method by which they were obtained has already been described. Plate 51 shows the chart constructed from these values. The isoclimatic lines are shown for intervals of 25, with full lines for the values 150, 50, and 25. The total range of this index, for the entire country, is from zero (Cape Hatteras, North Carolina) to 299 (Los Angeles, California). The meridian of 101° west longitude again forms an important demarcation, separating the more humid east from the more arid west, and some other features are like those of the other precipitation charts. In the details of the Southwest this chart has peculiarities somewhat like those of plate 48, and will be referred to below. (9) Normat ANNUAL PRECIPITATION. (PLATE 52.) Since total annual precipitation is surely of considerable value in a general estimate of the aridity or humidity of a region, we include in our series a reproduction of the chart of this feature published by Gan- nett. This chart has been drawn, as its author states, with consider- able reference to topography as well as to the records of about 4,000 stations, and it appears to us to be the most useful annual rainfall chart of the United States thus far published. Data for normal annual precipitation for 167 stations are given in the second column of table 15, for use in other connections, but these are not the data from which this chart was constructed. The data given in that table are taken from Bulletin R of the U.S. Weather Bureau. Table 15 also includes other data, which will be considered below. In Gannett’s chart, as here reproduced (plate 52), the isohyetal lines for 10, 30, and 50 inches are dotted and the others are full. All are drawn for increments of 10 inches. By the emphasized line rp) for a precipitation of 30 inches the country is divided into 3 main Gannett, Henry, Distribution of rainfall, U.S. Geol. Survey, Water Supply Paper No. 234, reprinted from report of National Conservation Commission, 1909, Washington, 1909. The chart referred to is Plate I, and is published in color. The isohyetal lines of our chart (plate 52) have been copied from Gannett’s plate I by means of a pantograph. ee = ASE, Wt SR te ES —————eE = a Fa a S eyed st oseq oyy, ‘sedutAoid uoryezIdioeId aay o7UT deur oy} aprArp soul [[Ny “youUBL 10938 ‘(soyouT) san[VA Ut UOTZePIdIOVId jeNUUe [VUTION Ot ATT cell “qasegq)_ yseJoy u981310A0 uonnisuen _ ¥sadoy uaasd10A0 ay Aydos3hy qseioy snonpioap S1yAydosoul ussYy LION i -puryjsseisy G da Za N ae ee Aree UE|SSEI AK OF 3 ur9jSeeyINOS pred . _purysses9 \\’ N 3 : RA we qaseq-1wiag o9 SAV XN NY Wy < Ss ee Sa) : AS ‘ . 7 NS N N “ Xe WS i NN ‘ Vy EN \ SIRES VG o N\\: 3 { a a S07) é Fok y ‘ PLATE 62 aN Doe SKS 5 ~. KO0O>> yt IWS SRS Ss EN $05 : ES; Yas, ae SNH WSs iN S 4 hb meee WSS Ins SSS | N S aN XS ih I il SSES SAS ae Jnl ~ 2% ast XQ 18 68 Sf6 86 6 QL6 280 aw ~ § “YO oLTE GILT FOE .€2 CLIMATIC CONDITIONS OF THE UNITED STATES. 281 regions. The humid northwest occupies the western half of Washing- ton and of Oregon, practically the full width of northern California, and the whole of the Sierra Nevada Mountains. The arid and semi- arid central region occupies the country south and east of the zone just described, and extends eastward as far as a line drawn from the western end of Lake Superior to the Rio Grande at a point about 100 miles above its mouth. In this general description we of course neg- lect the restricted mountain areas of Idaho, Wyoming, Colorado, etc. The humid east occupies the region lying east of the line just men- tioned. It should be added that the northern half of the southern peninsula of Michigan is also to be classed as semiarid on this basis, since its normal annual precipitation is less than 30 inches; this is a restricted area. _ The arid precipitation zone is here shown as having values below 10, and it occupies the Great Basin and extends southward into Mexico from Arizona and southern California. The humid region, as above defined, is here considered as divided into two provinces by the line for value 50, thus indicating a humid and a semihumid, or a rainy and semirainy province. ‘These four precipitation provinces do not require special discussion; their general characteristics are very similar to those pointed out for plate 46. The general north and south trend of the isohyetal zones is here seen to be modified by the Gulf of Mexico and by the southern Atlantic so that the lines of the eastern portion of the humid region trend north- eastward, or even eastward, instead of southward. The mountainous regions, of course, have higher precipitation indices than lowland regions of the same latitude. In general, the zones tend toward an arrangement parallel to the two coast-lines, which is readily explain- able on meteorological grounds and which is the reason for the north- south trend noted in all charts representing moisture relations. (10) ConcLusions FROM Strupy oF PRECIPITATION CONDITIONS. The charts of precipitation conditions (plates 46 to 52) exhibit features that are markedly unlike those of the temperature charts (plates 34 to 45), as was of course to be expected. The precipitation zones have a strong general tendency to extend in a north-south direction, while those of temperature generally extend from west to east. We have found it convenient to consider the following four pre- cipitation provinces in the United States: (1) the humid (or rainy) rain- province, occupying a small area of the extreme Northwest and a larger ‘area of the southeastern Gulf and Atlantic coasts; (2) the semihumid (or semirainy) rain-province, occupying a rather narrow strip of country southeast of the northwestern humid area and nearly all of the country east of a line drawn from Corpus Christi, Texas, to Winnipeg, Manitoba; (3) the semiarid (or semidry) rain-province, occupying a narrow strip 282 ENVIRONMENTAL CONDITIONS. east and south of the northwestern semihumid area, the plains region, roughly defined as between the mountains and fhe Winnipeg-Corpus Christi line, and portions of the States bordering the Great Lakes; (4) the arid (or dry) rain-province, occupying, roughly, the region west of the Rocky and Big Horn Mountains that is not included in the west- ern and northwestern portions of the other provinces. The general forms of these rain-provinces are set forth in figure 2, which is taken from plate 46. pee ADS Fig. 2. Moisture zonation, according to precipitation indices for period of average frostless season. Precipitation provinces: Humid, more than 140; semihumid, 100 to 140; semiarid, 60 to 100; arid, less than 60. Numerical values are in the thousandth of an inch. (See also plate 46.) Plates 48 and 51 show somewhat marked departures from this generalization, consisting mainly in the westward or southwestward displacement of the arid province, so that the latter comes to include the southern half or more of the Pacific coast and little or none of the Great Basin. The other features of these two plates are somewhat different from those of the other precipitation charts, but still agree with them in a general way. The southeastern fed province appears on plate 49 as three localized areas, two of which are where they would be expected (from a study of plates 46, 47, 49, 50, and 51). The third area, however, is differently placed, occupying portions of Minnesota, Iowa, Mis- souri, Wisconsin, and Illinois. On plate 51 this southeastern humid, or rainy, region is much more extensive northward and northwestward CLIMATIC CONDITIONS OF THE UNITED STATES. 283 (than in the case of plate 46, for example), and southern Georgia and Alabama, and most of Florida are here shown as in the semiarid province. 3. REMOVAL OF WATER FROM THE PLANT. A. INTRODUCTORY. (1) GeneRAL ConTROL OF WATER-LOSS. The external conditions! that are effective in the control of water- loss from ordinary land-plants are generally confined to the aerial environment, for water is probably seldom lost through the subterra- nean periphery of the plant-body. The water-extracting conditions of the aerial environment are more directly related to climate than are the water-supplying conditions of the subterranean surroundings. Some of these conditions have been studied by meteorologists and climatologists, and the published records of the U.S. Weather Bureau will once more be drawn upon for climatological information wherever possible. There are just two features of the aerial environment of plants that are directly effective in controlling their rates of water-loss—the evaporating power of the air and the intensity of absorbed radiant energy. These two conditions should not be confused; one is dependent upon air-temperature, air-humidity, and velocity of air movement, and the other depends upon the quality, intensity, and duration of sunshine, which is not generally a function of the air conditions immediately about the plant. Also, these two conditions should not be confused with evaporation, which is almost always done in common parlance. The rate of evaporation from a given water-surface is deter- mined by various internal conditions (resident in or back of the sur- face) and by these two external conditions. We shall, however, still frequently employ the term “‘evaporation”’ as practically synonymous 1 On the internal conditions that are effective in this regard, see Livingston (1906, 2).—Idem (1913, 2). Bakke 1914.—Shreve, F., The vegetation of a desert mountain range as conditioned by climatic factors, Carnegie Inst. Wash. Pub. No. 217, 1915, and the citations given in these papers. The xerophytism, mesophytism, etc., of plant forms, as these have been roughly con- sidered by observational and classifying ecologists, are mainly based upon the appearance or structure of the aerially exposed parts and, until the recent development of the concept of transpir- ing power, or resistance to transpirational water-loss (which is quite distinct from the transpira- tion-rate itself), but little progress has been made toward the quantitative definition of plants in this regard. If the transpiring power of plants might be as well known as the shapes of their leaves and the arrangements of their floral parts, a great impetus should be given to the more permanent aspect of ecological study. With a knowledge of this power for the various plant forms should of course go a similar knowledge of water-absorbing power and water-conducting power (see especially Livingston and Hawkins (1915), in this general connection), for the xero- phytism, ete., of a plant may depend on one of these latter rather than upon transpiring power alone. The measurement of these more recondite internal conditions has not as yet been seriously attempted, and methods therefor are still to be devised. Ecological plant geography will eventually need to define its plants physiologically as well as taxonomically, and the geographical distribution of species (itself as yet attempted only in a crude way) will become of little interest without some real knowledge of the physiological qualities by which these species resist or favor the various influences of the environment. In the present part of our study we confine attention to environmental conditions. 284 ENVIRONMENTAL CONDITIONS. with atmospheric evaporating power, since this will be readily under- stood and since an attempt to avoid such practice seems somewhat pedantic at the present time. When the evaporating power of the air begins to enter seriously into climatogical studies this meaning of the word ‘‘evaporation”’ may be dropped. In short, it seems desirable to avoid clouding the main issue for the present, and we shall frequently employ the word “‘evaporation”’ to correspond with the word ‘‘pre- cipitation’’ as here used. The expression ‘‘evaporating power of the air,”’ or ‘‘atmospheric evaporating power,”’ will also be used, however. (2) ATMOSPHERIC EvAPoRATING PowER. This term is here used in Livingston’s! sense, meaning the tendency of the air about the plant to accelerate transpiration. The expression has been seriously opposed as an “‘inaccurate and misleading expres- sion,’ by certain members of the staff of the United States Weather Bureau. Some of the discussion that has been raised in this connection is indicated in one of Livingston’s papers (1915, 2) and in footnotes, editorial and otherwise, incorporated therein. The objection to the term, as so far brought out in the literature, seems to reside mainly in the consideration that the non-aqueous gases of the air actually hinder vaporization of water (which they do to a comparatively slight degree), so that a decrease in the amount of these gases present must increase the evaporating power of the air. It does not appear, however, that this is really an objection to the term in question, especially since the meaning is understood immediately by everyone, and since no better term seems available as yet. Doubtless some of the misunderstanding brought out in this discussion hinges on what may be meant by air. The air is a mixture of varying proportions of various gases; it always contains (in nature) nitrogen, oxygen, and a little argon, but it also contains carbon dioxide and water-vapor, and frequently numerous other gases. We see no reason for not considering these last-named gases as a part of the mixture, and it is in the sense of air as the gas mixture bathing the evaporating sur- face in question that the word has been employed by Livingston and is here employed. Now, such a gas-mixture as the air may vary in the nature and proportions of its constituents, and it may also vary in its density, or pressure. As the pressure decreases the air becomes less dense, and this purely physical change makes it possible for evapora- climatic factor influencing vegetation, Hort. Soc. New York, Mem. 2: 43-54, 1910.—Idem, A schematic representation of the water-relations of plants, a pedagogical suggestion, Plant World 15: 214-218, 1912.—Atmometry and the porous cup atmometer, Plant World 18: 21-30, 51-74, 95-111, 148-149, 1915.—Idem, Atmospheric influence upon evaporation and its direct measurement, Monthly Weather Rev. 43: 126-131, 1915.—Idem, A modification of the Bellani porous plate atmometer, Science, n. s., 41: 872-874, 1915.—Idem, A single climatic index to represent both moisture and temperature conditions as related to plants, Physiol. Res. 1: 421-440, 1916.—Idem, Atmospheric units, Johns Hopkins Univ. Cire., 160-170, Mar., 1917. > De Sy WEP A CLIMATIC CONDITIONS OF THE UNITED STATES. 289 tion to proceed at a higher rate than is obtained with greater pressure. It is likewise true that an alteration in the water-content of the air changes the rate at which evaporation may occur, ceteris paribus. Furthermore, a change in the temperature or velocity of movement of the air (wind) over the evaporating surface also alters the possible rate of evaporation. It is thus seen that both physical and chemical changes in the air exert an influence on the rate of evaporation from exposed liquid or solid water. That a decrease in the amount of gas present per given volume should accelerate evaporation is surely not a matter to cause misunderstanding, for we regard the mixture as air, at what- ever density it may occur. It thus appears that the evaporating power of the air increases as the density of the air decreases, and this con- sideration appears to clear up the whole difficulty above mentioned. The usual popular quibble over the conception of limits arises here, as elsewhere in physical science, when we consider the result of decreas- ing the air-pressure to zero. it such a case the air approaches, and finally should "become, an absolutely empty space, without tempera- ture and without phemical nature. Such an absolute vacuum would have the highest possible evaporating power, in Livingston’s sense, and after such a condition had been reached (if it could be maintained) the rate of evaporation from exposed liquid or solid water should be controlled only by conditions resident in the liquid or solid itself. This condition is impossible of attainment, of course, so that the evaporat- ing power of the air never becomes infinite, but this consideration is valuable in that it shows clearly how this power becomes greatest when there is the least gas present in the air-space. The quibble arises over the popular interpretation of the apparently paradoxical statement that the evaporating power of the air is greatest when all the air has been removed. Of course, when the limit is reached and the air-pressure is actually zero, we have to broaden our definition of air so as to let the term mean the space abutting against the evaporating surface into which water vapor may diffuse. That this is necessary at the limit of reduced pressure (which is never really attained) seems to be no reason for changing our term, though if it seems desirable we are free to admit that the term in question really denotes the evaporating power of the circumambient space in which air usually occurs. Another objection to the term ‘‘evaporating power of the air”’ is parallel to the one always raised against the word suction. The water vaporizes because of conditions resident in its solid or liquid phase, and the energy thus transformed does not come (directly) from the air-space. Just as the term ‘‘suction,”’ or sucking power, has to be regarded as referring to the removal or decrease of a resistance, rather than to the application of a driving force, so the evaporating power of the air is to be regarded as proportional to the reciprocal of the measure of the resistance offered by the air to evaporation. The resistance thus 286 ENVIRONMENTAL CONDITIONS. offered may be expressed in terms of the water-condensing power of the air, but, as Livingston has remarked, air without actual tendency to precipitate or deposit liquid or solid water still offers resistance to evaporation: 4 “Air without water-vapor offers resistance to evaporation but has no condensing power; it can not deposit water upon a surface, no matter what its pressure may be. The resistance offered by such dry air can be expressed in terms of an equivalent condensing power, however.” In answering this second objection to the term ‘‘evaporating power of the air,” a third possible objection is also partly answered. This objection arises from the various senses in which the word power is used. If we are interested only in the statical phase of the matter before us, then the evaporating power of the air is proportional to the reciprocal of the measure of the capacity of the air-space to retard the vaporization of water, from a liquid or solid water surface exposed to that space. The dynamic phase of the problem of evaporation, how- ever, allows the use of the word ‘“‘power” in its ordinary physical sense, as denoting the time-rate of doing work. The conditions resi- dent in the air-space are thus thought of as somewhat like a brake on a wheel, and we consider a time-rate of the reciprocal of resistance to evaporation. ‘Thus, our use of the word ‘‘power” is not with the meaning of spatial capacity, but we employ the word in its true physical sense, as though the air were a machine acting to retard evaporation. As in other cases of power measurement, it is necessary to measure the power in question in terms of the amount of work capable of being performed in a given time period. Internal conditions, resident in the solid or liquid phase of the water, determine what would be the rate of evaporation if the air-space offered absolutely no resistance, and if these internal conditions remain constant the amount of evaporation occurring per time period is proportional to the reciprocal of the power of the air to behave as though it were condensing water-vapor upon the exposed surface. The reciprocal of the rate at which water would be condensed if all of the tendency of the air-space to retard evapora- tion were effective toward actual condensation is thus proportional to the tendency of the air conditions to allow evaporation to proceed, and this may be relatively measured as a power by determining the amount of water actually vaporized per time period. Of course, the conditions resident within the solid or liquid surface are never even sensibly con- stant for long, and the actual rate of evaporation depends not only upon the evaporating power of the air, as above defined, but also upon the internal conditions. The evaporating power of the air is thus relatively measured as the time rate of the reciprocal of the resistance offered by the air to evaporation, this resistance being measured in terms of equivalent condensation. But condensation is merely negative evaporation, so that when the air conditions aresuch as to make the external resistance just equal to the internal tendency EE ee ee ee Se ee ee CLIMATIC CONDITIONS OF THE UNITED STATES. 287 (within the solid or liquid phase) to vaporize water, then the apparent rate of evaporation becomes zero. Going further, the external condi- tions frequently become such that the resistance offered by the air to vaporization of water is greater than the tendency of the internal conditions to cause vaporization, this resistance being due toa ten- dency of the air to deposit water on the surface, and actual condensa- tion ensues; 7. e., the evaporating power of the air becomes negative and the evaporating surface gains water instead of losing it. There seems never to have been any attempt to define air according to its chemical content; it would still be air if it were largely carbon dioxide or hydrogen, etc., and it seems unadvisable to attempt a restriction of the terms ‘‘air’”’ and ‘‘atmosphere”’ at this late day. For the rest, the expression ‘‘evaporating power of the air’”’ has been in use among students of this power at least since 1906 (when Living- ston used it). Itwill probably appeal to most students of this poweras quite unobjectionable and it need not be dropped. Livingston (1917, 1) has suggested atmometric index as still another term, to avoid the difficulty just mentioned and to avoid the necessity of employing evaporation to mean both the process and one of the conditions controlling its rate. We shall not employ this new expression, how- ever, preferring to allow others to decide the question thus raised. The evaporating power of the air is of the utmost physiological importance to vegetation, and it can be rather readily and directly measured, in relative terms. Nevertheless it has not been seriously studied in the United States, and most of the information so far obtained in regard to it is only indirect. To appreciate what ones of the climatic conditions usually measured may be valuable here, it is necessary to consider the secondary conditions, upon which depends the atmospheric evaporating power. The vapor-tension deficit—Without air-movement, and supposing the air and water temperatures to be the same, the evaporation-rate should be nearly proportional to the vapor-tension deficit; that is, to the difference between the maximum vapor-tension for the given air- temperature and the tension of water-vapor actually present in the air. The actual vapor-tension in the air is a closely approximate measure of the tendency toward condensation and the maximum vapor- tension for the given temperature and pressure is a measure of the whole tendency toward evaporation; the former tendency overcomes a portion of the latter and what remains is very nearly the actual tendency toward evaporation. The maximum vapor-tension of water is, of course, a constant for any temperature and barometric pressure, and its value may be obtained from physical tables. The actual vapor-tension is seldom as great as the maximum; it is so only in the case of water-saturated air. If we allow HZ and EL’ to represent evapora- tion-rates from the same surface at different times, P and P’ the 288 ENVIRONMENTAL CONDITIONS. maximum vapor-pressures corresponding to the respective air-tempera- tures, and p and p’ the corresponding vapor-pressures of water actually in the air at those times, then | Oise ii E’ ay Pre oy! Under such conditions P—p and P’—p’ are measures of the respective forces tending to drive water-vapor off from the surface into the air. To determine the values of p and p’, we may measure the absolute humidity by chemical methods, we may resort to the sling psychrom- eter or any form of wet and dry bulb thermometer with constant and rapid air-movement, or we may employ the Regnault dew-point apparatus. It is clear that the values of p and p’ depend upon the absolute humidity and upon the air-temperature and barometric pressure, while the values P and P’ depend only upon the temperature and barometric pressure. Since the influence of barometric pressure is relatively small under natural conditions, it need not be seriously | considered here. The vapor-tension deficit is seen to include the air- temperature influence. | Relative humidity—The vapor-pressure deficit is not one of the climatic features usually determined by climatologists, who have rather uniformly followed earlier workers in the employment of the concept of relative humidity in its stead. Relative humidity is the vapor-pressure of the water-vapor actually present in the air expressed as percentage of the maximum vapor pressure for the given temper- ature and pressure; it is simply the percentage of water-saturation of the air. This bears no quantitative relation to atmospheric evaporat- ing power, even with wind and barometric effects left out of considera- tion, for it is obvious that air with a given relative humidity must be more effective in promoting evaporation at a higher temperature than at a lower. It is not the percentage of the maximum vapor-pressure actually present, but the difference between the maximum pressure and the actual, which measures this influence upon evaporation-rate. Since the maximum increases with temperature (though not propor- tionally), a given percentage of deficit must represent a larger actual deficit as the temperature rises. If H and H’ represent the relative humidity of the air at different times, the remaining symbols being the same as above, then dE H’ rr py’ / P’ From this it is clear that, if the air-temperature is known in each case, thus furnishing the values of P and P’, the vapor-pressure deficits may be found; from this equation and the one for E/E’, given above, it follows that E P(i—H) PoP aie CLIMATIC CONDITIONS OF THE UNITED STATES. 289 In other terms, the rate of evaporation is, under the assumed condi- tions, proportional to the product of the maximum vapor-pressure of water, for the given air-temperature, and the complement of the - relative humidity. Relative humidity is commonly measured and discussed in climato- logical studies, and its complement is sometimes employed as a measure of atmospheric dryness. They are both easily seen to have no definite relation to the evaporating power of the air. There is here, however, a general and merely qualitative relation; high relative humidity usually corresponds to low atmospheric evaporating power, and the reverse. We shall have to deal with relative humidity in our discus- sion of the climatic conditions influencing evaporation, but this con- cept is to be clearly appreciated as without logical foundation; it is simply a mathematical abstraction and its value to agriculture or ecology will have to be determined by direct empiricism. It may be here suggested that vapor-tension deficit is the climatic dimension that should be measured by ecological workers, if the analysis needs to be carried so far! Fortunately, the evaporating power of the air can be directly measured, and much more readily and usefully than can this deficit, and it seems not at all necessary at present, for ecologi- cal purposes, to analyze this power into its components. Wind.—Besides the vapor-tension deficit, atmospheric evaporating power is greatly influenced by air-movement; with increasing wind, ceteris paribus, the evaporation-rate is accelerated. Here again, however, the relation between wind velocity and evaporation-rate is not a linear one; with low velocities the effect of alteration in wind velocity is great; with high velocities this effect practically vanishes, and the relation of the two features for any given range of velocity depends upon the kind and upon the exposure of the evaporating sur- face. As has been mentioned, an enormous amount of effort has been expended in attempts to find empirically a formula by which evapora- tion might be calculated from measurements of other climatic condi- tions, and the argument over the wind factor has been greatly pro- longed. Such attempts have failed, as they always must until the problem is first solved by controlled physical methods, which solution has not yet been seriously attempted. When a solution is reached, however, it will obviously hold only for some particular kind, size, etc., of evaporating-pan or other atmometer. As a climatic feature that must surely influence water-loss from plants, but the exact nature of whose influence is still quite beyond our reach, wind velocity will be but briefly touched upon in our study. On theoretical grounds this is not a promising criterion for ecological 1 Livingstcn, B. E., The vapor tension deficit as an index of the moisture conditions of the air, Johns Hopkins Univ. Cire., Mar. 1917, pp. 170—175.—Johnston, Earl S., The seasonal march of climatic conditions as related to plant growth, Maryland Agric. Exp. Sta., in press. 290 ENVIRONMENTAL CONDITIONS. climatology, and it is practically unsatisfactory on account of the inadequacy of the information in this regard which is now available. (3) ABSORBED RapDIATION. Reverting again to the conditions controlling water-loss from plants, we have said that there are, generally, two of these—the evaporating power of the air and the intensity of absorbed radiant energy. The first of these has been discussed in sufficient detail for present purposes and the second remains to be considered. By far the greater portion of the radiant energy intercepted by plant surfaces comes directly from the sun; other sources of radiant energy appear to be practically negligible under most natural conditions. It is therefore absorbed sunshine (light and heat) that needs attention at this point. The intensity of absorbed solar radiation is determined by three conditions—the intensity of the impinging rays, the angle at which they meet the exposed surfaces, and the absorbing power of the sur- faces. The last is an internal condition, effective within the plant, with like transpiring power, water-absorbing power, etc. With this, as other internal conditions, practically nothing of a quantitative nature has yet been attempted. The angle at which the impinging rays meet plant surfaces varies with the time of day, with the season, and with the shape and position of the plant; but since ordinary plants offer absorbing surfaces to solar radiation at all possible angles, it is only in special studies of special species (as of ‘‘compass plants,” for example) that this matter may require attention. We may ignore the angle of incidence in our present discussion.” | The intensity of the impinging radiation is obviously the feature dealt with in climatology as sunshine intensity. For the measurement of this, various methods have been devised from time to time (such as the black-bulb thermometer, the bolometer, the pyrheliometer, the Hicks solar radio-integrater and several forms of photographic actinom- eters), but no data are available for a quantitative climatological study of this condition. It appears probable that the radio-atmometer® may furnish adequate information for ecological purposes, when its value in this connection has become appreciated. A very distant approach toward the measurement of sunshine intensity, and the only systematic attempt in this direction thus far 1 See, in this regard, Livingston 1911, a. 2 Briggs and Shantz have argued that only the vertical component of solar radiation is to be considered as effective upon plants. It seems to us that this question requires experimental investigation before its detailed discussion may be attempted. We may add here the remark that the surfaces of most plant leaves occupy almost all conceivable angles with the vertical, so that the exposure of the plant as a whole must approach being equivalent to that of a sphere. or of a vertical cylinder with spherical top. For the opposite argument, see L. J. Briggs and H. C. Shantz, Hourly transpiration rate on clear days as determined by cyclic environmental factors, U.S. Dept. Agric., Jour. Agric. Res. 5: 583-649, 1916. 3 Livingston, B. E., A radio-atmometer for measuring light intensity, Plant World 14: 96-99, 1911.—Idem 1911, 6; Idem 1915, a; Idem 1916, 6. fi : : CLIMATIC CONDITIONS OF THE UNITED STATES. 291 carried out by the United States Weather Bureau, consists in the determination of the number of hours of sunshine occurring each day at the various stations. It is to be emphasized that the sunshine recorders now generally in use give but little information as to the intensity of the sunshine itself; they record the duration aspect of that range of intensities which is called direct sunshine, but the limits of this range have never attracted attention and are not established, so that the whole mass of dataso derived are anything but precise. Never- theless, some of the sunshine data of the United States Weather Bureau will be considered below, since they furnish the only available measure- ments having any bearing at all upon the matter before us. B. ATMOSPHERIC EVAPORATING POWER IN THE UNITED STATES. (1) Very LimitEp Nature oF AVAILABLE DATA. To obtain data bearing on atmospheric evaporating power it is only necessary to operate a number of atmometers of the same form in the various climatic regions dealt with, being sure that all have similar local exposures. The importance of this condition to plant and animal life and the relative ease with which it may be measured makes it appear surprising that practically no organized study of evaporation throughout the United States has yet been undertaken. Had evapora- tion been recorded as thoroughly as precipitation has been, we should now be able to construct relatively satisfactory atmometric charts, but the almost utter lack of data makes this practically impossible at present. To render our position in this connection still less satisfying, it is to be remembered that observations of any climatic condition, extending through a single year, are of but little value; if evaporation measure- ments were to be systematically begun in the present and were to be systematically continued, it would require many years of records to render these measurements as valuable climatologically as are those of temperature and precipitation at the present time. It seems now, however, that students of climate will hardly be able to persist much longer in their too common attitude of ignoring the evaporating power of the air. As we have emphasized, this climatic feature is probably as important from the standpoint of agriculture and etiological plant geography as either temperature or precipitation, and its investigation seems likely to be carried forward first by agriculturists and ecologists. While it is possible to collect from the literature numerous instances in which evaporation has been measured at a single station for a longer or shorter period of years, such measurements can not usually be correlated with those for other stations, either because the same years are not involved or because different kinds or sizes of atmometers have been employed. Aside from such cases,! which are all valuable—at 1 Most of these cases are mentioned in: Livingston, Grace J., An annotated bibliography o evaporation, Monthly Weather Rev. 36: 181-186, 301-306, 375-381, 1908; 37: 68-72, 103-109 157-160, 1938-199, 248-253, 1909. 292 ENVIRONMENTAL CONDITIONS. least in showing the importance of this climatic condition—there are available just two logically planned series of atmometric measure- ments in the United States. One of these series was carried out by Russell for a single year, beginning in the summer of 1887. The other was conducted by the present writers during the summer of 1908. Approximately 20 years elapsed between these two series of observa- tions, and no thorough study of this feature has been completed since the last-named year, although the U.S. Weather Bureau is giving in- creasing (but always secondary) attention to evaporation. It should be noted that the United States Signal Service, the precursor of the United States Weather Bureau, carried out the earlier of these series, the second series being under the auspices of the Department of Botani- cal Research of the Carnegie Institution of Washington. These two series of atmometric observations, and the results derived from them, will now be considered in order. (2) RussELtu’s Data oF EVAPORATION IN THE UNITED STATES. Evaporation intensities for period of average frostless season. (Table 11, plate 53 and fig. 14.)—-Russell’s! study of evaporation extended from July 1887 to June 1888 inclusive, and this author prepared an evaporation chart of the country, but the data thus used were cal- culated. For the period from June to September 1888, Piche atmom- eters were exposed in louvred instrument shelters at 19 stations. An experiment in a closed room, employing two Piche instruments and two open pans of water, gave data from which Russell calculated that the Piche instrument lost 1.83 times as much water as did his free water surface.2, By use of this ratio the readings of the Piche instruments in the louvred shelters were converted into losses from the free water surface of the particular kind of pan used in the labora- tory test, and these, as tri-daily readings, were compared with the corresponding dew-points and wet-bulb temperatures within the shel- ters. From this comparison Russell derived a formula by which he afterwards calculated the evaporational loss from free water surfaces in the shelter, for 140 stations in the United States. In his paper he presents a table of the monthly calculated rates (July 1887 to June 1888), and also the annual totals. In order to make use of these data in connection with the length of the average frostless season, as we have employed the latter, we have proceeded as follows for each station involved. The evaporation data for all whole months included in the average frostless season have been 1888. See also Kimball, H. H., Evaporation observations in the United States, Monthly Weather Rev., 32: 556-559, 1905. 2 Of course this relation must vary more or less markedly with temperature and humidity conditions, even where the wind influence is out of account; but Russell seems to have ignored this consideration entirely, along with the other important consideration that the amount of evaporation is dependent on the sort of pan used. PLATE 53 ‘Z oyed sroseqoyy, ‘soouraoid uorye10dvAo INO} 0O7UI dvul oY4 eprlAIp SOUL] [[NY *Z WUINOO “TT o[qvy WOA] BVP “MTOSBOS Sso]}SO1J OSvIOAG JO potsod OJ UOTYeVIOdvAD Jo (YOUL UB JO SYypUBSNOY}) soye4 A[IVp UvOLy alo} us91FIaAa uot}IeUue sy oyAydosB Ay ySa10} snonpisep d1jAydosoul wreyyON -purlsse1s) == Se WA ys070} 21Aydosew ui9jyseayynNos purisse15 (4s s010} at S83 11W 009 Tra ct a i | 7 “% % {> ‘al 1 me =e af SSS Sz dite y < Ze NS SS RY WS QO \\ . , WW SARA WX AW AN 5 FEO CF NUS QBN SRG AUN N22 Re Ag NX ; vas g 5, Sy bP. An ‘Y WOW; 0G i Lite, ies B DY > fa ee 4 We Ne “ey no i AD) x RRA ESS WSs SSS ~S NE arene “SS hs SS N N NS SS KAR . Cy EMSS 7 Se aK SNR Z C aeioga ee ae paz S YS c x WN SN we . >< TANSEY ANS esas AP NIETO LISS TERS ASS | ae eC\ | BB ores OE sae ane pes aN pol geok. —-9Sb — .LZ1 a /\_. ek 69 Ah 82 OL oh OL JS 88 8 .£8 68 .16 86 G6 26 .60 JOT 20% GO .40T GOT [II SIT (STE .£1% .6IT PLATE 54 294 worye10dvAs Inoj OFUT deur oy} OprlAIp soul, [Inq “¢ wuINjoo ‘GT 9148} Ino Ul UsAIZ eyep SSW 009 008 U EEA Ss ar a EX SS are SS ; SE : Ge 2 er D iz rea a! A \ as\ \ SRN ANY WS ‘ \ es Lean ‘S , Sooo Nes SS SAW 777 damm or eat Neat vr) Ag ‘YG, Ee y v= x St 4 ot Ue % eee = Sf \| 5 LWiay, GOD We eats @ = ee = A= 5 = was 3 My, ra Wil —, N \ i il mater eee LV [R 4 348) Ses ew el San Oy 1a ik | DS 69 COU erCOUMmCLC oot 6= (8k 0S ohh SC LSCKTSSsi‘«c BBC] (Cs«C«@KS COB SCCCG ren mole a ld S6 a ESS Ss & Sy zune AO Ns . 1: | IBID) J Ny \ ds iK ~ ST OSVQ OU T N . \\ iil | ih Th ADeo.| te? vi YY \\ WG, ¥, ,o > \\at ‘\ SS \ AS DA = = e 9 2 tes ot 6 L686 66 — *gOQN0TT 5 =}e < ey NSN G777 2 . SY ENN) “ WLI WENN ZF GZ re Pa 7) ea WANES SERN SAW HABA : ee 7 YG an Y ae N S <7 ss PP SSN . Ix 4 5) SNE HOU LOr .G0% LOT (seq) YSd10} UdIITIOAD SnAydosow wy JON 8 Jjessny ‘(Soyour) sonjva uoNeiodeAs yenuuy on Aydosaw ussyyJONy POORER] Ps!) Ge 9 G7 © Gs CLIMATIC CONDITIONS OF THE UNITED STATES. 295 summed, and to this sum have been added two quantities, representing the evaporation for the two fractional parts of a month at the beginning and at the end of the frostless season, respectively. These added amounts have been derived, in each case, by dividing Russell’s evapora- tion-rate for the month in question by the number of days in that month, and then multiplying the resulting quotient by the number of days of the same month comprised in the period of the average frostless season. The total evaporation for the season thus obtained is next divided by the number of days in the period of the average frostless season. Thus, for example, if the season extends from April 24 to October 3, we sum Russell’s monthly rates for May to September, inclusive, and add to this six-thirtieths of Russell’s rate for April and three thirty- firsts of his rate for October. We then divide this total by 162, the number of days from April 24 to October 3. The seasonal totals and the approximate average daily evaporation-rates (1887-88) for the period of the average frostless season, obtained as just described, for 133 stations, are given in columns 6 and 7 of table 11, and the latter data are spread on the chart of plate 53, where the positions of the stations employed are again shown by small circles. It should be emphasized that Russell’s data for June, and earlier, refer to 1888, while those for July, and later, refer to 1887. We have merely made the best possible use of the available data. The isoatmic lines of this chart are drawn at intervals of 20 thou- sandths of an inch of average daily depth of loss from some hypothe- tical pan of water, Russell’s measurements being in such terms. The total range of values is from 52 (Tatoosh Island, Washington) to 349 (Independence, California). On this chart of the approximate average daily intensities of atmos- pheric evaporating power for the period of the average frostless season, from data of 1887 and 1888, it appears that the isoatmic lines in the vicinity of the oceans have a very pronounced north-south trend. They also have a north-south direction in the plains region. Little relation to latitude, or to temperature, is here discoverable; during the frostless season temperature is not usually a prime condition in the determination of differences between different stations in the evaporat- ing power of the air. The lines for values 120, 160, and 240 are shown on plate 53 as dis- tinct from the others, and these may be taken as dividing the country into four evaporation provinces. Following our usage in the case of the precipitation indices, these provinces will be termed arid, semi- arid, humid, and semihumid. They are shown also in figure .14, which is derived from plate 58. This zonation is different from that shown for precipitation in several important respects. Here the humid province (values above 120) appears again as a western and an 296 ENVIRONMENTAL CONDITIONS. eastern portion. The western portion is much larger in this case, how- ever, occupying the Pacific Slope for practically the full length of the western coastline and widening at the north to include about the western half of Washington. ‘The eastern humid region has an entirely different form from that shown on the precipitation charts. Here it does not occupy the southeastern part of the country, but embraces the northern margin from about the one-hundredth meridian eastward. It also occupies portions of the Atlantic coast as far south as Cape Fear. It appears that the line for value 120 passes into Canada from Wash- ington and reenters the United States in North Dakota, so that these two portions of the humid province are probably to be regarded as a single one. It should be noted, furthermore, that the Atlantic coastal portion from Massachusetts, or New Jersey, southward appears to be separated from the northeastern portion, and that a small area of humid conditions is shown about Corpus Christi and Brownsville, Texas. These features will appear more prominently on the charts of pre- cipitation-evaporation ratios and on those of relative humidity, to be considered below. The arid province (values above 240) occupies much the same region as in the case of the precipitation charts, but it does not here extend west of the Sierra Nevada Mountains. Of course, the western mountains are largely humid, but our charts do not generally present such details. ‘The semiarid province (values between 160 and 240) occupies a belt outside of the area of the arid province, and this belt is extended eastward in the middle of the country nearly to the Appa- lachian Mountains. This eastern lobe of the semiarid province will also be pronounced on the charts of moisture ratios and relative humidities. The line separating the semiarid from the eastern semi- humid area (value 160) does not here bend eastward at its northern end as it does on the precipitation charts; on the contrary, it here bends westward and apparently joins the corresponding line which enters Canada from western Montana. Annual evaporation intensities. (Table 15, plate 54.)—Russell’s table gives the yearly totals for his series of stations, in inches of depth from some hypothetical pan of water, and he also presents a chart to represent these annual data. The data are reproduced in the third column of table 15 and they are shown graphically by the chart of plate 54, which is not exactly the same as Russell’s chart, a number of obvious errors in the latter having been corrected here. The total range for the country is from 18.1 (Tatoosh Island, Washington) to 101.2 (Fort Grant, Arizona), and the isoatmic lines are placed at intervals of 10 inches, with full lines for the values 30, 50, and 80. This chart has a pronounced general resemblance to the one repre- senting evaporation for the period of the average frostless season (plate 53), but it differs quantitatively therefrom in several important 297 PLATE 55 ‘Z aye[d stosvq oy, ‘seourAoid uo1yes0dBao IMOJ OFT dvur oY} OPlArp souy [Ny “9 UuANjoo ‘FT 9[qQvy Ino UO UOATI BYP SJJoSsNY ‘sy}UOUI JOUIUINS 9914} IO} SoNjBA UOTyVsIOdBAD [B40], 38910} u901Z 199 uoljyisuey 4S210J Uud01919A9 S910} UZIIDIDAD oAydoiZ Ay yH10} srlonpls9p ~puelssriy oIAydosow usoyyIOoN §«=—-_-« 9 .AYydoseur wiayy0N es ies Hi HH Uy 48010} 9nAydoseuz UJ9}SeIYINOS AX (4seq) (199M NOY eS -: 75 3 ec tre Z 3 ‘ : V8 ‘ 4i2 4 R e. j A Z SS , wal ¢ 72x a ee. Sah Wg 18. f Z * } : ORL AUN NEN 3 Stolen, Tal \ fee ; \ A wy e ] Bet ee c \ SY oS . \ y} » 7X5 i ; ¢ ji a if os ars A DY x AWW ~~ N x RS yy) 4 Oo : ~ = 2 * \ 1, iY aZ4 AA na if 2 eS x] > y t y, 754 d a , Nw eo ‘ S V Z d , re Me 5 1) Z A ites \ | p a SA bs EWS Yi ARDY, Nie : \ ‘ ld = .) x NOAH, > We "" vi , et ty, i 9’ 4 Pp C2EES <\ y GY; OG SOA LI I NS SREY 4) SS SANS wa D LA Ses i) 4. ts RAS ‘ Bee Ne 4 z uJ ae i/ Yan 2 SSN 6 Ma Pay D . a a . J f Sh 4 nai 4 —S eu e i ¥ BS 4 g coed re - " ve i 7-3 ; x A SO : . aed i { nll NS ‘I ALD is < if 7 tail! ol . t XS Fs ash eS as Figs one oO” SAN wa D pa EN ey 4 ee P 5 = 4 4 = 7 4, J é pe ]e STS Z as > : : 2 gf be a 3 ¢ fj é SS Ofek 2 d Z J 3 1 an hy ‘ 2 = = = ALAR va r aaa A Z g YAR pes Lif, pe 4 é p u SG p a / - es ya Q 4 ~ ie, ~ : 4 7 - == me Ta ® 4 BOK s 5 g wi RS sof MK i : 2 eer! = 4 a A ra CG Le LG) 4 Ox OF Beri ooh ‘iis I A , ds 4 4 4 y! q e i Y 4 . P Me, Se 2 = r ; 4 AL Pes $ f + vere! <4 K "A Ie tn aren 2 ‘j SOI SEE oe + Eee 0% b ESS <7 on £5 950 eee ~ <= aa 0 Orgs a Y ed tmigias inl is So == Dy ee ak =a WN ww L ee ( a 4 28 69 6 <6 Z ‘ é fe 4 Snr | - sivas $2 Clee He ss 298 ENVIRONMENTAL CONDITIONS. features. The northwestern portion of the humid province (values below 30) is less extensive, and the Pacific Slope is here depicted as in the semihumid province. The eastern portion of the humid province appears here about as in the case of plate 53, but it does not extend southward farther than Rhode Island, on the Atlantic coast. The arid province (values above 80) is here shown as smaller than in the pre- ceding case. The great eastern lobe of the semiarid province (values between 50 and 80), reaching nearly to the eastern mountains on plate 53, is not present on plate 54, but a large area of values above 80 is shown as extending from St. Louis, Missouri, and Louisville, Ken- tucky, to Key West, Florida. Evaporation intensities for the three summer months. (Table 15, plate 55.)—Because we shall wish to compare the Russell evapora- tion data with those obtained by ourselves (to be considered below), and since it is impossible to employ the length of the mean frostless season as duration factor in connection with the latter, it is expedient here to study Russell’s data for the period of the three summer months, June, July, and August. For a period approximately comparable to this our own data may be studied. TaBLE 15.—Precipitation and evaporation data for the year and for the three summer months June to August. ee ae ee 3 rb ats 6 a te * 36 &% - = So a=) re ae @ a ie 4 ® he ° & 8 as AN a 5 e iae : “ |£$¢ p> AVY fe} “5 wo aa eae ae wo Ao O78. [oo s 5 =) 35 Ry “KR joog 5 <= aa ow ww es) Station. a ae © Ao et s aS) = @ ~ Ss l s ~ g ‘= ras} S qa ol q ae 3 a 5 36 Bo |868s 6 re Oo 0 Ras s Re a = ~ oun a 8 > ., mn > on EAN ee a5 | 5. \eecn aa | °S |S fae | we loses} #8 | 38 los sais aS Soe 8 el a eg (Ses Za & fam Z fon] Alabama: inches. inches. inches. | inches. ADTISCOM hoe ais ae 2: AO SO Alii ey Oh nln ble Rent 13.09.01. oo oe Birmingham. i oe ie AO RAB Riel ENE a Bae he, 13:06. | 22.4505 NEG bUe ey Pe eRe Eee 62.04 42.1 1.47 19.80 12.7 1.559 Montgomery.............-. 51.16 56.6 0.90 13.13 14.6 0.900 Arizona: Fort Apache (S3)........... 18.90 65.5 0.29 7.28 22.9 0.318 Port: Grant.(S3).< 2h 14.24 101.2 0.14 6.12 36.7 0.167 IPHGONER iF rae ole sete veces TOE AN REET) See ole 2. TS hs oe nce eee Prescott (S4) iinet yee Se ase 17.40 56.0 0.31 6.29 21.2 0.297 NGL DE 60 be Yates eae VLAN aren ancy aan 3.10 95.7 0.03 0.47 33.8 0.014 Arkansas: Fort Smith oo ee ook Geta 41.34 49.6 0.83 11.50 14.8 0.777 Tittle Rock: 25.28 es Skies 49.89 51.7 0.97 Lives 15.4 0.762 California: Cedarville (S15)............ Be ae Wee a ; 14.58 48.9 0.30 122 20.9 0.058 : ) : | | CLIMATIC CONDITIONS OF THE UNITED STATES. 299 TaBie 15.—Precipitation and evaporation data for the year and for the three summer months June to August.—Continued. s 5 |8o & A |e ae "A 4 ae a j= ‘3 (Sp = Be eee © Fe Bae = 09 aa 2 Pah = fe) Sa . SS z a £ ht =] s =e on ta 3.8 "2.3 < Ry Bog : 2 Sf 1ER cS A oe Station. q 8 I S c Ew A te 3 2 33 & ae ta aa = SB o> arty 3 be Sas 3 Aili | a8 | 88 (Ess 3 2s |3e NSH mie (een S his Bs > o a5 - Sule ce aay hea) boo fe gos as | ae lecSS] gf | a8 loi sale Ba oo |e | 83 Sg |S aswN 7, S ee Vi Bi a California—Continued: inches. | inches. inches. | inches. PUREE nats aes leah anes Sal PUSS AT YES lI OSI oh SN inary edema 147 AA A on ea res) Par RS ON 9.73 | 65.8 0.15 0.10 | 26.3 0.004 Independence.............. ELE yea ie gk ais annahal a, 9.53 | 100.6 Hibs foe eet Je Mos Ameeles!... .. Soils se Be: 15.64 | 37.2 0.42 0.07 | 10.5 0.007 BECOMES hos. ay ee 25.03 | 84.8 0.30 0.48 | 28.6 0.017 SacramentO..... 2.55.0... 55 20.09 | 54.3 0.37 Or L6rh) heat 0.009 BameMiera. 466 10.01 | 37.5 0.27 0.03 9.3 0.003 San Francisco.............. 22 Fl SON? 0.61 0.18 8.0 0.023 BAGMIGSE alas le ee PRA APAD His GE Pie oeslane OPW ao elas Po arses San Luis Obispo............ POG) Gd IN DE ION oacsicueec cre LO Ue ae er Sac ta i Colorado: Colorado Springs (S7).......| 14.28 59.4 0.24 6.82 18.2 0.375 MBE OTN cies Scie se vice 8 14.02 | 69.0 0.20 4.43 | 27.3 0.162 Montrose (S9).......05.2.. 9.54 | 68.3 0.14 2.56 | 29.6 0.086 16 LEO AA eae eel ee PIO Yy Gea WF. cocke ie te, ahs CUS aS ice OME ree tOe Connecticut: PAGACULOTO Seale ee Ske d whals cs yarco 5 LON HD ae NL ae NO PERO U Se ate Mita ee vem TAVEN Sk ol oa Uo A719" | 34.8 1.48 12.94 | 11.6 1.116 New London (H)........... 43.80 | 31.8 1.38 9.90} 11.3 0.876 Florida: DRCKPONVINE Le we es 53.25 45.7 1.17 17.94 15.0 1.196 cl TEN C7) CAE Ba aR COMB aM eran en oer ee: ys yee Sa ee ae | oo LEQ" IC: A 38.66 51.6 0.75 12°53 1) 15.0 0.836 New Smyrna (S83)......... “Thine Ait AN sluipseaar A hes phlei tora alan eal WOMGROOl a i) te a 56.25 48.8 Pers 19.30 15.0 1.287 Cedar Keys (S83).......... 51.53 49.5 1.04 24.24 15.6 1.554 Georgia: PACT Penne ase t ter eke tM Saks St 49 .36 51.5 0.96 13.09 14.2 0.922 PAEPUIS EER Sh Scarves Crd els ore ciate 47.89 49.3 0.97 15.39 14.3 1.076 PTAROM RS Ath Pac ck, ators eidievess ACO, Sut) eo enc a 3 F240! hv coeeue Te ee « HERRON E80 ca Ee 50.34 46.0 1.09 19.71 13.5 1.460 | Whomeasvilles 4... 666i... UN Ue Sf dha aaa EP OA We ce BOCOe? le cate Phan eae Idaho: SoTL Baer a et OU 19.20 G89." |). 70. 20 1.22] 25.8 0.473 | MSQOISCOD cb cco acc mck es artes 1S he! oe ea | Sea ca On DBS Pete, hi eae a | HAOGHUGHO isd \iacicaie gals we UTS 1 Gok ds Mig | eg a ae BES oA eer 8? toveee: « Tllinois: | GBIPOR ie Wy ein ales Oe cates 41.71 48.9 0.85 10.69 16.4 0.652 | La Led ogy Te Ne An 33.28 36.8 0.90 10.18 15.5 0.657 | OPA SHULER Oui hata a cit toe ee oie SIRE -UNEE | ea | eee 1 Rb A a PROT can acres Wain wale 4 NRO eta eke de aia Store: « Se Rhee Ok nk wine 300 ENVIRONMENTAL CONDITIONS. TaBLE 15.—Precipitation and evaporation data for the year and for the three summer months June to August.—Continued. 3 |. |gse [48 [ts legzas a Paula ‘8. CO, | one ae 2 oS I BS = 2} a . =) S ee a et ak gS [fee of ane So Sax a& £2 aa felg oe =a Pee Station. S2 | Bt hee Boa a8 eae ra | #3 (886@ | SS. | 25. | eee on > 00 a= > © Pe BF & O-> [Sen S A fa | PO eRe tT |g | fag os eee pe | os [S282 | £88] ese lobes eek mae o”™ ged A S) = Oo 20 53 8o aN EY jam Zi HH any Indiana: inches. | winches. inches. | inches. Evansville......... UG SA ae a iecgec dk oll oos os ct eee 1122) | Si ka | eee Indianapolis....... 41.48 48.6 0.85 ath rare 20.3 0.580 Iowa: Charles City ....... 24) IAN ae B® 2a ete | meen aoa Re IO oe oe Davenport......... 32.69 39.0 0.84 11.30 a fea" 0.639 Des Moines........ 32.45 36.0 0.90 4S 15.5 0.802 Dubuqie:; 2.42 34.01 One 1.02 11.89 1522 0.783 Keolales 25 fae ses 30.07 42.9 0.82 G2 18.1 0.642 Sioux: City) .cns > coe DOO Meee she t|en\c caver eelee 10.49 ae Ee Kansas: Concordia 2.2... 27.40 47.2 0.58 11.40 18.2 0.626 Dodge City ...5 .2.. 20. 84 54.6 0.38 9.29 Does 0.417 MODES. ice eet 33.76 36.1 0.94 13.95 13.9 1.004 NWWiehitac shoe ac ae (5 Let pe ae eed See ea a VAS | occ. A eee Kentucky: Gexineton. .. 2. .22% AO ASU cen ee i ae eee 12.000 222 On ae Houisville: cs. 28 44.33 54.8 0.81 11.58 20.0 0.579 Louisiana: New Orleans....... 57.42 45.4 1 27, 18.24 12.5 1.459 Shreveport......... 45 .68 45.6 1.00 9.54 14.3 0.667 Maine: AStDOLb sce. aes 43.27 2502, Lav2Z 9.92 7.8 1,271 Portland? 32s 42.51 29.7 1.43 10.18 11.0 0.926 Maryland: Baltimore. ¢ oi... .% 43.18 48.1 0.90 12.87 16.6 0.775 Washington, D.C..| 43.50 45.6 0.95 sees 16.3 0.812 Massachusetts: IBOStOn = 28> ose 43.38 34.4 1.26 10.42 13.1 0.796 Nantucket... 37.00 25.6 1.45 8.14 9.2 0.885 Michigan NIDEN aS Viens. aes 33.20 24.3 130 9.95 i fa Peak 0.896 Detroit so ks oes 32.16 36.0 0.89 10.14 15.9 0.638 Hiscanaba...ccces. oak 371 Nea) Boel A ae ae kl (aera cee 10250 sci 1 eee Grand Haven...... Bla 87/ 28.6 1.10 7.67 1223 0.624 Grand Rapids...... oH tbat eee ede A eae Oe CAEN oo oe eel) ee Houchtonsg 1. sce BONG ee eee oo os ce Ne 9546 We a ES ee Lansing (S63)...... 30.99 270.6 1.12 10.10 ioe 0.828 Marquette.........| 32.63 24.5 iL 38s 9.47 10.0 0.947 Port Huron. 3.5.0.2. 30.65 29.3 1.05 8.61 12.6 0.683 Satlivotes Miarie. Site geen nn seeded) tte. 0c te Sie 8.66) «:...... | eee Minnesota: Wombat 2 eee ak 29 .93 Pea) 1.30 i baal 9.8 1.196 Minneapolis....... DO ONO I) “core. AN ieee ac ce i ass A eran eee Woorhead) 2)... 24 .92 26.3 0.95 10.97 10.8 1.015 hei raped B22 0 Legge gel i ei 28.68 28.1 1.02 11.27 tae 0.883 Pembina (857)..... (Gp ema. \ 20.31 22a 0.92 9.04 9.6 0.942 Mississippi: WMerdian of. ooe058 ONY eee Meg a ete POUCA. ccs a kee Vicksburg. Jee 2.5 53.74 47.1 1.14 12.44 13.8 0.902 CLIMATIC CONDITIONS OF THE UNITED STATES. 301 TABLE 15.—Precipitation and evaporation data for the year and for the three summer months, June to August.—Continued. ak Ae Nee Be. | 2h [Wak ar ot sa | feu | es lane |e0es® ae Bo Ea bei By 2S Ean a Station. £8 Seesaw |e eles lie Ss ra Oo Aas eae | Ber, REE ce = 00 Ko 0 Pon 3 O-> wea BS . iS: oi 32° © — 8) Sap |e se" os aaN~ ae | er eae | aad |. 4a lone ee ck Sa) ee lene 2 eee | sae [esas oN Zz H jen} Z H law) inches. | inches. inches. | inches Missouri: Columbia. ......... OO NE Bina aii etis be Gn chat MONE Ni) sacri ee a fees og te Mannibal. i) 2) ARTZ Oi Se hombre Wie cL 8 EORGOmh ce cles fi irekp nhs Kansas City oi). 062. (Leavenworth, Kan.) 30-28) | 2120 0.90 ae ae pee Lamar (S49)....... 41.24 39.6 1.04 13.51 14.6 0.925 BG Ouls. fF.) 37.20 e202 0.71 10.56 20.5 0.515 Springfield......... 44.57 | 38.3 1.16 14.29 | 12.4 1.152 Montana: Crow Agency...... er Custer\c. 14.56 52.0 0.28 5.04 22.5 0.224 MAINTE ssc gel odie fie Secinibome) 13.67 39.5 0.35 6.00 16.5 0.364 Helena. oo ks Ss Lae, 53.4 0.24 3.87 20.4 0.190 WWalispell: 2. c/s e gO A Ne Rt A SE itertots ew laid eeceadere Fort Maginnis (S30)} 16.52 | 35.8 0.46 5.20 | 16.0 0.325 Miles City......... J B33) War ROP Sipe eS OER G al cooralet ver ii sae teres Poplar (S30)....... ne ; 13.59 | 35.4 0.38 5.66 | 16.5 0.343 Nebraska: KETC (SO1) oo 0is . Os 29.06 35.5 0.82 13.02 14.8 0.880 Mamcoln . 06k. ed Per icra Wiel eins, ah ane Ce ea PE SSG he ee SS Vey Anil iy Beaton Bee North Platte..... 18.86 41.3 0.46 8.39 Mee? 0.474 Omaha i eck. 30.66 41.7 0.74 13.00 16.6 0.783 Malentine.. 0.6. 22 22.46 43.8 0.51 10.03 Lie? 0.584 Nevada: Heenan na eau TOWAS Ci Sa Ro SOIR Sy Ce aes QHGS) hi: Sass ono Ute ae coal Winnemucca....... 8.40 | 83.9 0.10 0.98 33.6 0.029 New Hampshire: : chester) ee \ 40.11 | 33.3 1.20 10,87 | 12.4 0.877 New Jersey: Atlantic City...... 40.82 Zone 1.62 PL ky 9.8 1.133 Cape May........ AOS CAE e Galen Carat ae DOSS! fe ecte a Adel Sees ae. New Mexico: | Fort Stanton (S2)..| 16.70 76.0 0.22 8.07 S19 0.253 Samte Fe. oc eee. 14.49 79.8 0.18 6.11 31.9 0.192 New York: CITY oT yaa 36.38 34.8 1.05 11.62 1432 0.818 Binghamton....... 2 Ae FT ROPES nl (rm | eS Oe ie ae a CM PORE Oe MSUNALON cca jore es se 37.28 32.9 1S; 9.53 14.0 0.683 CO aMCOD GH Beene Se AGES THD sarevaeecmraly cobhede Gals LTRS La ppceedil, eeu MAP emer et ad 1 Ero) a1 Ck eee ce SN Cae tattle NTL Ac Veber eua: PO RSC) be ces. co A) eee INTE WOT a whee aus 44.63 40.6 1.10 12.33 14.8 0.834 WEWERO. hii Sh ewe. 36.18 28.9 1.25 9.35 A 4 0.799 Rochester......... 34.27 32.4 1.06 9.18 13.6 0.675 SISTACUSB yt llc uae. SG EF ERE RR ee | A Sa OBR 3B ash, oat et eee inte 302 ENVIRONMENTAL CONDITIONS. TaBLE 15.—Precipitation and evaporation data for the year and for the three summer months» June to August.—Continued. —= — ! h t fn 1 ie-_- t i ae gee See oe) eg eee Spee : I S ox aerorr as as =| ag = “ a oe) s as 2 By a = L : 3 4 + So 0 1,2 SA ee) a aes I | Se eee aA SO | eeoais | Loa) 8a | eae ; + 2 Srl Bam BC Se ae ee Ai“tss, a Station. as as ages ont | 28 a 8-8 = > oO Oe Pam! Sh [e.g 8 ? eS, 2 tS ey. ee a RS Pe ane a ~ 2 | ai | e8e es | ga2!lad-loeeeeee Fe | $2 | 36a 8 | Bee | $28 Soe 5 eS ZA = = Z a ee North Carolina: inches. | inches. inches inches Asheville: 5352.4 5oh AQ pee cuets ok tien eee 14.00 [oo 2 A Charlotte? 2.4 23.46. 49.20 49.0 1.00 15.50 13.8 1.123 Hatterass2.5. 202222 60.85 S158 1.94 16.30 10.4 1.567 alee. oN soe 49.60 37.0 1.34 16.73 1228 1.307 Wilmington........ 51.05 38.4 1.33 19.10 112-7 1.632 North Dakota: BisMArelken. ak 17.64 31.0 0.57 7.66 13.9 0.550 Devils Lake........ (Fort Totten)...... 20.16 A (ae 0.74 10.07 11-7 0.861 Walliston. 3.) 4)... (Fort Buford)...... 15.07 35.5 0.42 6.91 16.1 0.429 Ohio: Cimeinnatis: 2. Sy as: 52.0 0.72 10.85 19.5 0.556 Cleveland.) o's. 35.04 Ba 0.98 10.38 14.5 0.716 Columbus: 220. 22:5: 36.92 47.8 0.77 10.36 19.1 0.543 Sandusky. 2.55... 34.02 | 36.6 0.93 10.98 | 15.4 0.713 oledow:.)k- ae ae he 30.62 38.6 0.79 9.32 17.0 0.548 Oklahoma: Fort Sill (S41)..... 30.85 46.1 0.67 9.83 16.7 0.589 Oklahoma’ 3.222 paar We NS aol Se eA a) ae ce Se 9:39 |e Oregon: Astoria, (S17) sac... 152385 2are 2.98 5.62 8.6 0.653 BakeriCity..).2 ae DISET HES ea ic MM ee 22038 bo eee irortiand::.!Orono?! .. ste ee motes La) UR Weer Wis ec ied HAO ba 1 en ll es Al ee er 2s AN eB ace Reap ns 0 0.00) 124 (3) Manitoba: Winnipeg.......|..... 1/3 Ue eS ane VWB9) ed SWE OQ, Ee a cia ee 124 (3) Maryland: Easton?........ 0.02} 98 | 0.05 | 106 | 0.08 0.32] 120 | #7 | 102 | 0.09] 98 Michigan: Grand Rapids.c%..1.5).8 OFO0 154) O03 i) T2663) OeG2 TOMES. os oles cel cutee cacpe a ene 0.25) 119 (8) Houghton. 52 A028 oe 0.04) 172 | 0.15 85 | 1.87 2 BA MS |e aoe |e 0.69] 111 (3) Stmtelem yrs Sh eee 0.00} 297 | 0.00 | 237 | 0.47 O200VNTO' | 3: 2 30 eee 0.12} 236 (4) Minnesota: (Minneapolis... 2123723) dane, oS OMIM se be OR ci a ee ee ea 3.23} 174 (1) Missouri: St. Louis........ 700) AAO O6F 149 ed USE a BI. SL ie ola cpa 0.03] 160 (2) Montana: Bozeman....... ORCS HAT ONO SSH dT oer eke. UI ee cee ne ee 0.22) 139 (2) Nebraska: Himeoins). \Gos0 VOY ae eo 0.00) 85 V0rs Toa, WSO OL Shall A208 aol. Bee eee 0.17) 165 (3) North: Platte 6... 5.44 FD AZOG ENO OOM 209 Fe fogle Ae le et 0.00} 208 (2) Nevada: Reno............ OOS se ORS le ieee: OOG i siete el sees Tne as I | OD eee res New Brunswick: Fredericton! 0.13] 63 | 0.00 SAS On MA eA yeas ok ea lee 0.08} 64 (3) New York: IWeweVork: 0 tiie sk 0.00} 80} 0.00 | 101 | 0.00 Oa eds ChE: de tis Aan ea een 0.00] 71 (8) Syracusen. (ee cee cee 0-00) Site * Bi 294° jan4 2 QT5 Ui LOO. ore OU SAL 0.00} 293 (38) North Carolina: Pisgah Porest:. 2s ie SANs. ae D272 500) 2 ae eee Re Nk Cena (>| ee Ve Aa eee ee Mallee WS 124 (1) West Raleigh.......... 0.00} 76} 0.00 | 108 | 0.12 SoRIO LAS INGT hc kole aewere 0.15} 91 (4) North Dakota: Dickinson?.| 0.02] 273 | 0.77 | 269 | 0.84 7G 7s Nees ene mee teanal PAR ACS re, (hs 0.54} 249 (38) Ohio: Oxtord)) odie ie 0.00} 233 | 0.00 | 185 | 0.36 11S (2) 0) ge ih even ARH AE 0.12] 206 (8) Oklahoma: Stillwater...... 0.00; 95 | 0.80 (a Ae ot 52 | 0.00} 90 | 0.60} 90 | 0.54| 80 Oregon: Eugene........... 0.00; 1388 | 0.00 | 112 | 0.00 128) 4-0. 23) 102 se eee 0.06; 120 (4) Quebec: Ste. Anne de Bellevue...| 0.00; 108 | 0.02 |..... OZAO TD etek OER er oo all 0.00} 108 (1) Saskatchewan: Regina.....|..... LOLA. 2 BOP Ne sou FO RAE ole sites 0 [it oe 75.(C) Tennessee: Knoxville...... 0.00} 94 | 0.00 97 | 0.00 106 | 0.24) 141 | 1.32} 81 | 0.31} 104 Pexas: )Dalhartis: se 2: 0.00} 538 | 0.19 | 426 | 0.05 ALO, «del on. tls | ene eee 0.08] 481 (3) Utah: Salt Lake City...... 0.87| 107 | 0.06 | 141 | 1.79 (0153.9 tO )RPG5) UN eee) Weems Ue 0.91) 104 (3) Vermont: Burlington...... 0.00} 186 | 0.01 | 172 | 0.00 1S YS5 ay CME 9 Pd NSO NR! 0.00} 171 (3) Washington: Seattle....... 0.18} 89 AE 55 | 0.04 55) | 0.50) 42.| 0.31). 15 “nOezt ieee Last 3 WEEKs (Ocr. 13 To Nov. 2). Oct. 13 to 19. | Oct. 20 to 26. OS 27 to Average. Station. ON 2: iP E an. C.C. CalifomiiasiSanm Dieses a aici kee eee ke 0.51 119 Blondes Mirani co salen t oe ee clea hs oa) 4.28 103 Bi me@isisss Wiloa wey Be ooo es ora ah iy ie aT 111 Maryland: WBlastome: fice be) eee eles fee 0.00 122 ennessee| Kioxville goes so Ue 0.00 108 Washinaton: Seattle: oii) ae wi a wale ci oon 0.96 15 ™ Much interpolation on account of anfrequent readings. CLIMATIC CONDITIONS OF THE UNITED STATES. 311 Summer march of evaporation at selected stations.—The variation in the intensity of atmospheric evaporating power as the season advances at any given station is surely of very great importance in determining the kind and extent of the corresponding variations of developmental changes occurring in plants. These variations are therefore of consid- erable interest in other ways than because of the general novelty of atmometric data. We therefore give, in the following paragraphs, a short discussion of this feature for each of the 10 stations represented by the graphs of figures 3 to 12. These graphs are of gradatory form and each one is double. The upper graph of each pair represents the weekly evaporation rates (in cubic centimeters) from the standard cylindrical porous-cup atmometer, and the lower one represents the weekly precipitation. The dates given below, in each case, denote the endings of the consecutive weeks of the series, and the numbers on the graphs themselves are the ordinate values, representing cubic centimeters of evaporation and inches of rainfall. The features brought out by these figures will now be considered. (4# 2b 28BATS /2 9 Fig. 3.—Weekly precipitation and evaporation indices, summer of 1908, Seattle, Washington. 230235 LVAPORRTION 2/4 /29 aoe pre 164 16 ReVoT | 5/ 13 PRINFALL 2 00|.00\.00|.00}|.00 |.00 el Pe 00 |.00 |.00'!27) .00\.00[ —}.00|.00 & 00 |.00 June2@2 29uy6 13 20 278063, 10 19 24 GISER? t# 21 28QAFS s2 19 2ENOK2 Fig. 4.—Weekly precipitation and evaporation indices, summer of 1908, San Diego, California. Seattle, Washington (fig. 3): In this graph the intensity of atmos- pheric evaporating power attained an early maximum of 200 c.e. (week ending July 13) and then fell generally to the end of our series. The weeks ending October 12 and 19 showed an average rate of 15 c.c. per week, which is the minimum rate encountered, In the latter alo ENVIRONMENTAL CONDITIONS. half of our period considerable precipitation occurred. It is to be noted, as is generally the case, that weeks with much precipitation are phe iereeaeed by low evaporation intensity. San Diego, California (fig. 4): For this station the weekly rates of evaporation show a striking uniformity for the period, with a minimum of 119 c.c.anda maximum of 264 c.c. The period was nearly rainless. EVAPORATION aie 167) | | | HAL 90 |.00 |.00 |.00 | T |.00\.04| = | War 25TuNEl BCS TUYVE—Oo—i 2 2G F 70 7 24 B3WGEP? /4 , | | | | RAINFALL. Fic. 5.—Weekly precipitation and evaporation indices, summmer of 1908, Tucson, Arizona. Tucson, Arizona (fig. 5): From the beginning of the series to June 29 the intensity of evaporation rose rapidly to a maximum of 635 c.c. for the week ending on the latter date. With the advent of the sum- mer rainy season the rate then fell in 3 weeks to a magnitude of 206, less than one-third of the maximum. During the remainder of the series (ending September 14) the rates varied between 229 and 302. This latter half of the summer is a season of relatively great precipita- tion at this station, and the low evaporation intensity of the rainy CLIMATIC CONDITIONS OF THE UNITED STATES. 313 period is here well shown.' This is the time when summer annuals are active. Dalhart, Texas (fig. 6): This station is characterized by exceedingly — high rates for our series of observations—higher rates than were obtained at any other place—in spite of the fact that there was here considerable precipitation throughout the summer. No observation was obtained for the week ending August 3. The maximum weekly rate was 656 c.c. (week ending June 22) and the minimum was 329 c.c. (week ending July 20). The march of the index of evaporation intensity suggests a periodicity with a period of several weeks. EVAPORATION aly 270 : 28 19 ee ) 00 SO S13! go MAY 25 JUNE! se 5. 22 era 13 | t-| 10 109 @#& HSER? + 2 28 Fig. 6.—Weekly precipitation and evaporation indices, summer of 1908, Dalhart, Texas. St. Louis, Missouri (fig. 7): The maximum weekly rate (212 c.c.) was not attained here until the week ending September 7, and the minimum (71 ¢.c.) occurred early in the season, for the week ending May 11. The highest rate at this station was but little higher than the lowest encountered at Tucson. There appears to have been a general upward trend of the rate values throughout the whole series, to about September 7. There is here also a suggestion of a periodicity. Rains were frequent and plentiful until the latter part of the series of observations. Oxford, Ohio (fig. 8): Here there was a general increase in evapora- tion intensity throughout the season, until about August 31. The rates vary irregularly, from a minimum of 78 c.c. (week ending May 25) to a maximum of 249 ¢c.c. (week ending August 3), the highest ones being nearly as great as those for San Diego. 1 Livingston 1907, 1. 314 ENVIRONMENTAL CONDITIONS. Ste. Anne de Bellevue, Quebec (Macdonald College, fig. 9): The highest weekly rate for this station was 181 c.c. (week ending June 29) and the lowest was 43 c.c. (week ending August 10). The last 3 weeks of July and the first 3 of August were characterized by low evaporation intensity. Here the highest intensity recorded is much lower than the lowest experienced at Tucson. Rainfall at Ste. Anne de Bellevue was not great, but the rainy weeks were somewhat regularly spaced. le lat | LIF 129 102 E a Ni i APR27/TAYS tf 48 @5JwwEt 8B 185 22 20burx6 13 20 278&E3 10 12 24 HWSEFD 64 at Z, : 99 a | io Fic. 7.—Weekly precipitation and evaporation indices, summer of 1908, St. Louis, Missouri. /@ 2 2é Fig. 8.—Weekly precipitation and evaporation indices, summer of 1908, Oxford, Ohio. Orono, Maine (fig. 10): The minimum rate for Orono is 48 e.c. (week ending June 1) and the maximum is 178 c.c. (week ending July 13). The week ending June 29 is without a record for evaporation. CLIMATIC CONDITIONS OF THE UNITED STATES. 315 The evaporation-rates are here shown to have been rather uniform, on the whole, with a suggestion of a 3-week periodicity. Easton, Maryland (fig. 11): Here the weekly rates of evaporation varied from a minimum value of 59 c.c. (weeks ending August 31 and November 2) to a maximum of 308 c.c. (week ending June 20). There occurred a general rise in these rates from the beginning of the series to about July 20, after which the evaporation intensity was low and strikingly uniform. It is interesting to note that the highest rate for Easton is higher than any rate encountered in the summer rainy season Fic. 9.—Weekly precipitation and evaporation indices, summer of 1908, MacDonald College, Ste. Anne de Bellevue, Quebec. EVAPCRATION 1/22 Juve / 8 iS 22 gure 43 20) 27AUEF 2) 17 24 FSR? we 2 28 Fie 10.—Weekly precipitation and evaporation indices, summer of 1908, Orono, Maine. at Tucson, and the three highest for Easton are higher than any rate experienced at San Diego during the whole series of observations at that station. Curiously enough, the two graphs for Easton are similar in their general form to those for Tucson. In both cases a fore-sum- mer of low rainfall and of generally increasing evaporation intensity is finally broken by a heavy rain, which ushers in a period of greater 316 ENVIRONMENTAL CONDITIONS. rainfall and of relatively low evaporation values. This drought- breaking rain occurred in the week ending July 20 at Tucson, in the next following week at Easton. Miami, Florida (fig. 12): The exceptionally long record for Miami shows a maximum evaporation rate of 232 c.c. early in the season (week ending May 18), and a minimum of 35 c.c. near the end of the series (week ending October 5). While the general trend of the graph of atmospheric evaporating power is downward as the season advances, there are rather pronounced variations, which have some tendency to occur periodically, with an interval of about 8 weeks. The intensity of precipitation appears to increase throughout the season, and heavy rains have relatively but little relation to the evaporation values. EVAPORATION tT £60 ii 00 3 OS. : 7 \00\20 A! £5) “22 Fae 49 29 27783 10 172 24 31577 WW 21 28S 2 19 2EMexre Marva wt £8 25 kme/ Fig. 11.—Weekly precipitation and evaporation indices, summer of 1908, Easton, Maryland. Mean evaporation values for 5-week periods and for 15-week season (Table 17, plate 56.)—As has been indicated, the average weekly rates of loss from the porous-cup atmometer, at the several stations, have been calculated for the 5-week periods, April 20 to May 25, May 26 to June 29, June 20 to August 3, August 4 to September 7, and September 8 to October 12. For a few stations the average rates for the last 3 weeks of the series (from October 12 to November 2) have also been calculated. These averages are given in the final columns of table 16 and they are all brought together in table 17. Where data are not available for all the 5 (or 3) weeks of a period, the average has been made from the smaller number of weekly records at hand, and the CLIMATIC CONDITIONS OF THE UNITED STATES. 317 number of records so used is denoted by the number following the average, in parentheses. It will be seen at once that many of our 5-week averages are rendered unsatisfactory in this way, because full records are lacking. EVAPORATION 6 19373 72 2.60 RAINFALL 48/ 18/ 10 10) BB S/SER7 aw 2/ @8TS 2 Fig. 12.—Weekly precipitation and evaporation indices, summer of 1908, Miami, Florida. For the three 5-week periods (May 26 to June 29, June 30 to August 3, and August 4 to September 7) the records are generally more nearly complete than for the earlier and later periods, and these three aver- ages form the basis of our chart of summer evaporation intensities 318 ENVIRONMENTAL CONDITIONS. TABLE 17.—Summary of data of precipitation (P) and evaporation (E) for three 5-week periods for the summer of 1908 (data from table 16), together with averages and precipi- tatton-evaporation ratios (P/E) for the 15-week period May 26 to September 7. 15-week period. First period. | Second period. | Third period. Station. Average. Ps, 1908 i P E P E EE 3: P Eg | Bs 1908 im CE in c.c mn C.C m NG Alabama Florence: 32/222 2 te eee 0.82 | 122 Ose ats 0.70 | 118 (2) | 0.0059(2) Arizona: Tuecson............ 0.00 | 511 1.55 | 358 1.12 | 249 0.89 | 373 0.0024 California: San Diego....... 0.00 | 198 (2) | 0.03 | 221 0.12 | 201 0.05 | 207 0.002 Colorado: Boulder.......... 0.09 | 225 (3) | 0.41 | 180 0.66 | 161 0.39 | 189 0.0021 Florida: Gainesville. oe. tS... 1eS6 COG dial Al Gee eel eee ok 1.80 | 171 (2) | 0.0105 (2) Nigam. 3%. es sate oe 3.23 | 136 0.92 | 144 1.34 92 1.83 | 124 0.0148 Illinois: @harleston) 2.2.3. sda. ee 0.70 | 189 0.59 | 158 0.39 | 229 (2) | 0.56 | 192 0.0029 Wroana rs eee kee 0.52 | 113 (4) | 0.66 | 110 O00 ieee 0.59 | 112 (2) | 0.0053 Towas dowa Cityoeas ck in see aeeee 1.26 | 165 (3) | 1.55 | 139 1.41 | 152 (2) | 0.0093 (2) Louisiana: Cameron......... 1.03 | 234 2.66 | 167 (8) | 1.49 | 116 (4) | 1.73 | 172 0.0101 Maine: Orono.............. 0.88 | 120 (4) | 0.57 | 126 0.95 87 0.80 | 111 0.0072 Manitoba? Winnipeg: 95,03 .ik oe alun came eels ee 156. ee aon De Me cfc a te fe eer Maryland: Haston.......... 0.58 | 158 0.95 | 229 1.84 | 107 1.12 | 165 0.0068 Michigan: Grand Rapids... 4... 2 os - 0.34 | 153 0.63 | 161 0.80 | 128 0.59 | 147 0.0040 Houghtone 22230. secon OL9t | 172 Cy) 0. 7a 127 0.20 | 163 0.62 | 154 0.0040 Si-pnlelenas -ec i bee ee ot es sea ho ere ok 0.61 | 202 (2) | 0.52 | 234 (4) | 0.57 | 218 (2) | 0.0026 (2) Minnesota: Minneapolis..... 1.58 93 (4) | 0.63 | 144 0.23 | 159 0.81 | 132 0.0061 Missouri: St. Louis..........| 0.75 | 152 0.96 | 154 0.31 | 176 0.67 | 161 0.0042 Montana: Bozeman......... 1.77 39 0.09 | 162 0.22 | 150 0.69 | 117 0.0059 Nebraska: Wincolme2 ec. ee ce Dey | 27 Sly | eee a 0.69 | 134 (4) | 1.61 | 104 0.0155 North: Plattes.. 25: 20. 4... 1.04 | 118 0.63 | 127 Osst oie 0.66 | 139 0.0047 Nevada: tenons. 205. 25 shales se hes Sh ele 0.03 | 475 (4) | 0.04 | 371 (8) | 0.04 | 423 (2) | 0.0001 New Brunswick: Fredericton | 0.96 94 0.48 | 118 0.80 59 0.75 90 0.0083 New York: New: YORK 6.0.5 ABS eie 8 0.25 | 132 (4) | 0.30 | 148.(8) 1 1.39 71 0.65 | 117 0.0056 SyPACUSE. Eo dus ie ene whee ONG Stas crete 0.70 | 305 (4) | 0.16 | 348 0.43 | 327 0.0013 North Carolina: Pisgah Forest. oc. .0..<. 0.88 67 (4) | 1.42 70 3.64 43 (4) | 1.98 60 0.0330 West Raleiwh. 2.5.0.3... 1.29 | 196 1.23 | 164 3.34 74 1.95 | 145 0.0134 North Dakota: Dickinson....| 0.85 | 268 0.30 | 319 0.35 | 258 (4) | 0.50 | 282 0.0018 Ohio: (Oxford. ae eich an. 0.52 | 149 0.69 | 188 02224) 215 0.48 | 184 0.0026 Oklahoma: Stillwater........ 1.31 | 109 0.62 | 191 1st |) Gs 1.09 | 154 0.0071 Oregon: Eugene............ 0.41 95 0.00 | 219 0.00 | 179 0.14 | 164 0.0009 Quebec: St. Anne de Bellevue | 0.36 | 171 (2) | 0.33 99 0.34 65 0.34 | 112 0.0030 Saskatchewan: Regina.......|...... ANITA) ys) eae TGA ou als een 4 ROG | Skee 132... eee ee Tennessee: Knoxville........ 0.63 93 (3) | 0.65 | 128 (2) | 0.73 92 (2) | 0.67 | 104 0.0064 Texas; Dalhart. 22... ssc. 0.51 | 565 0.71 | 404 (4) | 0.25 | 440 0.49 | 470 0.0010 Utah: Salt Lake City....... 0.45 72 (4) | 0.05 | 170 0.28 | 178 0.26 | 140 0.0019 Vermont: Burlington........ 0.63 | 157 0.55 | 196 0.44 | 160 0.54 | 171 0.0032 Washington: Seattle......... 0.02 | 156 (2) | 0.05 | 167 0.17 96 0.08 | 140 0.0006 To obtain a single number to represent each station for this 15-week period (May 26 to September 7), the three 5-week means have been averaged, to give a mean intensity of atmospheric evaporating power for approximately the three summer months. The three 5-week aver- ages and the resulting 15-week means are shown in table 17, together CLIMATIC CONDITIONS OF THE UNITED STATES. 319 with the corresponding precipitation means and the precipitation- evaporation ratios for the 15-week period, the latter to be considered below. Where the 15-week mean had been obtained from only two averages this is indicated by the figure 2 in parentheses. Scrutiny of the means for this summer season shows them to vary, with the geographic position of the stations, in an apparently rational manner, and there is no reason to doubt that they furnish an approxi- mately correct picture of the distribution of intensities of evaporation over the United States for the period in question. There are two marked exceptions to the last statement—the means for Bozeman, Montana, and Salt Lake City, Utah, appear to be far too low, though no explanation is at hand to account for this. The data for these two stations have been ignored in the preparation of our chart. ~ Plate 56 is a chart of evaporation intensities constructed from the means just considered. The relatively few stations for which data are available makes it unadvisable to attempt any detailed study of climatic zones in this case, and isoatmic lines are shown for only 150 and 300 c.c.! The most significant features of the chart of plate 56 are the follow- ing: (1) The Canadian region of low summer evaporation (less than 150 c.c. per week) extends, as a great lobe, southwestward from Lake Superior, as far as the valley of the Arkansas River. Another southern extension of the northern area of low summer evaporation intensities reaches south-southwestward from southern New England, occupying the whole of the Appalachian Mountain system south of Massachu- setts. This area broadens toward the south and embraces most of South Carolina, Georgia, Alabama, Mississippi, and eastern Kentucky and Tennessee. Miami, Florida, northern and western Washington, and northwestern Oregon lie in the region of low intensity, as must also the high altitudes of the Rocky and Sierra Nevada Mountains though our numerical data do not show this feature. (2) The main region of high evaporation intensity (over 300 c.c. per week) extends northward from Mexico and occupies western Texas, New Mexico, and Arizona south of the plateau, and the lower altitudes of Nevada and of southeastern California. This is obviously the so-called desert or arid region of the United States, and corresponds to the arid evaporation province as shown on plates 53 to 55, and in 1 Tt is to be remembered that the numerical data are in terms of cubic centimeters of weekly loss from the Livingston standard cylindrical porous-cup atmometer, exposed as were our instruments. They are to be regarded merely as comparable indices of atmospheric evaporating power with reference to this instrument, just as are numerical data in terms of depth of water-loss from some specified water-surface exposed in a specified manner. Prevalent ideas in this connection require repeated emphasis upon the fact that rates of water-loss from one form of atmometer can not be mathematically deduced from those obtained with another form of instrument, ex- cepting in a very general way. If this can be generally appreciated it will aid much toward atmometric progress. 320 ENVIRONMENTAL CONDITIONS. figure 2. There is also clearly indicated a limited region of high summer evaporation in the vicinity of Syracuse, New York. (3) The region of intermediate evaporation intensities (from 150 to 300 c.c. per week), lying between the other two, of course extends eastward from the California coast to about the one-hundredth meridian of west longitude, where it is nearly replaced by the great embayment of the northern region and by the northeastern termination of the arid region. It then broadens southward to include the Gulf coast and also extends northeastward. It occupies the Atlantic coastal region as far north as southern New England (excepting southeastern Florida). Between the two great southern extensions of the zone of low inten- sities this zone of medium intensities extends northeastward as far as Burlington, Vermont, broadening to include most of Michigan. Comparison between plates 55 and 56.—Plate 55, as has been stated, presents a chart of summer evaporation intensities based upon Russell’s data, and is here published in order to allow a comparison of our own summer data (1908) with those of Russell (1887-88). As might be expected, the details of these two charts are not at all in agreement, but a study of the two brings out certain features which may be worthy of brief attention. (1) It is seen at once that the desert region is clearly shown on both charts. On one scale this zone has an evaporation intensity of over 300 c.c. per week; on the other scale, of over 30 inches for the three months, and the geographic areas represented by such intensities are satisfactorily similar in the two cases. | (2) The region of low intensities of evaporation, characterized by indices below 150 c.c. on the 1908 chart, may be taken to correspond to the region of intensities below 15 inches on the other chart. Sucha convention shows, not an agreement between the two, but such differ- ences as might be expected to occur between charts for different summers, even though these were derived by the same methods. On the chart from Russell’s data we find the zone of low evaporation (below 15 inches) to extend southward along the Pacific so as to include the whole coastal region, while in the 1908 chart the corre- sponding zone apparently can not be extended nearly so far south- ward. On the 1888 chart, instead of the southward-projecting lobe of the zone of low intensities, west of the Great Lakes (shown on the other), this northern zone merely widens to include all of the Great Lakes and the country west of them to the middle of the Dakotas, and continues eastward to the Atlantic coast. On approaching the coast its southern boundary (plate 55) still bends southward and south- westward and reaches the continental margin only at the mouth of the Rio Grande, thus producing the counterpart of the eastern or Atlantic lobe of this zone (below 150 ¢.c.) on the 1908 chart. Thence the isoatmic line of 15 inches (plate 55) apparently bends again to the CLIMATIC CONDITIONS OF THE UNITED STATES. BAI east (in the Gulf of Mexico) and reenters the continent sufficiently to demark the Gulf coasts of Florida and also a little of the Atlantic coast near Jacksonville, as pertaining to the zone of medium evapora- tion intensities. Thus the northern area of low intensities is broadened southeastward from New England, to include nearly all of the Atlantic and Gulf coast region, which suggests no very great alteration from the condition of affairs depicted by the 1908 chart. This way of regard- ing the zonation thus considers that the Minnesota-Kansas lobe of the northern zone of low intensities is represented only on the 1908 chart, that the northern zone is otherwise much widened southward throughout its eastern half on the 1908 chart, and that the Maine- Mississippi lobe of this same zone is represented on both charts, being, however, more extensive on that for 1888. (3) One of the main differences between the two charts lies in the portion of the great eastern lobe of the zone of medium evaporation intensities. While this lobe extends northeastward from Oklahoma and Texas in the 1908 chart, it extends eastward from Nebraska in the 1888 chart. In the latter it does not attain as great a northerly exten- sion as in the former, and it practically reaches farther east in the region of Chesapeake Bay (on account of the localized area of that region) in the 1888 chart. As has been noted above, the zone of inter- mediate atmospheric evaporating power occupies practically all of the Gulf coast and all of the Atlantic coast as far north as New Jersey, on the 1908 chart, but this zone is, as it were, nearly crowded off from the continent on the 1888 chart. From the above considerations it appears that the two charts are not in nearly so great disagreement as a first view might suggest. They agree very well in depicting the desert region. They agree in showing a southward extension of the northern zone of low evaporation, on each ocean border, and in showing the eastern of these extensions as embracing the Appalachian Mountains south of Pennsylvania. They agree in depicting a zone of intermediate evaporating power, including, roughly, the western half of the country (excepting the most arid part), the region of the main great mountain-mass, and the high plains east of this. Finally, they agree in showing that a great lobe of this inter- mediate zone extends eastward or northeastward from the main area, and that this lobe embraces the region immediately west of the Appala- chian Mountains. Whether all these generalizations from imperfect observations, for two periods 20 years apart, may prove generally true throughout a long period of years will hardly be known by the present generation nor even by the next following one, unless atmometry begins to attract serious attention in the very near future. They are of little value at present, excepting as very rough approximations and as they indicate how important among climatic features is the evaporating S22 ENVIRONMENTAL CONDITIONS. power of the air, and how readily it might have been and may be studied. Summer evaporation, 1908, as shown by geographic profiles—To obtain another kind of picture of the geographical variation in summer evaporating power of the air, as brought out by the 15-week means, attention may be directed to the 6 profiles shown in figure 13. These profiles aim to present graphically the changes in summer evaporation intensity to be encountered in traversing the country from west to east and from north te south. Two west-east profiles are shown, one Yyy, REGINA. WEST RALEIGH EASTON. NEW YORK. PISGAH KNOXVILLE. FOREST. 154 MY PIU EEEZZ_EEEZB Ze -, py Lf, Sy ptf fy f HOMME MMEEELLLIX(X“EWV HOUGHTON. S TE.ANNE FREDERICTON DE BELLEVUE. Evaporation PROFILES. | EVAPORATION IN C.C._ PER WEEX. VEGE TATIONS INDICATEO BY HAT CHIRG Grass. 7 NE. Evera NN DESERT. Decio-Ganss. EverRG NWMesEvera. DECIO FOREST. Fig. 13.—Evaporation profiles, weekly rates, summer of 1908, with vegetation indicated. The lines along which these profiles are constructed are indicated on Plate 56. passing from Seattle, Washington, to Fredericton, New Brunswick; the other passing from San Diego, California, to West Raleigh, North Carolina. Three north-south profiles are presented, the first passing from Regina, Saskatchewan, to Cameron, Louisiana; the second from Houghton, Michigan, to Miami, Florida; and the third from Frederic- ton, New Brunswick, to Miami, Florida. Those of our stations through CLIMATIC CONDITIONS OF THE UNITED STATES. 323 which these profiles pass are indicated at proper distances along the horizontal axis. As ordinates, extending upward at the points so marked, are represented the mean weekly losses from the porous-cup atmometer, as given in table 17, these numerical data being placed upon the profiles. Below each profile are conventionally indicated the vegetational types traversed and their approximate boundary lines, these boundaries having been obtained from the generalized vegetation chart (plate 2). We need not digress here to discuss the relations ' brought out between vegetation and summer evaporation intensity as here indicated ; these matters will receive attention in their own place. The northern west-east profile (lowest in figure 13) shows little variation in the intensity of evaporation throughout its extent. The southern west-east profile, on the other hand, shows a very great variation in evaporation values, the maximum being at Dalhart and the minimum at Pisgah Forest. The north-south profiles bring out the relatively high summer evaporation values obtained at Dickinson, at Easton, and at Gainesville and Oxford. (4) CONCLUSIONS FROM THE STuDY OF EVAPORATION CONDITIONS. All the evaporation charts agree in their main features, especially the charts derived from Russell’s observations. The four evaporation provinces are represented in figure 14, based on plate 53, and may be 9 Dey 134 ach) 65a N67) 16S; | 1 CW Yoo Vv | : \) 1299) 4272 1 1252 9 193% 01% > 4 PAL REE & Z| Na Y 7 fa } N ES ees, LAN Sez | a ime Sis [ SAK) PLLA \7 YY - ava. \ SSO sas RS ‘eyed ANN RAN \\ ‘ WAX N Lr = at £75 ‘ . 08686 \ \ : “GNA AWS NY 4 NA (39M 38210} Usd1dI2A9 IAYydosew WiainJoON x ARAN sill “tl id ce SNS p YNONZ7: IY \y VINE id Yr SS SS SY Ca So- % 4 Ma AA YG SA SSW \ 2 AS) N N free-..+” y QX aS b mule | (as —— Lb 6 4saI0} S1yAydosaus >, 3Sa1QJ snonpisaq WN Sa. 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SS asaq-1uag — =] 4 SS Qy SAS NY SEQ SY LSS \\ AS vd NS SS » : SARS NY “ a NS Yili) V2 a) L SWS ie | & WS In SNS" 4 ON a, \ a C ”, nN ty 4!” Y A Q % YS LI SA Su ? 2 ! y S Q 5 = BS Yi \ Bi 4, 7 +4 sa Je HS ax A ps \ Y h, Ly D V g & \ . \ A . q ry é Sess: ~~) c= N ° : yi LS oy NY) SW Sos ae »s A aN J J % \ ‘om ca Wy = PLATE 57 ° tl ct ; £8 $8 £8 \) WAALS KD SW 4 N RA Ra.\ SS , t\ SO cee’ ot Ss A&R RS Sones NA A \ a SS | ——_\_} ¥ = o, . oe ry - Gs vN P, | NS U7 2-1] Roy HENS BES WN = lit NS 1ag|8 a = ae 5 : : = \ a oy Se r\ wr at zx KZ St S ji | Dh see / —N = ss eukls. Ohi SE. lk. e6L: JG. 088: G8. 1 68 Ot SOL LO1 Cor TF HU all N SS 326 ENVIRONMENTAL CONDITIONS. characterized as follows: The arid province extends northward from Mexico and occupies the Great Basin. The semiarid province is shown as a belt lying outside of the arid area, this belt not being wide enough to reach the Pacific at any point, but extending into Canada at the north and also extending eastward, from Nebraska and Oklahoma, in the form of a large lobe that reaches nearly to the Appalachian Mountains. The semihumid province occupies a narrow belt outside of the semiarid one, but not reaching to the Pacific coast (on plates 53 and 55, at least). This belt broadens at the north, extends into Canada, and lies just outside of the great eastern lobe of the semiarid province. It includes much of the Gulf and southern Atlantic region, a feature that is quite unlike the corresponding state of affairs on the precipitation charts. The humid province occupies a small portion of the northwest (reaches southward along the Pacific coast on plate 54, fig. 14), extends into Canada at the north, reenters the United States west of the Great Lakes, and occupies most of Minnesota, Wisconsin, Michigan, New York, and the three northern States of New England. Another portion of the humid province lies along the Atlantic coast, from Massachusetts (or southern New Jersey, see fig. 14) to North Carolina, and a narrow strip appears on the eastern coast of Texas. C. RATIOS OF PRECIPITATION TO EVAPORATION. (1) PRELIMINARY CONSIDERATIONS. Following the lead of Transeau (1905), we have employed the ratio of precipitation to evaporation as the nearest approach that is as yet possible toward an ideal index of the external moisture-relation of plants. Transeau’s introduction of this ratio marked a very definite and important forward step in climatology, which will, no doubt, be- come more thoroughly appreciated as data of evaporation become available. Of course this ratio, like other intensity factors, may be employed in connection with any duration factor or factors that may seem desirable, and we have thus employed it in six different ways. As has been said, however, it is not yet possible to obtain evaporation normals, and all that can be done is to use Russell’s data for the single year, July 1887 to June 1888. Transeau obtained his ratio by divid- ing the normal annual precipitation, for each station considered, by the corresponding total evaporation for Russell’s year of evaporation data. Our various applications of the Transeau ratio will receive attention below. (2) Ratios or Normat Totat PRECIPITATION, FOR PERIOD OF AVERAGE FROSTLESS SEASON, TO TotaL EVAPORATION AS OBTAINED BY RUSSELL FOR THE SAME PERIOD, FOR THE YEAR JuLy 1887 ro June 1888. P/E. (Tasue 11, Puate 57, Fia. 16.) The two terms of this ratio, for each of the stations included in our list, are given in the second and sixth columns, respectively, of table 11, and theratio values themselves (P/E) aregiven in the eighth column CLIMATIC CONDITIONS OF THE UNITED STATES. S26 of the same table. These ratios are shown graphically on plate 57, where the numbers on the lines represent hundredths. Inspection of table 11 and plate 57 shows that the moisture-ratio values range from 0.04 (Independence, California, and Winnemucca, Nevada) to 1.76 (Cape Hatteras, North Carolina) and to 3.84 (Tatoosh Island, Washington). The highest values are in western Washington and Oregon and the lowest are in the region of the Great Basin and in the arid Southwest. The isoclimatic lines show that the country may be divided into three main zones or regions: (1) an arid zone (ratio values below 0.20), (2) a humid zone (ratio values above 1.00), and (3) an intermediate zone (ratio values between 0.20 and 1.00). The intermediate zone is conveniently subdivided into a semiarid zone (ratio values between 0.20 and 0.60) and a semihumid zone (ratio values between 0.60 and 1.00). There are thus four climatic zones or provinces to be considered, as in the case of our precipitation and evaporation charts. Their limits are denoted by full lines on plate 57. The arid province extends, roughly, from the Rocky and Big Horn Mountains westward to the Cascades, the Sierra Nevadas, and the Coast ranges. It includes a little of southeastern Washington. The semiarid province forms a belt lying west, east, and north of the arid region, extending westward nearly to the coast of Washington and northern Oregon, and to the coast of southern Oregon and Cali- fornia, northward into Canada, and eastward to about the ninety- ninth Pueniicns of west longitude. The semihumid province is shown northwest and east of the semi- arid area. It includes a narrow strip of western Washington and north- western Oregon and extends eastward from the semiarid region to about the ninety-third meridian at north and south, but is broadened to include most of the country in its middle portion. This zone also includes southern peninsular Florida. ‘The western portion of the humid region occupies western Washington and a little of northwestern Oregon, while the eastern portion includes the Gulf coast east of the Mississippi River (excepting extreme southern Florida) and the Atlantic coast north of southern Florida (excepting the northern part of the New Jersey coast and the coast about Boston). It also occupies the country north of middle New England and extends south- ward from Canada, to include northern Michigan, northern Wisconsin, and eastern Minnesota. The most interesting special feature of this chart is the enormous eastward enlargement of the semihumid region, which corresponds to a similar eastern lobe evident on the evaporation chart for the period of the average frostless season (plate 53). It should be remarked that a localized portion of the semiarid region here appears to be located in the middle of this enlargement, occupying southern Illinois, Indiana, and Ohio, and northern Kentucky. 6 ose ek ay one ere 12.88 10.39 1.24 0.92 Mississippi: Vicksburg (80)............ 29.74 37.34 0.80 0.93 Missouri: — Geil rag €y Hh aa Le ae. 2 i 31.97 30.26 1.03 0.86 CAV CIEWOELN 7.3 Contes 6 ee eae erates Wear C49) oho eee iences, aregors ane oe 23.81 25.83 0.92 1.03 Si cepa L 0): Te apeee ie iemienneie: Neen hs Cait Poe 1h 20.60 39 .29 0.52 0.58 pprneneld (49) 126. J os ees Ss 23.34 24.96 0.93 1.00 Montana: row Ateney (Ab). . ao. oe eee eee 9.22 31.30 0.29 0.23 Por, Assenibome:. 35. 2 S545 ose eke 9.79 20.86 0.47 O.an Piclewans(O 7) Ae Feo ce) Ae Oe eye 5.99 29.70 0.20 0.22 es (SO) S ees katate tee nie he } 11.44 20.48 0.56 0.34 QUA RIVEE fk Se eee Se ac Nebraska: Grae) fae Gy p \aps ea eg ees ape me the Bea Yd 21.94 22.60 0.97 0.90 Wort Platte tes). ook eee Aen ih ae 25.05 0.46 0.51 rms (36) 226s so So ee ewes iW fae | 27.09 0.64 0.82 Nevada: Winnemucca (12)............ 0.96 45.99 0.02 0.04 New Hampshire: Concord (105)........ 23 .64 17.84 1232 0.94 New Jersey: Atlantic City (99)......... 21.20 17.48 1234. 1.30 New Mexico: Hore otantion yo. Vee Se 11063 43.19 0.27 0.23 SEER Spe (2) ROt Se eee ERO Were ae eg 9.24 54.79 0.17 0.18 New York: Albany (104) ho ee ek Coes 18.99 eA aN 0.80 0.84 rate GOL) i ors Se ia. ig 15.02 22.94 0.65 0.78 New Work (104) ate 2 28 io. PES. ise. 24.08 29.43 0.82 0.87 Gawero ie) 2 see ee cena 6 nae 49-25 19.97 0.56 0.87 Rochester (Gy chaos bo cee eek tie oes 11.67 22 OW, 0.51 0.71 North Carolina: ChariGhioNtea) ceosutekosece ea as Sore 35.89 34.06 1.05 0.88 CLIMATIC CONDITIONS OF THE UNITED STATES. ook TABLE 18.—Data of precipitation and »vaporation for the pertod of the average frostless season, for the year of Russell’s observation (July 1887 to June 1888), and corresponding ratios of precipitation to evaporation, together with similar ratios derwed by employing normal data of precipitation instead of those for this single year.—Continued. ‘ | H Ob : HD > Bases | £8388 | S © ie D q © oi = ve ‘a 3 I Bul ieee g ee A go |' 8, 28 « ee Station. em silioen -s p/E (From | 5 2 2 Seve + table 11.) | av o+ OF ee te | eats | re oo. | Skee | #2528 | HH cm North Carolina—Continued: in. mM. EEL eras (O'L)Mtaten aie oleott cllats eratete 44.56 24.65 1.81 1.76 | Seat) Koa oH 8) 0) J ta nM a nr er Dee 41.03 26.13 Paz 22 Walmametony (GO) ii ei Beek. aie clare 33.84 27.35 1.24 1.35 North Dakota: PRISM AT KAS Vie aeee) evidvs Ama haat cat ahteve 13.09 18.94 0.66 0.55 \ A/V DIS) ero oa 23) 1) ne ne ep Mi Be Bord a a, a } eee ene vey 22 Mel il Werrals/ Wake (G2) es this sakes ooae ere sealers 14.96 15.38 0.97 0.75 Ohio: | Winremnmay (ZO) sso eee ele Coates p B iersy) 37.20 0.31 0.51 Cleveland (GO sive aes Jie 21.31 26.39 0.81 0.78 @olamab ys) (Cie oe eae etal wai ol heeanee eels 11.39 33.29 0.34 0.58 Saas ky. (G9) Cte Sole un oem alien ian) L233 PA Cees 0.45 0.74 EOE O (GO) eee ae eS Maeva ohalte ss 13.48 26.84 0.50 0.62 Oklahoma: Fort Sill (42) .00..02 00. .2..-. 31.80 33.81 0.94 0.70 Oregon: PMS COMI CUM )ie ese ale is Mestad ous hu Gees ales 36.29 ONT, 1.67 1.90 OVA CLG) yeaa sola. cite Vole eueneseheits ae aleuece 16.35 29.42 0.56 0.66 HVOSEOMEE. Cyl) ae cecteene ler iiotel, Sel cleans 9.19 28esa 0.32 0.29 Pennsylvania: | TE (IG) eee eben LL eae ene hee Ll eeeoe@ 17.48 i552 0.90 Philadelphia (QS) ics eke Re. set 22.14 332) 1153 0.69 0.75 | ES GLAS] ON OT GFE oat AMO SRP ae Reta RR ey la CAO UE 20.55 29.69 0.69 0.66 Rhode Island: Block Island (105)...... 20.80 17.56 1.18 1.39 South Carolina: | Charleston (S8)).cs cesicic store Oe tle aves 31.85 36.25 0.88 1.16 Wolumnoras(S 7) lw. ee nek el sal elo oeae 30.94 oy Gee! 0.97 0.98 South Dakota: PERU OM CBA) ier darters a ei ters scutes ale aietat se 15.43 19.00 0.81 0.66 ROE LO (SD) We seeks eaten antes A 12.87 27.60 0.47 0.39 a mIsbor (BA) ria say ethen iN shai esate 25.27 18.79 1.34 0:98). 0 Tennessee: CS HattanGOZa (ZS): cic, spcteow ester siue ee lee 2825 31.00 0.88 0.81 GOR VLE G 1703) 8 tana lates, archers cyahote duel eked exe 25.56 30.70 0.83 0.82 IMPEMBNISNCE cians iets « ck dindatae ys eele 18.46 37.00 0.50 0.75 NaS ValleKCZ Oia abs xoe csertig Sew Rieke elees 26.67 36.66 0.73 0.69 Texas: PAULO MEON CEE hac sie. cicle sveavetaaucreirare tigers 23.83 46.00 0.52 0.44 PSTOWIS VIS EL io adicclervc kte wie Goole Ga ae POMP BTOWD hiesdiaks, civ shila accuteais wie ara oes \ os eae ae 5s Sole Corpus Christi (1).............00- 38.12 35.09 1.08 0.65 | TSILIEE ROY CDA it ae ed eee ae 6.06 64.41 0.09 0.12 | GIG) EAPO LE OD ile oi adel ayetane «kewierane EUG TAMA CIGION cs ces weg ays cae s } a eS — inh | CARVESCOM MCL DR eenth ctaeererccue a ta ead cok 51.84 44.06 LES 0.97 PROS TENG) (44) ic: sieve tiene keine ours 32.97 36.25 @.91 0.7 BAM ANGOMIO (Lyi cad iwc saens aac 29.00 43.63 0.66 0.51 332 ENVIRONMENTAL CONDITIONS. TABLE 18.—Data of precipitation and evaporation for the period of the average frostless season, for the year of Russell's observation (July 1887 to June 1888), and corresponding ratios of precipitation to evaporation, together with similar ratios derived by employing normal data of precipitation instead of those for this single year.—Continued. = : Tay are 2236 | 3388 q o = ore) q 5 ar ea ns 36668 | S5¢o5 aia ie ee P/E, Station. ievsye & Sog°a p/E (From ON Si Nias a anton table 11.) Ko 8S | 508" q Das | aa eS $252) $2825 H a an. in. Utah: Salt Lake City (11)............. 4..32 51.71 0.08 0.13 Vermont: Northfield (105)............. 19.02 12.28 1.55 1.16 Virginia: Neynchpure: (OS) ceesin oe caus hee eee 24.95 28.68 0.87 0.87 INGrfolle; (G2) 235; 3s ares an loeca siete 39.82 27.26 1.46 1.24 Washington: North: Head (iS) ao eee eee Fort, Canby: ene 33 2 cis sutect ele een 43.68 Mote Sole 1.73 Olyanpia (EO) Beenie wcrc eee ee 11.22 19.85 0.56 0.70 Spokane'!(20) 22 .ee eu a hy 11.28 33.80. 0.33 0.23 Walla: Walla (20): so cee nee Us Bsth 45.87 0.16 0.18 Wisconsin: Green Bay: (GO)... Soe ae wes 14.57 19.39 0.75 0.86 Tea Crosse (SO) wears evessl oops te ee 18.67 21.97 0.85 0.94 Milwaukee (60) io). occ hoe eee ee). 17.63 19.11 0.92 0.87 Wyoming: Cheyenne (24)............. 7.09 32.48 0.22 0.20 The chart of plate 58 was prepared from these ratio values (p/E), the isoclimatic lines representing increments of 0.20. This chart agrees in its essentials with that of plate 57; the great eastern lobe of the semihumid region (values between 0.60 and 1.00) is here again apparent and the localized area of semiarid conditions, within this lobe, is more pronounced than in the former case. The arid region (values below 0.20) is here indicated much as in plate 57, but the line for the value 0.60, in the middle of the country, here swings farther westward at its northern end than in the other case. In general, it appears to make no serious difference which of these two charts is studied, since all their essential features are so nearly alike. Whenever agricultural climatology begins to receive attention in this country, and when evaporation observations are made for the period without frost, it will be desirable to prepare a chart similar to that of plate 58 for every year. Finally, a normal ratio value for each _ station may be actually obtained, after which the value for any par- ticular station and season may be stated by comparison with the normal for that station, just as is now done in the case of temperature and rainfall. CLIMATIC CONDITIONS OF THE UNITED STATES. 333 (4) Ratios or NormMaut ToTaL PRECIPITATION FOR PERIOD OF AVERAGE FROSTLESS SEASON PLUS PRECEDING 30 Days, TO ToTAL EVAPORATION FOR THE SAME PERIOD, JULY 1887 TO JUNE 1888 (7/E). (Tasue 11, Puate 59.) This form of the moisture ratio is based on the idea, already men- tioned, that some of the precipitation occurring before the beginning of the frostless season is effective to supply water for plant activities in the early part of that season. The numerator (P) of the first form of ratio has thus been increased, in each case, by adding to it the normal total precipitation for the 30 days just preceding the beginning of the average frostless season. This increased precipitation value has been termed 7, to distinguish it from P and p, so that the form of ratio here considered becomes 7/E. The values of a and E, and those of 7/E, are given, for our list of stations, in table 11, the ratio values occupying the last column. The chart based on these ratios is shown as plate 59. The essentials of this chart are so nearly like those shown by plates 57 and 58 that no special comment is here needed. It may be noted, however, that the full line separating the humid from the semihumid zone is here taken as having the value 1.10 instead of 1.00, as in plates 57 and 58. (5) Ratios or NorMAL ToTat ANNUAL PRECIPITATION TO TOTAL ANNUAL EVAPORATION, JULY 1887 To JUNE 1888 (Pqg/Eq). (TABLE 15, Puate 60.) These annual ratios are derived by the method employed by Tran- seau. We have termed the normal total annual precipitation P,, and 149° 137 “195° iss” ae 119° Ny? 118° 41 r 108° 1 10 7° 95 93 of 69 87° BF BF we WO ie Ne Wiel DATA Way: sent C] AE ‘= NSa J LS On. is NIN2 Meas ZX \ Sb /\N2u Ee ar RS PRR ae ry Sa pea KN oe PSESAG ==, ste f] YC | Ne AS (ict Re wl <_ we ia Fie. 15.—Moisture zonation of the eastern United States, according to precipitation-evaporation ratio (annual), after Transeau. PLATE 58 ‘a . ——— 334 ‘sooUTAOId OIN4SIOUL INO} OFUT Ceul oy} VPIAIp soul] [MY “p WouNjoo uoryei0deaAe Aq poprArp we ors kk MXN q “4 1 \) NN SS N.S Wy iy Ys \ ‘4 KA ON ® ss ER Xr at NRN “ RS Ly 5a \ oy Wah \\ YASS INN Foe i's y~ eae Ni Ply. Na Al 4 Z) V4 Cee a QT 21GB} Wor BYVp | ([essny WoT} dN Aydosaw WIIYIION OW S CS VSS YY S y aN N NN Yet rw w- Sy ve » DAR SASS i 37. SS NS 3 a allt < WW ai N p il a nS a NY N QJ YJ . a = SS NN "Z, oye] BI oseq ‘reah OWES IO} SON[BA Q-J RBI Oj Son[eA uorye}Idioe1d [eUIIOU) MOSES SSO]}SOIJ eBvIOAB JO porsod 10J sonjea uorye10d¥eAV-UOT}e}IdIDeIg ysa10y UseIZIBAD uornisuey d13Aydoss AY }s010} shonpisep snonpiseq puejssessy \\ < CA | } pal fe ?, *Z, 078 /d 81 o8Bq OTT, SOOUTAOI 9.ANgStOUT INOJ OFUT Ava oy} OPLATp sou] [NT G6 WuINjoo ‘T_T o[qv7 UOT Bywp { (TjossNyy W101} ‘8-2/8 10} sonyva uolye10dBAO Aq peplarp sonyva uoryeptdtooid [euri0u) skep Og Surpoooid snd uosvoes ssop}sory OFVIOAB JO powod 10j sanyva uores0dvAd-n0rey Ider g (1seq) O59 18910} 09018199 uonisuRLy ISO} U99IB.IAND 38910} UsV1d DAP on Aydosshy $910} Snonpizep on Aydosow uray von C9189 4YLION -purjesesy —ee ———s SST SS 4 : oe % 1 ee ETE | yso20} 21Aydosaw y RN aay, e N \y \) KY NI BO Norse A ANS WS N NC NW L | U19}SBIYINOS . . RR PAE LLLE Gis rH NE a jh LN NYS. ye VS RY J 7 i De |: BN \ N SENOS WY \ aS oy \¢ \ \ . ne NN XY : ss s N x ' NX WON 22:Z iN BWA NX Ye N \e WY) RY A BS PLATE 59 yy ys OU, oF q SRY N SARS. : ot ON SA i q [| | a USS SWE IN wis Wa age Halal a “il . scl SN Ss a SANS S i il Me a pe ie S Se ~ SOO Ly) D : 5 , aM eS i Uo | SA BS pe wy Las. ‘ail Mi, ‘itl Y P Naa) SH \\ Seed PENG aS WSs Crea, ™ Ss sane \ C3 HEN S NOS ae ie a h > Ele ATR | AY Xt Be LS) ae eae eee a eee B —_| . ey | a" 4 ies = iP ‘Hip i AIS ait | 2. | Ik =~ Vl ™® ei / ‘ ‘ fi BAS ( i | hes > ol ADM el 89° 87° 85 83° Db] 95° 93" «91° Ne RSS Ls 97° s& a Z 4 | 109° 107° 105° 108° 101% 99° ay ~ 118° 111° aed 3 tN deh iris \ 4 ay NL Ne \ Bz: WS Ne i ry pial aa ~ [EES J 7 — S RSE SAS 5 y U PLATE 60 ‘4 Bcts AG, x LIL: l NK \ ie TTL A ¢ Ly A ( = | Ini Be gl . Sy i 2 Aaa ARON e Bi ; ol Ss 8! " a \) \ W n% aa AS PANN ® NY 7 < OR -, Ma Ps ck CS His NC we NS ANNNS \ ve IS C\ QW S.\\ \\ BA K a: AS <3 S) = box A a 5% = é 50 Se. || — “af: yD Mines HL ini ee) VED WS Northern mesophytic | Northern mesophytic evergreen forest evergreen forest evergreen forest (West) (East) Northwestern hygrophytic deciduous forest transition Precipitation-evaporation values for year (normal precipitation values divided by evaporation values for 1887-8, from Russell); data from The base is plate 2. table 15, column 4. Full lines divide the map into four moisture provinces. ‘2, oped st osvq ayy, ‘“soouTAod anoj OyUT deur oY) OprAIp sour] [Ny *2 WuINTOo ‘GT o[qe4 UIOIy ByEp : ([JoSsNY WOIJ “QRRT oun PUL 18%] qsnsny pus Ajne roy sonyea uoresodeas Aq poprarp sonyea uorpeytdwoid peuTIOU) syyUOU JOUTUINS 9014} IO} Son[BA uolye10dBAd-uolyey dias 80 of 0T /LOl 2 0 & of ¢ Alt (aseq) (189M) }8910] W997 19Aa uolisuen 18910} u901910A2 1S210] UsaiB IAAP an AydosBAy 18910} snonpisep oAYydosow WreyVION onAydosew u19yVION - purlesei‘y — Aud 348910} s1Aydoseu ages it Ny, Somer u niece Ne U1a}S2IYINOS Ye - Yj i a WN RY AA: OG, \ NN ‘ WN \ Y \ ‘ NY WH y ST wi SS \ Sy W AX ¥, Vs z Ws WS Ne nN 5 Ni NX TH & . a SAAN Si NY 4 RRR (sd \\ Sal i — x wees J \ x x y | ~ Y wiz ’ . \— im \ \Y e a= o" - : AN hee DOK y : ch PLATE 61 SSIS KO) S oO ey S ; ¥2) yey OY v7 SS | Sie v7 ut) Wiss BN SDA eo LR ~ mA oy nf t my pit BS .¢, i! | NS Al Nill Ss Ye Bact Sera } | cS ai | ae a, ee ee eae eee ee ee eee ee eee ee 8 68 “GOT GOT 601 IIT ELL. GIL LIL 611 ,I@t eal oat lel Ana 338 ENVIRONMENTAL CONDITIONS. the total annual evaporation for Russell’s year, E,, so that this form of ratio becomes P,/E,. The values for both terms and for the ratios themselves are given in table 15, and the chart derived from the ratio values is here presented as plate 60. This chart has the same essential characteristics as those of plates 57, 58, and 59, and it agrees, in general, with Transeau’s similar chart, which is here reproduced for comparison, as figure 15. It includes only the eastern half of the country. Since he did not publish the station data on which it is based, it is impossible to determine just wherein lie the discrepancies between Transeau’s calculations and our own. The agreement between the two charts is close enough, however, for present purposes. If the chart of plate 60 is compared with those of plates 57, 58, and 59, the main difference is seen to lie in the fact that the line separating the humid from the semihumid zone, in the East, bends northward in plate 60, to include in the humid zone all of Mississippi and Alabama and parts of Tennessee and Missouri, which is not true for any other moisture-ratio chart of our series. (6) Ratios or NormMat Torau PRECIPITATION FOR THE THREE SUMMER Montus, JUNE TO Aveust, To Totat EvaporaTION FoR JULY AND AucGustT 1887 AND JuNE 1888, Ps/Es. (TABLE 15, Puate 61.) As also in the case of the annual ratios just discussed, the duration factor employed for these summer ratios is the same for all stations; all represent the period of the months June, July, and August. The two terms and the ratio are shown, for each station considered, in table 15, the ratios occupying the last column. Plate 61 shows the chart based on these summer ratios. Here the zonation is different from that of the preceding moisture-ratio charts in several particulars. In the first place, the arid region (values below 0.20) is here extended west to the Pacific and includes nearly all of Washington and Oregon and all of California, this difference from the preceding charts of this feature being probably related to the charac- teristic summer drought of California. The semiarid and semihumid regions indicated in the northwest are very restricted. Looking at this chart from any point of view, it is clear that the whole Pacific coast and the Pacific Northwest are characterized as far more arid for the summer months than for the period of the average frostless season or for the year. In the East, the most pronounced difference between this chart and the preceding ones lies in the fact that the great semihumid lobe pro- jecting eastward from the Plains is here shown as extending farther to the north than on the preceding charts. This suggests that New Eng- land and the states bordering on the Great Lakes are more arid for the period of the three summer months than for the other periods we have considered. CLIMATIC CONDITIONS OF THE UNITED STATES. 339 (7) Ratios oF ToTaL PRECIPITATION FOR 15 WEEKS IN THE SUMMER of 1908 To ToraL EvAPoRA- TION FOR THE SAME PERIOD AND YEAR, THE EVAPORATION DATA OBTAINED WITH THE Ie CYLINDRICAL Porovus-cup ATMOMETER 7g 1908 of - 1908 ). (TABLE 17, PLATE 62.) These ratios were obtained to accompany the evaporation and rain- fall data of 1908. The numerators and denominators and the ratio values are presented in table 17. The chart of plate 62 represents these ratio values, as well as the small number of stations will permit. It is to be noted at once that the values obtained by dividing inches of precipitation by cubic centimeters of evaporation have an entirely different order of magnitude from those heretofore considered, being very much smaller. In order to render these numbers more readily comparable with those used on the preceding ratio charts, the values from the last column of table 17 have all been multiplied by 10,000 before employing them for the chart of plate 62. On this chart the humid zone is considered as having ratio values above 75, the semi- humid zone is characterized by values between 25 and 75, the semi- arid zone has values between 10 and 25, and the values representing the arid zone are all below 10. By this convention the chart before us appears to agree in a rather satisfactory manner with the other mois- ture-ratio charts. Like the chart for the three summer months (plate 61), the arid zone is here shown as including the Great Basin, the Pacific coast, and most of the Colorado Desert. In the present case, however, the arid zone is extended northward, so that no semiarid, semihumid, or humid conditions are encountered in the extreme western part of the United States. The eastern margin of this zone lies farther west (except at the south, where it is farther east) than the corresponding margin on plate 61. In short, the arid zone of plate 62 may be approximately obtained from plate 61 if we conceive that this zone on the earlier chart is simply extended northward, curtailed along most of its eastern margin, and extended eastward at its southern end. The line for the value 25 here corresponds with that for 60 on plate 61, indicating that the eastern margin of the semiarid zone here lies much farther west than in the other case. The semihumid zone, as shown on plate 62, appears as nearly cut into two portions by the great lobe of the humid zone that extends northward from eastern Texas, but its eastern projection is still as clear as on the other ratio charts, only this is displaced northward. This great eastern lobe of the semihumid zone here occupies the whole Atlantic region from southern Maryland nearly to the Canadian boundary, being thus also more extensive eastward than in the case of plate 61.. The localized area of semiarid conditions is once more apparent in the region of the lower Great Lakes, being displaced northeastward from its position on the other ratio charts. Lack of stations in Canada brings it about that no humid zone can here be depicted north of the Great Lakes region; it appears simply to be displaced northward from its position PLATE 62 aul oe ‘Z 048] d St oseq ‘SOOUTAOIA OINYSIOUL NOJ OUI deur oy OpPrAIp Sour] [NZ “OT WuaNzoo ‘,T o[qe} wos Byep {(sro}oUI0UTye dno-snosod [votmpuréD YIM poureyqo 10748] oy} ‘sonyea Uotye1odvAs Aq peprAlp sonjeVa orzeyId10eI1d) QOGT JO JOWIUINS IO} SoN]VA O11 MOT}VIOdeAI-UOT}e}IdIO9I1g (3Seq)., 4810} UVDITIOAD | oAydosour wisy}ION NS i | rt SS NN i 7 NS ZZ SN Y SNS SS NX s VOX GL f LY 6 \Y AX YO RW = aX * ¥ Kh LEOLLNEL OOS RNAs 7 S SERS “= SSeSOSOF RNY t se SOS War SS EN is We: X\ Y Z At OM SS RS Wy ~< N WS ANS J i 4S, D | l ay sD: D Ni \ x ai N aS PRS. pen ill ul tl \ : R i LE 2 y ” ie hE: » 7 a) bet P 4 AS~L quill il HU Nu Ni SS 39 8669 9 OLE LsCOLECCHL CSCS CK CSCS CG CGC . ft’ 6IT aM. ght tir. LIT qsor0y U991819A9 a1yAydois Ay ob IT uorjsuey 48210} snonplep -puryssely _ yd1Ey snonpiseq AN rt JOE a ee f——fak Px ST) SY 4) GTC purjsse1y COAL ALES “2 OIV SONTVA [BOI AN YN < g \ INAS XY ‘ .Y . NS \) q Kei PLATE 63 : WSN » NAYS x >) NY iN i} 1D Ik WA N 4 U \Y ty i ! | I } rs Iie iN 1) q ly a ik y a a »PL\_\ (GENS 8 48 68 SRR AUR ARTZ. 777 AAA SY RA YEAS eS DSO NS vA ZL: SS Ws l EN x KR WN WN 2 7 Fy la | : Wi i , Wy) { yy rd otek : AAR TA RPS 6 16 6 A686 ° Hall itses Vi, ; { ia iB Barn ite . Watt I = Soacmsesaaned ——_ 8 ae a (QSs ON al 2: rs is Uy i a | Ly N VUE LDS Yr oe \ \\ WS Ay Ni x “atest % . ae a KZ 4 ee ae ON as Ns “SANS ‘3 \ oe S NS SNQOS RSS Sh RZ xy \) , iy NINN = iN i fl ii 19! SS WY es Ae Ys fs fl er RASS x S ‘S DES ig es uc Bs eyuid st oseq oY], ‘qour uv jo syyporpuny OUINN *g UUINOS ‘GT 9[qGeI WOI] BYEp fUOSTOS SSo]SO1J ODv.IOAV 94} JO potsod Oy sornssoid JOdvA snoonbe uvour [BULLION (1827) 38910} u901819A9 ds Aydosom aray710N) Se O89 M 38910} usd1B IDAs on Aydosow wisyy0N ie tod KS Kir fs IO SARS 48910} 91,A4ydosem W19}seayjNOS 16910} usaIBI9Ae on AydosB Ay 019199 AULION tf ij t isisibserer0 Sisimisiwininis bt ty at reg evar ieisien SSG aisibieierws uolisuen 48910} Snonpioep - puLlsseisy saehalatyt : eS Wl ers Tt 125° an 1 Four tk 10F oF a — ieee : | TERY Noe ae an ape aneee / RET Teh Pd RNS Rae, y : 43 / * 3 at 342 ENVIRONMENTAL CONDITIONS. on the other plates. The separation of this eastern humid region into a northern and a southern portion, indicated on all the ratio charts, is here much more pronounced than in any other case. The northern portion is here indicated as occupying eastern Maine, while the south- ern portion extends from eastern Texas to southern Maryland, reach- ing farther inland than in any of the other cases, especially at its southeastern extremity, where its great northern lobe reaches southern Minnesota. This lobe appears here like an exaggeration of the similar but smaller lobe shown on the chart of plate 60. It is thus seen that plate 61 differs from the other ratio charts only in relatively minor details, the main essentials being about the same. . (8) CONCLUSIONS FROM THE STUDY OF THE PRECIPITATION-EVAPORATION Ratios. The results of our study of the various forms of Transeau ratios above described lead clearly to the conclusion, which is in full agree- ment with that reached by Transeau from his first use of this ratio, “Sabon See) Wer — sS my eA Week TSDC Lc SHUR eee BA V wi paces Cie casas Fic. 16.—Moisture zonation, according to precipitation-evaporation ratio (period of average frostless season). Moisture provinces: Humid, more than 100; semihumid, 60 to 100; semi- arid, 20 to 60; arid, less than 20. (See also Plate 57.) that we have here a climatic index by means of which the zonation of the country with regard to moisture conditions may be clearly shown. As will receive emphasis later, the climatic zonation thus brought out is closely paralleled by certain prominent features of the zonation of vegetation types, and there is little room to doubt that this division of the country into moisture-ratio provinces will be of very great value in the study of climatology with reference to agriculture and forestry. CLIMATIC CONDITIONS OF THE UNITED STATES. 343 Our charts represent the country as divided into climatic provinces, which may be conveniently considered once more as (1) humid, (2) semihumid, (3) semiarid, and (4) arid. The following general descrip- tion of these areas will serve to summarize the descriptions of the separate charts. Reference may be made to figure 16, which is de- rived from plate 57. Three humid areas are apparent, one in the Pacific Northwest, a second in the region of the Great Lakes and northern New England, and a third in the Southeast along the Gulf of Mexico and the Atlantic as far north as northern New Jersey or southern New England. The last two humid provinces are nearly continuous, and may be repre- sented as such by charts drawn from certain forms of moisture ratio or from data of certain years. Our plate 60 shows them as continuous by a narrow belt that embraces about the southern half of Delaware and the eastern half of New Jersey. The two semihumid areas are irregular in shape. The eastern one ‘occupies all of the country not included in the humid area and east of about the one-hundredth meridian of west longitude. The western semihumid area occupies a rather narrow strip of country east of the western humid province and extending southward along the Pacific, south of that province, to about the middle of the California coast. These two areas are almost surely joined at the north, in Canada, though this point is not actually demonstrated by any of our data. The semiarid area appears to be made up of an eastern and a western portion, joined together at the north. The eastern portion extends, approximately, from the one-hundredth meridian westward to the Rocky Mountains and to the San Francisco Mountains of the Arizona Plateau. Its eastern boundary appears to cross the Rio Grande some- what southeast of El] Paso. In its northern part this eastern semiarid region apparently broadens westward and extends through the lower passes of the mountains to Washington, where it joins the western portion of the same region. This western portion lies east of the western semihumid area as above described and extends southward to the Mexican boundary, along the coast of southern California. From Washington to Lower California it is a rather narrow belt. The arid area occupies the intermontane region of the West, extend- ing from the Rocky Mountains to the Sierras and from southern Cali- fornia and Arizona to Idaho and southwestern Washington. It is thus surrounded, on three sides within the United States, by the belt of the semiarid area. Of course, it is understood that all the higher mountain ranges are to be considered as belonging to the humid area, at least in their upper portions, and that such high mountain masses are surely each bordered by a zone of semihumid conditions when they lie in an arid area. No attempt is here made to consider the innumerable small areas of 344 ENVIRONMENTAL CONDITIONS. humid, semihumid, and semiarid conditions included in the arid, semiarid, etc., areas as above described. A detailed moisture-ratio chart of a single county in Arizona or Nevada would doubtless be vastly more complicated than is any of our general charts for the entire country. D. AQUEOUS-VAPOR PRESSURE. (1) PRELIMINARY CONSIDERATIONS. The pressure of aqueous vapor in the air should be an index of the relative influence of the air (aside from its rate of movement) toward the retardation of evaporation from wet surfaces. Roughly, this index should be somewhat nearly inversely proportional to the evapora- ting power of the air, disregarding the wind factor. This is, therefore, a climatic dimension the measurement of which should be valuable in studies of the relations between plant activities and environmental conditions. The vapor-pressure data for the United States, for the years 1873 to 1905, have been reduced to a system of homogeneous monthly and annual means by Bigelow (Bull. 8., 1909), and these means have fur- nished the basis for our work in this connection. We have employed (1) the normal mean vapor-pressure for the period of the average frost- less season, and (2) the normal mean annual vapor pressure. (2) NormaL Mean AQuEots-VAPoR PRESSURES FOR PERIOD OF AVERAGE FROSTLESS SEASON (TaBLE 19, PLATE 63.) The indices here employed were derived from the monthly means of Bigelow, in the way already described for such cases. Our results are given in the last column of table 19, and plate 63 represents them graphically. TABLE 19.—Normal mean relative humidities, for the year and for the period of the average frostless season, mean relative humidities for the three summer months, 1908, and normal mean vapor-pressures for the year and for the period of the average frostless season. E eae Mean vapor-pressure Mean relative humidity. Yes of water. Station. For period | For June, | For period of average! July, and | of average Annual frostless August | Annual frostless season. ADB. 4 season. | a Birminph oreo ee Ee Sie ea oe Sere ae 16. Jwdsenwest eee Mobile. 80 : 457 .953 Montromery. 3.2. 2225042: 72.4 TLS 71 Arizona: | CLIMATIC CONDITIONS OF THE UNITED STATES. 345 TaBLE 19.—Normal mean relative humidities, for the year and for the period of the average frostless season, mean relative humidities for the three summer months, 1918, and normal mean vapor-pressures for the year and for the period of the average frostless season.— Continued. Mean relative humidity. Mean vapor-pressure of water. Station. For period | For June, For period of average}] July, and of average Annual. frostless August Annual. frostless season. 1908. season. California: D. ct. D. Ct. p. ct. inch. inch 1 Oasis es Naat Pe em ME 86.8 87.5 89 .325 348 EE STN y eb ects est Soke Pe otis acsal grea oie shee 48.9 30 Sp 279 Independence............... 29.7 22.6 340 Heli VA DME Vaio Psa Pd eRe Sy BospAMoelegien ah hal). ch oene ca Te Wie. se 74 367 378 1 Gere 111 B41 Ud TORR ORT at A OI ne 48.1 49.9 36 .281 296 Sacramento. 2.0.0 i) Jue 66.7 62.8 55 .324 347 DAMEMDIELO} Wis wth cola apes ARS Rae iS abe at Sef 73 PO: MOM. ote be SE TATICISCO.).. st) ie coe chee 79.9 80.0 83 340 348 San Luis Obispo..........-. 69.0 69.9 rire 314 335 Colorado: 1D Yanai (eo OUND AN ACHR ey Det me A 48.7 46.7 54 185 285 1 GUE HO RELO Ne A oe seers Ae Ae SU A yO (53st ee i Feet, © Pabieaged [hoe maaan, Sa CE eA Hd LINC GI OM oi ciehy) eh eee ices ice sh ook saa i Seo hay PE bona Cant! wee Me ep ce ae 1 PEE TEHCOY RIVES anaes aL eo Te 48.1 45.8 47 LW Ark 274 Connecticut: PACE ER ORE iy Seer eau icus aN iu diae sual Niet Rue cy ak ACN | Weems 2 NES CURE eta NGS WRUETA VOM. oe is o's 3) elas 6 gs 75.9 77.6 12 298 447 Florida: ' MACKSOMVANE! 050 ie bs a 79.5 76.8 85 SDL 604 BRRTTOE DETOUR We MRLs Wikia ie 80.5 78025 84 664 692 1 CENTAGE ie a CO A i a td Ui aie 707 707 PBCMSACONA Sis oe) ol a acim ee: 78.3 CAFU SOO Re Sa ee 549 610 “CEN COTO VRS Ee era Sa oR 80.5 80.4 80 .592 612 Georgia: BU LERTAT Ue iy en ceig CSN L « (xl 71.0 76 396 503 RU TST ee Oe TS 73.4 73.8 79 450 565 SSECA\U721905 01) 0 VO re 78.5 79.0 81 514 600 POMS VAL EM Cua rid Mata. Misa Mila Satie OES, oie alien! (Ah 2 AP aya chee lg Peeled A iaem te Idaho: J BATISTA MP RS NEST es ees pe 56.7 45.6 42 209 262 POO TUCO CMO et ley areas ae ee ie MTL SUE anal 2 GS Taa a 1 a Os | USCS Gee Re UE Tilinois: AIR OMe Nhe Ten oe ngeweh 74.2 Cone 74. .390 .534 TCHR ON il he uo ae 74.8 71.1 71 . 286 .423 J EYED Lee! ESN RR Sica enue Ue SUM IOGnY INN er NE SRT a Cy Meet dL tal acianas rare Ge x ener a poy 1 O03 612) Ko A ae er 71.4 69.0 65 Be | .464 Indiana: Indianapolis.......... 69.2 65.6 63 310 448 Iowa: (CHA ERIN GRA Omen Me Ce ge Oe OF IMRAN Nee ei cote Ree) SPR ee WMavienportee kk ey ews w206 68.5 v1 290 452 Mes: Momesye yok weeks! Fal: 68.5 71 285 450 TO UOMO erica on ce Sos 75.0 COLe 70 275 432 PCO RUMI ae eie Gah Sumac es 72.0 64.5 ez 313 4558 STUER TDN uri Lt Gc lai aah es wie 69.0 LOPS UI | NPR arene) Ra nets ge! SRY Fa aa Kansas: GORCGOTUR ett eke cnc eae 68.6 66.3 74 98 463 TOME Cateye ee we RRM cue 66.9 62.9 69 284 431 AYA) OTE He, SIR eRe Oa ORE ee OL 66.0 71 321 466 Kentucky: WOORINPTOM ve s.s)< cues gee es wae CO Rae ck, LEE eas xara tyes 328 466 DUOUIS VEG eke ak eck hale re 67.5 65.6 64 340 476 Louisiana: INC COPLGAT Sie so ce wi eraiseeees cower (0.8 75.9 SO 545 585 346 ENVIRONMENTAL CONDITIONS. TaBLEe 19.—Normal mean relative humidities, for the year and for the period of the average frostless season, mean relative humidities for the three summer months, 1908, and normal mean vapor-pressures for the year and for the period of the average frostless season.— Continued. (gam awigiee Grea Mean vapor-pressure of water. Station. For period | For June, For period of average | July, and of average Annual. frostless August Annual. frostless season. 1908. season. Louisiana—Continued: p. ct. p. ct. p. ct. inch. inch. Shreveport. 2.6.00. one 72.9 72.9 76 .470 .567 Maine: ID aStDOTE 2h oh ts ae ies sara 77.9 81.8 79 .229 .345 Portland: 6802) ace, eee 75.1 78.2 72 . 259 .410 Maryland: Baltimore fi ois oe ee eee 69.5 68.6 68 .336 .460 Washineton, D. Coys. nee S. i2eea (ee 74 343 488 Massachusetts: BOStOMieek cen bee eee Woe 73.0 69 . 280 .411 Nantucket :). sb Unease eee 82.1 83.9 87 316 .425 Michigan: Alpenayn7 258 2 ene sr ese 80.2 77.4 76 . 240 .403 WCtrONGS coc Oe emcees “pie 74.4 70.2 74 . 282 437 1 SHSTEES 0 HR Metaanra oc MUNCH Arco PN Ui Gia «game BR RR A va 71 52a .401 Grand Maven orc. sie skola: 77.5 toot 74 Baie .417 Grand Aplas gai ieee me ee cella (eels ee eo 64.0 ck se eC eee ee Marquette soos co 2k Seo ele nies 78.6 74.8 67 BAe ofl BOrgsHUTon: 2s eee cee 76.7 (ae2 tL . 266 .423 Sault Ste. Marie............ 79.9 78.8 77 2a .ol4 Minnesota: Mev GHy fe sees hee Ree eeacehe 75.1 (203 81 2212 Bat) NMFoornNea ds to o.5 co Bek etree ees 74.1 71.5 75 .221 .405 STE tue aes Eg 71.9 67.3 68 247 .416 Mississippi: INGCTIGIAN he Oe Seccsclet docs eaiwiees 78.3 716 (9) leo ee See Pat ais nice’. Wicks blame eee isi e. k Wok a eae 73.5 73.9 78 474 .569 Missouri: Heitanaraniyalh ee eee eee cae 70.7 69.0 -- Poise Ale ae a KansasrCityo jn ii. aceue 70.3 68.4 72 322 .466 UM OUNS tae hon Mager ince 69.5 67.3 69 . 342 485 Sprinsiweldie ove ie ko eeu 72.6 71.9 75 .343 .495 Montana: aire oe Ane ices Se Rea a 66.4 NOM 62 .186 .308 1 5 Ke) es 0) see eae Ne a fe arte pa ee 56.1 48.0 56 .165 .249 FRESNO LL PRE cP See UR EAE ces TR de Ae fe ee GEe bc ew ce. cole INES City eis sw cee ian eee 69.7 57.8 59 . 223 367 Nebraska: | DNC) bo Ren i oo inves Sivan Prot 70.0 66.9 G3) leases saat. ee Worth Platte nsec Revco aehes 66.3 65.3 69 250 421 GT ERE) os Wee ie ere pr em oc 69.2 66.4 71 289 463 Walentine sun vine ok mre ee 66.5 63.8 67 222 386 Nevada: CWarsonq@ ity ne. ok ees Raina 50.2 39.6 P40 Never a ee ee ROTA Alls Saree aye ae Oe SAIN, Pepe mae ca A ee BS 9 | ede otcie a er Wannemilcea. = 6.6. ss. oe 46.5 30.4 45 .148 183 New Jersey: AtlamtlGOity. nests he ais 2 eae bie 81.4 82.3 78 .356 .491 New Mexico: 1 Reno instead of Carson. CLIMATIC CONDITIONS OF THE UNITED STATES. 347 TasBLE 19.—Normal mean relative humidities, for the year and for the period of the average frostless season, mean relative humidities for the three summer months, 1908, and normal mean vapor-pressures for the year and for the period of the average frostless season.— Continued. Mean relative humidity. Mean vapor-pressure of water. Station. For period | For June, For period of average | July, and of average Annual. frostless August ee frostless season. 1908. season. New York: p. ct. p. ct p. ct inch. inch PND BING s/iisteress wieloues oi oie. See ahs 76.2 74.0 68 . 284 405 BS Uitalo aia. Meare ikls Seah 73.4 71.6 (74 B76 | 414 BNEW OTE a) oy a Aa el 13.2 (Psa: 69 314 433 BSWEL Oi cietere wie\apaiens oarcleiene ae 75.8 73.4 72 .270 408 PPOCHESEER Sitio .idhe Wier oo olsue levee 73.4 70.4 67 .267 410 North Carolina: ENV OVERIA UL | SUANG MSIEN ee eter Dera | eet et oeset Ue (i a ES ARRAS OUR RS) UMN RS ge @harlottesyrs ce oso. ae (tng t (88: 78 382 500 IGE RASS heres iso sk sa wtaneisueus 3% 82.9 82.7 86 484 573 WE Lane WIKIES fc euteks . hBNeKal oe pS ONE Ts MINTS sn, Ae el SU Pa ees MEER R gee) > | Nar Jez (SF 0 RN So a 73.8 74.6 78 .394 527 Vale tOMe. | ss fk iia Na kre ote 80.1 80.9 82 471 588 North Dakota: PEprSmia Ee ayes he A dA le 69.9 65.8 64 . 206 377 ON rr Saeed KE at ic) Shier wana tee Sega ok tralia oI latter ena cere « Go ie AR ence eae Bn oe PNISEOM Wie eats:c\eie'c'sis sieteikee s 6 68.8 59.7 60 184 334 Ohio: CP MCIMMATHs5\5.0 sige oc cele oos 69.0 65.8 60 .325 459 @levelamdyii es se. ee Re wc 72.9 70.9 68 .290 414 GolmmbuUsiye sees. os oad cas 72.6 68.9 66 .305 449 S26 EOI) fy UIE Os ee eR 74.4 GOR ee abet ae So 294 423 IP e)IEYG (0 RR ap i aa ee 73.9 69.9 67 290 440 Oklahoma: Old an Oma 6. sole 5 shoo BOOK Se HY 69.8 68.7 75 .361 494 Oregon: Baker Cityare ss lost) ssh oes 60.7 49.3 54 173 236 JCS FRIES 0X6 Daan ee al SOE i Oa Toao 71.4 67 293 329 PRORE DUG es. Sal esoig isla Sioa dee 7: VX Oy ah Ry ea 63 282 323 Pennsylvania: JEL TTCESE ee MSA LR 75.5 f2).6 66 . 286 416 WA AITISUT OAs so bk oe ciekeve ene fone 72.0 310 ea Sag Or Ie (tel aot ee Philadelphias oo 500 ae a8 70.3 69.8 67 322 450 PEE CS DUTT oreo) oe ais, ak wht delet's (Pay 69.3 65 312 455 “SUGLREUIE CON CE SIAM rly AAT] | ARCO Ur nat (MURR ete A Oa Bao aio ied che terete ee arnt Rhode Island: Block island's i. sd cca cs eted « 81.2 84.0 85 320 428 HVOVAC CINCO SC) osc tane ks haters ear ath unateoar et dietar a [pe arate we alle TO? Wy Tabs Gd ser Lebo Sadat South Carolina: Charleston sic s s «ue svete ss 78.0 78.2 80 511 586 MOLLER)! RU cuealete ened 60e cy odes Wasa hhGe GO nile o codeReia bay Oy CLEAR SCE. ce etl South Dakota: IEIMEE OD chsucis Siecle: ac fbuk stick aks 70.2 65.2 75 229 415 IPS mera iat) 6. or ane wie lc 64.7 57.6 60 .219 370 1 sth ay ko tal © ny Gee Rae Aa ge 59.8 53.2 61 .197 322 YPUINCUOII Sree eo tin orcas 70.4 GZS teu he aw cae. 262 454 Tennessee: Chattanoowaie ek es cs dim aes tye 72.8 72 .3891 520 WSNORVELLG LS ovat ines cee anes risvey f 73.7 75 374 505 IVES RIAY ik pik Ov nen Oe ea ss 71.8 71.3 76 417 545 INBSEVILIO S yicethee ned eal 70.7 69.1 74 379 5138 Texas: PD UlenOs SN ki ince aladibe 63.9 62.6 65 369 456 348 ENVIRONMENTAL CONDITIONS. TaBLe 19.—Normal mean relative humidities, for the year and for the period of the average frostless season, mean relative humidities for the three summer months, 1908, and normal mean vapor-pressures for the year and for the period of the average frostless season.— Continued. Mean relative humidity. Mean vapor-pressure of water. Station. For period | For June, For period of average | July, and of average Annual. frostless August Annual. feces season. 1908. season. Texas—Continued: p. ct. p. ct. p. ct inch. inch. Amara ll@ oA 5 82.2) hl aeons ae 59.3 59.4 68 . 262 a 6s! Corpus Christhis.:, be oc eee 82.1 81.9 80 .618 .675 PASO sees ks tet ee ee 38.8 37.0 43 . 243 .300 Galvestons 10 see oe 85.2 80.2 74 .595 .622 Palestine oc tah pc eas peer 73.8 Cook 78 .467 .569 Sal Antonio. iio: eee eee 66.6 66.7 73 472 .540 Utah: Salt Lake City....... 52.8 40.9 45 .193 .250 Vermont: Nori hitel di ei eee ae 77.6 78.1 86 . 239 .423 Virginia: Pynchbure. Poko Stee ce ee ctor 72.8 ae .356 -498 INortollkeny.c. cs para aes aes ee 78.6 79.1 79 .410 .525 Way Chevalle eyes 9s ees ete Pa ee RG) BR eg 900 Wiener Washington: SGA GLLE oe ak ec cia aati as nene 16.2 73.6 co . 286 .318 SPOKANE sue das vena Sara eee 64.0 52.9 46 . 209 .253 PPACOMIAR AE. A365 Ceo Sl eke reine eee ciel eas Uae w 3). | twas ee a COOSME Shams 2 are eis ll Rae ane eal ncn ere) Sees 89 . 304 328 Walla Wallace seo eens 64.8 54.6 46 .250 297 West Virginia: MU KDTAS oil hoc Skcik, a Sat: Bouse ce ena ep eS | OU ee re a 83. la eee Sil oe Warkers purge «fis. ao ckbeghe Oe 1920 Tae 73 soon .482 Wisconsin: Greene baviees oo bot anee cee 74.0 70.6 69 . 245 .407 Mean C@noss@n toc se ee (ake GO a neem Vite . 266 .438 VICE CISOM oe iL ee Ee Se ee bees a ee Fae | ov tnes diel Malwawkeen! ie. 28s hea 74.9 72.6 71 . 265 .420 Wyoming: Cheyenne en © eee eee 53.7 52.9 61 .163 .274 WGC EN ee ee Ane |e Ser 5i8 47.9 58 a15o on DCHIG ANE Cees on oie sae atin be ee eee el eee ee 62). belecs Ree MelGwstoness .w ees eee ee eae | Bick cia ae Gh. ie hoes ef e aeee The chart of plate 63 is markedly different from any of the moisture charts heretofore considered, excepting that it somewhat resembles some of those for precipitation. It is not very similar to any of the temperature charts with which we have been concerned, but it appears to partake of the general characteristics of both temperature and moisture charts. In the East the zonation here shown is markedly similar to that for temperature, the isobars having generally a west- east direction. Each of these lines, however, is seen to bend rather sharply southward in the middle of the country, so that the region west of about the ninety-eighth meridian of west longitude is generally characterized by isobars that have a north-south trend. The western CLIMATIC CONDITIONS OF THE UNITED STATES. 349 mountainous region, west to about the middle of Washington, Oregon, and California, is shown as an area of low vapor-pressures (below 0.300 inch), this area apparently extending a little into Canada at the north, but not reaching the Mexican boundary at the south. The whole Pacific coast region is shown as having very low values (mainly between 0.300 and 0.350 inch), about like those of the region of the one hundred and third meridian, in the plains area. Southern Florida has the highest values, that for Key West being 0.707 inch. (3) Norma Mresan AQUEOUS VAPOR-PRESSURE FOR THE YEAR. (TABLE 19, PLATE 64.) The means here used are taken directly from Bigelow’s tables. They are reproduced in the fifth column of table 19 and are shown graphi- cally by the chart of plate 64. The zonation shown by this chart is so similar to that of plate 63 that no special discussion is here needed. Neither is it necessary to derive any generalization from these two vapor-pressure charts, since the discussion given for plate 63 brings out all the points that might be mentioned in a generalized statement. EK. RELATIVE AIR HUMIDITY. (1) PRELIMINARY CONSIDERATIONS. Data of relative air humidity, obtained by means of stationary or whirled wet and dry bulb thermometers, have been accumulated for many years at the various stations of the United States Signal Service and of the United States Weather Bureau. These were brought together by Stockman,’ as monthly and annual means for the period 1888-1901, for 130 stations. Stockman’s means are stated to have been ‘‘derived from observations made at 8 a. m. and 8 p. m., seventy- fifth meridian time.’ They form the original source of our studies of humidity in the United States. The theoretical inadequacy of data of relative air humidity in char- acterizing climate is tacitly suggested by a brief but well-chosen state- ment with which Stockman prefaces the table above referred to. He Says: “The relative humidity furnishes no direct indication of the absolute amount of mois- ture in the air. For purposes of comparison consideration should be given to the fact that as the temperature is lowered the capacity of the air to retain moisture is decreased. Of two stations having the same average percentage of relative humidity, but different mean temperatures, that station which has the higher mean temperature will have the greater amount of moisture.”’ We have already emphasized the fact that vapor-tension deficit appears to be the climatic feature which should be recorded in con- nection with air humidity, this being the difference (in pressure units, as bars or as millimeters of a mercury column) between the maximum 18tockman, W. B., Temperature and relative humidity data, U. S. Dept. Agric., Weather Bur. Bull. O: 25-29. 1905. 300 ENVIRONMENTAL CONDITIONS. vapor-pressure of water for the given air-temperature and the actual vapor-pressure of water in the air. As has been pointed out, this deficit should be an index of the relation of air humidity to evapora- tion; it should measure that portion of the atmospheric evaporating power for any given time, which is not related to wind-movement. The arguments of air-temperature and air moisture-content are thus combined in a single function, which becomes the more significant when it is pointed out that different parts of the country do not generally differ very markedly in relation to wind. The terms from which the vapor-pressure deficit might have been obtained were at hand when the relative humidity observations were recorded, but it is not possible to deduce them from the recorded percentages, espe- cially since Stockman’s published data have been reduced to normal monthly means. It is readily seen, however, that the higher the temperature (2. e., the farther south is the location of a given station), the more a given percentage of relative humidity is to be discounted, as it were. Thus, if a northern and a southern station (as Duluth, Minnesota, and Little Rock, Arkansas, for example) agree in having the same normal mean relative humidity for the period of the average frostless season—say 72 per cent—we are perfectly safe in concluding that the normal mean evaporating power of the air at the southern station is greater than at the northern, supposing the air-movement to be alike in the two cases. But it is not possible in such a case to weight the humidity records in a quantitative way. Before proceeding to our results in this connection it is necessary to mention one other very important point, which requires s attention from climatologists who hope to relate climate to plant activities in a detailed way. As has been stated, the humidity data of Stockman’s table were derived from observations ‘‘made at 8 a. m. and 8 p. m., seventy-fifth meridian time.” This is the regular practice of the United States Weather Bureau in dealing with humidity, and it will be seen that the longitude of a station determines the times in its day when observations are to be obtained. Thus, the observations for any day at North Head, Washington, come to us as though they were made at about 4° 40™ a. m. and p. m., while those for a day at Eastport, Maine, are to be similarly considered as made at about 8> 30" a. m. and p. m. Now, humidity alters very rapidly, in most cases, during an hour or two about sunrise and about sunset, and the morning observation on the Pacific coast is usually made well before sunrise, while that in the northeast is made well after sunrise. A simi- lar consideration applies to the evening observations. It is clear that neither the morning observations nor the evening ones, throughout the country, represent the true humidity conditions for the given date, and it remains to be determined what the mean of these two percent- ages may denote. The question is, simply: Can the humidity con- CLIMATIC CONDITIONS OF THE UNITED STATES. ZAEM ditions for any day be as well derived from observations made, say, at 5 a.m. and 5 p. m. as from those made at, say,8 a. m. and 8 p. m.? When vapor-pressure deficit attracts the attention it deserves the same problem will arise in connection with it, and then the local times of observation will have to be seriously considered before the data may be regarded as quite suitable for studies involving plant transpira- tion and other ecological or agricultural features.’ On the whole, it needs to be borne in mind simply that the moisture conditions of the air deserve as much attention as do its temperature conditions, if agriculture and ecology are to employ climatological results. Our aim in the above paragraphs has been, not to point out what might or might not have been done in the past, which can not now be changed, but rather to emphasize what seem to us to be the needs of ecological and agricultural climatology for the future. We shall deal here with three kinds of indices of relative humidity: (1) the normals for the period of the average frostless season, (2) for the year, and (3) the means for the three summer months of 1908. (2) PercenTAGES REPRESENTING NoRMAL MEAN ReEwativE AiR Humipiry FOR THE PERIOD OF THE AVERAGE FROSTLESS SEASON. (TABLE 19, PLATE 65, AND Fic. 17.) The data here employed were derived from the monthly values given by Stockman (1905), by the same general method as we have heretofore resorted to in obtaining indices for the period of the average frostless season from monthly normals. Our values are given in the third column of table 19, and they are shown graphically on the chart of plate 65. The chart of plate 65 shows that the relative humidity values are high (above 75 per cent) for the Pacific coast region and also for the Northeast, East, and Southeast. The lowest values (below 40 per cent) are found in the arid southwest. As a whole, this chart resem- bles the charts of precipitation-evaporation ratios (plates 57 to 62), and certain lines are here shown as broader than the others, to bring out the division of the country into climatic provinces, as was done on those charts. The arid region may be characterized as having relative- humidity percentage values below 50, the semiarid region shows values between 50 and 65, the semihumid regions show values between 65 and 75, and values of over 75 characterize the humid regions. In this case the northwestern humid area is extended southward, along the Pacific coast, to middle California, and the adjoining semihumid area extends to the Mexican boundary. The semiarid region extends east- ward to about the hundredth meridian of longitude, somewhat farther at the south and not as far at the north, thus agreeing, in general, with 1The hours of temperature observation in the United States have been very thoroughly studied, in relation to the daily means derived therefrom, and several important considerations bearing on the readings of the dry and wet bulb thermometers have been taken up. In these connections see Bigelow, 1909. Alsosee O. L. Fassig, Report on the climate and weather of Bal- timore, Maryland Weather Service 2: 29-312, 1907; especially pp. 152-158. ‘Z, oped st aseq oy, “Your Ue Jo sYIpeIpuNy ore sonyea [voloWNN ‘G UUINOO “GT e]qe} Woy “yep ‘eed Joy Somssord 10dvA snoonbe UvoeUl [VULION \! BIL Stl oLIT bul (seq) (3S9 A 18910} UaaIFIBAP goTISuB — 3S210} dao1s12Ae SIO} USIISISA on Aydo. IB AY 382J0} snonpiaap —— mnAydosaw usayoN = AY WI9}ONy tLia]S9MyIION . . purjssessy ee aaa "eM AX) ry i if an Z YX ___- 3 __ 8 Ea JSO10} snonpideq \\ : ‘2 S31" ooo = a fh ki xy | l | ( 0 YY 977 4 IN SS s( Nt XN x > ; Bo RY N Oven ‘| NX CAA. 44/77, Day \ IN RES RS 7 SLU SX x \ S } Ss N qQ we. SU Li "WG hyp, & te s i, = SS SES Yigg SY ‘ SANs RRwZ Z SIT. KS] % BM SN Vet sos SSS > il if BS 4 1% PLATE 64 Z, hte SE aa NA e o Si EE aw % SAM . LER SS N ; Is Ae ii i (A a O_O ht w/. Cal > SRS S252 KS o v5 bx <5 eo y } | i < RK ICS 302 318: 88" 2e9@= 228 268) — 516" =006=-.96— 7.26 266) c10l s A iG ee) 9 ‘Z oyeyd st oseq oy, ‘sooutaoid Ayrpromny anoj oyur deur oy} oprarp soury IMT“ WuINyOo “GT 9]qv} WMOIy VFEp FUOSLOS Sso]}SOIJ OFV.OAV JO portod soy AYIpruny Are OALYepoL UBOUT [eUILOU Zurjuososdos SoFeyU9010,4 6 66 LOI 801 A , & c 6 (48eq ) ’ (159M) 18910} U9018 199 UolisUuey a] §sa10} usaIZI9A9 1S910} Usd1d IAAe mn Aydosshy 19910} Snonpioep Bas oAydosow uz9y110N -puRlseessy , ry et WY, : eh tt a t b # = O q MUO ih 1D", Peeee a ia | Pir S311 009 ==s¥ Lmauaiiie’ = = = [SI Sy 48010} 91yAydosow 48910} Ula}seay NOS snonpwoq AW S Swill NS Y ALS Ni AN, Ws RIN NsN AAs \ a QS vel d WX WOON < Se ¢ x S RI QYS 4) & Ly, Bi My iB A ee hy SESW & GY ‘S WY MY, x \ -—} a $6 KY Wi va DOORS V2 NY ‘ x — PLATE 65 aN 2 Be Z i ea y 6 (gall ™ Shee 4 cS t\ Albin ws SRLS. we ae il Ws \ KRY SS ss i uty 3) is LMS Aen ei es ep Sie “s > Ces ~ Spey 7 « a’ yl ; ah ” | M t. TR Wan eS Ke SENS SINS rw AW WJ “0 SN lll Ne RO rites RECA SEs : a) 7 NOD J Fr 2 = SI} Fin ie ait ~£ Wy eae. te yee aeore sli = 6 per ofS 88 354 ENVIRONMENTAL CONDITIONS. | plates 57 to 62. This relative-humidity chart also agrees, in general, with the moisture-ratio charts just mentioned, by showing an east- ward projection of the semihumid area from Nebraska to New England. The eastern humid area occupies the Gulf coast from the Rio Grande eastward, practically all of the Atlantic coast (excepting northern New Jersey and southeastern New York), northern New England, northern New York, and northern Michigan. In its northeastern portion this chart resembles that of plate 61 more than any of the other moisture-ratio charts. (3) PERCENTAGES REPRESENTING NorMAL MEAN RELATIVE AIR HUMIDITY FOR THE YEAR. (TaBLE 19, PLATE 66.) Our data for this index are taken directly from Stockman’s table. They are reproduced in the second column of table 19, and are repre- sented by the chart of plate 66. This chart also shows a pronounced general agreement with our charts for the Transeau moisture ratios. The general zonation of the country is again shown by broad lines, but the lines for the value 65 on plate 65 are here represented by those for the value 70. The semi- arid region is here thus characterized by values between 50 and 70, and the values for the semihumid region lie between 70 and 75. The line for the value 72 has been added in the central part of the country, to emphasize the eastern lobe of the semihumid area (shown also on plates 57 to 61 and on plate 65). An area of values a little below 70 is shown about St. Louis, Louisville, and Indianapolis, thus differing from plate 65, but agreeing, in general, with plates 57 to 61. The eastern humid region is here shown as much like that of plate 65, but the line for 75 here lies considerably farther south in the regions of the Great Lakes and of New England. In this respect plate 66 resembles plates 57 to 60 more than plates 61 and 65. (4) Percentaces REPRESENTING MEAN RELATIVE AIR HuMIDITY FOR JUNE, JULY, AND AUGUST 1908. (TasBLe 19, PLATE 67.) The data for these indices were obtained from the Monthly Weather Review for 1908, the means for the three separate months being simply averaged in each case. The results are given in the fourth column of table 19 and are charted in the usual way in plate 67. | This chart has the lines for the index values 50, 70, and 75 repre- sented as full lines, to exhibit the general zonation of the country, just as in the case of plate 66. The northwestern humid area (values above 75) here extends southward, along the Pacific coast, nearly to Los Angeles, California, and the corresponding semihumid area reaches to the Mexican boundary. The arid area is depicted in much the same way as on the other two charts of relative humidity, but is not quite as extensive here 4s in the other cases, this being due, no doubt, to the effect of the characteristic summer rains in western Texas and New CLIMATIC CONDITIONS OF THE UNITED STATES. 359d Mexico. Instead of completely surrounding the Rocky mountains, as in the other two charts, this zone extends eastward only to these mountains, but there is here a small local area of values of 50 or below, indicated by the data of Santa Fe, New Mexico, and Pueblo, Colorado. The eastern limit of the semiarid region (70) is here placed about the 99th meridian and this line has nearly a north-south direction. The region here called semihumid, in the east, is somewhat restricted in this case, but shows a very large eastern lobe, reaching from Nebraska to Maine. The localized area of semiarid conditions within this lobe is here very large, extending from Minnesota and Illinois to Maine. It will be remembered that the area in question is not shown at all on the humidity chart for the period of the average frostless season (plate 65) and is represented as much smaller on that for the year (plate 66). The eastern humid region is here exceptionally wide in the southeast and is narrowed at the north, somewhat as on the chart for the moisture ratio for the year (plate 60). This chart of relative-humidity values for the three summer months of 1908 was prepared for comparison with the chart of evaporation for a similar period of the same year (plate 56). The stations for the 1908 series were not numerous enough to give a satisfactory chart, but these two charts agree, in a general way, in showing the great eastern exten- sion of the region of semihumid and semiarid summer conditions, from Oklahoma to northern Michigan and New England. For details, the two charts can not be compared. (5) GENERALIZATIONS FROM THE THREE CHARTS OF RELATIVE HuMIDITY VALUES. (PLatTEs 65 To 67, AND Fia. 17.) The main points brought out by our study of relative humidity values may be briefly summarized as follows, reference being made to figure 17, which is derived from plate 65. The country may be divided, on the basis of relative humidity—as on that of other moisture features—into four humidity provinces, which may be termed arid, semiarid, semi- humid, and humid. The humid relative humidity province occupies: (1) western Wash- ington and Oregon and a variable portion of the California coast region (depending on the form of index employed); (2) the whole of the Gulf coast region and that of the Atlantic coast as far north as Long Island or Massachusetts; (3) northern New England and New York - and a variable portion of Michigan, Wisconsin, and Minnesota. It appears probable that portions (1) and (3), as just defined, are con- tinuous through Canada, so as to form a single northern humid region. The southeastern portion (2) appears to be quite cut off from the northern one, but only by a narrow neck. The semihumid province lies just interior to the humid one, being very narroW in the Northwest and West. The eastern and western portions of this zone, as shown on PLATE 66 306 Te reat rAord Myipramnd INOJ OFUI Aeur oY} OPIAIp soul] [INT °Z WUANjoo “GT 9[qQe} MOTs BFep ‘reo ioy AIPTUUNY VAVpeI UBeUA [eUIIOU SuIyUoSeIdel SsoseyUedIIg % : eg G8 oL8 068 16 306 086 oL6 366 Ol of 01 9801 ~LOl 601 : lll etl oall. Wal <61l (se) 38010} U99Id.19A9 uoryIsuet} Jser0y Use1d19A9 a1 Aydoi3 Ay 3se10} snonpioap I - purjssets) S371IW 00S ort ni’ Lia S we yY AX —~ oy bn St ROC Wi) SS uaIseaunoS < ee dé = e7AY N Y Ot: \) \ 1 SOG LGA SRY 7737 \\\ \ EE OX \ Ws, : \ SSS WAS FZ a st < ‘ ge \" WK oR . . Ybor 1c Li a. a oe 4 < SN \ieae=s eA ee Wa CG 5 ay CS == @, ee LLY 10724 ; 2S ONS =——= —— OF == ee 2 fond PSS PSS os Pox BSSOPOR SS ‘7 | (> ~ ~s | S ANN Cy \\ , os 5% >. > <> $ oO 60> Sotete’ BSS Otero SS SS N ne oN WBS t SS z KIES <> iS AS ., oS Ss ~ IN Mii AY NG asa ares > 4% Ss Dox Se ‘eM oH KM 358 ENVIRONMENTAL CONDITIONS. these three charts, are probably continuous in Canada, to form a single zone. In the eastern half of the country this zone occupies all of the interior, as far west as about the hundredth meridian of west longitude. The semiarid province embraces the Great Plains and a belt lying east of the western semihumid zone. Finally, the arid province occupies the region generally known as arid, extending approximately from Arizona to eastern Washington. This zonation is in general agreement with that shown by the precipitation-evaporation ratios. From these considerations it appears quite clear that the data of relative humidity, as here employed, furnish an exceedingly valuable and rational climatic zonation of the United States. This may be taken a { rok : iv, 4, f A t ef Vs H 48 | i / i i 2 AES are ds Se as ag Bg SS: 4 ye eS \ u \ ie 5 Cak ED eel | | 7 ek ml Le a Patan Na lia Naa A bat Fic. 17.—Moisture zonation, according to indices of relative humidity for period of average frost- less season. Humidity provinces: Humid, more than 75; semihumid, 65 to 75; semiarid, 50 to 65; arid, less than 50. Numerical values represent percentages. (See also Plate 65.) as satisfactory evidence that the theoretical objections to the concept of relative humidity and to the usual manner of its employment are not serious enough to prevent this method giving a clear zonation that generally agrees with that obtained from the precipitation-evaporation ratios as we have used the latter. It seems hardly probable, however, that detailed studies of the annual march of climatic conditions as related to plants may be as well served by these data as by those of vapor-tension deficit, evaporation, and the precipitation-evaporation ratio. Considering the fact that data from 14 years of observations are here employed, and that many more years are now available, so that CLIMATIC CONDITIONS OF THE UNITED STATES. 309 much more satisfactory charts might probably now be made, it appears that these charts of relative humidity must be regarded as perhaps the most valuable of all air-moisture charts with which we have been able to deal in a practical way. F. WIND. (TABLE 20, PLATE 68.) Wind influence upon plant growth occurs in several ways, the most generally important of which is probably effective through increased transpiration. As has been emphasized, air-movement is very influen- tial in determining the evaporating power of the air, which, in turn, is the main external condition governing the transpiration-rate as well as the rate of water-loss directly from the soil-surface. This influence depends upon the velocity of air-movement. Strong winds tend to break plants as well as to dry them, but this feature of wind influence appears to be of importance to vegetation only in relatively restricted areas. If wind were to be studied in this regard, it is very high wind- _ pressure and its duration that would require attention. The direction of the wind, so important in weather predictions, is of no importance to plants in general. If the ecology of individual plants or small groups is to be studied, then wind direction may sometimes become important. : Wind as a climatic condition influencing vegetation may be con- sidered: (1) in terms of its average velocity—perhaps the most useful wind-dimension as far as the evaporating power of the air is con- cerned; (2) in terms of its maximum velocity and the duration of very high rates of air-movement; and (3) in terms of the maximum pres- sure developed and the duration of very high pressures. The United States Weather Bureau has accumulated anemometric data for many stations in the United States, and we have employed some of these data to prepare a chart of average wind-velocities for the period of the average frostless season. The data employed are as yet unpub- lished, but have been very kindly furnished us by Professor P. C. Day, of the United States Weather Bureau. They consist in a table of average wind-velocities (in miles per hour) for each month of the year and for 151 stations, based generally upon the 20-year period 1891-— 1910. For each of these stations the average wind-velocity has been calculated for the period of the average frostless season, as in the other cases where monthly averages were used in deriving means for the frostless season. The results of our computations, together with the annual average velocity in each case (obtained from the records of the United States Weather Bureau) and the height above the ground of the anemometer are given in table 20. 360 TABLE 20.—Average wind velocities for the year and for the period of the average frostless ENVIRONMENTAL CONDITIONS. season, usually from records for the period 1891-1910. i & o S| iS) S @) las 3 Station. = S & fed) 28 a0 a3 an Alabama: feet. Birmingham 32) fx<5 2. 22: 48 Mobiles Sak te cece een 106 Montsomeny. ss2) 0 Sone 112 Arizona: Plapstafi 2h Ss: wean ee 57 PHOCHIK se echt. ee 56 OY qT at de os Soe d athe eee 58 Arkansas: Hore smiths.) 26. 3 oie 94 Little Rock). s.= 6 ves: 147 California: Ge Ka ee Dire shaken eee 88 HTeSHOe eh et ee ee 70 Host Ampeles ean iece ce oa aL Ok Point Reyes Light....... 18 a i(evs bal Ba ot ee ee eI 56 Sacramento. 2 sic. Wei. S. : ilnlyé Sane DIerO sree so seca 102 Sanbllrancise@.2 <<. 2. 22. 204 San Luis Obispo......... 54 Ssh Barrallgme 2-0... 48 Colorado: ICH MERR ess eee i eae 172 DURAN EOS Ae te wrens Ge 56 Grand Junction. .<¢.>..,.. 51 IPUCDIORE. Le alcae hee oe eee 86 Connecticut: INGwellavenes = su nso. 155 Florida: Jacksonwvalle.. >. fan ge 129 Key Westie sc cts ess 53 Pensacolaces sieves 183 EAN Hh cls ie Recteds ns tena eaee 96 Georgia: A lamba eee sce 216 AVIGTIStAY coi. open ice 97 Wisconr et oe so ees 87 SavannahpPsscen .6.5 2 ae 194 aA homasville;s. ss-88 ne Vf Idaho: Boses. BAe ee Rae 86 PiewisStonin. «6. ks See el Pocatellos ees 2s 54 Illinois: Gare & eer eae a ae 93 ChieseOn ee no ee hee 310 SPEC asc ents 91 Indiana: vansvilles. 2-22 see ese 82 Indianapolis: si.// 25 ee 164 Average annual velocity per hour. miles. pat pa = Ow NWHM COMO WNHHOR NOD at on © & OO a NW OBN ONIN bo Oo Ow Nod CON OLD & WO WO NI 0 — Average velocity per hour for period of average frostless season. miles. see ee ee a “Im COR NI CO Or ye Or 00 G1 Or © & © © 00 on oor Ors] © 00 bo on o& bo & CO eo Om Ww NINN bo a S feb) g re) =| o . ag Station. i = © bh jb} zs Se} aS an Iowa: feet Charles City 234 2222325 8 Davenport iae6 sch ee cee 79 Des Moimess 325.054 sme 98 Dubuque ke 5n- oe eee 115 Weg katheys she seca igs oe 79 SioUm Cityiae ste bee 164 Kansas: Concordia 6a 50 Woedeer nis a acme eee il Waichitae a Seo oka eee 12 Kentucky: WexiN PEON cy. ai aoe oe 102 Ihouisvalle, | niente Ne ce Louisiana: New, Orleans). 5...) 232265 12 Shreveport. e = Hb a GO 00 ~J 00 (3) em) QO OI © 00 Coe D> bt et “J © oo 8 © 0 per hour. Wo NRO © ARH NWhRNWWOWHE NOaAOwhy pp? for period of average Average velocity per hour frostless season. 3 2. a _ et rT HOON OD Ww 00 Of Ob 00 w 00 © OG “I 09 CO C1 OS © IP 00 1 0 oon con Hm 09 oo QO Ot > POONwWh ? — “I 00 © © CO COD (o>) “IO bo IO OD OO © OC CO — ee ee ee een ON ee I Se a ne CLIMATIC CONDITIONS OF THE UNITED STATES. 361 TABLE 20.—Average wind velocities for the year and for the period of the average frostless season, usually from records for the period 1891-1910.—Continued. er y Average annual velocity o si ) | 7) ° ag Station. < 2 55 o =i 2 aa ae Indiana—Continued: feet. CNS] 0)2) CUA ae 34 Nebraska: Morty Platte... 6.0.6... 51 OFT 208 ea ery aie ana 121 DVNCTADLING ¢ o.5 75 Gis alee’ ocean) as 54 Nevada: @arsome@ity. 6 is... ek es 92 Winnemucea............ 56 New Hampshire: GHC OTC: Wee 2). Wis ee 79 New York MUERTE SEONG cic ils s).c ess 115 Binghamton. ..)...... 65 88 [BATCH a ey er oe 206 (CIENT) 1050) ae 61 IN 2 CCE hs ee 314 (CSI GEL OU eee 91 PROCHESEET. c cicce es coc be 102 IVMACUSEK 6 cle elcys a bio leo eS New Jersey: Pebampie @ity 6. es kc 48 New Mexico: PROSE re oi bo ar oie 455 57 Same. ck ee 56 North Carolina: PS SMGNAMC oc) o u's ci wiein ss « 84 Chranotte oo ee. 76 GET AS cy. cd eles es ele AT MRPURCTER ogc vc eoeiceieeis ie ss 110 Walmimeton. 05.5... 66. 91 North Dakota: PUSTIUARO Kc ors) c 6 a's ois se + wie 57 Devils Lake............. 44 AVS EGTA ee ek Sle dail 47 Ohio: WIiMCMMAY ek 160 Cleveland: «vic bd ok ewe. 201 WOMUMIDUBIY sores 5/45 dhe oes 222 See ho (VS) 5 ge A 70 PERC he ie Radin ga 246 Oklahoma: Oleighomas.. oe eee 47 Oregon: J eS clltc he (a REM au eaten pA 106 MUOSOOUTE. Geis cae howe elute 57 Pennsylvania: PATE ae Guiles choiare ew eae! ah week 102 EPRIPPIGOULE : yc tet eek cou als 104 PPieclelm bias... vik gs gieie ee 184 PXGUSUTI EN, w cache. cistechaliacecsns 410 MOPANIUON oer. cat cmoece.s 119 Average annual velocit — + i —_ —_ —_ —_ UB hg 10 per hour. ORONRNEN & OH NBS OF emomors oN © OOH ON > COOwn hy He» bo CW HB & 00 & COOr RW ho oro bo ko o ae 5 Se g HP ° SyeN Ss SI BS § a3 S70 $ Station. 5 rt) on So n Oo tp 2 88 © ae 25 aie er S 4 oH o < a0) miles. || Rhode Island: feet. 5.4 Block Island psc), a ois 46 South Carolina: 8.8 @harleston’ seit .2/. ele es 10 7.8 Columbia} 94),) 2 jase cae 57 10.6 || South Dakota: EMarowes Soot oes eee 3 67 (ie 7¢ PACET OMA 0500, Uh ee teak nesses ie 75 8.6 Jgy2y O10 WK OFT A Ole errn ee: 50 Wem kton hike ots Gs elete 57 4.7 || Tennessee: @hattanooga.... .as4s..- 213 TA Knoxville nice sca ces. ie 100 Dis: Memphis. cckioec es ses 97 15 Nashville yy. ccissina nor. « 191 9.7 || Texas: 2 Aibilenek si ./a.pe.e s saya 52 8.9 AVE Oe veratcis eave hg eee coe 49 3 Corpus) Christi..\. 23... 77 10.0 FOL RasOn wisi gia emi abe e 133 ROE GA ORU I Wa seep assis @ee8 alae 114 9.6 Grav eatom nc sak Wet sa eo 112 Palestimenjoas.e< drt ives 79 5.8 San AmtOniOne ejeica is gars 3 91 6.8 Peano Rer cc niee ee aha etna 63 Utah: 6.0 IND OGe Tay Mosc re eecacuns cde 43 6.2 Salt Wake @ity.:.2 5... .. 189 13.5 || Vermont: 5.9 INortheld ys ese cece ccs ox 60 8.0 || Virginia: ymehburg :) < 25 bose ie 8s 10.0 INOTLOLaide eiemierne Oe eel. 19% 10.9 UICHMONG NS cc cake cc kc. 52 9.3 Wytheville......... 47 Washington: , 6.3 North: Head: 266 6s <0. o% 56 12.2 BOR bhGrsice arin oacsedh Goat 224 8.9 SDORAMB sel saccrdiclain aos Jatin xt 110 7.8 PACOMAe ec aes woe wae 121 9.7 Tatoosh Tskand. os #ciid. 00 MD & 00 00 © rP ON OCOHHDWORDMD ABNHO —" tH» Or Orc & _ per hour. OD © (0/4) He» OO bo Ol OMOMDW oe ies | for period of average Average velocity per hour frostless season. miles. _ nS Om © — Orny O1 Or NIN OF —" ww) TUM ODMWWH Or © O O1 bw mMomeo no o _ ~] an Oo mR bo He O&O ee ee ee 362 ENVIRONMENTAL CONDITIONS. The average wind-velocities for the period of the average frostless season, given in table 20, are presented in the form of a chart in plate 68. Perhaps the most striking features of this chart are the prevalence of high average wind-velocities near the coasts and near the Great Lakes and the apparently low average velocities encountered in the mountain regions. In connection with the latter feature it is to be noted that stations in mountainous regions are generally in valleys, and are therefore protected from the general air-drift of the region. This chart appears to be of little or no value in defining rational climatic zones; either the average wind-velocity per hour during the period of the average frostless season is not a suitable feature by which to measure climate as related to plants, or the data upon which our caleu- lations have been based are too inadequate to bring out any relations that may exist between this feature and plant distribution. We are persuaded that both of these alternatives express the truth. The average wind-velocity during the growing-season for plants is so little different in different parts of the country, and the evaporating power of the air is so greatly influenced by other conditions than wind, that it seems hardly to be expected that average wind-velocity may prove of great value in vegetational climatology. At the same time, if the distribution of climatological stations and the methods of wind observa- tion employed by the United States Weather Bureau should ever be reorganized according to the needs of this sort of study, it is possible that average wind-velocities might assume more importance than is here apparent. A glance at the various heights of the anemometers above the ground, as given in table 20, makes it clear that these instru- ments have been placed rather for convenience than for the obtaining of useful results, as far as climatology is concerned. As Livingston has remarked (1913), the population of the cities of the United States may be estimated from decade to decade by the average height of the Weather Bureau instruments above the ground; the instruments seem to have risen higher in the air as the population has increased. This, of course, is due to the pernicious habit of locating the recording-stations generally in cities and towns instead of in the open country, where the first principles of climatological study demand that such stations should be placed. As towns have become cities and cities have enlarged, the anemometers have been elevated from time to time, so that the back- wardness of a town—as far as large buildings are concerned—may be inferred from the low elevation of its Weather Bureau station. Table 20 shows that the anemometers are generally about 50 feet above the ground in small towns. In New York City the anemometer is 314 feet above the ground, and for Pittsburgh (the highest elevation given on our list) its height is 410 feet. When better wind data become available other lines of attack may be begun, as, for instance, a study of the relation holding between CLIMATIC CONDITIONS OF THE UNITED STATES. 363 vegetation and maximum wind-velocity, but such attempts would be well-nigh useless at present. G. SUNLIGHT AS A CONDITION INFLUENCING WATER-LOSS FROM PLANTS. (TABLE 21, PLATE 69.) As has been remarked, the influence exerted by light conditions upon plant growth is very complex, comprising several kinds of influences that are themselves quite different. With regard to general plant growth, which mainly interests us in the present studies, it is obvious that the most important light-relations are those of transpiration and photosynthesis. The second of these relations is quite out of reach at present, for before the light conditions of different climatic regions may be com- pared with reference to the possibility of plant photosynthesis, the light-supply must be measured especially in terms of those ranges of wave-lengths that are known to influence the photosynthetic process; it is clear enough that the total light-supply is not in itself the condition to be studied in this connection, and spectrophotometry has not yet progressed far enough to furnish the instruments and methods here required. When it becomes possible to measure and record, at each climatological station, the daily supply of solar radiant energy of cer- tain relatively small ranges of wave-lengths, then, and then only, will the photosynthetic powers of different regions become capable of being satisfactorily compared, but this seems unlikely to occur in the very near future. The light-relation of transpiration is much more easily approach- able than is that of photosynthesis, but the climatological records so far available are not suitable for even the relatively simple com- parisons required in this connection. Here the climatological con- dition to be studied is the power of the surroundings to accelerate the rate of water-loss from plants through the action of impinging solar radiant energy. Since no two plants are to be regarded as exactly alike, and since the internal conditions of the light-absorbing surface are as influential in determining the light effect upon evaporation as are the external light conditions, it becomes necessary here (as in the case of the evaporating power of the air) to adopt some standard light- absorbing surface and to measure the light-effect upon that surface. The measurement of sunshine has usually been accomplished by methods that depend upon the increase in temperature occasioned by the exposure of a certain blackened surface for a specified time period. Thus, the black-bulb thermometer has been employed by various authors in the comparison of the total intensity of sunshine energy received at different stations or for different days, etc., at the same station. The instruments so far described have not been generally satisfactory, being difficult of adequate operation and of calibration. PLATE 68 364 °z, oped Sl asvq OY, “Pp UUINIOD ‘Oz 9]q'B} WOLy BYVP {UOSBOS SSO]}SO1] BSVADAT JO pOr1od AOJ (SopTUL) SOTIOOTOA pur ATANOY osvAVAY 5 GB MLE 66 OLS «LOT it GOT ah LOT - GOT AIT AF CLT by: OUT. ATT 7 OIL NEw SY | de | of). J(QGEG). sme (aso. 48010} u90I1319A0 * > uosue » | bmn .-ysa1dy u9d1F10A0 48910} U901B.19A9 onAydor8Ay ysasoy snonpioap |” ee PIN d1yAYydosaur U1IyIIONY gg eet -purysseis) ay m SS sets ysox0y © LW Rete we We . usoyseayjNoS WN INN ~ SN x ys ae IW \\\ 2 RAR SWNT CAN yy Yr . J J We SARA FAN Ways NAW WSN 5777 ata ; we S ANG \ SN NZ WE 2 Z \ 4 AS SEE A Y CABG: é 3 ESSA Av ER S\CWA EG ie ao we yan’ s WS “ \\ ANANS SENS DEISIN ONAN SENN RA \ NY ASS ENN F V7 eee : gue NS A 7 ee a Y \ § Fi NWA WS SNS 7322-2 Led KMS BOOS a= \ \ SS \ N NS NS 6 SAP || | ae OSS Uy a P ini 5 doo ‘<| Tlie P woe 1AUBU i ! r HTT crm ype Le [<=] Ses KA Ko QAO VRE JSP YY GG i 6 7 “We \ S * 4 BV No2 Caw \ \ pager a EEE eh Wn ’\ SUK elasg \\ VES i | t : U | Iss a S. iS i | IW ; ~ \ cs %% oy St iin ue GA: R pail il NU Sea (VY al of9 hd 69 AL EO eee Liemte Lane LHe Cie a Sire Sm = SILO nbecal ie ecalkoe cian dale e crt ee EC TmeacT sS en ay dales | Ki ane ‘z oyu st osuq OUT, “TZ ofqe} Wory Yep fUOsvOS ssoT}SOIJ OSvAOAT JO pOltod UIGYIM OUTYSUNS Jo (SINoY) WOLeINp [CULLO | ie ~ y aie G Yen) $2 OL AH) ACY) ee Se a ae ar m an 066 ~—SCC LOL 801 i (seq) (189M) 18910} ugaaih1949 ¥ uonsuess \ X rr h 18910) i red oh wl : \ \K uid Soa 110 ~ purleseiy “TL | ot et 7} x wa \ RV) ce. RAS «Seas Spee 1a \ . ——— at S QAR Fre 007777 hd KS i; {| WG EY) XQ) Sot WQS, UNI VSL = A ye = | BRAS AAS AS ASS Tint eee ag P| \ WES Sa Sc Ze A ja=' | ESR RRR HAN SWB = aN we| ey fel" i 7e ol 3 ||, EX SO OR RI eee | | ETT | \ eX ee 7 ae, || =| AX NOI Gro eZ \We VE NOK ONY IG Nie MONA 77 7 GY) Bae Ee See/ Ea BL Be, Maer | (C= Le ES == || Le ee. N\ 2 2 eee oe Ms : x a ery Cn y, \ Wises Joa a pe ie ee 0 a {\ 9 Zh0 00. yea Gh = ehh abe IG, Ge OR 08 KOS O06. 0B lc. OB LOT. 80K | i YTS AIS | amas 2Sene ZZ sf L Az Le g Ds pe a f———— | [-F = = 9 V7 7 i = = (| Saar b im fy. 7, Ss a BS as — i Y £ v4 a A ——p Aa E j é K f = —~ : = ae = =: N ‘ 4 415 la 2 may, Zé eee | wall SS Se Ss os Bay, LF = DZ ZN AY 4 i \\ : Ww ( Ni = Yn} oO = 366 ENVIRONMENTAL CONDITIONS. The bolometer and the pyrheliometer seem not yet to have been em- ployed in climatological comparisons and the initial cost of these instruments, as well as the labor required in obtaining readings there- from, make it probable that they will not, in their present forms at least, be of much climatological value. It must be remembered that, for such studies as we are considering, the operation of the instruments must be simple, the results must be satisfactory, and the cost must be low. Livingston! has discussed and compared various other simple forms of instruments intended for measuring light intensity, including the Hicks solar radio-integrator, two forms of actinometer employing photographic paper, and his own radio-atmometer. Reference should be made to his paper for what little has been done by way of comparing the readings obtained from these instruments with the corresponding degrees of light influence upon plant transpiration. This extremely important subject is deserving of much further study. The Hicks instrument is faulty in its theoretical conception, in several ways; its readings are as much determined by air-temperature as by the intensity of the light which it aims to measure, and they are also greatly influenced by the changing amounts of liquid in the exposed bulb, in the shaded reservoir, etc. The various forms of photographic-paper actinometers, such as the Wynne photographic exposure meter, the Clements ‘‘ photometer,’ and the instrument employed by Wiesner? are all valuable in measur- ing and comparing sunlight intensities with reference to their possible photochemical effect upon the particular paper or film employed, but they show nothing in regard to the corresponding possible photo- synthetic or evaporational influence upon plants, since the photosyn- thetic process in plants has nothing essentially in common with the photochemical alteration of silver salts, excepting that both are photochemical, and transpiration has nothing at all in common with the photographic process. Livingston’s radio-atmometer has been greatly improved since its first description,* and it seems probable that this instrument may prove to be of very great value in climatology as well as in plant physiology, ecology, agriculture, etc., but its general employment in such lines of study is yet to be accomplished. The most improved form of the radio-atmometer consists of two spherical porous-cup atmometers, one of the spheres being black and the other white, but the two being otherwisealike. Theseareseparately mounted and are operated side by side in the location where the light 1 Livingston, (191la). See also, for the best sunshine records yet available, Briggs and Shantz, 1916. 2 Clements, F. E., Research Methods in Ecology, Lincoln, Nebraska, 1905. 3 Wiesner, J., Der Lichtgenuss der Pflanzen, Leipzig, 1907. 4 Livingston, 1915, 6. CLIMATIC CONDITIONS OF THE UNITED STATES. 367 intensity is to be measured. The white surface absorbs but little radiant energy, while the black one absorbs a large proportion of the sunlight that reaches it. Both instruments are similarly affected by alterations in the evaporating power of the air, due to whatever cause, and the difference between their losses for any given time period is the amount of water vaporized on account of the energy absorbed by the black surface, over and above what is absorbed by the white one. This difference is thus an approximate measure of the radiation inten- sity for the given period, as this might accelerate evaporation from moist exposed surfaces of the kind here employed. The instrument is calculated to integrate the effects of sunshine throughout the time period that occurs between the readings, and it is exceedingly sensitive to relatively weak light intensities, so that it can give a wide range of rates. The period of exposure may of course be made of any conven- ient length. Attention should be called to the fact that the readings are to be interpreted as the time-rates of work done in vaporizing water from the standard surface, so that it thus becomes possible to consider sunshine, from the climatological point of view, as to its power to do the work of accelerating evaporation from the instrument. For a simple term to denote this power we may use ‘‘the evaporating power of the sunshine.’?’ No doubt this expression can be shown to be faulty in certain respects, if interest seems to lie in such a direction, but until the very important climatological factor of light intensity begins to attract serious attention it makes little difference in what terms we emphasize its present neglect and its great importance. The sunshine records of the United States Weather Bureau consist of observations on the number of hours of sunshine occurring each day at each of the stations provided with the Marvin sunshine recorder. This instrument is virtually a differential thermometer, having two bulbs, the surface of one being a very good reflector and that of the other being blackened. The automatic recording device records the time periods when the blackened bulb has a temperature higher than that of the other bulb by more than a certain small amount. During periods of sunshine these two temperatures differ in this way. It is thus seen that the instrument is not calculated to give any information regarding comparative intensities of the impinging or absorbed radiant energy. It simply records for each day the amount of time when the sunshine was intense enough to produce the stated difference between the temperatures of the two bulbs. While this recorder leaves much to be desired, its records are probably more valuable than are periodic ocular observations of the amount of cloudiness during daylight hours." 1 In this connection see F. T. McLean, A preliminary study of climatic conditions in Maryland as related to the growth of soy-bean seedlings, Physiol. Res. 2: 129-208, 1917. See also: F. Merrill Hildebrandt, A method for approximating sunshine intensity from ocular observa- tions of cloudiness, Johns Hopkins Univ. Cire., March, 1917, pp. 205-208.—IJdem, 1921. 368 ENVIRONMENTAL CONDITIONS. From the records of the Marvin sunshine recorder, the United States Weather Bureau has derived data of the normal number of hours of sunshine, for each day of the year, for each of the stations included in the sunshine study. These numbers are expressed as percentages of the possible daily hours of sunshine in each case, the possible number of hours being, for each day and station, the number of hours between sunrise and sunset. Through the kindness of Professor P. C. Day, of the United States Weather Bureau, we have been able to obtain these data of the percentage of possible hours of sunshine for each month and for 57 stations in the United States, and these have been employed as basis for our sunshine computations. From the present point of view the percentage of possible hours of sunshine is quite without interest; what affects plant activities is, of course, simply the amount of sunshine, and, if we consider this in terms of hours of light intensity above the threshold of the sunshine recorder, it is the actual number of hours of sunshine which should attract our attention. Our first step was, then, to calculate the normal number of hours of sunshine for each month, in each case. This was done by finding the number of possible hours of sunshine for the latitude of each station and for each month included in the period of the average frostless season, from Marvin’s Sunshine Tables,' and then multiplying this number by the corresponding percentage of the possible, con- sidered as hundredths. The next step was to sum the numbers thus obtained for all whole months occurring in the average frostless season for the station in question, and to add to this sum quantities calculated to represent the fractions of a month with which the average frostless season generally begins and ends. The final sum represents the normal number of hours of sunshine occurring in the period of the average frostless season, for the particular station in question. The sums thus obtained are given in table 21, the summations being plotted on a chart, with isoclimatic lines drawn in the usual way. The chart is given as plate 69. It is obvious, from the small number of stations for which data are available, that this chart is very crude and super- ficial. Nevertheless, a rational and self-consistent arrangement of cli- matic zones is here brought out, and this zonation is very similar to that based on temperature conditions. The stations receiving the most sun- shine (measured in terms of hours by the Marvin recorder) are in the extreme Southwest, while those receiving the least lie near the northern boundary of the country or in the mountain regions. The lines of the western portion of this chart are shown as distinct from the rest, to suggest the greater uncertainty with which they have been placed. mean solar time and the total duration of sunshine for every day in the year, latitudes 20° to 50° North, U. 8S. Dept. Agric., Weather Bur., 1905 (numbered ‘‘ W. B. No. 320’’). CLIMATIC CONDITIONS OF THE UNITED STATES. 369 TaBLE 21.—Normal total number of hours of sunshine within the period of the average frostless season. Normal Normal total total Station. duration Station. duration of of sunshine. sunshine. hours. hours arizona: Plagstaft }.). 0... eis as 6 a2 1,134 New Mexico: Santa Fe......... 1,892 Arkansas: Little Rock.......... 2, 166 New York: California: MD ATI eros ole kay sade bis. exdeyd 22 1,504 Pas wAmeeles 6 Fei 3) ase aback 2,995 JESU UHI) oes feel ie ih EN aN ee, Daa 1,479 Sail PTAMCISCON soe) hein wil oes = 2,615 INC WHIL OFT eae ISRO. 1,626 Colorado: TROGI CSET pita pai! eilniaa a artis 1,418 NBSMMeN oiaies) Asie e cielehs wate aU al 1,261 North Carolina: Wilmington.... 1,942 TOMASO hal A ee ta eee 1,367 North Dakota: Bismarck....... 1/227 Grand Jmnmetion,, ji ).5. 6S.) 1,865 Ohio: Florida: Jacksonville........... 2 2397, CAMCMAN AGN sire aa. ores etaeeee Livi5 feeorrian Atlanta.) ie 83 ooh 1,946 WlevelandiAsask Fs ete ths) 1,567 I G2) s¥o sind Bo (steel neon eRe 1,870 Columbus. eet ae a. ake 1,651 Miinots Chicago sc) es 1,774 PROLOG De irep tots cal ole rare ewes ne 1,512 Indiana: Indianapolis.......... Lack Oregon Portland 3 wna .t ee senso 1,578 Iowa: Des Moines............. 1,544 Pennsylvania: Memsas:/ Dodges. oe... cl... 1, 784 1 yeaah tsi ea el a ely Sel a Lore Kentucky: Louisville........... 1,743 Philadelphia ssc. t0o bee ne ek i ia2 Louisiana: New Orleans........ 2e23 Patiala ier eae iA pales okay ih mae ce 1,403 Maine: South Carolina: Charleston..... 2,026 TEAZISISO\ CI ELGY MIN ea ab lan NAL A 1,225 South Dakota: Huron.......... 1,267 Eo ib FEN Ih Se At ah Pa 1,365 Tennessee: Maryland: Chattanooga a sie «ee oc 1,836 NS MUNROE pots 6s ie S yoherane ee 1,736 Knoxvallen oh) SaURe Ve Saale L772 Washineton,, DD) Ceo. 1,646 Nasingille a hae Neils aid Sic 1,878 Massachusetts: Boston......... 1,499 Texas: Michiegn: Detroit... 056.620. 5. 1,468 Amarillo Settee Se ein tS oe 2,057 Minnesota: St.\Paul.......2.... 1,367 Galveston a Aisei cyan Wei ott Nae 2,650 Mississippi: DAMMPATLOMIONA wicrtetats okie ec ekee 2,343 14 BTCC (72h 0 gE eS 1,895 Utah SaltlakerGitye sts one 1,927 HERES) OND hae eR 2,301 Washington: Spokane.......... 1 ,927 Missouri: St. Wouls. i... 2. 1,832 Wyoming: Montana: Helena... 0260.00.04. 1,286 (Mhevennes yA Ue id wets make fhe 1,127 INebrasiea:| Omaha. oi.) os 3! 1,548 ISSA enc cee eyc.y «Siecle eevee: 1,167 370 ENVIRONMENTAL CONDITIONS. IV. MOISTURE-TEMPERATURE INDICES. A. INTRODUCTORY. An attempt on the part of Livingston! to obtain a single climatic index for moisture and temperature efficiencies combined resulted in a climatic chart of the United States that has certain interesting charac- teristics. These indices are based on the tentative suppositions: (1) that the temperature efficiency of a climate, to produce plant growth, is proportional to the temperature summation-index of that climate (obtained by whatever method may prove most satisfactory), and (2) that the moisture efficiency is proportional to the Transeau ratio of precipitation to evaporation. ‘This last supposition considers that if two stations differ only in rainfall and in the intensity of the evaporating power of the air, then plant growth at these two stations should be directly proportional to the rainfall and inversely propor- tional to the atmospheric evaporating power, as far as climatic condi- tions are concerned. In short, the moisture-temperature index of a climate (for any given duration factor) is taken as the product of the temperature summation-index and the moisture ratio. To employ Livingston’s terminology, if J,,, represents the moisture-temperature index, if J, represents the temperature summation-index, if I, repre- sents the summed precipitation for the period considered, and if I, represents the total evaporation from some standard atmometer for the same period, then = 1,4,f1. Inspection of this formula shows that the value of this moisture- temperature index is increased by higher temperature (supposing that the optimum temperature for plant growth is not surpassed) and also by lengthening of the time period taken into account. The higher are the daily temperature-index values and the more of them are summed, the greater must be the resulting sum (/,), and the product index is of course increased by increasing its first factor. Also, this product index is increased by higher values of the Transeau moisture-ratio (I,/I.). This ratio value, in turn, is increased by more rainfall and by lower atmospheric evaporating power. The efficiency, for plant growth, of the moisture-temperature complex is thus greatest with a long growing-season, with high temperatures (not surpassing the optimum), with great rainfall, and with low evaporating power. Livingston’s product indices were based upon the duration factor of the length of the period of the average frostless season and upon the physiological summation-index of temperature efficiency. We have calculated these values also for temperature indices derived by the remainder method and for those derived by the exponential method. The results obtained for these two forms of moisture- ILivingston (1916, 2). CLIMATIC CONDITIONS OF THE UNITED STATES. att temperature index are presented below, and these are followed by those obtained by Livingston. It is perhaps not out of place here to remark that these moisture- temperature indices represent no more than a first rough approxima- tion toward an environmental index, which might state the efficiency of the environment as a whole to produce plant growth. It is quite obvious that such an environmental index will not really be attainable for a very long time; it must embrace many other terms besides those representing climatic conditions, and also terms for all of the influential climatic ones, and, as has been emphasized, methods for the measure- ment and weighting of most of the environmental conditions are yet to be devised. Nevertheless, progress can best be favored by employ- ing the two climatic indices that seem most promising, with the hope that the shortcomings of the resulting interpretations may suggest closer approximations to the form of index required. It may also be remarked that but little real progress can be hoped for in this direction until laboratory facilities become available, by which the relations between plant growth and environmental condi- tions may be experimentally studied. As has been emphasized, this sort of experimentation will require well-planned physical equipment for the control of environmental conditions. It will also require a group of workers who can bend their energies toward gaining a com- mon end, for a single individual, no matter how well equipped with apparatus, can not hope to find it in his power to enter very deeply into these complex relations. Nevertheless, expensive and difficult as the project may seem at present, there can be no doubt that it will be eventually undertaken, nor can it bedoubted that the benefits to be derived from properly planned and conducted experimental studies on plant environmental relations will prove fully as great and as valuable to the human race as have been those derived from experi- mental physics and astronomy. It is in the laboratories and observa- tories of these sciences that the nearest approach to the sort of work here contemplated is now being carried on. On the practical, bread- winning side, it needs only to be suggested that the greatest and most important of all human industries, agriculture, rests entirely upon what little knowledge we already happen to possess in regard to the relations between plant growth and environmental conditions. When- ever a workable environmental index for plant growth may be approached, it is certain that the arts of agriculture and forestry will be markedly improved. B. MOISTURE-TEMPERATURE INDICES BASED ON TEMPERATURE SUMMATION- INDICES OBTAINED BY THE REMAINDER METHOD (ABOVE 39° F.), FOR THE PERIOD OF THE AVERAGE FROSTLESS SEASON. (TABLE 22, PLATE 70.) These values were derived by multiplying the summation index for the period of the average frostless season, for each station (table = “+g ayeyd st oseq oyy, *z wUMNjoo ‘zz, o[qe4 WOT; BYBp { (poyyoUT sepuTeUeI Aq poureyqo sonyea UOTyeUIUINS AousTOYyo oInyer1edurE} - .: ane porydy[nor pu g-/ggy 10j sonra uoryerodeae Aq poptArp sonjea wo1;e}Id1O9I1d [BUIOU) MOSES SSOT}SOIJ OSBIOAG JO POLIOd 10} SodIPUT 91N4eIOdUI04-o1n4SIO J] 16 66 0 ol IT (seq) (SSA) 48910} u9b18.19A0 uoljIsued}. — qSa1OJ udd1BOAd 4910} U991DIBAS oy Aydors Ay 70103 snonpisep — pe dAydosow uayWON dA Ydosaw Usd YIIONY I -puejsseis SS cy ot 4 4so10j S1yAydosour 4so10J U.19JSB9Y INOS snonpisaq7 ot S }, AY AN Te eee tet aN ‘s + S \ ; \\ \\ 4 SS SOK KR : So< 4 — 34 p NS: j ; Y oi SSS SSS AN 4 ! t << WSs Lek WAS oUt yi \ YX We \ aS VSS: yy S ; WY : IGT Foe Se Uy a : hs SRY AY Y YW) b set < K fry ON i A % As es B LEA LIER SAR Goi | WALL NALA ; Sr en OS 5 y RY) ip t q j } ak mt ’ AAR Y y wees rh eet Ss = a 6 y ZY, eke CLA gS SSE Yo : 5 ys Gf AZZ, ie S J > he (J - , f- : j —e GY . rose SOF Y > = Z = Yy p Setatets 8 ' 3 HY le s ee : . y VL ai | a i, 4 8 °S nN = LA wax e L\. ba SS DE ee i. YAN Z| PAL AY os IK Ly | AL obL i p6L. 8 88 G8 28 68 16 £6 $6 .l6 66 J : oll BIL ol GL ob bl oGbl ——— CLIMATIC CONDITIONS OF THE UNITED STATES. 313 6, column 5), by the corresponding Transeau ratio (table 11, column 8). For simplicity, we may represent the first of these factors by the letter 7 and retain the expression already used (P/F) for the second, whence we may term the resultant index P/EXT. The results obtained are set forth in the second column of table 22. The chart for this series of values is shown as plate 70. Its discus- sion may best be combined with those of the two following charts. TABLE 22.—Moisture-temperature indices (P/E XT) for the period of the average frostless season, by remainder (above 39° F.), exponential, and physiological methods. The moisture ratios (P/E) from table 12, and the summation indices (7) from tables 9 and 10. Temperature summation Temperature summation obtained by— obtained by— : Remain- 5 Remain- Station. der Expo- | Physio- Station. der Expo- | Physio- method | nential | logical method | nential | logical (above | method. | method.? (above | method. | method.? 39° F.). 39° F.). Alabama: Indiana: Minpiee es 0 12,106 | 1,314 | 23,652 Indianapolis.........| 3,376 359 | 5,967 Montgomery........|. 6,114 665 | 12,400 || Iowa: Arkansas: Dayenport a2... 20 5 3,672 384 6,255 Port/Smith...2.'..... 5,543 601 | 10,782 Des Moines......... 4,364 456 | 7,457 Eigtle Hoek .. ....0. 5. 5,795 627 | 11,246 Dubuguees: .... 8.4. 4,583 478 7,472 California: Weokulk, Gixt 0) mre 4,138 440 | 7,241 LEWES COAT tO 625 68 1,186 || Kansas: Independence....... 254 27 449 Concordia....... Rattle oid UL 401 7,114 Los Angeles......... 2,721 993) | 13 oe Dodee mache 2,410 256 | 4,474 1 S-(e(o (01 2710 bs Ae en 1,285 142 2,409 MOWER seater ekercidieves 5,744 611 | 10,599 Sacramento......... 1,399 146 | 2,046 || Kentucky: San Francisco....... 2,598 283 1,991 TOWISVAMe Fie sears, tegc 3,498 371 6,590 Colorado: Louisiana: WME T eile ss 786 81 1,204 New Orleans........ 11,956 1,304 | 23,381 Connecticut: Shreveport......... 6,846 751 | 13,874 New Haven........ 5,330 556 7,869 || Maine: Florida: TSS POrus onic is oe es 3,406 391 2,747 Jacksonville......... 10,813 1,196 | 21,760 Portlands occ Ses 3,712 386 4,528 Wey Westic cc... .. 10,877 1,155 | 23,266 || Maryland: WPOMSAGCOMA cise s veg css 10,175 1,113 | 20,465 Baltimore: |. sin. 6... 4,540 483 7,947 MIATA cts ckate cise es «> Washington, D.C...| 4,704 497 8,322 (Cedar Keys)!....... M1 , 122 L,271 | 28,155 Massachusetts: Georgia: Boston as. don se 4,097 429 5,714 PMGUAID UE. 6 3 6 se sles cas 5,175 549 9,686 Nantucket. ..02 0003. 4,396 474 5,193 LA COUNE |: Gal es 6,420 695 | 12,879 || Michigan: mavennan. 6.0.66. 9,385 1,014 | 18,294 AIDEN Eero cise de eek 3,008 312 3,300 Idaho: Detroit nian s ciate lee yeee 309 4,569 BISON sihck. sues, «viaccess 405 42 598 Grand Haven....... 3,147 327 4,189 Illinois: Warquette cc... Ser. 2,997 314 3,113 2110 oe 4,174 446 7,807 Porno ELUTen wt ok 2,918 301 3,819 MICABO Wc ce 6 cee 3,384 355 5,100 || Minnesota: BOMMEMald. 0. cade el) Cy Ord 418 7,032 DER os sins hen ee 3,751 401 4,064 1 Where a second station is named in parentheses, the evaporation value is for this station. 2 The values in this column have appeared in Livingston's paper (1916, 2). 374 ENVIRONMENTAL CONDITIONS. TABLE 22.—Moisture-temperature indices (P/E XT) for the period of the average frostless season, by remainder (above 39° F.), exponential, and physiological methods.—Continued. The moisture ratios (P/E) from table 12, and the summation indices (T) from tables 9 and 10. {i Temperature summation Temperature summation obtained by— obtained by— : Remain- : Remain- Station, der. | Expo- | Physio- ——— der | Expo- | Physio- method | nential | logical method | nential | logical (above | method. | method.” (above | method. | method.” 39 F.). 39 F.). Minnesota—Continued: Oregon: Moorhead: <7.) 7: + =; 3,163 315 | 4,043 Portinnds =. 223 2352 3,052 332 | 3,160 “Si gs 2771 | Ii ee es 4,269 442 6,423 Resehur 8 es 1,213 126 1,313 Mississippi: Pennsylvania: Wieksire. 3 2s ns 7,663 834 | 15,125 Biie He Seo eee 4,185 441 | 6,047 Missouri: Philadelphia........ 4,174 441 | 7,010 Kons City. 2 32222 eS = Patisbareh<. : 522222 3,354 349 5,672 (Leavenworth, Kans.)! \ — po) eae Rhode Island: ; >) ae PT cae aes ee 3,635 390 | 6,824 Block. Islande./: 2/44 6,164 668 | 7,555 Springfield.......... 5,631 591 | 10,061 || South Carolina: Montana: Charleston... 22 526 10,116 | 1,100 | 19,608 Hayre os 633 bases ae Columbia /55 -< 352: 7,432 807 | 14,837 (Fort Assiniboine)! . . } ao S16 | 22008 South Dakota: Piclena. 2... ess 2; 691 72 809 Baron). (= 2-5 ete 2,389 243 | 3,687 Nebraska: BRCETE ai h 2 2 ec North Platte........ 2,205| 229) 3,682 (Fort Sully)... ..... 1,71 | Onialiag sos: 2). oo. 4,151 436 | 7,406 Wankton: 0652 4,080 424 | 6,961 : Walenime.. 2S. 2252 2,309 238 3,861 || Tennessee: Nevada: Chattanooga........ 5,295 562 | 10,052 Winnemucca........ 127 13 197 engavilles ecu 2 5,040 530 | 8,970 New Hampshire: \ Memphis 25-7 655 5,253 593 | 10,837 ance 2)5..6,.ct < i Washwalle: oo 4.5<6% 4,593 493 8,930 (Manchester)!....... f 3,356 Sie) ee oe! New Jersey: ADHERE 2 2 ess 3,520 385 | 7,028 Agianine- City. +62 <. : 6,858 707 | 10,241 Amare oo oeo . oe = New Mexico: (Fort Eliot)!........ i 2,082) Sant Pea. wh. Leer 772 81 979 Corpus Christi...... 6,690 737 | 13,926 New York: Darga se ee 906 98 | 1,790 PRY Bok 2 oe 3,780 394 | 5,598 Galveston... 2224". - 10,331 | 1,142 | 20,570 51, itr a pe ae 3,257 340 | 4,511 Palesiates fs i. jc = = 6,410 700 | 12,977 New York... .: ss... 4,541 481 7,034 San Antonio........ 4,734 520 | 9,716 OSweece . fat 4lSosk 2 3,572 373 | 4,784 || Utah: Rochester........... 2,962 307 4,100 Salt Lake City...... 623 66 1,052 North Carolina: Vermont: Chatlotie. ofc). «te: 5,914 630 | 11,022 NomBHele 52 so 2 3,362 345 | 3,884 BPAeras: 2 een e ons 13,511 1,418 | 24,265 || Virginia: Pnteiph. 0. eas 7,992 851 | 14,980 Lynchburg.......... 5,139 544 | 9,228 Wilmington......... 9,781 1,034 | 18,240 DEA ores 2 es seeds 8,300 887 | 15,060 North Dakota: Washington: Bismarekse > cise 2 1,590 188 2,626 Norte Head 2. 2 .....\<. Devils Lake......... 2.210 997 2.893 (Fort Canby)!....... } 2,684 345 1,874 (Fort Totten)!...... 2 ise S)Gt a a 934 101 1,148 Wallistane 2 Se. < Tatoosh Island......| 11,724 1,566 7,475 (Fort Buford)". ..... eS SEE | a Mdina... 950 101 | 1,475 Ohio: Wisconsin: Cincinnata >. . 50. 2552 3,007 319 5,513 Ee fer it ee 3,193 330 | 4,270 Glevelaud 45 es =: 3,782 399 | 5,606 Sree: Ss Ss = os 4,085 422 | 6,296 Colmebnise. oso eee 3,019 316 5,112 Milwaukee......... 3,373 351 4,582 Sandusky........... 3,635 390 | 5,778 || Wyoming: TP AMCMGEE ot 2 aioe oe 2,914 303 4,647 Cheyenne.......... 563 58 710 1 Where a second station is named in parentheses, the evaporation value is for this station. ? The values in this column have appeared in Livingston’s paper (1916, 2). CLIMATIC CONDITIONS OF THE UNITED STATES. 379 C. MOISTURE-TEMPERATURE INDICES (P/EXT) BASED ON TEMPERATURE SUMMATION-INDICES OBTAINED BY THE EXPONENTIAL METHOD (TEM- PERATURE COEFFICIENT OF 2.0), FOR THE PERIOD OF THE AVERAGE FROSTLESS SEASON. (TABLE 22, PLATE 71.) The same values for P/E are used here as in the preceding case, but the temperature indices are taken from table 7, column 2. The products are presented in the third column of table 22. They are shown graphically on the chart of plate 71, the discussion of which will be postponed until the next following chart has been presented. D. MOISTURE-TEMPERATURE INDICES BASED ON TEMPERATURE SUMMA- TION-INDICES OBTAINED BY THE PHYSIOLOGICAL METHOD (LIVINGS- TON’S, 1916) INDICES FROM LEBENBAUER’S 1915 MEASUREMENTS FOR YOUNG MAIZE SHOOTS, FOR THE PERIOD OF THE AVERAGE FROSTLESS SEASON. (TABLE 22, PLATE 72, AND FIG. 18.) The values for P/E are the same here as in the two preceding cases, but the temperature indices are taken from table 7, column 4. The products are given in the fourth column of table 22, and the chart therefor is shown as plate 72. The discussion for plates 70, 71, and 72 will now be given. E. CONCLUSIONS FROM THE STUDY OF THE THREE FORMS OF MOISTURE- TEMPERATURE PRODUCTS. (FIG. 18.) The direction of zonation on all three of these moisture-temperature charts is at once seen to be essentially the same. A glance at the data i TA SOIT onaddos ne as R is DS iN iy Fra. 18.—Moisture-temperature zonation, according to moisture-temperature products (physio- logical method) for period of average frostless season. Moisture-temperature provinces: Very high, more than 13; high, 7 to 13; mediwm, 4 to 7; low, 1 to 4; very low, less than 1. Nu- merical values represent thousands. (See also Plate 72.) aia % -) oTn OT: " » y VUIlOTTo 2 BLVAUTII AQ . J nnn ¢ / ATTAATSS TATTAN < gr Ee ata oa. oll Pan ee Ey , ~~ 6b .(pouyo GLYUVUOOCAI AG PIUleTdoO svnlv UO TVG OULU S ayB[d SI oseq OUT, ‘“& UUINTOO ‘Zz 8{qQey UOT] B S paydypnur pur g-)ggT soy sonyea uoresodead Aq poprarp sonyea uoryeytdroord yeursou) uosBeS SS9[]SOIJ OFLIOAT JO Ported 10} Seorput 9.1N7B.10dUI94-91N SIO J] ot I oLIT oS IT (seq) (sem) 48010} U9013.19A9 uOT}ISURID 48910} U9d.1310A9 JSa10} UVIIBIIAD onAydoss Ay 3sa10} snonproap d1yAydosour uszayjzION d1yAydosaw us9y}10N uJa}saMmyjzI0 -purjssein XX XX] KOO ‘0 DO BOS SS S37IW 009 i | 48010} d14yAydosour U19]Se9YyINOS e i L MY y i » we , + aren as b Y » " ee S # @ \ ) + R hed I nf PHO a s 4 " ~— ae. ‘oD S 7? YY rh 1 VAs >I fi | ‘ [I Y f “4 x _ \ 4 i 74 ‘ ; ¢ ¢ ‘ ss > : x 7 : ; q CANE R ay SS q ar r p f = : . ‘ " iet ? y 3 . ‘ He . y : A ‘ , b q DOG : d : : RO \ Nb } i Bs Dy et m begs 49 z te te é mf ; ve ~ S 7 S4. \e- we Ss . Shire = A "4 4 ; ; : . a \ f b J . SP) i . 4 v 13 %%er . zs tS) . p t ey | : Le Ly ay WO 5 q § S 1s > . Kb *® potas XY . r y MG : RV.” ; ‘ Z h % Ww ah 4 b S B 4 _—— 6 r , yy r b 4 AZ ¢ : é A v4 Seb ROSES sie » Won —| N y h COOK % M4. Se . J § xe t ¥ a = q © g ’ rey ‘ : ‘ I , : ‘ ' Sa J Pighe = -\ \ 2s Siero, ra Y fy PLATE 71 4% SSK SOs SSS or LT si say > ae w \ ‘ ie ; } Ww | WAN $ y ¥ SAN Vs , SS aS os ope ni i Ni S 1, ia} Ns he DS ll Pry if as == 376 LOTl) S211 Gly meeicleacerhe.cal CULM LICL Laem COL n “e ee : SOS SON y ~ RXR se mi beene Ge | Ne ) \\ NS \ dj I I ‘Z oyu] st osuq oT, ® \. See fp WUINO ‘Zz, S-LSST LOJ sonywa woreszodvas Aq poprlArp sonywa worzeyIdr1o91d yeuIIOU) MOST (SP) JSa10J UddIT VAI dy Aydosau Way oN (189M) 1S910J U9dIB19AI os Aydosour wid ION 1so10} 91;Aydosour Wi1a}SBayINoS Z x rS cS ne PRB Sa Mu Ea &/ (2 Bg) A \ A KX ON XN . Oe . | ‘ 4 “N \ No ARE GN aN re ‘ NS USS FAN ea Z Le \ PLATE 72 Satay SZ $s, 50 \e , J tr y yr = : é y ‘D y O A x \e en. <> (tx Cx Les sosoces POSSESS 2 SK xs a 4 LOR QF en ay 28s el S 3 aR a Os g tj 7 ta Y NW’ aH [bos \ Ne 557] RS CARR ee ay — a : \ .O8-o alah } / H aN Ss tS) "a Le ty I L 4 jaw ayy Ee ani/aae | GUL 2211 1S910J UDdIB1DAD IT oj AydoisAy utoysa/nyion ra: oat nes is Gi } My WEILL, o 36 [ ry Cc re 5. Sésiiens tes 5 SUS oe oe 10 30+ CORRELATION OF DISTRIBUTIONAL FEATURES. 401 TABLE 24.—Climatic extremes for the semidesert—Continued. Plate | Evaporation: Low. High. 53 Daily means 1687-88, fe (NCW) sic osc vs 2 leo ba vee wo burs 6 .102 . 268 54 Total annual, 1887-88 (inches)............--0+eeee0:: 32.5 65.8 Moisture ratios: 58 Mormmaliey Mere. n sutra t ecialecdete rece Mmiada erin oe Wels erase: .08 Bf if 59 NOMA aE TSN oiler teem sm peredlc ld ote eréce ale « .10 81 60 IGEIIAL Ey, MORE. cise chet) deaeeie) acai Paste tae oie evens 92 se 5. .76 Vapor pressure: 63 Normal mean, fs (hundredths inch)..................- 296 675 Humidity; 65 Normal mean, fs (per Cent). siieee sce cies cue es suse ord S - 48.9 81.9 66 Normal mean, year (per cent)..............-. Perera cp 48.1 82.1 Wind: 68 Normal mean hourly velocity, fs (miles).............. 4.5 12:3 | Sunshine: 69 Normal total duration, fs (hours)................00+: 2,615 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method............... 68 737 | 71 Normal P/E XT, fs, exponential method.............. G25 07) 6,690 72 Normal P/E XT, fs, physiological method............. 1,186 13,926 | TABLE 25.—Climatic extremes for the grassland. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 36 245 35 SAUDER GANS CanS lo; dials eeaces ge vale dunes ste tlanetas ater e cnietinrecalic month ore oa 18 163 36 SEDONA VS OISP esse ose iel aren ye RUL nL ak aise aie 2a nat 0 158 37 Remainder summation above 32°, year (thousands).... 10.0 18.0 38 Remainder summation above 39°, fs (thousands)...... 2.9 7.9 39 Exponential summation, fs (hundreds)............... 3.0 8.7 40 Physiological summation, fs (thousands)............. Se7 15.9 41 MATEO LUN GE TATE TOR URTID 85558 oa iisds els 6 lalate uo. ia eye's bee ee a eee —65 +4 43 Normal daily mean, coldest 14 days of year (° F.)..... 0 42 44 Normal daily mean, hottest 6 weeks of year (° F.).... 64.4— 78.8+ 45 Normal.daily mean, year (0 F.)............0000-e ces: 35 65+ Precipitation: 46 Normal daily mean, fs Gineh): 305 O00 he lo ca ca ee us .045 .116 47 Normal No. rainy days (over 0.10 inch), fs........... 0 99 48 Normal No. dry days (0.10 inch or less), fs........... 55 192 49 Dry days, percentage of total, fs (per cent)........... 36 100 50 Days in longest normal rainy period, fs.............. 0 75 51 Days in longest normal dry period, fs................ 26 153 52 Mean total, year;Gnehes) oo 6. fas ci ceed ce ce clea tes 20 30 Evaporation: 53 Daily mean, 1887-88, fs (inch)................20000- a Bi ly .275 54 Total annual, 1887-88 (inches)....................- 220 54.4 Moisture Ratios: 58 Nore ad AFF 8B Sf Soh. sons eT ah aetlis Mt ob Acai che 19 .94 59 ANroMeaan Bulag WEL AS) 6a sass vs oi < AURORE Re tehg etna reee RQ weahete a 25 1.10 60 INGO rin EL MOAN ec. cic dicta ate anc Mic GMa ORTON clalide ottaedeae 20 1.74 Vapor Pressure: 63 Normal mean, fs (hundredths inch).................. 253 456 Humidity: 65 INormalimean,78).(per Cent) s. eset Gee ain i ke Olekhan oak 45.8 71.5 66 Normal mean, year (per Gent) i. ses alee gp calek swe 48.1 74.1 Wind: 68 Normal mean hourly velocity, fs (miles)............. 7.4 14.2 Sunshine: 69 Normal total duration, fs (hours) 's 4s 04 Goss ie ve ks 1127 2,100+ Moisture-temperature indices: 70 Normal P/E XT’, fs remainder method............... 116 385 71 Normal P/E XT, fs, exponential method............. 563 3,520 72 Normal P/E XT, fs, physiological method............ 710 7,028 402 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 26.—Climatic extremes for the grassland—deciduous-forest transition. Temperature: Low. High. Days in normal frostless season (fs) 125 276 Hot days, fs 02 173 Cold days, fs 150+2 Remainder summation above 32°, year (thousands).... 18. Remainder summation above 39°, fs (thousands) 9. Exponential summation, fs (hundreds) 10. Physiological summation, fs (thousands) 19. Absolute minimum +4 Normal daily mean, coldest 14 days of year (°F.)..... 51 Normal daily mean, hottest 6 weeks of year (°F.)..... : 78. Normal daily mean, year (CR.) 2)... 55 2. ecw ee 70 Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs 151 Normal No. dry days (0.10 inch or less), fs 211 Dry days, percentage of total, fs (per cent) 78 Days in longest normal rainy period, fs 136 Days in longest normal dry period, fs 59 Mean total, year (inches) 40 Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal 7/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperaiure indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TABLE 27.—Climatic extremes for the deciduous-forest. | Plate | Temperature: Low. 34 Days in normal frostless season (fs)................. 128 35 PG Ga Vay Fee. Cia ae oo Seo Pe RE LR 63 36 Cle Gaya Gs oases be ta obs see Aa AEE eet 0 37 Remainder summation above 32°, year (thousands).... 11.5 38 Remainder summation above 39°, fs (thousands)...... Sth 39 Exponential summation, fs (hundreds)............... 3.8 40 Physiological summation, fs (thousands)............. 6.1 41 Absolute minimiung . fo ea 2 i. —27 43 Normal daily mean, coldest 14 days of year (°F.)..... 21 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6 45 Normal ‘daly mean, year (CE) | so202 <5 «so a3eee eee ee 45 Precipitation: 46 Normal datly; mean, fs: Gnch) > jose oe eee ee .091 47 Normal No. rainy days (over 0.10 inch), fs........... 26 48 Normal No. dry days (0.10 inch or less), fs........... 19 49 Dry days, percentage of total, fs (per cent)........... 11 50 Days in longest normal rainy period, fs.............. 17 51 Days in longest normal dry period, fs................ 4 52 Mean total: year (Giches)....... 2 ieka ined sees uss 30— CORRELATION OF DISTRIBUTIONAL FEATURES. 403 TaBLE 27.—Climatic extremes for the deciduous-forest—Continued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fs (inch)...........020c0ses005 .081 .200 54 Total annual, 1887-88 (inches).........+.+s2seseee05 20.3 54.8 Moisture ratios: 58 DNV rerrt AVES 1 Eee Bio osu, x, Selleck sisirey ones > Pate cahs NEG Lave ribo lana a 51 1.39 59 Normal f 98) 66 << 5c: haptckaapinapspd sal ME ciaydia' si sudden .66 1.63 60 Normals (E, YORTs i).5 nile, cjece.os, > 4 ee apie was oid epee 51 1.85 Vapor pressure: 63 Normal mean, fs (hundredths inch)................. 411 600 + Humidity: 65 Normal mean, fs (per Cent)........c0ccceeceeeenvees 65.6 83.9 66 Normal mean, year (per cent). ........2.ceeceeeeees 67.5 82.1 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.6 12.5 Sunshine: 69 Normal total duration, fs (hours)............+2+.06: 1,468 2,300+ Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 301 1,1002 71 Normal P/E XT, fs, exponential method............. 2,914 10,0002 72 Normal P/E XT, fs, physiological method............ 3,819 20 , 0002 TABLE 28.—Climatic extremes for the northwestern hygrophytic evergreen forest. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs).............000- 103 316 35 ETO AY Asif Sie ors ie ale ah cls sie ove em crene leravdiel dutaletae eielele eaters 0 0 36 OG GAS IS sie as: cis staie ereiekereieia ove eobayperans eee Rear 0 0 37 Remainder summation above 32°, year (thousands).... A a apie 38 Remainder summation above 39°, fs (thousands)...... 3.8 4.6 39 Exponential summation, fs (hundreds)..... a Fayohisiohetie’s lor 4.1 5.0 40 Physiological summation, fs (thousands)............. 1.9 4.8 41 AAD SOLUILS MALT UT 4 os o.y 0 o's os 6: s, oiieslwimt elose eiei gaya enayaie Se —6 +30 43 Normal daily mean, coldest 14 days of year (°F.)..... 354 45s 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 ayik 45 Normal daily mean, year (°F.).........ccccccceecces 50— 55+ Precipitation: 46 Normal daily mean, fs (inch)............0.0ececce0. .042 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 1 199 48 Normal No. dry days (0.10 inch or less), fs........... ae 200 49 Dry days, percentage of total, fs (per cent)........... aT 100 50 Days in longest normal rainy period, fs.............. 0 99 51 Days in longest normal dry period, fs ............... 56 198 52 Mean total, year (inches). ..........ccccecccccccees 50 90 Evaporation: 53 Daily mean, 1887-88, fs (inch).............0.ee0c00- .052 .143 54 Total annual, 1887-88 (inches)..............cceeeeee 18.1 39.2 Moisture ratios: 58 INGOT AUME WIE 8 <.cc/e cele SH wei wuts stone dee ewe weleakts .29 3.84 59 INODIIN ERS FS la5 65: i'n ig RRR idles GES wh aan 41 4.48 60 IROLIG RINE YORE Sie dale da hicc.g sia uveere amen ue Ss Sitieatae .88 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 318 328 Humidity: 65 Normal'mesn, fs (per cent). sce ic ck ee a wee ewe as 71.4 80+¢ 66 Normal mean, year (per Cent). .......ccccc ccc eeces 74.6 76.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.5 16.4 Sunshine: 69 Normal total duration, fs (hours). .......e...eeecees 1,500 1,500 + Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 126 1,566 71 Normal P/E XT, fs, exponential method............. 1,213 11,724 72 Normal P/E XT, fs, physiological method............ 1,313 7,475 404 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 29.—Climatic extremes for the southeastern mesophytic evergreen forest. Plate | Temperature: 34 35 36 37 38 39 40 41 43 70 71 72 Days in normal frostless season (fs)..............00. Hot Gages. 2.2. Rhee hat ws Oe ee KS OVE GRY RIS a ae ore aod foc oka cs inte eee rae Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. Absolute maimimune 2234-05605... > s Se! Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Wormal xdaly mean, igear (CF .))./.0.6455412.2 eeee e e eee Precipitation: Normal ‘daily mean, fs’ Gnch); . 2220's 0. See. Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Mean totale veari(Gnches) is. aol eee ee a: Evaporation: Daly anedn) 1367 —Ge0 9s GNC) «0.565. . 6. +2 sae seer Total annual, 1887-88 (inches).............5...0000- Moisture ratios: Jhb pi Tet WP 27 0/5577 08, ale ee SR Normal 7/E, fs........ Teen Sic ake ceehe UE eee Normal Pry yearse a.) Dated ic 0s 2 eee See Vapor pressure: Normal mean, fs (hundredths inch).................. Humidity: Normal mean; je (percents es fe) eee Ae Normal mean, year (per cent)....5..........0.2000- Wind: Normal mean hourly velocity, fs (miles)............. Sunshine: Normal total duration, fs (hours)........... SEE PGE. NE Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. Normal P/E XT, fs, exponential method............. Normal P/E XT, fs, physiological method............ 00 GE ON | @ . 106 6,000 — — ts me HR O1 © 13.5 2,650 1,314 13,511 24,265 TaBLE 30.—Climatic extremes for the northern mesophytic evergreen forest (West). Plate 34 Temperature: Days in normal frostless season (fs)......... ...-.5. Het days 76.5235 0 fe ica See hoo eae eee eee G0) Gre Cs sa 2 ee Sea oer pein pM, Oi 0 te be amo Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. (A: bsohute THOU 6. oo «728 Ss oe DE ee Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily nian, year (CB) ~ .3.(oc.0.bs ce Pe BS, Precipitation: Wornsial daily niean, js Gnch).., ..eetiie) eo eee cee Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Mean-total wear Guches);. so... odebeek Vie ces. ht sy to bo Ww O CO Ore RR © CORRELATION OF DISTRIBUTIONAL FEATURES. 405 TaBLE 30.—Climatic extremes for the northern mesophytic evergreen forest (West)—Continued. Plate | Evaporation: — Low. High. 53 Daily mean, 1887-88, fs (inch)...........-2e+eeeeees .120—4 . 262 54 Total annual, 1887-88 (inches).............+-.++00:. 30-— 68.3 Moisture ratios: 58 INOTIIALY EY Hig, $8 ticles ¢ eshorsabeleraeh sis Mtelera 6 SIGE Bidens iad ie .10 123 59 INSTT or PIE VIS sia cos, « Raat aMelne ee Wao NUE eld ie aha ne AZ .60—2 60 INGONIN aA REEy VAT sco. cease) abs diese Seto ARTSY GD «des laensoecs 14 1.30—2 Vapor pressure: 63 Normal mean, fs (hundredths inch)................-+: 253 348 Humidity: 65 Normal :mean, fs (per CONt. 66s ic 6: eraieisr eis ie specie ce ve 52.9 87.5 66 Normal mean, year (per cent).........00ecececerees 60.7 86.8 Wind: " 68 Normal mean hourly velocity, fs (miles)............. 5.4 6.6 Sunshine: 69 Normal total duration, fs (hours)...........2.2.208: 1,134 2,3002 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 101 2004 71 Normal P/E XT, fs exponential method............. 934 1,000 +2 72 Normal P/E XT, fs, physiological method............ 1,000 2,000 Plate | Temperature: Low. High. 34 Days in normal frostless season (fs).............+02. 85 167 35 EHUIC AVS Sire saic seis yee ere rea slave clio sveetefledal shay atelaietouecers 0 rir 36 RO OIG GAY SUS. yisaes) o)seye o aeiaie olele ena sveiabaveie: sister vaieiteuay apabs 66 149 + 37 Remainder summation above 32°, year (thousands).... 10.0 11.5 38 Remainder summation above 39°, fs (thousands)...... 2.6 4.5 39 Exponential summation, fs (hundreds)..............- 2.8 4.7 40 Physiological summation, fs (thousands)............. 2.1 6.7 41 PAISOMIUGE) ALUN 655. 5. 5 does 6 « Slaieerevera Glerermuebalete iene offs —48 —7 43 Normal daily mean, coldest 14 days of year (°F.)..... 5-4 30+4 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 71.6 45 Normal daily mean, year (°F.)..........ccccccce0ees Stay To 50 Precipitation: 46 Normal daily mean, fs (inch). ...........cccceeesees .091 lon 47 Normal No. rainy days (over 0.10 inch), fs........... 35 124 48 Normal No. dry days (0.10 inch or less), fs........... 28 136 49 Dry days, percentage of total, fs (per cent)........... 18 80 60 Days in longest normal rainy period, fs.............. 22 106 61 Days in longest normal dry period, fs................ 9 58 52 Mean total, year (inches).............ecc000eseeees 30 — 50+ Evaporation: 53 Daily mean, 1887-88, fs (inch).............0.00e0005 .084 .149 64 Total annual, 1887-88 (inches)...............00ee005 21.3 30+ Moisture ratios: 58 NOTA ROE IS 3 ale ey ae Wehr Res AME aS Mrecchewlatehas la c eal 1.23 59 UNEGEMAL LUTTE» cialeie nove ce eRe eters Uda Oke teed alten 81 1.52 60 BARON GLUE ALUN VIGAIT alle sie sole soieeoain ed OPE MOAN ways SaaS .82 1.72 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 345 450-4 Humidity: 65 Normal imesn,. fs (per Gent). sided sea cides oe We een. os 70.4 81.8 66 Normal mean, year (per Cent). ........ccccecececees 73.4 80.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.7 12.9 Sunshine: 69 Normal total duration, fs (hours). ..........00e0eee: 1,225 1,500 +2 Moisture-temperature indices: 70 Normal P/E XT’, fs, remainder method.............. 301 401 71 Normal P/E XT, fs, exponential method............. 2,997 3,780 72 Normal P/E XT, fs, physiological method............ 2,747 7,000 +4 406 Plate 34 70 72 Plate CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 32.—Climatic extremes for the Boreal Region. Temperature: Low Days in normal frostless season (fs)..............05. 25 HOt Gayerys es. 6 sion ies a Skokie Sake el LE eee 0 COLAIA AWTS) 5 Soaks ee se ais oo bs aio ois BTR els SO Eee 0 Remainder summation above 32°, year (thousands).... 10-4 Remainder summation above 39°, fs (thousands)...... 2.4 Exponential summation, fs (hundreds)............... 245 Physiological summation, fs (thousands)............. 1,947 Absolute mamimunn. <) 6% =o) 56s ce eee ee eee —54 Normal daily mean, coldest 14 days of year (°F.)..... 0 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4—4 Normal daily mean, year (CF:)....%. 5.5%. 2s eee oe etek 354 Precipitation: Normaldaily mean; fs:Gnch) . <.52 20.2)... 2 ote. Be .025 Normal No. rainy days (over 0.10 inch), fs........... 25 — Normal No. dry days (0.10 inch or less), fs........... 75 Dry days, percentage of total, fs (per cent)........... 78 Days in longest normal rainy period, fs..............- 25 —4 Days in longest normal dry period, fs................ 25 —4 Mean ‘total, year @uches). 2.0 8S S20) ee AA 20-4 Evaporation: Daily mean Ssi.05. 75 (NEN) 27.55.55 50s ees 6 eee eee .052 Total annual, 1887-88 (inches).............2.e00e0: 20-4 Moisture ratios: AN GEIN Ge PBN Li CEL a oii o/s wlth le Sinica ce TEaNe -10 NORE IS eee Cee ric bla a Rena GSA de ee eee Bp I Normal PY years) 220. via nk 47 Normal No. rainy days (over 0.10 inch), fs........... 161 234 48 Normal No. dry days (0.10 inch or less), fs........... 84 204 49 > Dry days, percentage of total, fs (per cent)........... 26 56 50 Days in longest normal rainy period, fs.............. 112 174 51 Days in longest normal dry period, fs................ 19 182 52 Neeani total, year Cmehes) 5). eke oe ha hee wl wes weds 06— 60+ Evaporation: 53 “aDaaly mean’, T887—S8;, fs CnCh) 650.0 he ea. PR .140-4 .141 54. Totalbannual, WS7—-SS Gmches).: occ 6 eisrecers occa etre ae 50 —4 51.6 Moisture ratios: 58 ROTH ET a aiacct cel Aa ROE AULT OO Soleil a Kaui .75 1.00+2 59 Someta (By Paice toes chee eeetate Wes La Me CRG STR .75 1.202 60 PNG HRM GE YP: VERT ea alsin cletacewisteres caaod aire wows ala « ORTEARL .75 1.36 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 650 —4 707 Humidity: 65 iINormealsmesn, Jex(per cent) 0.025. BoP L COC, CO ee Ok Viecl 80.5 66 INommalsmern, year (per Cent) ic ces oa ER wk weil 80.5 Wind: 68 Normal mean hourly velocity, fs (miles)............. 8.0—4 9.7 Sunshine: 69 Normal total duration, fs (hours)... Oo... ee 2,300 + Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method. ............. 1,155 1,200+4 71 Normal P/E XT, fs, exponential method............. 10,877 11,000 + 72 Normal P/E XT’, fs, physiological method............ 23,000 + ae | 426 TABLE 62.—Climatic extremes for region with 1 to 7 species of a selected group of 13 deciduous CORRELATION OF DISTRIBUTIONAL FEATURES trees of the eastern states. Plate | Temperature: Low High. 34 Days in normal frostless season (fs)..............--- 85 335 35 HAGE GAGS yeas ne ee ee iced bas hes bs tek ee Se 0 226 36 Cole ays. ys eee OR i oe es a ee ee 0 150 37 Remainder summation abe @ 32°, year (thousands)... 10.0— 26.0+ 38 Remainder summation abcve 39°, fs (thousands)...... 2.6 10.6 39 Exponential summation, fs (hundreds)............... 3.0 pm Bae 40 Physiological summation, fs (thousands)............. Aaa & 21.4 41 A bsolute nviminannt een | s,s Sees pees —d9 +22 43 Normal daily mean. coldest 14 days of year (°F.)..... 0 sy 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal daily mean. :vear (FP .) .2- 2... . 2 > Leelee g 35 70+ Precipitation: 46 Normal daty mean. Js Gnech).. . .< dedi! ao cate eet .077 . 1z2 47 Normal No. rainy days (over 0.10 inch), fs........... 13 284 48 Normal No. dry days (0.10 inch or less), fs........... 28 259 49 Dry days, percentage of total, fs (per cent)........... 8 92 50 Days in longest normal rainy period, fs.............. 14 235 51 Days in longest normal dry period, fs................ 11 88 52 Mean total, went (mehes) . 3.0 6 boeken cc te Colt we 20 —- 60+ Evaporation: 53 Daily mean, 1887-88, fs (inch)...................-4- .084 .188 54 Total annual, 188-788 Gnehes).. «6... Aces: oe noc ck we pa | 54.4 Moisture ratios: 58 ye COS EN UW agp ing Done onecatlnc 2 on on ee a ee eR .39 1.36 59 Mornay Paper errs fon. ote Oke ae. wad GSR Bae .43 1.52 60 Darennleey Pacyennertn cee hae soci oe S25. eee .38 1.72 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 322 675 Humidity: 65 Normal mean, fs (per cent)-:.... 0. <2 3.2. Re 53.2 81.9 66 Normal mean, year (per cent). ..............200000: 59.8 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. iy 12.4 Sunshine: 69 Normal total duration, fs (hours). .................. 1,225 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 179 1,314 71 Normal P/E XT, fs, exponential method............. 1,711 12,106 72 Normal P/E XT, fs, physiological method............ 2,747 23,652 TABLE 63.—Climatic extremes for region with 8 to 12 species of a selected group of 13 deciduous trees of the eastern states. Plate | Temperature: Low. 34 Days in normal frostless season (fs)............2200- 112 35 Heroayacieke Se ee en eee ee es csi < eee ane 0 36 COM AAS Sa ee es Bh a wed euml's Rigs eine 0 37 Remainder summation above 32°, year (thousands).... 10.0— 38 Remainder summation above 39°, fs (thousands)...... 2.9 39 Exponential summation, fs (hundreds)............... 3.0 40 Physiological summation, fs (thousands)............. 4.4 41 Alpsiatuite rermatentarn 2 25 oe Nh I od —44 43 Normal daily mean, coldest 14 days of year (°F.)..... 7 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 45 Nonmal daily mean, year (CF.). ... ..... 22 denen canes 45 — Precipitation: 46 Woernrval daly mean} fs-(meh) és. . sc ocd: Seek ce .089 47 Normal No. rainy days (over 0.10 inch), fs........... 26 48 Normal No. dry days (0.10 inch or less), fs........... 0 49 Dry days, percentage of total, fs (per cent)........... 0 50 Days in longest normal rainy period, fs.............. 17 51 Days in longest normal dry period, fs..............+-. 0 52 Mean tatal ‘year Gnehes) . 01 Socaics Sunk eens ce 30 — CORRELATION OF DISTRIBUTIONAL FEATURES. 427 TABLE 63.—Climatic extremes for region with 8 to 12 species of a selected group of 13 deciduous trees of the eastern states—Continued. Plate 53 54 58 59 60 63 65 66 68 69 70 71 72 Evaporation: Low. Daily mean, 1S87-88;.7s) GME). obvi ccs e ee ene eee .088 Total annual, 1887-88 (inches).............--202000- 20.3 Moisture ratios: I sioyg ct Nye 4 01 OAs 7 aD Eee og 3 Ba a ie a .58 Marinial a PY fails siege. aks PRR yt bak ein bia .66 Normal WE year so). aise ese Mabe Sinaia Sie wisicta aie at Vapor pressure: Normal mean, fs (hundredths inch).................. - 416 Humidity: Normal ment fs (per COMG. cic. emcee 6 a «+ 6 t=: ole of Mapetede ena -62.0 Normal) mean, year (Mer Cent) ye cs be tek oslale ce we 69.2 Wind: Normal mean hourly velocity, fs (miles)............. 4.7 Sunshine: Normal total duration, fs (hours)..............+50- 1,365 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 301 Normal P/E XT, fs, exponential method ............ 2,918 Normal P/E XT, fs, physiological method............ 3,819 TABLE 64.—Climatic extremes for region with all species of a selected group of 13 deciduous Plate 34 35 36 37 38 39 40 41 43 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 71 72 trees of the eastern states. Temperature: Low. Days in normal frostless season (fs)..............46- 124 1S IHE Co StH lay ND ae pea GRRE RIAN oe oy PE sy AYO 47 (POLE 1 Co eT ar SRE VD Ve a cA 0 Remainder summation above 32°, year (thousands).... 11.5— Remainder summation above 39°, fs (thousands)...... 3.9 Exponential summation, fs (hundreds)............... 4.0 Physiological summation, fs (thousands)............. 5.4 PROSOMIGE OTN aU! oe ee ho eo ee ia. Gale e's, suseeee evens a —38 Normal daily mean, coldest 14 days of year (°F.)..... 16 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6 Normal daily mean, year (CF.).............00 cc ee ees 45 Precipitation: Normal daily mean, fs (inch)...................000- .095 Normal No. rainy days (over 0.10 inch), fs........... 49 Normal No. dry days (0.10 inch or less), fs........... 19 Dry days, percentage of total, fs (per cent)........... 11 Days in longest normal rainy period, fs.............. 23 Days in longest normal dry period, fs................ 4 Mean total, wear GMehes) oii. sie ees ka actele ie sale cua 40 — Evaporation: Waly mean, L8S7—S8; fs Gmeh) .ccc05 8s eke cece cw ce cn .108 Total annual, 1887—88. (inches)... 6. wad ste eee ee 25.3 Moisture ratios: PS OUMAE ME EIS t chs Re Were ain Cama aoe se oe ee 51 IST EN] cy fd Py RT NL ee NET AC AE .60 (Notes Pu VORB fos oe Ke wind hone cee eeswew ce con ep Vapor pressure: Normal mean, fs (hundredths inch).................. 405 Humidity: INormal\imeéan, Je (oer Gent). i. oe ee el ee ee ee 65.6 Normal mean, year (per cent). osc e ecw eceses 69.0 Wind: Normal mean hourly velocity, fs (miles)............. 4.2 Sunshine: Normal total duration, fe (hours)... cee ee ees 1,403 + Moisture-temperature indices: Normal P/E XT’, fs, remainder method.............. 303 Normal P/E XT, fs, exponential method............. 2,914 Normal P/E XT, fs, physiological method............| 4,511 High. 231 141 (=>) D bs | D 428 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 65.—Climatic extremes for Pinus teda, area 1. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 106 335 35 Hob GAysis. sco Peso We oe RO oo clos nels Sea 91 226 36 COldidAya ays a). sis or uerpeiials ASU es Ce EE Bee 0 27 3 Remainder summation above 32°, year (thousands).... 18.0— 26.0 38 Remainder summation above 39°, fs (thousands)...... ayes 10.8 39 Exponential summation, fs (hundreds)............... ao ce Dee 40 Physiological summation, fs (thousands)............. 8.4 21.4 41 Absolite Manian eee eae ose ee acca ieee ea ee —15 +22 43 Normal daily mean, coldest 14 days of year (°F.)..... 32 ay 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 78.8— 78.8+ 45 Normal datlyemesan; yeariCl.): 2.60.56 66 eo BO 55 70+ Precipitation: 46 Normal dally means, (neh) 2... sss ssi sok eee .110 .172 47 Normal No. rainy days (over 0.10 inch), fs........... 91 248 48 Normal No. dry days (0.10 inch or less), fs........... 28 170 49 Dry days, percentage of total, fs (per cent)........... vt: 51 50 Days in longest normal rainy period, fs.............. 47 233 51 Days in longest normal dry period, fs................ 16 78 52 iean total vear Linehes) «oi a SNe Ses oo ee 40 —-— 60+ Evaporation: 53 Daily mean, 1887-88: fs: Gneh) <0... 6s. ve. 6 ose eee ee .084 .138 54 Total annual, 1887-88 (inches)...................0-. PAS ES 49.5 Moisture ratios: 58 INOraVaL 29) Fs, fs oli ee Se RS NN, ee WES By) 1.36 59 INOEMMAL aE PIAS seme ee fae be Ast ce Lae .87 be 60 INGrnAl i Mim earr ye ake wt. Ca Pay aie nn ic ee .90 1.62 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 460 612 Humidity: 65 Normal means fs (perm Gent iiccnes meskes ares sie whe eye 68.6 80.6 66 Normal mean, year (per cent)... 5... .252%..0-200:- 80.4 81.4 Wind: 68 Normal mean hourly velocity, fs (miles)............. eh 9.6 Sunshine: 69 Normal total duration, jsi(hours) .%.. 0606: c=s205 1,646 2,300 +4 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 4,540 11,722 a Normal P/E XT, fs, exponential method............. 5002 1-271 72 Normal P/E XT, fs, physiological method............ 7,947 23,155 Plate | Temperature: 34 Days in normal frostless season (fs) 35 Hot days, fs 36 Cold days, fs 37 Remainder summation above 32°, year (thousands).... 38 Remainder summation above 39°, fs (thousands) 39 Exponential summation, fs (hundreds) 40 Physiological summation, fs (thousands) 41 Absolute minimum 43 Normal daily mean, coldest 14 days of year (°F.)..... 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 45 Normal Gatly mean, year (CH) i220 6 b-c..e is Rios > 6 oss Precipitation: 46 Normal daily mean, fs (inch) 47 Normal No. rainy days (over 0.10 inch), fs 48 Normal No. dry days (0.10 inch or less), fs 49 Dry days, percentage of total, fs (per cent) 50 Days in longest normal rainy period, fs 51 Days in longest normal dry period, fs 52 Mean total, year (inches) CORRELATION OF DISTRIBUTIONAL FEATURES. 429 TABLE 66.—Climatic extremes for Pinus teda, area 2—Continued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fe Gnch),.355.......26s0c0ce0s Bs 3: A7Z 54 Total annual, 1887-88 (inches)...........-2cceeeeee- 37.0 56.6 Moisture ratios: Jil ey i dn lel 2] SUN Cen Pm A Dei a) 2 al a ee ee 7M: 1.35 Top sg nH eff EN PI Is A EN CORI La a a a aa 88 1.47 MOTTA ME eVGA Ay. ole ghee baie olaheee ta Maa eles vo ch nub dec eae .90 1.33 Vapor pressure: Normal mean, fs (hundredths inch).................. 500 622 Humidity: Wormal meanw7s (per Comte. 2 sles 5.0 5's 2b) auette, Syeosda, o o.0 0 80.2 Normal mean, year (per cent). ..........2.00c00008. 7g Heat 85.2 Wind: ; Normal mean hourly velocity, fs (miles)............. 5.5 11.0 Sunshine: Normal total duration, fs (hours)................... 1,946 2,650 Moisture-temperature indices: Normal P/E XT, fs, remainder method....... ele fork ye 5,175 10,331 Normal P/E XT, fs, exponential method............. 549 1,196 Normal P/E XT, fs, physiological method............ 9,686 20,570 TABLE 67.—Climatic extremes for Pinus teda, area 3. Plate | Temperature: Low. High. 34. Days in normal frostless season (fs)................. 188 310 35 NER AANA VIS ee eens oe ie een INA ep sae ase hay di Bo dig fabs 157 192 36 AG) a Dat Is SPS aR aR AUP eh SUR td Lee 0 0 37 Remainder summation above 32°, year (thousands).... 18.0+ 26.0— 38 Remainder summation above 39°, fs (thousands)...... 7.4 8.1 39 Exponential summation, fs (hundreds)............... 8.0 10.3 40 Physiological summation, fs (thousands)............. 14.6 18.9 41 Absolute minima 2 oN ae cae coe eos —15 +20 43 Normal daily mean, coldest 14 days of year (°F.)..... 45 52 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 78.8+ ae ie 45 Normal daily; mean, year (CF.). 000.3. ee ek. 60 65+ Precipitation: 46 Normal daily..mean, fs (neh) 230 7 eee MATS .158 47 Normal No. rainy days (over 0.10 inch), fg........... 154 226 48 Normal No. dry days (0.10 inch or less), fg........... 45 92 49 Dry days, percentage of total, fs (per cent)........... 20 34 50 Days in longest normal rainy period, fs.............. 69 131 51 Days in longest normal dry period, fs................ 24 63 a2 Mean total, year (nches) 3 2... .0 Soc nls beee cc bece 40 50+ Evaporation: 53 Daily mean, 1887-88, fs (inch)..............00.0000. .138 .154 54 Total annual, 1887-88 (inches)...................0-- 43.2 48.8 Moisture ratios: 58 Nays rm) OU SRR CRIM | haa Sa ccs. le ats Ce a Lee 85 1.08 59 IORI I/O FG ahs chive Na eve a disk get eure a, LN 89 1.19 60 EN Grint AUVs ce WORT. (cee wg ate os cc aed MCRL oe Oo 91 1.15 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 565 610 Humidity: 65 Normal mean, fs (DEL CONG). «cle os oe ba ets awe lo eeank 707 77.6 66 Normal) mean, year (percent). ccc sccec vccuese eek us 72.9 78.3 Wind: 68 Normal mean hourly velocity, fs (miles)............. 5.6 SY Sunshine: 69 Normal total duration, fs (hours) . os... ei se 02. 8 1,900 —¢ 2,500¢ Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 6,410 10,175 71 Normal P/E XT, fs, exponential method............. 695 1,113 72 Normal P/E XT, fs, physiological method............ 13,0004 23,0002 | | 430 Plate 34 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 68.—Climatic extremes for Pinus teda, area 4. Temperature: Days in normal frostless season (fs)................-- TIOGA seek eee aoe eee Se oe See ee COldsdayeg a octet stale os) eS 8 See Ne Sata eae 2 Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. ALDSOUEbe TERMEMAT Mee ort dos vai 5 ks 3. cutee icbeis oe eats Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily, mean, year (CR.) 000.06 060.5 2. ee ee Precipitation: Normalidaily mean w7siGQnen)). 335 629s te Sec ee ee Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Mean totalicvearGimehes) <2. fais sile < eieee wits uence Evaporation: Daily mean, 1SS87—S357 SANE) 5 6-055 osics cioce.raven ss oes aces ciesene Total annual, 1887-88 (inches)...................... Moisture ratios: GY ETT EY 20 Dies FOR ce AE oes aOR ASL MANIC UM Rete RE Sri IN OEM ala Der pe eee er cise, one see Sa cl IG Tr EB Zyl! DP a fehe re eds Ae A as gE, Vapor pressure: Normal mean, fs (hundredths inch).................. Humidity: ‘Normal mean. i)S.(per CONt ys o 65... oi She ee =, sakes Normal mean, year (percent)... . . os wee ws ke oe Sy te = Wind: Normal mean hourly velocity, fs (miles)............. Sunshine: Normal total duration: fse(hours)).... 2 2s.< <.e -c,cioecncd fe Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. Normal P/E XT, fs, exponential method............. Normal P/E XT, fs, physiological method............ .170 256 75% 26 256 19 50+ .123 35.6 1.76 1.96 1.94 573 82.7 82.9 13.5 2,100 +-2 13,511 1,418 24,265 TABLE 69.—Climatic extremes for Liriodendron tulipifera, region of infrequent occurrence Plate 34 35 36 (fringe). Temperature: Days in normal frostless season (fs)................. RVG GH AY SAIS os es esc aera k oie Se oes Se ae COLO Sete Ne a tame a oe ae 22 ee ue iar, Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. ‘A bsoluitecmimimmtimin . 625 ou oconis cae eee ae oe ee Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily aean, year (CH) ..6 he be 65 Rees Precipitation: Normal daily mean, fs: Gneh). . ... Qe.cho hate sae ose Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs...............-- Mean total year (inches) .. 4. oo hee deneeeeteee oe .089 TABLE 69.—Climatic extremes for Liriodendron tulipifera, region of infrequent occurrence Plate 53 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. (fringe) —Continued. Evaporation: Daily mean, 1887-88, fs (inch)..........-0-20seee008 Total annual, 1887-88 (inches)...............-....6- Moisture ratios: ; cs rare AED /PB yy Wf ioe i tn MO ONE etek chs tele CAN) Bawah INGormmialpa S78 ye cies veateraaoeete erie dao ety vtale ee ees Worms 22H Vea 251-0) nieces uate « fis alee nen Vapor pressure: Normal mean, fs (hundredths inch).................. Humidity: Norma! mean, fs (per cent). .........20020ee ec eeeee Normal mean, year (pericent)).5....220)20 3 lee. oe eel ee - Wind: Normal mean hourly velocity, fs (miles)............. Sunshine: Normal total duration, fs (hours)................... Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. Normal P/E XT, fs, exponential method............. Normal P/E XT, fs, physiological method............ 431 High. .172 56.6 1.76 1.96 1.94 600 82.7 82.9 14.9 2,300 10,0004 1,418 24,265 TABLE 70.—Climatic extremes for Liriodendron tulipifera, region of greatest abundance Plate (center). Temperature: Days in normal frostless season (fs)................. [SIO COLE STAT ay AS Si a A a eR A COTSIVEL COTE S150) Eo AIL AT AUR SEU pia a SN ag Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. Absolute maimimam: 2.060) 8) Pe ole ad maid eek ccoust Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily mean, year CHE.) 0) sscactes acess ue sen Precipitation: Normal daily mean: fs Gneh) sob. see ee cee cake Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Wiean total, vear (inches). ..:\) wos. pice c cece ewes ane Evaporation: Daily mean, 1887-88, fs (inch)..................000- Total annual, 1887-88 (inches)...................00- Moisture ratios: INGLE IV 2 ORG ORE oR ARUP MO RU ior CVs Ie a Oe Ra on Se A RR NR Ie evp ais oY 2) Diet ete 1 a laa One ces i eae CARRS EH Vapor pressure: Normal mean, fs (hundredths inch)........ Humidity: INGrmel menn, 7s (Her Gent) ics. vs ik ooaces cca aah Normal mean, year (per cent). ........cceeccccecaee Wind: Normal mean hourly velocity, fs (miles)............. Sunshine: ‘ Normal total duration, fs (hours)..............0e00- Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. Normal P/E XT, fs, exponential method............. Normal P/E XT’, fs, physiological method............ Low. 145 63 0 11.5+ 3.8 High. 217 141 66 18.0+ 6.6 7 | 12.9 —5 40 78.8+ 60+ .131 166 83 48 140 56 60+ . 200 54.8 “J oy) ay og 10,052 432 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 71.—Climatic extremes for Bulbilis dactyloides, region of infrequent occurrence (fringe). Plate | Temperature: 34 69 70 71 72 Days in normal frostless season (fs)..............--- 1B Uo) yo S732) Ke a A OMNES chi ye eM COld da SS a7 Sie cd verte hol oy ged eeageieoel acne pike Ee Ss Remainder summation above 32°, year (thousands)... . Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. Aso lupe mma MnieTe ck ee a Sb o's (elats @ oe Bictauae Sea Rota Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normalidaily mean, year. CE.) .. >... 3. 6... eee Precipitation: Normal daily: mean: fsGneh)). 2... . ke oe eae cae Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Mean totalyear (imehes)::. .. natok ae oe Evaporation: ; Daily mean, 1887-88) fecGnceh). 62.02 ei se oo ee Total annual, 1887-88 (inches)... 2 ....0-2.: 0.266 22s een Moisture ratios: Normal P/E, faves oc. e eo: PO er of Seas SA ine aU cl Norn ae IG Ap Se Me ik he OS ate io am anarnaeg INGEMal Ee VCAT es 59.4 | 67.8 | 66 Normal mean, year (per cent)...................... 59.3 70.4 | Wind: 68 Normal mean hourly velocity, fs (miles)............. ae 14.2 | Sunshine: 69 Normal total duration, fs (hours)................... 1 a7 2,057 | Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 1,590 3,781 71 Normal P/E XT, fs, exponential method............. 100 —4 5004 72 Normal P/E XT, fs, physiological method............| 1,000—¢ 10,0004 | TABLE 73.—Climatic extremes for Bulbilis dactyloides, region of greatest abundance (center). Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 1711 71 Normal P/E XT, fs, exponential method............. 100 —¢ 72 Normal P/E XT’, fs, physiological method............| 2,000—4 3,000 +4 4004 7,0002 Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 120 211 35 RC AV SHUTS ene ww Dilvun Mae ACME cae La aueg utes aul 78 3 85 114 36 | OCOIE Le eed 14 Aes OUR ee RE eae Le BL OR a Fenaet ge 0 129 37 Remainder summation above 32°, year (thousands).... 11.5— 18.06 38 Remainder summation above 39°, fs (thousands)...... 3.8 5.8 39 Exponential summation, fs (hundreds)............... 4.6 6.0 40 Physiological summation, fs (thousands)............. 7.6 10.7 41 PAO O UGE TOVUITIVUETID 282 OLN pe eae Oahu ho ta — 44 +7 43 Normal daily mean, coldest 14 days of year (°F.)..... 14 34 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6— 78.8 45 Nenmnal daily mean) year CED.) 0622. eek 45 — 60+ Precipitation: 46 Normal: daily mean, fs Gneh) 3.) eos ee oe. .070 .103 47 Normal No. rainy days (over 0.10 inch), fs........... 13 HY 48 Normal No. dry days (0.10 inch or less), fs........... 60 140 49 Dry days, percentage of total, fs (per cent)........... 46 92 50 Days in longest normal rainy period, fs.............. 20 59 51 Days in longest normal dry period, fs................ 38 88 52 Mean) total) year Gmehes) i. 0. ees es oS ce bc eee k sees 20 — 20+ Evaporation: 53 Daily mean: 1887-88, fs Gineh). 6. se es cod . 166 .203 54 Total annual, 1887-88 Gnecheés)...... 2.5.00. 0.000 0000. 41.3 54.6 Moisture ratios: 58 Iie) was a 4) NG CS Ae LA: Ae Ne AA En Cee cone Pa ae 39 60 59 NCE re ere FSi ach Nk PM ete HORM Bilge lh 3 ee 43 72 60 BNO ENA NGA io.) 54) 84 oy io WhesR URE AVRARN Sod k UAE ae 51 . | Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 370 431 Humidity: 65 INGIrIMeaTRe AN: 78) (DET GENE)’, Gdansk wivkeinvn! geekaume ews ous 57.6 65.3 66 Normal mean, year (per Gent)... bo. oa. ee oN wees ae 64.7 66.9 Wind: 68 Normal mean hourly velocity, fs (miles). ............ 8.8 11.5 69 Normal total duration, fs (hours)................0-. 1,300 —4 1,900 +¢ | | Sunshine: | | | 434 TaBLE 74.—Climatic extremes for region of cumulative occurrence of four species of grasses common in the great plains. CORRELATION OF DISTRIBUTIONAL FEATURES. Plate | Temperature: Low High 34 Days in normal frostless season (fs)................. 94 254 35 1S os ais Ee SEL Ca SIP eb ahabn GAAS UM aa URC NMR A DR bezel dS Wala 4 173 36 Cold Gaye: fs) Seay st Wega ae Aisle panes spine he 0 158 37 Remainder summation above 32°, year (thousands).... 10.0—4 18.0+4 38 Remainder summation above 39°, fs (thousands)...... 3.0—4 8.0+4 39 Exponential summation, fs (hundreds)........... ie Mae. 3.0 9.6 40 Physiological summation, fs (thousands)............. Bu 76 1¥26 41 A bSoliyte cine ese) ec Mis eigen) Meare a —54 +8 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 44 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6-—4 78.8+4 45 INormal?daily mean. yeari(CH:) 29.7 82.9 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.5 14.9 Sunshine: 69 Normal total duration, fs (hours)................... 1,134 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 13 1,418 71 Normal P/E XT, fs, exponential method............. 127 13,511 "2 Normal P/E XT, fs, physiological method............ 197 24,265 TaBLE 76.—Climatic extremes for total range of all species of Cylindropuntias. Plate | Temperature: 34 Days in normal frostless season (fs)................- 140 311 35 ELMIRA SMAI S rete ire ee oy nie Isis ws cae ie clea ardie s io! odes 38 AL 36 OLA Se HS hye ilehie' cig abirenas chguae teva io: aa RMR REG END RENTS. 2 0 88 37 Remainder summation above 32°, year (thousands).... 10.0— 26.0+ 38 Remainder summation above 39°, fs (thousands)...... 3.4 10.1 39 Exponential summation, fs (hundreds)............... Po idler 0 | PS 40 Physiological summation, fs (thousands)............. 4.1 20.6 41 PISOMELE UAT TAMIL 05). Le sack ee ano M cnetateld als, wees —32 +23 43 Normal daily mean, coldest 14 days of year (°F.)..... 29 54 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal daily mean, year (°F.).....................- 55 70+ Precipitation: 46 Normal daily; mean) fs Gneh)i.cs). O20 A ees 0.20 .088 47 Normal No. rainy days (over 0.10 inch), fs........... 0 57 48 Normal No. dry days (0.10 inch or less), fs........... 142 283 49 Dry days, percentage of total, fs (per cent)........... 71 100 50 Days in longest normal rainy period, fs.............. 0 26 51 Days in longest normal dry period, fs................ ES, 283 52 Mean. total year (mehes) clo. pek ccs Baeeees boone es 10— 20+ Evaporation: 53 Daily mean, 1887-88, fs Gnch)...0.. 08... e oe ee cee .201 .349 54 otal annual, 1887-88 Gnehes) 0.2.65. 0.05 foe ok Sore 101.2 Moisture ratios: 58 CDT TAYE 73/61 A RTC al RL dh kal ile 04 44 59 DSi gaa TEU (iA Bye teal Mi ae deena re a Sr A Ae Ba .06 47 60 HSiovameall We VAT ORRRUCT Voie eas MDI atid A a A Balai .03 .28 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 233 450 +4 Humidity: 65 NOI am efi. Facer CONt). < sc cclcccce cs mie cee eek es 22.6 59.4 66 Normal mean, year (percent)... of... bike ccc eck 29.7 59.3 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.5 14.2 Sunshine: 69 Normal’ total duration, fs (hours) .. 0.5.0... 6... 0S 1,367 2,900¢ Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 81 262 71 Normal P/E XT’, fs, exponential method............. 772 2,532 72 Normal P/E XT, fs, physiological method............ 979 4,673 436 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 77.—Climatic extremes for Tsuga heterophylla. Temperature: 34 Days in normal frostless season (fs)................. 25 316 35 FEOG ORG SHGS 3 | Ps ce be oko batbtcve 0 CEES Le eae ae 0 30+24 36 Cold GaVangs 5 oe See ee Pe eis ie ee eee 0 120 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... so 4.6 39 Exponential summation, fs (hundreds)............... 3.0-—4 5.0 40 Physiological summation, fs (thousands)............. 1.9 4.8 Al ASO Le PASTITNAA Gos. ce Shoe occ, tdi ec oe eae cee —46 +30 43 Normal daily mean, coldest 14 days of year (°F.)..... 204 46 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — 71.6+ 45 Normal.daily mean year (CF .) .... oo... nb eee 45 — 55+ Precipitation: 46 Normal daily: mean, fe Gch) . 2... 6.5 66. ass eee = Se . 0404 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 28 199 48 Normal No. dry days (0.10 inch or less), fs........... 72 257 49 Dry days, percentage of total, fs (per cent)........... 27 90 50 Days in longest normal rainy period, fs.............. 21 99 51 Days in longest normal dry period, fs................ 56 187 52 Mean totalesvyear Gnches) .). 6 4).5ios Ns baat ® SES See 30 90+ Evaporation: 53 Wary mean: tNSi—so. 7s “GNneh) os es eee .052 . 1804 54 Total annual, 1887-88 Gnehes)....... 2...6 20s pecac dens 18.1 40+4 Moisture ratios: 58 STi ciir Wy 2) Sper 2.) Nene eek ot Se ee oe ne NO PRL RU EASEE by . 204 3.84 59 Morisiaica Wyeee © hae oi OS ae ae lie ae a eae ie 41 4.48 60 Normal by Hoven en ss ae hess be een ee ee 404 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch)........ Sele epee 300 —4 329 Humidity: 65 Normal mean, js. Goer Cent) 2.2020 32. ee eee 60.0—4 87.5 66 Normal mean, year (per cent). >... 2-2. 55.2 Se os 74.6 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. re 16.4 Sunshine: 69 Normal total duration, fs (hours)................... 1,300 —4 2,100 +4 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 100 —4 1,566 71 Normal P/E XT, fs, exponential method............. 1,000 — 11,724 Normal P/E XT, fs, physiological method............ 1,313 Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)..............-.. 196 316 35 TIGL GAVE HIS S oo oe ees CR as ore ee Sea ae eee 0 30-4 36 Col Gayaiiis saan oa sore se ee ee ee ee ae 0 30-4 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 3.0 3.8 39 Exponential summation, fs (hundreds)............... 4.1 5.0 40 Physiological summation, fs (thousands)............. 1.9 Se 41 Absolute minnniim 5-4. 2 aonaes ©. ee Bost anes —3 +30 43 Normal daily mean, coldest 14 days of year (°F.)..... 354 46 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 Bee, 45 Normatvdaly mean, year (Cl )osen ss 2 Se tee aa Rea 50 — 55+ Precipitation: 46 Nomualdaily mean, fs Gneh):. 5. 3.26 i oeee a le, .070 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 55 199 48 Normal No. dry days (0.10 inch or less), fs........... 72 200 49 Dry days, percentage of total, fs (per cent)........... raf 81 50 Days in longest normal rainy period, fs.............. a! 99 51 Days in longest normal dry period, fs................ 56 187 52 Mean ‘totaly year Gnehes) 62-5 605 25 % water ick ee oss 40 90+ CORRELATION OF DISTRIBUTIONAL FEATURES. 437 TaBLe 78.—Climatic extremes for Picea sitchensis—Continued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fs (inch)...............2-22055 .052 . 1402 54 Total annual, 1887-88 (inches)..................200-: 18.1 26.8 Moisture ratios: 58 INO EQAL Fo) ey Saeed, nae She IEE Nar .404 3.84 59 Normalan Be Ssh vente 1 dy enna pies time ais hoa coh, Ulsenes .80—4 4.48 60 Normal P/E, Years by anns cad sept Geis ae eal, . 904 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 318 348 Humidity: 65 Normal mean, fs (per cent)..........0... e+e eee eee’ 73.6 87.5 66 Normal mean, year (per cent)..............-eeeeees 1622 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 6.2 16.4 Sunshine: 69 Normal total duration, fs (hours).................-- 1,500 —4 2,100+2 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 200 —2 1,566 71 Normal P/E XT, fs, exponential method............. 2,000 — 11,724 72 Normal P/E XT, fs, physiological method............ 1,874 7,475 TaBLe 79.—Climatic extremes for Pseudotsuga mucronata. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs) ..............2... 25 316 35 LOGON ee tot Negra reN Ae Prune anal geen la hat 2 aie dor hag 0 38 36 EUG AY AES oy sei ccuei Sis res leiteh ches Havoc case, eeanitee Musyanadaiet sie ae 0 149 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.8 5 aS 39 Exponential summation, fs (hundreds)............... Bae 5.0 40 Physiological summation, fs (thousands)............. 1.9 5.0 4] PAVOSOLUte. HUTT 6 oy 5 bs oi dvene el bale Sci Wk wala hee eves —49 +30 43 Normal daily mean, coldest 14 days of year (°F.)..... 15 —4 50+2 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal daily mean, year (°F.).............00e eee ees 40 — 65+ Precipitation: 46 Normal daily mean, fs (inch)..............0..00000- .025 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 1 199 48 Normal No. dry days (0.10 inch or less), fs........... 72 250 49 Dry days, percentage of total, fs (per cent)........... 27 100 50 Days in longest normal rainy period, fs.............. 0 99 51 Days in longest normal dry period, fs................ 56 247 52 Mean total, year (inches)...............-0c0eceeees 20+ 90 Evaporation: 53 Daily mean, 1887-88, fs (inch)............. ...-008. .052 . 262 54 Total annual, 1887-88 (inches)..................0005 18.1 39.2 Moisture ratios: 58 Isfay ont lhl SVU Deis CARR) Ul hea a A es ange Lt 10 3.84 59 INTE Ey FS!) Voc ey ee MU ORES 2 OS) 6 NPA ELT Ne at .12 4.48 60 Noro all PB years iit tte crie Oe Aes le ER 14 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 300 —4 348 Humidity: 65 IN@rmal men, ss(per Gent) cP. Git PPO Veins 504 87.5 66 Normal mean, year (per cent)...........0cc cece ees 50¢ 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 5.4 16.4 Sunshine: 69 Normal total duration, fs (hours) .............. 00005 1,300 —4 2,500 Moisture-temperature indices: | 70 Normal P/E XT’, fs, remainder method.............. 100 — 1,566 71 Normal P/E XT, fs, exponential method............. 1,000 — 11,724 72 Normal P/E XT’, fs, physiological method............ 1,000 — 7,475 | 438 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 80.—Climatic extremes for Pinus ponderosa. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs) ............000-. 25 209 35 IGG AR SIS sic. Rin eee io we Si es eel oe ee 0 88 36 Coldidays is. ace ei ae i ce Pals We eS 73 149 37 Remainder summation above 32°, year (thousands).... 10.0— 11.5+ 38 Remainder summation above 39°, fs (thousands)...... 2.4 5.4 39 Exponential summation, fs (hundreds)............... 2.4 5.4 40 Physiological summation, fs (thousands)............. 2.6 6.3 41 ADSonite pITE hs noe Os che A eee aL —55 +12 43 Normal daily mean, coldest 14 days of year (°F.)..... 15-4 50+4 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — 78.8+ 45 Normalidartiy mean, year U-)\. << 5 sis ss 2 ete ieee 40- 65+ Precipitation: 46 Normmaligatly-menn. 7sGnch). ~ 62652605 GAs a Bete .025 .103 47 Normal No. rainy days (over 0.10 inch), fs........... 0 ‘ 72 48 Normal No. dry days (0.10 inch or less), fs........... 104 202 49 Dry days, percentage of total, fs (per cent)........... 46 100 50 Days in longest normal rainy period, fs.............. 0 59 51 Days in longest normal dry period, fs................ 38 202 52 Mean-tatalb wear GNCHES) . wSs:c Saydisc 2 3a Oe nee 20—- 60 Evaporation: 53 Daily mean. 1887—-s978 GHeH)< 00 oo. Se See a a | . 262 54 Total annual, 1887-88 (inches).............0.-.e000- 30.8 76.5 Moisture ratios: 58 Nua ese eat shea ke Sle etna Sak ae eee .10 .60 59 AN GEST a IPS ARE ois 5 ond Sarco ee yen Bea ed .12 : .60+2 60 IN Gravity EAE stil cide td qo bo ha eS OR 14 ay | Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 249 300 +24 Humidity: 65 Normal menan.;js-Gaer centys.i6< 681 35.88 Se ee 46.7 704 66 Normal mean, year (per cent)... 2.2002 6. 5-20.20 e tb: 48.7 704 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.3 6.0+4 Sunshine: 69 Normal total duration, fs (hours) ..................- 1,167 2,3002 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 58 3004 7t Normal P/E XT, fs, exponential method............. 563 2,000¢ 72 Normal P/E XT, fs, physiological method............ 710 2,000¢ Plate | Temperature: 34 Days in normal frostless season (fs) 35 Hot days, fs 36 Cold days, fs 37 Remainder summation above 32°, year (thousands).... 38 Remainder summation above 39°, fs (thousands) 39 Exponential summation, fs (hundreds) 40 Physiological summation, fs (thousands) 41 Absolute minimum 43 Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... 45 Normal daily mean, Year (oP) ond ses on x Se Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 81.—Climatic extremes for Pinus contorta—Continued. 439 Plate | Evaporation: Low. High. A” 68 Daily mean, 1887-88) fe Aneh)) 33 6.. 2 4) See eas .052 . 262 54 Total-annual, 1887-88 Gnehes)) sso. ers eae vee ea ese Lok 68.3 Moisture ratios: 58 INEM AR SOLAN)! bis, UN AREA T b ERAN Oe ty De ho Gy, .10 3.84 59 Normalan) Beifsis tos Wy SUN nea) at) MPL DRC TA irate us 14 4.48 60 Nosmalweih. Veare che hdd fhe ela po 2 Ra, .14 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch)................ 249 348 Humidity: 65 INormmalmean. Js (per icentis Poa totes vee ale were ab ole 47.9 87.5 66 Normal mean, year, (per cent) 36 1. ioe. ees Ves oe 56.1 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.3 16.4 Sunshine: 69 Normal total duration, fs (hours) ................2.. 1,167 2,3004 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 72 1,566 71 Normal P/E XT, fs, exponential method............. 691 11,724 72 Normal P/E XT, fs, physiological method............ 809 7,475 TABLE 82.—Climatic extremes for Pinus edulis. Plate | Temperature: Low High. 34 Days in normal frostless season (fs)...........2-2005- 83 267 35 Tate eode ecrtaie cite ids Goma tavsiortay ety eke & ilaitoretecalnv'el o¥ec ove 0 105 36 EONAR AAW ANUS eel bic te sovadegsiaseee Guecan te RELIED Bid kam ee 0 110 aii Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.4 5:4 39 Exponential summation, fs (hundreds)............... 2.4 5.8 40 Physiological summation, fs (thousands)............. 2.6 9.9 41 A GORCOH Nh ee 08 111001, 0 8 0.0 ye a RPA De eee Noe Ue Sri ee rR —37 —3 43 Normal daily mean, coldest 14 days of year (°F.)..... 20—4 50+4 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal daily mean, year (CE .) ei. oc see ck hme ews 40 70+ Precipitation: 46 Normal daily mean, fs (inch)..............e00ce0ee: .0204 .088 47 Normal No. rainy days (over 0.10 inch), fs........... 0 57 48 Normal No. dry days (0.10 inch or less), fs........... 142 2754 49 Dry days, percentage of total, fs (per cent)........... 71 100 50 Days in longest normal rainy period, fs.............. 0 26 51 Days in longest normal dry period, fs......: Sie ME rege 75 —4 225+4 52 Mean total vear Gnehes) (oc ccuckcece esses euse ens 20 — 30+ Evaporation: 53 Daily mean, 1887-88, fs (inch).............2.0cc0 ees .180¢ .330 54 Total annual, 1887-88 (inches)...................065 55.4 101.2 Moisture ratios: 58 INC EY A OAD REA SOM Rn ane SIRT OR Bree Bs .10 44 59 NVM te Doe feria a's fobat ssh Werte Re digest MeN aN wheat RB s: .39 60 INET aa ORIN. «7, More allies “a donaravenet @ tare ane watlatata Wiel oy L3Z Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 233 450+4 Humidity: 65 Normal mean,)fs: (per cent) oi ic. Soon s Oe eee als 37.0 46.7 66 Normal mean, year (per cent)... 22... ccd eee eee es 38.8 48.7 Wind: 68 Normal mean hourly velocity, fs (miles)............. 5.6 10.2 Sunshine: 69 Normal total duration, fs (hours)... ...........-008: 1,134 2,300¢ Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 58 4004 71 Normal P/E XT, fs, exponential method............. 563 4 000% rer) Normal P/E XT’, fs, physiological method............ 710 7,000¢ 440 Plate 34 35 36 ae 38 39 40 41 43 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 fi | 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 83.—Climatic extremes for Pinus palustris. Temperature: Days in normal frostless season (fs)................. WAGE, CAV Shs es tenn ie tn cd Sia Sc lae hen pa oa ai BICLIG GG ER TZSI Fae 2 1s Si ta ine MeN Ls tle an 5h Aa Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)............... Physiological summation, fs (thousands)............. JP DSOLUIte aie. os i lc ois ope ae ae cata lee ees Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily; mean, year:(F'.).. 23...) 3.) Seer Precipitation: Normal @aily mean; fs Ginch):..;. - adios sd < Skea ek Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Mean total aear Gmnches) ; .. «0 bewiddsis Siwiaienas baie oe Evaporation: Daily mean... 1887-88, Js Gnch)° >... OSs eee Total annual, 1887-88 (inches).............-......... Moisture ratios: SDT TTL bs STE Ei Sis A oa a a Oe a Ne rant sala Pips ee se eels wate insei in W mien td eo Normal (27s wear xh se sore ik te Vapor pressure: Normal mean, fs (hundredths inch).................. Humidity: Normial :mean: fs: (per: cent) site ais Acs Oe Se Se 71.0 Normal mean, year (percent) ~. 4 eis a eek bes | Wind: Normal mean hourly velocity, fs (miles)............. 5.0 Sunshine: Normal total duration, fs: (hours). 22 228k eae 1,900 —2 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 600 —4 Normal P/E XT, fs, exponential method............. 6,114 Normal P/E XT, fs, physiological method............ 10,0002 TaBLE 84.—Climatic extremes for Pinus echinata. 2,300 +2 1,314 13,511 24,265 82.7 82.9 13.5 Plate 34 35 36 37 38 39 40 41 43 44 45 46 47 48 49 50 51 52 Temperature: Low. Days in normal frostless season (fs)................. 143 IGT AAV SR ISie bia eee ioe Aes tiie ee A ae eo eee ra ater 63 CONTA GS APS coe etre a eRe OSS I RI Cen aLe bi 0 Remainder summation above 32°, year (thousands).... 11.5— Remainder summation above 39°, fs (thousands)...... 3.9 Exponential summation, fs (hundreds)............... 3.9 Physiological summation, fs (thousands)............. 5.7— PA Dsolrite TMeMENUITIA es bo shin eo co ole AS ede ee —25 Normal daily mean, coldest 14 days of year (°CF.)..... 25 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— Normal idaity mean, year (CE)... 252 65 fds dete sae st 50 — Precipitation: Normal dasy. mean, Js» G@neh) » >s.y Seigler esse ess sET2 Normal No. rainy days (over 0.10 inch), fs........... 102 Normal No. dry days (0.10 inch or less), fs........... 0 Dry days, percentage of total, fs (per cent)........... 0 Days in longest normal rainy period, fs.............. 48 Days in longest normal dry period, fs................ 0 Mean: totalityear Gimehes). +... Seadeee dete tisichey te ces » 40 High. 279 183 55 18.0+ 8.7 9.6 17.8+ +16 50+ 78.8+ 65+ .170 256 90 51 256 50 60+ Plate 53 54 58 59 60 63 65 66 68 69 70 71 72 Flate 34 35 36 Yh 38 39 40 41 43 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 84.—Climatic extremes for Pinus echinata—Continued. Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal r/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TasBLe 85.—Climatic extremes for Pinus caribea. Temperature: Days in normal frostless season (fs)................- EP URLR VMI Sie ticle, a essen ches cent hanvatans mucin ye sak Ey yaneed lye COLO ICTR S05 SA NIA a RPO POUR Ce a Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands)...... Exponential summation, fs (hundreds)......... peda Wes Physiological summation, fs (thousands)............. PANS SO MNEGERTIATTAUTIUUITDD 5 (6.6 6 orice, che pilarlalueeeibch oyatlareis ena lsuekaicuareuste Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily mean, year (°F.)..............0020000- Precipitation: Normal daily mean, fs (inch)...................000- Normal No. rainy days (over 0.10 inch), fs........... Normal No. dry days (0.10 inch or less), fs........... Dry days, percentage of total, fs (per cent)........... Days in longest normal rainy period, fs.............. Days in longest normal dry period, fs................ Mean total year Gmehes)ie. i ses odes kaa wea were e ole Evaporation: Daily mean, 1887—88, fs Ginch)..........0.0.0.00cceues Total annual, 1887-88 (inches).................0000: Moisture ratios: ISVS TEAL EoHCEL TS ciiioid alas gt SeeeaR ane hi Shark FON B andes toe cae NM MERA ergy ED PS) 5c 2 yas tu so Ace is Hedy i OW Mdwthab ards awe Ney ees UN PRA HPN NAT oo 1s fey 6%. vs me eAOIOERIANRL Abts Na ataiteleen Vapor pressure: Normal mean, fs (hundredths inch).................. Humidity: Normealrmenns fs (oer cent). } eines ig ebantin Us aise austere Normal mean, year (per cent)... 6... 6. cede eek We mees Wind: Normal mean hourly velocity, fs (miles)............. Sunshine: Norms) total-duration; fs: (hours). oi aw ceed Wik dk cen Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. Normal P/E XT, fs, exponential method............. Normal P/E XT, fs, physiological method............ Low. 241 168 0 18.0+ 8.4 9.1 16.4 —1 49 78.8+ 65+ .141 165 28 11 117 Ty 50 — .124 42.1 1.08 1.004 1.09 1,314 12,106 23,652 44] 2,300 +4 442 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 86.—Climatic extremes for Pinus strobus. Plate | Temperature: Low High 34 Days in normal frostless season (fs)................. 85 207 35 ETO t Ga VSi aise) joie Sel On ot etek Me hasok eckson uce: svc eS ee 0 128 36 COLT Y Sai Site nics oe oer oul ta be (Shc uae. aris NU at pcpdee ALOT ANS 0 150 am Remainder summation above 32°, year (thousands) .... 10.0 11.5+ 38 Remainder summation above 39°, fs (thousands)...... 2.6 6.0 39 Exponential summation, fs (hundreds)............... 3.0 5.9 40 Physiological summation, fs (thousands)............. 2:1. 10.4 41 A bsoltte mri nie cess a aici ik Se —49 —5 43 _.¢ Normal daily mean, coldest 14 days of year (°F.)..... 0 ad 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8 45 Normal daily mean, ‘year (CE) ccciere ese. w100d oe & 35 60 Precipitation: 46 Normal daily meanw/s (neh)... 200 26) eh oy Se .091 13h 47 Normal No. rainy days (over 0.10 inch), fs........... 26 156 48 Normal No. dry days (0.10 inch or less), fs........... 28 154 49 Dry days, percentage of total, fs (per cent)........... 11 -83 50 Days in longest normal rainy period, fs.............. 17 140 51 Days in longest normal dry period, fs................ 9 91 52 Mean total, vear Gnehes):2 «2.02 ssn.) dese ERE oe 30 — 60+ Evaporation: 53 Daily mean, 1887-88. fs Gneh)\2.5c.. 0c 2 22 Meee se 1,225 1,700 +4 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 312 442 71 Normal P/E XT, fs, exponential method............. 2,997 4,269 72 Normal P/E XT, fs, physiological method............ DAT 6,423 TaBLE 90.—Climatic extremes for Abies balsamea. Plate | Temperature: 34 Days in normal frostless season (fs) 35 Hot days, fs 36 Cold days, fs 37 Remainder summation above 32°, year (thousands).... 38 Remainder summation above 39°, fs (thousands) 39 Exponential summation, fs (hundreds) 40 Physiological summation, fs (thousands) 41 Absolute minimum 43 Normal daily mean, coldest 14 days of year (°F.)..... 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 45 Normal*daily; mean, year: (CB:))«<...c.c0.0.0.«s os Ghee mee wk Precipitation: 46 Normal daily mean, fs (inch) 47 Normal No. rainy days (over 0.10 inch), fs 48 Normal No. dry days (0.10 inch or less), fs 49 Dry days, percentage of total, fs (per cent) 50 Days in longest normal rainy period, fs 51 Days in longest normal dry period, fs 52 Mean total, year (inches) CORRELATION OF DISTRIBUTIONAL FEATURES. 445 TABLE 90.—Climatic extremes for Abies balsamea—Continued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fs (inch)..............0020002: .084 .143 54 Total annual, 1887-88 (inches)...........2.ece0ecee% 24.3 34.4 Moisture ratios: 58 MaPef oor: 202 )') On MOREE US in CUR me ty Ul a aa 174. 1.31 59 Mornay 5 782). s.r Ne ee alate Bal Deed oe ES .81 1.52 60 Nor ew /- 5 SCAN 95.80.05 bile als ele pM MRE as eta ra ae 95 1.72 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 345 438 Humidity: 65 Normal mean, fs @per/ cent 2) Oy ee ee 67.3 81.8 66 Normal mean, year (per cent).............-----000: 71.9 80.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. ok 12.4 Sunshine: 69 Normal total duration, fs (hours) ..................- 225 1,500 +4 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 312 500 +2 71 Normal P/E XT, fs, exponential method............. 2,997 4,097 72 Normal P/E XT, fs, physiological method............ 2,747 7,0002 TaBLE 91.—Climatic extremes for Quercus alba. Plate | Temperature: : Low. High. 34 Days in normal frostless season (fs)................. 101 331 35 EVO AWS HS ei hie hi ceiee te MO ag Nes ag NM eh Ski lbw dl Vad 0 215 36 (SHO RIC RAYE 7 AIA A ne RR MIE te GSD eaIOUP SORA snot SUNOL FON Ue nD 0 137 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.6 10.6 39 Exponential summation, fs (hundreds)............... 3.0 Bl 7 40 Physiological summation, fs (thousands)............. Papal 21:2 41 PMOSOMUPE MAUD CIN 5 4))5 ols Sa) vices, & ch Gest io ae chee hveabewies ud ans —48 +19 43 Normal daily mean, coldest 14 days of year (°F.)..... 1l 53 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal daily mean, year (°F.).............000e ee eee 40 65+ Precipitation: 46 Normal dailyimean, fs Gneh) . . bie scay dabdowaderde oes .O91 .170 47 Normal No. rainy days (over 0.10 inch), fs........... 26 284 48 Normal No. dry days (0.10 inch or less), fs........... 0 136 49 Dry days, percentage of total, fs (per cent)........... 8 83 50 Days in longest normal rainy period, fs.............. 17 256 51 Days in longest normal dry period, fs................ 0 91 52 Meanstotal, year Gnehes) ois) is ei aes vod oe Selle ces 30— 60+ Evaporation: 53 Daily mean, 1887-88, fs Ginch).......0.. 000000000000. .O81 . 200 54 Total annual, 1887-88 (inches)...............00e008- 24.3 54.8 Moisture ratios: | 58 IO TeatE RATES f8 a o54.c a Re NR) Rane ae aR 51 1.76 59 Nearly) Bit. fis).b sso ack RRMA IAS, fs. ahi! 60 1.96 | 60 Nionrivel A RR/ AB NT GERT 5) sr ypiek eel Ca aie Wisi AOR a MN ate 74 1.94 | Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 345 622 Humidity: 65 Normal-meann, fs-(perident) (ies ees SL 64.5 83.9 | 66 Normal méban, ‘year (pen cent)» ass eens oe OR 69.0 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.1 14.9 Sunshine: 69 Normal total. duration, fs (howrs)\v v0 2) dove 1,225 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 301 | 1418 71 Normal P/E XT, fs, exponential method............. 2,914 13,511 72 Normal P/E XT, fs, physiological method............| 2,747 446 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 92.—Climatic extremes for Fagus atropunicea. | Plate | Temperature: Low. High. 34 Days in normal frostless season (/s).............-... 95 281 35 ist gaipet.. Pees co sors os Se eee 0 215 36 Caled ekagegs <0 We a ee oh oh 0 149 37 Remainder summation above 32°, year (thousands) .. 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.6 10.6 39 Exponential summation, fs (hundreds) sgh cen Ne ae 3.0 11 40 Physiological summation, fs (thousands)............. 2.1 ye | 41 Atmel snimmnn. 3: Ss .—.....:- » dea ee —44 +12 43 Normal daily mean, coldest 14 days of year (°F.)..... 12 52 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Nonmnali daily: mean, year (CF) . .).. 0-2 =. eek eee 40 — 65+ Precipitation: 46 Normal day mein: fs Gneh). . 2 ocelot oe | 091 ie 47 Normal No. rainy days (over 0.10 inch), fs........... | 26 256 48 Normal No. dry days (0.10 inch or less), fs........... | 0 154 49 Dry days, percentage of total, fs (per cent)........... 0 83 50 Days in it normal rainy periad; [s~-.< sau. - 17 256 51 Days in longest normal dry period, fs................ = 91 52 Mein total year Gnehes) _-... i404) padeieeodas ot 30- 60+ Evaporation: 53 Duly mean teers, js-Gneh). 22. 2. ee eee .084 . 200 54 Total annual, 1887-88 Gnehes).......-. 12-2. 25 eoe 24.3 54.8 Moisture ratios: 58 Piceeusteil ohn Pree OE oo ia cra Sto es PEE hee .62 1.76 59 Diarra Pea ieee et ee en ee ee ee .60 1.96 60 Normal (Py, youn S20 2022 2s can 1S Se Se .72 1.94 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 345 622 Humidity: 65 Normalitmean: jsi(neniecuyy i322... Ss. ere eee 65.5 84.0 66 Normal mean, year (per cent)............5.-..-.--- | 67.5 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.6 14.9 Sunshine: | 69 Normal total duration, fs flees) Seve Eo ae ig 225 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 301 1,418 71 Normal P/E XT, fs, exponential method............. 2,918 Hy 511 72 Normal P/E XT, fs, physiological method............ 2,747 265 TABLE 93.—Climatic extremes er ee es eM EE Castanea dentata. Plate | Temperature: = 34 Days in normal frostless season (fs)..............--- 35 IGG epee Hise ee 2. ok. Wo eee 31 160 | 36 SColekinl ype eee eee as ee eee ee | 0 117 37 Remainder summation above 32°, vear (thousands)... -| 11.5-— 18.0+ | 38 Remainder summation above 39°, fs (thousands)...... 3.6 7.6 39 Exponential summation, fs (hundreds)............... a7 7.4 40 Physiological summation, fs (thousands)............. 5.0 15.0 41 Absolute animmum 2. 0. sg. ss ss Ee ee ee ee —38 +4 43 Normal daily mean, coldest 14 days of year (°F.)..... 16 45 st Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8 45 WNermal daly mean year (CF) ou... . «<< ..dc ees 490 365 36 Caleltdayeis 6. fee ee. Se bee bial Ue as Seems 0 44 37 Remainder summation above 32°, year (thousands).... 11.5+ 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 5! 14.5 39 Exponential summation, fs (hundreds)............... ee 15.4 40 Physiological summation, fs (thousands)............. 7.9 =) ae | 41 Alsoluteamininmi ms 256203 o's di. + 6 oa eee —16 +41 43 Normal daily mean, coldest 14 days of year (°F.)..... 32 69 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6— 78.8+ 45 Normal: daly mean; year. (CF.).. .... . 0... 553i Das ee 55 — 75+ Precipitation: 46 Nornial‘daily mean, fs. Gneh) ....4c2 55. O6-2he Se Bee .106 .170 47 Normal No. rainy days (over 0.10 inch), fs........... 91 284 48 Normal No. dry days (0.10 inch or less), fs........... 0 92 49 Dry days, percentage of total, fs (per cent)........... 8 51 50 Days in longest normal rainy period, fg.............. 47 256 51 Days in longest normal dry period, fs................ 0 63 52 Mean totabcvear Gnches)..... {s260.00. see de a. 40— 60+ Evaporation: 53 DPiaty wean) Sara, 7s NCH)... 2 «se oc ook tee ace .084 Siva 54 Total annual, 1887-88 (inches)...................2.. 2a 2 51.7 Moisture ratios: 58 MIE ieee hee eke a oe eee wane 64 1.76 59 etry ee ions) 2 Dis) CSRs Sees Ie en A RE ar eee 75 1.96 60 Normally tavene 2 25902 Se yen Ek Coe ees .85 1.94 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 460 707 Humidity: 65 Normal-mean, JeiQper.cent). ce ets. S34 a Se 69.1 82.7 66 Normal mean, year (per cent) .):,: 2.2 32.24. eee 69.5 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.6 163 Sunshine: 69 Normal total duration, fs (hours) ................... 1,646 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 446 1,418 re Normal P/E XT, fs, exponential method........... ee ere! 13,511 72 Normal P/E XT, fs, physiological method............ 7,010 24,265 TaBLE 96.—Climatic extremes for Sapindus marginatus. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)...............-- 153 328 35 ERG bi eS Ags Si: ceo Ras Soe ee ae nd Co ee ee 113 226 36 GOASTAV SE IS Re ce Bi he te leis le ws Be, hoc anal Ge 5c 0 70 37 Remainder summation above 32°, year (thousands).... 11.5— 26.0+ 38 Remainder summation above 39°, fs (thousands)...... Suds 10.8 39 Exponential summation, fs (hundreds)............... 5.90 1st 40 Physiological summation, fs (thousands)............. 103 21.4 41 Abselite mimi <3) oes ei 68 5 2 bees ee eit —32 +19 43 Normal daily mean, coldest 14 days of year (°F.)..... 27 Le | 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6— 78.8+ 45 Normathdaty mean, year.) . <2 sc -. 20s. f 2S dhe 55 — 75+ Precipitation: 46 Normalidaly aican, fs’ Guch) «istic t oe oe Abts sctes .052 .172 47 Normal No. rainy days (over 0.10 inch), fs........... 254 284 48 Normal No. dry days (0.10 inch or less), fs........... 26 2594 49 Dry days, percentage of total, fs (per cent)....../.... 8 87 50 Days in longest normal rainy period, fs.............. 25 —4 235 51 Days in longest normal dry period, fs................ 18 1002 52 Mean total, year (inches)... ... bodies teetetalny gaits « 20 60+ CORRELATION OF DISTRIBUTIONAL FEATURES. 449 TABLE 96.—Climatic extremes for Sapindus marginatus—C ontinued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fs Gneh).ic settee ee eee. ee. .130 . 203 54 Total annual, 1387-88 Guches)..0..20)-i8s5)3is.002.. 42.1 804 Moisture ratios: 58 Nir al yn Fon karen ies MUI Ra! SOLON bs LEE be, 40 —4 1.36 59 Ira ili eR em ei Mh ee a Wis 1.52 60 Normal PVE, Veatnse as ones eee ter eee oe eee 24 1.47 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 350 —4 707 Humidity: 65 Normal mean, fs:(per Cent 2s. fee ee wee cc ee ae 59.4 80.6 66 Normal mean, year (per cent) ¢.. 0.12.02 6.2097 ..0". 59.3 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 6.3 14.2 Sunshine: 69 Normal total duration, fs (hours) ..................- 1,700 —4 2,650 Moisture-temperature indices: 70° Normal P/E XT, fs, remainder method.............. 256 1,314 71 Normal P/E XT, fs, exponential method ............. 7p Si 12,106 72 Normal P/E XT, fs, physiological method ............ 4,673 | 24,265 TaBLeE 97.—Climatic extremes for Populus balsamifera. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)............... 25 172 35 LEO CERT Os | aI aa, HERA a 1/7, 50 ce ea 0 88 36 COE 6 Hs. CTR Ea ap RUMORED Ss, oh kes a ae noc ga 92 137 37 Remainder summation above 32°, year (thousands) . 10.0— 11.5+ 38 Remainder summation above 39°, fs (thousands).... 2.6 4.5 39 Exponential summation, fs (hundreds)............. 3.0 4.90 40 Physiological summation, fs (thousands)........... Pap | aco 41 Absolute minimum..... Parr Ue me Meet) SV aa —59 —13 43 Normal daily mean, coldest 14 days of year (°F.) .. 0 24 44 Normal daily mean, hottest 6 weeks of year (°F.)..° 64.4 — 71.6+ 45 Normal daily, mean, year (CH). .0 3564 6 ele 35 50 Precipitation: 46 Normal dailyimean:,/s Gnch).. 92.00. esd Sa. .043 .126 47 Normal No. rainy days (over 0.10 inch), fs......... 0 135 48 Normal No. dry days (0.10 inch or less), fs......... 28 140 49 Dry days, percentage of total, fs (per cent)......... 1 W6 100 50 Days in longest normal rainy period, fs............ 0 100 51 Days in longest normal dry period, fs.............. 11 175¢ 52 Meantotal year (GnChes)’.. .)o. eed cece ae. va oe wen 20 — 50+ Evaporation: 53 Daily mean, 1887-88, fs (inch)..................5- 084 .220+4 54 Total annual, 1887-88 (inches...................- 22.1 50+4 Moisture ratios: 58 RS gyeTae 24 OA CRO LD GA MOR eA A ED a .20—2 1.23 59 Inicereenallre OPM i ORR rae bas tnt dk ge Aina SE .20+4 1.52 60 PN sUIE MALE PV BAT Wises wis a Ome Cee ee eter ee .20-4 1.72 Vapor pressure: 63 Normal mean, fs (hundredths inch)................ 3004 438 Humidity: 65 Normal mean, se: (mer eent) oP. ee a ee cw 50-4 81.8 66 Normal meéeany year (per cent) oo. cs. eee ee ee 60-4 80.2 Wind: 68 Normal mean hourly velocity, fs (miles)............ 4.7 12.4 Sunshine: 69 Normal total duration, fs (hours).................+] 1,225 1,512 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method. ........... 100 —¢ 442 re Normal P/E XT, fs, exponential method........... 1,000 —¢ 4,269 72 Normal P/E XT, fs, physiological method.......... 1,000 —9 6,423 ee ee N 450 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 98.—Climatic extremes for Quercus macrocarpa. | Flate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 85 261 35 Hatrdaysrissc: Jacceae oo ics le ee eee 0 173 36 CSO Y IIS oh yt ee ats eee each cd A Sg oe Lee oa 0 158 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ - 38 Remainder summation above 39°, fs (thousands)...... 2.6 8.04 39 Exponential summation, fs (hundreds)............... 3.0 9.04 40 Physiological summation, fs (thousands)............. 2.1 17.54 41 Absolute sain iit o..6:. oes ee oe disc ae Pee —59 seu: 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 44 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal idaily mean,syear (CP. s 2.655 26 316A a 35 65 Precipitation: 46 Normaltany mean; fs (anch)., . 102.) Se ae sae .072 .135 47 Normal No. rainy days (over 0.10 inch), fs........... mt 159 48 Normal No. dry days (0.10 inch or less), fs........... 28 154 49 Dry days, percentage of total, fs (per cent)........... 17 81 50 Days in longest normal rainy period, fs.............. 14 172 Bt Days in longest normal dry period, fs................ 9 88 52 Mean totals year iGnches) 32/22. 4a eee 20 — 60 Evaporation: 53 Darly mean; 1887-88; fs Gnch) os. ss Se ese: .084 .180 54 Total annual; 1S87—88 Gnches) =... 2... 2. eo 221 54.8 Moisture ratios: 58 NORMALE hare nee hese ek 3. Acie Lied haa? sea gaan. .42 1.39 59 INO Beall eae ee a cg cio ae eee ee .43 1.63 60 Nonmal"iy year ne sas sao alc a3 da eee RE 40 1.85 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 322 522 Humidity: 65 Normalavean:)fsaper Cent) o2065.) 0. cb ee ee ee 53.2 83.9 66 Normal mean, ‘year. (per cent)... 2.2 sees. se ees 59.8 82.1 Wind: 68 Normal mean hourly velocity, fs (miles)............. Sol 14.9 Sunshine: 69 Normal total! duration, fs (hours) 2:9. 2 222. Je). oe 1225 2,1002 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 135 668 71 Normal P/E XT, fs, exponential method............. 1,327 6,164 72 Normal P/E XT, fs, physiological method............ 1,902 10,782 TABLE 99.—Climatic extremes for Ilex opaca. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs) ...............-- 141 365 35 TOR Ay SSS os ence oae ae egy Si a hy ates tn a ene ae 47 365 36 Cr l GaN as ES Sir eet eleva a eciey tea, ore) eee ce in ae es een ake lead 0 55 37 Remainder summation above 32°, year (thousands).... 11.5—- 26.0 38 Remainder summation above 39°, fs (thousands)...... 4.4 14.5 39: Exponential summation, fs (hundreds)............... 4.7 15.4 40 Physiological summation, fs (shousemds) Mb Eo Pon ya, 6.7 ot Al Ase) abe ramen aria 25 2) A eee ee oe a —15 +41 43 Normal daily mean, coldest 14 days of year (°F.)..... 27 69 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6— 78.8+ 45 Normal tail mean: vear (CB) s35.0.o2)b. eres ve Sse 50-— 75+ Precipitation: 46 Normal daly mean) fs Grech): oe ne ce Soe .091 .173 47 Normal No. rainy days (over 0.10 inch), fs........... 55 284 48 Normal No. dry days (0.10 inch or less), fs........... 0 204 49 Dry days, percentage of total, fs (per cent)........... 8 74 50 Days in longest normal rainy period, fs.............. 1% 256 51 Days in longest normal dry period, fs................ 0 182 52 Mean total.cyear Gnches)< 2.4. haec ees ee es 50—- 60+ Plate 53 54 58 59 60 63 65 66 68 69 71 Plate 34 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 99.—Climatic extremes for Ilex opaca—Continued. Evaporation: Daily mean, 1887-88, fe (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal x/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal! mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TaBLE 100.—Climatic extremes for Magnolia grandiflora. Temperature: Low. Days in normal frostless season (fs)................- 221 — EPP CRCU A VST Beira peter ote autsien Al atlw aap al Seb A abu I mice gig? ov'aha rae onaiats 147 (OLS kG ie CRASS IIS UA a i NC Daa oo a 0 Remainder summation above 32°, year (thousands).... 18.0-+ Remainder summation above 39°, fs (thousands)...... FBS Exponential summation, fs (hundreds)............... ee fa Physiological summation, fs (thousands)............. 1326 Absolute minimum...........0...2200: Puan kate A —3 Normal daily mean, coldest 14 days of year (°F.)..... 45 Normal daily mean, hottest 6 weeks of year (°F.)..... 78.8— Normal daily mean, year (°F.)............0000.00000% 65 — Precipitation: Normal daily mean, fs (inch)..................0.00- .129 Normal No. rainy days (over 0.10 inch), fs........... 161 Normal No. dry days (0.10 inch or less), fs........... 26 Dry days, percentage of total, fs (per cent)........... 8 Days in longest normal rainy period, fs.............. 92 Days in longest normal dry period, fs................ 14 Mean total, year (inches)............... ccc cece cece 50— Evaporation: Daily mean, 1887-88, fs (inch)...................00- a 8 WY ¢ Total annual, 1887-88 (inches)..................000- 42% Moisture ratios: LOR aTCE CET (217) EY SS RRR ae Ra ay a" Ta STP UE 7 RR REN SA ORAL eg SRR Ae 1.05 PEEL ALM EAL iho wae dares orci emcateinle wmiare Cae same es P.02 Vapor pressure: Normal mean, fs (hundredths inch).................. 569 Humidity: INGrmalmmean, fa: (OOP Comb. sic ccc ace acy es caeuetes 73.9 Normal mean, year (per Cent). ........ ccc cece cees 73.5 Wind: Normal mean hourly velocity, fs (miles)............. 5.1 Sunshine: Normal total duration, fs (hours) ................00- 1,895 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 834 Normal P/E XT, fs, exponential method............. 7,663 Normal P/E XT, fs, physiological method............ 15,125 1,314 12,106 24,265 451 452 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 101.—Climatic extremes for Sabal palmetto. as Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)............... 228 365 35 FV OUGaAy Sey Sil eR eee hon sass aint eas iat Nea, Sea Rae 168 365 36 Coldidanysyfists {eR UR ei RoC ik Rte UR Bea a A 0 0 37 Remainder summation above 32°, year (thousands)..} 18.0-+ 26.0+ 38 Remainder summation above 39°, fs (thousands)... . 8.4 14.5 39 Exponential summation, fs (hundreds)............. 8.0-—4 15.4 40 Physiological summation, fs (thousands)........... 15.0—4 31.1 41 Absolute MANO UOY he eS i Ae ke ela olin Sos ee +1 +41 43 Normal daily mean, coldest 14 days of year (°F.)... 45 69 44 Normal daily mean, hottest 6 weeks of year (°F.)... 78.8+ 78.8+ 45 Normal daily. mean, year (CE:)\s.... 25. 62. 0h 4s. eee 65 — To+ Precipitation: 46 Normal daily mean, fs (inch)..................... .106 -173 47 Normal No. rainy days (over 0.10 inch), fs......... 206 234 48 Normal No. dry days (0.10 inch or less), fs......... 70 ; 204 49 Dry days, percentage of total, fs (per cent)......... 202 56 50 Days in longest normal rainy period, fs............ 112 235 51 Days in longest normal dry period, fs.............. 17 182 52 Mean total, year (inches).......... PEI ae a ONIN abi i rs 60 — 60+ Evaporation: 53 Daily mean, 1887-88, fs (inch).................... . 1204 .141 54 Total annual, 1887-88 (inches).................... 38.4 51.6 Moisture ratios: 58 Norra Ray MENS ied seas i actos cael cin 2 Liillea 8 ae UR Rael 75 1.20+9 59 IN @rraltr er We Sieele Ss cleln ache! sas 5 AA oa ig metal 75 1.404 60 Normal Py earete: so8 i clita. aos ape ates aan epee ete e 75 1.36 Vapor pressure: 63 Normal mean, fs (hundredths inch)................ 586 707 Humidity: 65 Normal} mean, fs (per cent). . ... 3. .daskiesed 3 oe sctenee 74 80.5 66 Normal mean, year (per cent).................... Piie sl 80.5 Wind: 68 Normal mean hourly velocity, fs (miles)........... 6.7 9.9 Sunshine: 69 Normal total duration, fs (hours)................. 2,026 2,297 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method............ 1,014 1,271 71 Normal P/E XT, fs, exponential method........... 9,385 11,722 G2, Normal P/E XT, fs, physiological method.......... 18,294 23,265 Temperature: Days in normal frostless season (fs) Hot days, fs Cold days, fs Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands) Exponential summation, fs (hundreds) Physiological summation, fs (thousands) Absolute minimum Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily mean, year (°F.)........0. 0000 ccc cence Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) Plate 53 54 58 59 60 63 65 66 68 69 70 71 72 Plate 34 35 36 37 38 39 40 41 43 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TasBLeE 102.—Climatic extremes for Serenoa serullata—Continued. Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal 7/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: ; Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TasBLE 103.—Climatic extremes for Washingtonia filamentosa. Temperature: Low Days in normal frostless season (fs)..............: 240 —4 L1G GEE 7) Sa AID Sn Ree ae A ae aa ae 120— MESERIMCLA YS SISter ctr ay odie 6! tte cea e/g gis ale gel aol yun wdeliey a ala! 0 Remainder summation above 32°, year (thousands).. 18.0 Remainder summation above 39°, fs (thousands)... . 8.0-—4 Exponential summation, fs (hundreds)............. 8.0—4 Physiological summation, fs (thousands)........... 12.544 J SSIS) S29 6015 0010010 000 nn ne —4+4 Normal daily mean, coldest 14 days of year (°F.)... 50+4 Normal daily mean, hottest 6 weeks of year (°F.)... 71.6— Normal daily mean, year (°F.).............2000005 70— Precipitation: Normal daily mean, fs (inch)....................- .020 —4 Normal No. rainy days (over 0.10 inch), fs......... 0 Normal No. dry days (0.10 inch or less), fs......... 250 +4 Dry days, percentage of total, fs (per cent)......... 90+2 Days in longest normal rainy period, fs............ 0 Days in longest normal dry period, fs.............. 250 +4 IiMean total; year (mehes) 6.00 0k eel. ek 10-— Evaporation: Daily mean, 1887-88, fs (inch).................0.- .180—4 Total annual, 1887-88 (inches)..................5- 80—4 Moisture ratios: POOR MUMEE MPA SATO Ns sees cucu csn' on key cada gtaeaapeliin alzysie .20—4 ISOLA TIEY SOR 3 (a NERA eS IE ache ae Se .20-4 INI IC CH 7 OR Gye a ag Shea ae .10-4 Vapor pressure: Normal mean, fs (hundredths inch)................ 300 +4 Humidity: Normal mean; fs (per comt):..... 0. cece cu ce ween eee 404 Normal mean, year (per cent). ............eeeeees 40+4 Wind: Normal mean hourly velocity, fs (miles)........... 6¢ Sunshine: Normal total duration, fs (hours) ...............5: 2,500¢ Moisture-temperature indices: Normal P/E XT, fs, remainder method............ 100% Normal P/E XT, fs, exponential method .......... 1,000¢ Normal P/E XT, fs, physiological method..........| 1,000 453 11 2,650 1,314 12,106 26,652 2,700% 100 +4 1,000 +4 1,000 +4 —— 454 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 104.—Climatic extremes for Cephalanthus occidentalis. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)..............- 111 365 35 NI OUIGAV As Secs ole ten eis hole cia ars Nata wine eee eee 0 365 36 LO) ci rd Cn ASP A pense 0 re Oe Rar RE IS 0 137 37 Remainder summation above 32°, year (thousands).. 10.0— 26.0+ 38 Remainder summation above 39°, fs (thousands).... 2.6 14.5 39 Exponential summation, fs (hundreds)............. 3.0 15.4 40 Physiological summation, fs (thousands)........... 24 31.1 41 VASOIICE MATA AUT Ee ie ieee saa ea bie sel oo Siemens eee ere —43 +41 43 Normal daily mean, coldest 14 days of year (°F.)@.. 11 69 44 Normal daily mean, hottest 6 weeks of year (°F.)... 64.4-—- 78.8+ 45 Normaltdatly mean, year (CE.).... 0.6225 See eee eae 40-— 75+ Precipitation: 46 Normaldaily mean, js Gneh)i oo 6c. eee eet ee ek .017 Be if - 47 Normal No. rainy days (over 0.10 inch), fs......... 0 284 48 Normal No. dry days (0.10 inch or less), fs......... 0 283 49 Dry days, percentage of total, fs (per cent)......... 0 100 50 Days in longest normal rainy period, fs............ 0 256 51 Days in longest normal dry period, fs.............. 4 283 52 Mean total! year GMCHES) ...5 s).es.k << alvsds ee oe 5 eee 10— 60+ Evaporation: 53 Daily mean, 1887-88, fs (inch).................... O81 .240+4 54 Total annual, 1887-88 (inches).................00- 24.3 101.2 Moisture ratios: 58 IN ration Sea / Pipers ects ek cote idtal's Lies oem ee eee tee ~ eS 1.76 59 INornial a Mpenieincd ba neo. 43 oa a ae tae .10 1.96 60 BW ONT i Ee pV EAE Meer iat Ur. aia'ci ccc < «Slate AO oes eS .03 1.94 Vapor pressure: 63 Normal mean, fs (hundredths inch)................ 279 707 Humidity: 65 Normal mean .)fs Qper Cent) <3. 3. 2. . Sctopewic 4 Gee ovate 48.9 82.7 66 Normal mean, year (per cent). ............-eceees SY 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)........... 3.1 13.5 Sunshine: 69 Normal total duration, fs (hours)................. 1,225 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method............ 68 1,418 7iil Normal P/E XT, fs, exponential method........... 625 13,511 72 Normal P/E XT, fs, physiological method.......... 1,186 24,265 TaBLE 105.—Climatic extremes for Adelia acuminata. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs) ............--- 180 335 35 IORIGRWS GS sece cme ok Sine ae oS apnseteunre Sree 129 226 36 Cold Gays cise seers ele ee Aaa lk vce Manca See 0 22 37 Remainder summation above 32°, year (thousands)... 18.0— 26.0+ 38 Remainder summation above 39°, fs (thousands).... 6.3 10.8 39 Exponential summation, fs (hundreds)............. 6.7 11% 40 Physiological summation, fs (thousands)........... 11.9 21.2 41 Absolute aitntmuan (p> eee eho ee vale ois 2 shee oe —29 +20 43 Normal daily mean, coldest 14 days of year (°F.)... 32 57 44 Normal daily mean, hottest 6 weeks of year (°F.)... 78.8— 78.8+ 45 Normal daily mean, year"(CR:)\ 3.04 02.0 ie cnx e oe 55 70+ Precipitation: 46 Normal dady mean, fs Gnch):.. 2.022.250 2 too ce: .109 .172 AT Normal No. rainy days (over 0.10 inch), fs......... 120 284 48 Normal No. dry days (0.10 inch or less), fs......... 26 2004 49 Dry days, percentage of total, fs (per cent)......... 8 54 50 Days in longest normal rainy period, fs............ 72 157 51 Days in longest normal dry period, fs.............. 14 78 52 Menn total yeur GMeHEs) ..)02. ee ae nee ee eee 50— 60+ Plate 53 54 58 59 60 63 65 66 68 69 70 71 72 70 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 105.—Climatic extremes for Adelia acuminata—Continued. 455 Evaporation: Low. High. Daily mean, 1887-88, fs Ginch)...............e085. .120—4 .188 Total annual, 1887-88 (inches)...............0.05+ 42.1 56.6 Moisture ratios: INGORE 18 oe ois ip eens Sn oaks ee RE 64 1.36 Tao) 03 2 Wr GAT SANG @ eM SEL 1 0 a a2 a 215 1.52 MOTTA Ey Ble VERT we eileleve srs ne laneras aeenelenara taper a stabi dees 85 1.47 Vapor pressure: Normal mean, fs (hundredths inch)................ 513 622 Humidity: Normal mean, fs (per cent)...........0ce ee eee ees 69.1 80.6 Normal mean, year (per cent)..............2e008- 70.7 85.2 Wind: Normal mean hourly velocity, fs (miles)........... 5.0 11.0 Sunshine: Normal total duration, fs (hours) ................ 1,878 2,650 Moisture-temperature indices: Normal P/E XT, fs, remainder method............ 400 —4 1,314 Normal P/E XT, fs, exponential method........... 4,174 12,106 Normal P/E XT, fs, physiological method.......... 7,807 23,652 Temperature: Days in normal frostless season (fs). .........2.0000: 1i1 348 NIE AVR Slo cereiny clots aual yy iustare emananaliey Sie ae bien a alee g 0 240 +2 MBLC AN SMUT Su sieve Weigh auuies Scae as: ehiei/Sy o tayrtnabaa ener auuet ah rash age 0 149 Remainder summation above 32°, year (thousands).... 10.0— 26.0+ Remainder summation above 39°, fs (thousands)...... 2.6 10.8 Exponential summation, fs (hundreds)............... 3.0 if es | Physiological summation, fs (thousands)............. Aa I 21.4 PANO SOLO CE RMUTATTINUITTD 500816106) ci sluna career pbaval aie o sisdereien aeons: eve —43 +22 Normal daily mean, coldest 14 days of year (°F.)..... 12 GY Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ Normal daily mean, year (°F.)...............000c00- 35 70+ Precipitation: Normal daily mean, fs (inch)................000000- ' .089 172 Normal No. rainy days (over 0.10 inch), fs........... 55 284 Normal No. dry days (0.10 inch or less), fg........... 0 170 Dry days, percentage of total, fs (per cent).........2. 0 83 Days in longest normal rainy period, fs.............. Me 256 Days in longest normal dry period, fs................ 4 78 Mean total, year (inches). ..........c.ccccscccccces 30 — 60+ Evaporation: Daily mean, 1887-88, fs (inch).............c.ee0ee0- .081 . 200 Total annual, 1887-88 (inches).................e0000- 24.3 56.6 Moisture ratios: BNE Es PHe irs kis seven e ene wR) cass aha G. ae rtrwreeale k tie aret Clde 51 1.76 IN(av Lane Ye 1d ah CE ee ice OT .60 1.96 eam Ae) SORTS chal UG as elie W wraceom bbe rid ics cae Goetale§ ek 1.94 Vapor pressure: Normal mean, fs (hundredths inch).................. 345 612 Humidity: Normalemeany ye (Der CeNb)..' hei wccau wtkiwwcaa cee cs 64.5 82.7 Normal mean, year (per cent).............ecce ee eee 67.5 2.9 Wind: Normal mean hourly velocity, fs (miles)............. 3.1 13.5 Sunshine: Normal total duration, fs (hours) ..............0000- 1,225 2,301 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 301 1,418 Normal P/E XT, fs, exponential method............. 2,914 13,511 Normal P/E XT, fs, physiological method............ 2,747 24,265 456 Plate 34 35 36 37 38 39 40 41 43 4 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 fi 72 Plate CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 107.—Climatic extremes for Itea virginica. Temperature: Days in normal frostless season (fs) Hot days, fs Cold days, fs Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands) Exponential summation, fs (hundreds) Physiological summation, fs (thousands) Absolute minimum Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal datlyimean, year (CB) 0... foe... eee ee Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal z/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TaBLE 108.—Climatic extremes for Artemisia tridentata. Temperature: Days in normal frostless season (fs) ................. et Gays (Sie eA oe eo ard 2 kere es oan OO ee 0 COVINA AWS cISh a ac bree ste ae Ee ee eS ete ee co 0 Remainder summation above 32°, year (thousands).... 10 Remainder summation above 39°, fs (thousands)...... 2 Exponential summation, fs (hundreds)............... = Physiological summation, fs (thousands)............. 2 ADSohute mami 2 oo 5 a. o 3 cats die 3 Co eee Normal daily mean, coldest 14 days of year (°F.)..... ie Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — Normal datlysmean, year CR)is. 2. os...) soca eS eee 40 — Precipitation: Normal daily mean; fs Gneh) o.oo ee oS eee ee .009 Normal No. rainy days (over 0.10 inch), fs........... 0 Normal No. dry days (0.10 inch or less), fs........... 104 Dry days, percentage of total, fs (per cent)........... 88 Days in longest normal rainy period, fs.............. 0 Days in longest normal dry period, fs................ Niean total, year. Gnches)s/. 2. . ek ae. Poe eee eee 24,265 High. 334 118 134 18.0+ 7.3 7.6 _ 8.4 +32 54 78.8-+ 70+ .078 40 294 100 25 299 30+ CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 108.—Climatic extremes for Artemisia tridentata—Continued. Evaporation: Low. Daily mean 887-88, fs (mebys .:.s< 26 bby evsla sletern donde. .104 Total annual, 1887-88 (inches)...............eec0-- 35.8 Moisture ratios: DNormaglvly MS i..y ace aommedt heb ahr jorial, sae o .04 Delia a tel i 2 0) SH ee OR, Pe ee gp 06 Intense 247 OHI 3 ame REDS BUS Oe UE a .03 Vapor pressure: Normal mean, fs (hundredths inch).................. 183 Humidity: Normalmean, fs (per cent): bcwines. ts visio oho phe eherybenis « 5 22.6 Normal mean, year (per cent) s/o ccs set o's beee se 29.7 Wind: Normal mean hourly velocity, fs (miles)............. 4.3 Sunshine: Normal total duration, fs (hours) ................... a Ip Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 13 Normal P/E XT, fs, exponential method............. 127 Normal P/E XT, fs, physiological method............ 197 457 Plate 34 35 36 an 38 39 40 41 43 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 rail 72 TasBLE 109.—Climatic extremes for Covillea tridentata. Temperature: Low Days in normal frostless season (fs)................. 172 POR ED CLASS AS ONT nie co Risa Stoia Tate aos WIE ea AA ea aoe latent ie sarsete 118 “CRE 6 GIES GSVTIS: © MOORS ORIG Ea caRNIQLeO a a arate bi A) 0 Remainder summation above 32°, year (thousands).... 18.0— Remainder summation above 39°, fs (thousands)...... 6.0 Exponential summation, fs (hundreds)............... 6.8 Physiological summation, fs (thousands)............. 12.4 PRO SOLIEC SMM TIAUIIEN: 222: a leceloudssi a a alarete auch ousyscuebsha: sieeais 916 —29 Normal daily mean, coldest 14 days of year (°F.)..... 30— Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6— Normal daily mean, year (CF.)............0000ccnces 50 Precipitation: Ivormalidailywmean, fs (MEN). . .06 4.48 60 NU corer A Fea Es VLE 2) cass Jad) sein ella oye clea la Mhihiao!'oaacertoy Avbiog .09 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 279 567 Humidity: 65 Normal mean, fs (per cent).............2000000e00ee 22.6 87.5 66 Normal mean, year (per cent).............00eeee00: 29.7 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.5 16.4 Sunshine: 69 Normal total duration, fs (hours) ................... 1,225 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 13 1,566 71 Normal P/E XT, fs, exponential method............. 127 11,724 72 Normal P/E XT, fs, physiological method............ 197 7,869 Temperature: Days in normal frostless season (fs) Hot days, fs Cold days, fs Remainder summation above 32°, year (thousands)... . Remainder summation above 39°, fs (thousands) Exponential summation, fs (hundreds) Physiological summation, fs (thousands) Absolute minimum . .» Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily mean, :year (CF .)....0.0.5...300.ennes. | Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal r/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles). ............ Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method 71 Normal P/E XT, fs, exponential method 72 Normal P/E XT, fs, physiological method eee 464 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 119.—Climatic extremes for Hilaria jamesit. Plate 34 35 36 37 38 39 40 41 43 — 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 71 72 Plate 34 35 36 37 38 39 40 41 43 44 45 46 47 48 49 50 51 52 Temperature: Low Days in normal frostless season (fs).............005. 72 FLOW GAVE UIST Sa en Nd AAs ree 2 cd Be Cy RE 38 ROGIER Sek Sees eS a COD i) Mae doy Sule 0 Remainder summation above 32°, year (thousands).... 10.0— Remainder summation above 39°, fs (thousands)...... 2.4 Exponential summation, fs (hundreds)............... DA Physiological summation, fs (thousands)............. 256 Absolute minimum...... SSE OR ee RA at a weeds otal ig cue —38 Normal daily mean, coldest 14 days of year (°(F.)..... 27 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 Normaldaily meant year (CP.) 2525. 666000 eee 45 Precipitation: Normal(daily mean? fs Gneh) 2.72. 8 a PS .015 Normal No. rainy days (over 0.10 inch), fs........... 0 Normal No. dry days (0.10 inch or less), fs........... 130 Dry days, percentage of total, fs (per cent)........... 71 Days in longest normal rainy period, fs...2.......... 0 Days in longest normal dry period, fs................ 51 Mian totalyear (menes) eo icice ss eee eek ee ee 10— Evaporation: Daily mean. 1e87—-S8. fs Gnch))... = 2)... sca ee ee eee .201 Total-annual; 1887—ss Unches)..... 22) ee 50.4 Moisture ratios: {SCRE UE [Gann oc ot .10 SSN SY ees hosp 1 DHEST Ba ea NOR ae wn se OER TI 12 INormalsisy ie NCAT ask eG 4s.) ce fas Pete ee eee at? Vapor pressure: Normal mean, fs (hundredths inch).................. 300 Humidity: Normalimean; js (per cent)’. ..... 6 Aces neces eee a 37.0 Normal mean, year (per"cent) ..6.. 0.0. es eb ee sk 38.8 Wind: Normal mean hourly velocity, fs (miles)............. 5.6 Sunshine: Normal total duration, fs (hours)..................- 1,134 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 81 Normal P/E XT, fs, exponential method.,........... 772 Normal P/E XT, fs, physiological method............ 979 TaBLE 120.—Climatic extremes for Andropogon virginicus. Temperature: Low. Days in normal frostless season (fs) ..............45- 108 Heotidays isi. ctr oe win a eas AER eee ee a 0 SC ONEARH AVS S/S Gare ee ne es can AY Ser CANE webb 22 0 Remainder summation above 32°, year (thousands).... 10.0— Remainder summation above 39°, fs (thousands)...... 236 Exponential summation, fs (hundreds)............... 3.0 Physiological summation, fs (thousands)............. Fae | A Vsolute Gratin 7.6.0.) eee eR re eee ee —41 Normal daily mean, coldest 14 days of year (°F.)..... 15 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— Normaltdaily mean; year) CP.) ees os ee ere 35 Precipitation: Normalkdaily means Gnehenn secre sere oes eee .089 Normal No. rainy days (over 0.10 inch), fs........... 58 Normal No. dry days (0.10 inch or less), fs........... 26 Dry days, percentage of total, fs (per cent)........... 8 Days in longest normal rainy period, fs.............. 21 Days in longest normal dry period, fs...............- 4 Mean ‘total’ year’ Gnehes): 5 2 es ed eas 30 — High. 296 156 92 18.0+ 7.6 8.3 15.0 +22 454 78.84 65 .088 57 275% 100 26 2504 20 + .330 101.2 i LS CORRELATION OF DISTRIBUTIONAL FEATURES. 465 TaBLeE 120.—Climatic extremes for Andropogon virginicus—Continued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fs (inch)..........2..0ccceeee. .097 . 200 54 Total annual, 1S8/-88 (mches) 2.00 ke eee 20.3 56.6 Moisture ratios: 58 I oraoc te yl TEM eae Snes ens SBD Ket in ARN, 9 nee Sgn 5 1.76 59 LOGY cho Me oA! Os {AL Ee RNS LI SR a Te 60 1.96 60 POS ERTU AD EN /eBic: MCAT © 4 054.0.) sSied sate vo anata, eee ae ara 1.47 Vapor pressure: : 63 Normal mean, fs (hundredths inch)................-. 345 707 Humidity: 65 Normal mean, fs (per cent)............ ps ih NAME AWE falda 65.6 B27 66 Normal mean, year (per cent).............22002008: 67.5 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.2 ino Sunshine: 69 Normal total duration, fs (hours) ................... 1,225 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 301 1,418 71 Normal P/E XT, fs, exponential method............. 2,918 13,511 72 Normal P/E XT, fs, physiological method............ 2747. 24,265 TaBLE 121.—Climatic extremes for Bouteloua hirsuta. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 94. 323 35 18 Loy 6 COE RASS ae Aaa Ma TST Sa ARR a Sn a EN 0 218 36 (COOSA FEA SH) GUNS ee aE oe Deg 0 158 an Remainder summation above 32°, year (thousands).... 10.0—4 26.0+4 38 Remainder summation above 39°, fs (thousands)...... 3.0—4 10.044 39 Exponential summation, fs (hundreds)............... 3.0 res 40 Physiological summation, fs (thousands)............. See 21.4 41 PMP SOLUS TAUTETAUI, so, ca es peck eee w Sev ahandtes savas aoe —59 +12 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 53 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 —4 78.8+4 45 Normal daily mean, year (CF.)........0.0.0...6.050:- 35% 70+4 Precipitation: 46 Mormal dailysmean, fs. (neh). 3) is sleijme dhe ale secse sktve acs .033 .143 47 Normal No. rainy days (over 0.10 inch), fs........... 2, 161 48 Normal No. dry days (0.10 inch or less), fs........... 28 2754 49 Dry days, percentage of total, fs (per cent)....... Lee 99 50 Days in longest normal rainy period, fs.............. 2 172 51 Days in longest normal dry period, fs................ 11 88 52 MEA tOtaly Year GNCheS) chen. ce sok ekicaw cae cla ee 10—4 40+ Evaporation: 53 Daily mean, 1887-88; fs (ineh) . ose se 4 hee Dee .101 .330 54 Totalannual, 1887188 Gnches)...........6.0e0ceec00- Ae | 101.2 Moisture ratios: 58 ISI STea ALI) oro ae Ea TP Re 13 a he: a 59 INVGP SAN REN NE oil ONG RVORD NOMEN NED STL FMT suUReS Rina COMER oe Mana Ee 1.16 | 60 INO ee MP VORT ce si, og: Sigvare olin SMR Wh oaebery 2 ORs <4 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 300 675 Humidity: 65 Norms) mean fs (per Cent)! cbse LaLa Oe iced ot 37.0 71.9 66 Normal mean, year (per cent)... ccc eccs ceeckaes ss 38.8 75.0 Wind: 68 Normal mean hourly velocity, fs (miles). ............ 5.8 14.2 Sunshine: 69 Normal total duration, fs (hours) wi. 0s. coda ei Oi. 1,127 | 2,343 Moisture-temperature indices: | 70 Normal P/E XT, fs, remainder method.............. 906 6,690 71 Normal P/E XT, fs, exponential method............. 98 | 1,100¢ | 20,0008 | | 72 Normal P/E XT, fs, physiological method............| 1,000—¢ 466 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 122.—Climatic extremes for Sparganium americanum. Plate 34 35 36 37 38 39 40 41 43 44 45 46 47 48 49 50 51 52 Temperature: Low High. Days in normal frostless season (fs)..............05- 85 310 HIGWEayS ao.) Son nee cee oss Ade ae eee 0 191 Celdidayanys ota. Cee mess de Cee GC Re 0 149 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ Remainder summation above 39°, fs (thousands)...... 2.6 9.4 Exponential summation, fs (hundreds)............... 3.0 10:3 Physiological summation, fs (thousands)............. pe Pe | 18.9 Absolute anna: so... oe ow os 4 acces CO —48 +20 Normal daily mean, coldest 14 days of year (°F.)..... 0 54 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ Normal datly mean, year (Cl)... 2... 32.2062 5 sande 35 70 Precipitation: Normal daily mean: f3(Gneh) ...)..036054 43% 2h eee ee .037 .199 Normal No. rainy days (over 0.10 inch), fs........... 0 248 Normal No. dry days (0.10 inch or less), fs........... 0 216 Dry days, percentage of total, fs (per cent)........... EE 100 Days in longest normal rainy period, fs.............. 0 256 Days in longest normal dry period, fs................ 0 216 Mean total. (year Gnehes)... 2: Joho... a See 10— 60+ Evaporation: Daily mean, 1887-88; fs.Gmeh).< .......<-. oe esese eee .052 iS Total annual, 1887-88 (inches).............2.20.0005 18.4 57.7 Moisture ratios: SSIS EE LS Uy RISE RN A SORBET APP 18 3.84 Norm aliases eee eile at 2 a ee hee ee eae 22 4.48 ING@EMIa Ws see ear ci hy) ots sn Ce ae Rea OU eRe Sok 4.90 _ Vapor pressure: Normal mean, fs (hundredths inch).................. 297 610 -. Humidity: INormalumean; fs iG@per cent) seco sie. Beaees eee eee 54.6 S20 INormal mean,. year. (@per cent)... vee eek oo cee: 64.8 82.9 Wind: Normal mean hourly velocity, fs (miles)............. 3151 13.5 Sunshine: _. Normal total duration, fs (houts). ...2- 22.2. ..5...- 1,225 2,297 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 101 1,418 Normal P/E XT, fs, exponential method............. 950 13,511 Normal P/E XT, fs, physiological method............ 1,475 24,265 TaBLE 123.—Climatic extremes for Dianthera americana. Temperature: Low. High Days in normal frostless season (fs) ...............-. 108 365 FIO PAV Ss VISE ce oreo crs cae a eg 0 218 CBO 19 Wr Fos FSB Cerna ae OE Se eA PA ORR) est ot oe) Senet ul kee 0 137 Remainder summation above 32°, year (thousands).... 10.0— 26.0 Remainder summation above 39°, fs (thousands)...... 2.6 10.6 Exponential summation, fs (hundreds)............... 320 17 Physiological summation, fs (thousands)............. 20 21.4 Absolute minimum, 2 03. \. hoe es hs 4 ee ee ee —43 +19 Normal daily mean, coldest 14 days of year (°F.)..... 15 69 Normal daily mean, hottest 6 weeks of year (°F.)..... © 64.4— 78.8+ Normal‘datky mean! year:(CE.) oo. scence ie 40 70+ Precipitation: Normal daily mean, fs Cinch) ..... 622225 is abeeee eke .052 ZAG Normal No. ramy days (over 0.10 inch), fs........... 26 284 Normal No. dry days (0.10 inch or less), fs........... 26 259 Dry days, percentage of total, fs (per cent)........... 8 87 Days in longest normal rainy period, fs.............. 25— 157+ Days in longest normal dry period, fs................ 4 91 Mean ‘totalyear Gnehes) . 65... Ghent tenn pee oe 30 — 60+ Plate 53 54 58 59 60 63 65 66 68 69 70 71 70 71 72 CORREL ATION OF DISTRIBUTIONAL FEATURES. 467 TaBLeE 123.—Climatic extremes for Dianthera americana—Continued. Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal r/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT’, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method Temperature: Low. High. Days in normal frostless season (fs)..........+22205- 25 334 TG LASS HIS e ret oie: the. Nlarterce) a cows iret alco ebee Mecha ssatie ei cacas 0 215 Gol May Sy isis elclh vee mua ue rafaltel&. 3:5) eanenete we eaaiel criele ota 0 158 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ Remainder summation above 39°, fs (thousands)...... 2.6 10.6 Exponential summation, fs (hundreds)............... 2.8 i Oy Physiological summation, fs (thousands)............. 2 212 PAMEISOUUL EG EIA TRETINURTEN oi 8) bos 5) 5 ok Coaicg Seo « allciie revs ones lees: ad he —65 +19 Normal daily mean, coldest 14 days of year (°F.)..... 0 54 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ Normal daily mean, year (°F.)...............000e08- 35 70 Precipitation: Normal daily mean, fs (inch)....................00- .022 .199 Normal No. rainy days (over 0.10 inch), fs........... 0 199 Normal No. dry days (0.10 inch or less), fs........... 19 294 Dry days, percentage of total, fs (per cent)........... 8 100 Days in longest normal rainy period, fs.............. 0 256 Days in longest normal dry period, fs................ 4 299 Mean total, year GQnehes) ij. sacle. oc ak ae ces ote ce ae os 10— 60+ Evaporation: Daily mean, 1887-88, fs (inch).....................- .052 . 268 Total annual, 1887-88 (inches).............2...00055 £S 3b 79.8 Moisture ratios: INT a Me AS x oe ak Mes Sete ia te URE a, Crea CNC Ae, ROM Ee .08 3.84 INCOM ale ate/ Eig fOr ooh ah. casa erahee eb Shee atecalwle cna tMe hee .10 1.96 INC ons WY yh ORY a ee eA, TR et ae 15 4.90 Vapor pressure: Normal mean, fs (hundredths inch).................. 233 622 Humidity: Noermal-mesn, fs’ (per cent... i ee Ue oe ewe 41.5 87.5 Normal mean, year (per cent). ...........0e.eeeeeee 48.1 86.8 Wind: Normal mean hourly velocity, fs (miles)............. 3.1 16.4 Sunshine: Normal total duration, fs (hours) ...........-...000. 1,127 2,650 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 42 1,566 Normal P/E XT, fs, exponential method............. 405 13,511 Normal P/E XT’, fs, physiological method............ 598 24,265 468 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 125.—Climatic extremes for Arundinaria tecta. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................- 178 365 35 VOU ASSIS: cee aliea ce Le ees ONL Gia rail Vesna) Se Oa | 116 365 36 Coldidar sis ccs ee niMn aa OU a Te ee anyk Un ert eamty 0 22 37 Remainder summation above 32°, year (thousands)... . 11.5— 26.0+ 38 Remainder summation above 39°, fs (thousands)...... yar4 14.5 39 Exponential summation, fs (hundreds)............... 6.0 15.4 40 Physiological summation, fs (thousands)............. 10.0 31.1 41 ADSO MIG TMU ees else ciinye a. Gey eae Aeron es eee Aap —15 +41 43 Normal daily mean, coldest 14 days of year (°F.)..... 32 69 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6 78.8+ 45 Normal daily mean, year (CB.) 100 0 ee ae 55 75+ Precipitation: 46 Normal daily mean, fs (inch)..................0000- .109 .173 47 Normal No. rainy days (over 0.10 inch), fs........... 120 284 48 Normal No. dry days (0.10 inch or less), fs........... 0 90 49 Dry days, percentage of total, fs (per cent)........... 8 56 50 Days in longest normal rainy period, fs.............. G2 256 51 Days in longest normal dry period, fs................ 0 50 52 Mean) total vear (inches)... 6 Weics ei. bcs ko ee 50 — 60+ Evaporation: 53 Daily mean, 1887-88, fs (inch)...................... .130 177 54 Total annual, 1887-88 (inches)....................4. S1es 56.6 Moisture ratios: 58 Normale iis mice. mnmieeeye! 58. CLIN SOUR Stas ap 64 1.76 59 INiornivaliae ey cfs ee NU CIT ove Sa aU aa i 75 1.96 60 Normal Pk year. coq meicg ea tl. kamen a aia .85 1.94 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 488 707 Humidity: 65 Normal mean, fs (per cent)............0..000..00000- oh 82.7 66 Normal mean, year (per cent)...................0.. 70.7 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. or 13.5 Sunshine: 69 Normal total duration, fs (hours)................... 1,646 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 446 1,418 71 Normal P/E XT, fs, exponential method............. 4,174 ~ 113,511 72 Normal P/E XT, fs, physiological method............ 1,807 24,265 TaBLE 126.—Climatic extremes for Dulichium arundinaceum. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs) ................. 85 310 35 1G Io ACG RSIS AS aOR Re OUR EAL MONS Mee Na ie Ey ee aE 0 189 36 Gold dawyspofsh. 6 ee OUI Ve A Sh eal ay tai en leg Soe Ue LY 0 149 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... a 2G 9.4 39 Exponential summation, fs (hundreds)............... 3.0 10.3 40 Physiological summation, fs (thousands)............. Dial 18.9 41 Absolute: mmaimina Wr). ie Wee een nee ate ap ame eaters —59 +20 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 52 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — 78.8+ 45 Normal.daily meam;’ year CES) ooo. 0.3 ee ee 35 70— Precipitation: 46 Normal daily mean: js Gneh)) 3) Cs 0. a ek sae ee 074 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 26 248 48 Normal No. dry days (0.10 inch or less), fs........... 0 200 49 Dry days, percentage of total, fs (per cent)........... 11 83 50 Days in longest normal rainy period, fs.... - CRA ale Re agih ate 21 256 51 Days in longest normal dry period, fs................ 0 187 52 Mean! totaljvear ((inehes) i), aon pie ee eee be 20 90 Plate 53 54 58 59 60 63 65 66 68 69 70 71 69 70 rh 72 CORRELATION OF DISTRIBUTIONAL FEATURES. 469 TABLE 126.—Climatic extremes for Dulichium arundinaceum—Continued. Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal w/E, fs Normal P/E, year Vapor pressure: Normal mean, /s (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TaBLE 127.—Climatic extremes for Spartina michauxiana. Temperature: Low. High. Days in normal frostless season (fs)................. 53 231 EEGCREROLARVN TRG Leck aie tata te oie eeate la ereva Spmati cla ree lalectmere ee 0 153 CAEL IG Ni0 (17a SR al AAR nes PP SR gee 0 158 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ Remainder summation above 39°, fs (thousands)...... 2.6 7.5 Exponential summation, fs (hundreds)............... 2.8 8.1 Physiological summation, fs (thousands)............. Zk 14.6 Absolute NaMIMUOM! 6k) 6 oes wialalbs «las ale wiaharencle aie —65 +4 Normal daily mean, coldest 14 days of year (°F.)..... 0 42 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ Normal daily mean, year (CF.)....0....20..0 e080 00008 35 60+ Precipitation: Normal daily mean, fs (inch)..................2005- .045 .136 Normal No. rainy days (over 0.10 inch), fs........... 0 182 Normal No. dry days (0.10 inch or less), fs........... 19 140 Dry days, percentage of total, fs (per cent)........... 11 100 Days in longest normal rainy period, fs.............. 0 144 Days in longest normal dry period, fs................ 4 144 Mean total, year (inches)...................0.-000% 20-— 60+ Evaporation: Daily mean, 1887-88, fs (inch)...................... .084 . 234 Total annual, 1887-88 (inches)...................... 20.3 54.8 Moisture ratios: INCona a aH Ty SE sate ston alae areata chord aha Wlaads Mea .21 1.39 Norm alsa Hi fe he 8s Wil ce atts Ootie ke oo lca cae etme eo hia .26 1.63 INOEMIAUME My MEATS. Cleo. ae eeicataeumesonkr a em ae wee 24 1.72 Vapor pressure: Normal mean, fs (hundredths inch).................. 249 545 Humidity: Normal mean, fs (per cent) oo 6. ee eek 48.0 84.0 Normalimean: year (per cent) i466 Ge eda wee eek 56.1 82.1 Wind: Normal mean hourly velocity, fs (miles)............. 302 14.9 Sunshine: Normal total duration, fs (hours) ................050. 1,225 2,166 Meoisture-temperature indices: Normal P/E XT, fs, remainder method.............. 72 707 Normal P/E XT, fs, exponential method............. 691 6,858 Normal P/E XT, fs, physiological method............ 809 11,246 470 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 128.—Climatic extremes for Arceuthobium cryptopodum. Plate | Temperature: Low. 34 Days in normal frostless season (fs). .............+.- 83 35 igi eirgpetee. © 22 oe oye EE oe bee ee ee 0 36 ealelieaye tes 5.32 oe ote aes os Be ace SO ee 0 37 Remainder summation above 32°, year (thousands).... 10.0— 38 Remainder summation above 39°, fs (thousands)...... 2.4 39 Exponential summation, fs (hundreds)............... 2.4 40 Physiological summation, fs (thousands)............. 2.6 41 Abeaitie mamnnmnthine oso. 0c ee eo tes. Yea de ee as —45 43 Normal daily mean, coldest 14 days of year (°F.)..... 24 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 45 Normal diy mean, year (..): .- 0% 52: 2.2. sees eee ee 40 — Precipitation: 46 Normal ebaby mean. .fe:(Gnch). «~~ < sci och te ow etc re ce .020—4 47 Normal No. rainy days (over 0.10 inch), fs........... 0 48 Normal No. dry days (0.10 inch or less), fg........... 153 49 Dry days, percentage of total, fs (per cent)........... 90-4 50 Days in longest normal rainy period, fs.............. 0 51 Days in longest normal dry period, fs................ 91 52 Be te Jaihetl GET CISTERN os en nhc ce eee 10+ Evaporation: 53 Daily mean, 1887- 88, ‘fs faniely foe ee oh oe eee .199 54 Total annual, 1887-88 (inches)...................-.- 56.0 Moisture ratios: 58 lier riatl Pa eee PO re lo ost o w'sn oe wae eo EO Ba ie 59 DS erent all we ere oe eae a eee eee 32 60 ornialsia) Pewyene ne tae sos cck'os J. eee Seite .12 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 233 Humidity: 65 Norwal mean) fs (ner centers. su. io. oe ee 37.0 66 Normal mean, year (per cent)...............-.-..<- 38.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 6.7 Sunshine: — 69 Normal total duration, fs (hours)................... 1,134 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 81 71 Normal P/E XT, fs, exponential method............. 772 72 Normal P/E XT, fs, physiological method............ 979 TaBLeE 129.—Climatic extremes for Arceuthobium americanum. Plate | Temperature: Low. 34 Days in normal frostless season (fs) ............-.... 25 35 Mint Maya iats. oe oo ee Oe aol 2c wee eee. 0 36 altho ha is ew bie os Sclce ae ee deere ee 26 37 Remainder summation above 32°, year (thousands).. 10.0 38 Remainder summation above 39°, fs (thousands)...... 2.4 39 Exponential summation, fs (hundreds)............... 2.4 40 Physiological summation, fs (thousands)............. 2.6 41 Absatuicannmunntin: 2303.55.53 Sets oa ee —4i9 43 Normal daily mean, coldest 14 days of year (°F.)..... 17 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 45 Normal dialy: mean. year (PF .) oct 2s vk ewes - 40— Precipitation: 46 Normal dally mean, Je Gneh).:. eek oe oe oe .009 47 Normal No. rainy days (over 0.10 inch), fs........... 0 48 Normal No. dry days (0.10 inch or less), fs........... 104 49 Dry days, percentage of total, fs (per cent)........... 90-4 50 Days in longest normal rainy period, fs.............. 0 51 Days in longest normal dry period, fs...............- 100 —4 52 Mire: tatals wear Gnehes) ooo. eee, bacco. = CORRELATION OF DISTRIBUTIONAL FEATURES. 471 TABLE 129.—Climatic extremes for Arceuthobium americanum—Continued. Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal 7/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) . Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 148 365 35 ENE AY SS ee eM: Mey cae ce thet al. ayia one eqidol ekecaee outta die euch oy ene 0 365 36 CHE) GL GE RUSS os ISIC beh sieht Eitan nAnAR Ane ene yh ir ehiNed se aL ape a 0 44 37 Remainder summation above 32°, year (thousands).... 11.5— 26.0+ 38 Remainder summation above 39°, fs (thousands)...... Ba 14.5 39 Exponential summation, fs (hundreds)............... 4.1 15.4 40 Physiological summation, fs (thousands)............. 2.4 SL ieie 41 PASO te IML sos 2s OP eS evo wae ee —34 +41 43 Normal daily mean coldest 14 days of year (°F.)..... 28 69 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — 78.8+ 45 Normal daily mean, year (CE icc. bw ws Sk eile ee es 55 — 75+ Precipitation: 46 INonmal daily mean, fs Gnch): i042 sto oes oe ale .020 :173 A7 Normal No. rainy days (over 0.10 inch), fs........... 0 284 48 Normal No. dry days (0.10 inch or less), fs........... 26 294 49 Dry days, percentage of total, fs (per cent)........... 8 100 50 Days in longest normal rainy period, fs.............. 0 235 51 Days in longest normal dry period, fs................ 9 299 52 Mean total? year Gnenes) oi 3) ens ee oe ee eh oaks 10+ 70+ Evaporation: 53 Daily mean, 1887-88, fs (inch).................0000% .084 .330 54 Total annual, 1887-88 (inches)..................000: 252 101.2 Moisture ratios: 58 SCO na aT Mis 2 Oe AR es ALG te Ft cae a td .08 1.76 59 INRIA ae LOTS yc ala slg) Se Seren Ne ERG e Wetchaeel OOKLA ea, anere .10 1.96 60 (Nemes PEM GA "hiss iase coe ane latel hereon Uae Uae m, chek a deve abs .03 2.004 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 279 707 Humidity: 65 Normal’ mean, fe'(per-cent) . .f6 oda feds oe eka eke 36.3 87.5 66 Normal mean, year (per cent)... 0). .waes dss oe Sek elec 38.1 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.5 14.2 Sunshine: 69 Normal total duration, fs (hours) ............2.0000: 1,651 2,650 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 68 1,418 al Normal P/E XT, fs, exponential method............. 625 13,511 72 Normal P/E XT, fs, physiological method............ 1,186 24,265 472 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 131.—Climatic extremes for Phoradendron juniperinum. Plate | Temperature: 34 Days in normal frostless season (fs) 35 Hot days, fs 36 Cold days, fs 37 Remainder summation above 32°, year (thousands).... 38 | Remainder summation above 39°, fs (thousands) 39 Exponential summation, fs (hundreds) 40 Physiological summation, fs (thousands) 41 Absolute minimum 43 Normal daily mean, coldest 14 days of year (°F.)..... 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 45 Normal daily mean, year (°F.)...................06- Precipitation: 46 Normal daily mean, fs (inch) 47 Normal No. rainy days (over 0.10 inch), fs 48 Normal No. dry days (0.10 inch or less), fs 49 Dry days, percentage of total, fs (per cent) 50 Days in longest normal rainy period, fs 51 | Days in longest normal dry period, fs 52 Mean total, year (inches) Evaporation: 53 Daily mean, 1887-88, fs (inch) 54 Total annual, 1887-88 (inches) Moisture ratios: 58 Normal P/E, fs 59 Normal x/E, fs 60 Normal P/E, year Vapor pressure: 63 Normal mean, fs (hundredths inch) Humidity: 65 Normal mean, fs (per cent) 66 Normal mean, year (per cent) Wind: 68 Normal mean hourly velocity, fs (miles) Sunshine: 69 Normal total duration, fs (hours) Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method 71 Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TaBLE 132.—Climatic extremes for Arenaria lateriflora. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................. 25 318 35 VOC AY Shi PS oe eis Vee cee SRY SUC NSN Ua Mma ee al 0 127 36 Cola ida surely petty cea uals tay weil ed EY TV Rd Maan aus Ea a 0 158 30 Remainder summation above 32°, year (thousands).... 10.0— 11.54 38 Remainder summation above 39°, fs (thousands)...... 2.6 5.7 39 Exponential summation, fs (hundreds)............... 2.8 6.8 40 Physiological summation, fs (thousands)............. 2 11.9 41 Absolute, mimimitim ee Oe i as aaa alae a —65 +30 43 Normal daily mean, coldest 14 days of year (°F.)..... (0) 42 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — 78.8 45 Normal’ daily, mean, year (CH.).6..0 02 oe ae ees 35 55 Precipitation: 46 Normal! daily mean)\/s) Gnceh) 23) oe yates aca .022 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 0 199 48 Normal No. dry days (0.10 inch or less), fs........... 28 216 49 Dry days, percentage of total, fs (per cent)........... 17 100 50 Days in longest normal rainy period, fs.............. 0 132 51 Days in longest normal dry period, fs.........4....... 9 216 52 Mean total,"year (Gnches) os). ibe ae eee ee oe 10+ 90 CORRELATION OF DISTRIBUTIONAL FEATURES. 473 TABLE 132.—Climatic extremes for Arenaria lateriflora—Continued. Plate | Evaporation: : Low. High. 53 Daily mean, 1887-88, fs (inch)...... EON AAS Ly nigh Vea .052 . 293 54 Total annual, 1887-88 (inches)...................... 18.1 79.8 Moisture ratios: 58 hot fosieetel Ay 24," S/R ae MA | PNR EAR A Ae UC SOe Mishoo ea eID aR .09 3.84 59 INR RITAN ae ABA GR Neopet SS NAN ar” RMN sti Nene onal a2 4.48 60 INGODERMAN CHORUS BAe |G Cheeta ae ata alt oleae fe .20 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 249 491 Humidity: 65 Normal mean, fs (per cent)..........0220c0 ccc ee ees 40.9 84.0 66 Normal mean, year (per cent). ..........2...00e ees 48.1 82.1 Wind: 68 Normal mean hourly velocity, fs (miles)............. BI03 | 16.4 Sunshine: 69 Normal total duration, fs (hours) ................... 1127 1,927 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method....:......... 42 1,566 71 Normal P/E XT, fs, exponential method............. 405 11,724 fips Normal P/E XT, fs, physiological method............ 598 10,241 TaBLE 133.—Climatic extremes for Parietaria pennsylvanica. Plat | Temperature: Low. High. 34 Days in normal frostless season (fs). ................ 25 318 35 EL CACy ShO PSR era a Gotaler al wler tur atecine hay ae neo aah Aue aee elle 0 141 36 DAV GAAG SHS a eliibe lisclval ei ouel Guat sehen Mute l hab oe eccaitalle 5d 0 158 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.6 6.6 39 Exponential summation, fs (hundreds)............... 2.8 Pa | 40 Physiological summation, fs (thousands)............. 2:1 12.9 41 PASSO AGE PUETENTIVUETINS oo ee acd occ ilesse Serdunile taeiles wont aneueiatiy aueyeeue i —65 +10 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 42 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8+ 45 Normal daily mean, year (°F.)...............00eeee 35 60+ Precipitation: 46 Normal daily mean, fs (inch)....................6.. .022 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 0 199 48 Normal No. dry days (0.10 inch or less), fs........... 26 216 49 Dry days, percentage of total, fs (per cent)........... 1l 100 50 Days in longest normal rainy period, fs.............. 0 140 51 Days in longest normal dry period, fs................ 4 216 52 Mean total, ‘year /(imches):..... s/s(o0c:c cane cee eee eae 10+ 90 Evaporation: 53 Daily mean, 1887-88, fs (inch)...................04- .052 .290 54 Total annual, 1887-88 (inches)...................08. 18.1 79.8 Moisture ratios: 58 INO IEL URES FB... css 5 do Nach RANE, lO MNRAC Biel Shecguaus eee dogg .09 3.84 59 INO pra eapAE, FONE Nici) sip See SULG BES OP PRRLS, aie gies ate ake yl2 4.48 60 NOLS OUEEN LU C7u OAC ake a ET ge 14 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 249 545 Humidity: 65 Normal mean; f3i (pet Gemt) iid. ms Letra lw we Wale barn ot 40.9 84.0 66 Normal’ mean. year (per Cent) oi. 6.66. le Sk Cok ck 45.4 82.1 Wind: 68 Normal mean hourly velocity, fs (miles)............. Se | 16.4 Sunshine: 69 Normal total duration, fs (hours) ..............0000. 1,127 1,927 Moisture-temperature indices: 70 Normal P/E XT’, fs, remainder method.............. 42 1,566 71 Normal P/E XT, fs, exponential method............. 405 11,724 2 Normal P/E XT, fs, physiological method............ 598 10,837 474 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 134.—Climatic extremes for Cornus canadensis. Plaie | Temperature: Low. High. 34 Days in normal frostless season (fs).............000-. 25 318 35 FT OUP ANS GS ss Se elec mite &. 6 anise GVS vc aisle 0 88 36 COVA A AVS pst ae ne PR ee ole maces a eae ayer eee 0 158 37 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.6 5.1 39 Exponential summation, fs (hundreds)............... 2.8 5.4 40 Physiological summation, fs (thousands)............. PaaS 8.0 41 PA DS late: Arie EN TATE is) ot es ok ae i «os Se oe —59 +30 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 46 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.8 45 Normal daily mean, year (CF.)....<....-0000) ee 35 60 Precipitation: 46 Normal daily mean, fs:\Gnch) . : 2. 59 9.5 20... Uae ee .037 .199 47 Normal No. rainy days (over 0.10 inch), fs........... 0 199 48 Normal No. dry days (0.10 inch or less), fg........... 28 202 49 Dry days, percentage of total, fs (per cent)........... 17 100 50 Days in longest normal rainy period, fs.............. 0 106 51 Days in longest normal dry period, fs................ 9 202 52 Mean total/year Gnehes) ..c4.e. 28 See 20— 90 Evaporation: 53 Daly amean, AS88788. ss GN) 22 c ec c ks aed ons wee .052 .275 54 Total annual, 1887-88 (inches)....................-- 18.1 76.5 Moisture ratios: 58 Normale Pian nets Oe och aoe ka ase eee ee .19 3.84 59 Monmialiay/ Ee iSeoe ye eee oie ie cise sic pro emes ee Cab .25 4.48 60 NOrmMa E/E OVAL Tree cect ek aoe mee .20 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 249 447 Humidity: 65 Normal mean. fs: Qper cent): .2.. 2. cokes ees chee ee 46.7 84.0 66 Normalimean, year. (percent) 5 .5550...5...2 ee ee 48.7 82.1 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.5 16.4 Sunshine: 69 Normal total duration, js Chours).....: 2. .......22 66 1127 1,927 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 58 1,566 71 Normal P/E XT, fs, exponential method............. 563 11,724 %2 Normal P/E XT, fs, physiological method............ 710 7,869 Plate | Temperature: Days in normal frostless season (js) Hot days, fs Cold days, fs Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands) Exponential summation, fs (hundreds) Physiological summation, fs (thousands) Absolute minimum Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal: daily mean, year (CE) ane. canis << steee oelens Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) CORRELATION OF DISTRIBUTIONAL FEATURES. 475 TABLE 135.—Climatic extremes for Spermolepis echinata—Continued. Plate | Evaporation: Low. High. 53 Daily meanwlS87-—S88, fs Gneh) . 2... c2 >. sctatinsia- elaiales .102 .330 54 Total annual, 1887-88 (inches)..................e05- 36.7 101.2 Moisture ratios: 58 Nonmial Gun JS. cis: 5 ayia maiysieirs sutaeas TU ats iable, syed uy WZ 1.36 59 INorenial sa) Br, $8) 2 ie a's sco) epee) hls SIRE was eeabic. waa .13 1.52 60 INO Py Ey NEAR oy. 81h) ds isjcvai tic) a SRR kecnycs ih .03 1.47 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 300 675 Humidity: 65 Normal:mean, fs (per cent)! ss ie. Se aces 22a. 36.3 81.9 66 Normal mean, year (per cent)...........+.200eec00% 38.8 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.5 12.3 Sunshine: 69 Normal total duration, fs (hours) ................2.. 1,895 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 98 1,314 rs Normal P/E XT, fs, exponential method............. 625 12,106 «2 Normal P/E XT, fs, physiological method............ 1,186 23,652 TaBLE 136.—Climatic extremes for Daucus pusillus. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)................- 166 365 35 1B (GY 0/76 KG SPS AUN Nr EE SR CA ST UL ar Ue eae Bon 0 365 36 COPE UG ES eaT IPS SEDER ae eS ec PSE eRe one eRe ee 0 43 37 Remainder summation above 32°, year (thousands).... 10.0 26.0+ 38 Remainder summation above 39°, fs (thousands)...... 3.0 14.5 39 Exponential summation, fs (hundreds)............... 4,1 15.4 40 Physiological summation, fs (thousands)............. 23.9 Ra | 41 ASD SOMUCE MAD UIT ee e —30 +41 43 Normal daily mean, coldest 14 days of year (°F.)..... 31 69 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 78.8 45 Normal daily mean, year (CE) 00. .geso oe): co & ceeic oye ese 50 — 75+ Precipitation: 46 Normal daily mean, CASH GSC) 0 GUAR RU RAT GOT A NN i .020 .199 47 Normal No. rainy days (over 0.10 ate SORA BR See 0 284 48 i Normal No. dry days (0.10 inch or less), fs........... 0 294 49 Dry days, percentage of total, fs (per cent)........... 0 100 50 Days in longest normal rainy period, fs.............. 0 256 51 Days in longest normal dry period, fs................ 0 299 52 Wiean total, year GMeMes) ac... 6 saeco oes see ies oe 10— 90 Evaporation: 53 Daily mean, 1887-88, fs (inch)...............0.e000% .052 .330 54 otal annual. 1887-88 Gnehes).. .. 6... < . cece cee oes 18.1 101.2 Moisture ratios: 58 Infos enitaG 2Y 0 Si Kaan SR Gr en eee eee ee 12 3.84 59 EN @ roast als acy SERPS a5 cw. 6 cas AS ome ed aire NA a ee Dire et 13 4.48 60 (Normale MB vient) eee Cle es ecto euie Teh calles .03 4.90 Vapor pressure: 63 Normal mean, Js (hundredths meh)... ......s0s000s 300 707 Humidity: 65 Nomnalimesdn,) fs (per centiyiy cous idaatonew te wed oda s 36.3 87.5 66 Normalimesn, year (per Cent) ic. ss beic ence wc oud bs eee wo 38.7 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.5 16.4 Sunshine: 69 Normal total duration, fs (hours) ...............005 1,578 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 68 1,418 71 Normal P/E XT, fs, exponential method............. 625 13,511 72 Normal P/E XT, fs, physiological method............ 1,186 24,265 476 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 137.—Climatic extremes for Parietaria debilis. Plate | Temperature: Low High 34 Days in normal frostless season (fs)................. 198 334 35 Hotidaysnseees 228 cae nee ee: Bi 9s Sl eh ogee ON ee 54 365 36 Coldidaysny sins trace ters hie el ES eh tee Wee San 0 0 37 Remainder summation above 32°, year (thousands).... PEs 26.0+ 38 Remainder summation above 39°, fs (thousands)...... TAS 10.6 39 Exponential summation, fs (hundreds)............... a0 11.8 40 Physiological summation, fs (thousands)............. 8.4 21.4 41 PA DSGlUGS AMMEN ss 6 a ees ee ede elie ns AIRS Se —9 +32 43 Normal daily mean, coldest 14 days of year (°F.)..... 302 54 44 Normal daily mean, hottest 6 weeks of year (°F.)..... AEB 78.8 45 Normal daily mean; ‘year (CF.) .. 6.6.6 06 si nehen sense 55 70+ Precipitation: 46 Normal*danly mean, ifs Gach)... oe 3. BR 020 .172 47 Normal No. rainy days (over 0.10 inch), fs........... 0 284 48 Normal No. dry days (0.10 inch or less), fs........... 26 294 49 Dry days, percentage of total, fs (per cent)........... 8 100 50 Days in longest normal rainy period, fs.............. 0 157 51 Days in longest normal dry period, fs................ 14 299 52 Mean'total year (inches): ..).6.0518. wis osu eee 10— 60+ Evaporation: 53 Daily mean, 1887-88, fs (inch)...................... .102 Lies 54 Total annual, 1887-88 (inches)...................... 37.0 95.7 Moisture ratios: 58 DUNC) nso es eel OST RIES A foo Na ee Ine ais PINRO 12 1.36 59 Normal) To peer ie ieee Soe a ons Bee eet en CAO A 13 1.52 60 IN Gr BIG) FeV eaEN unr erie a6, 2 OO Oe enh .03 1.47 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 300 675 Humidity: 65 Normal mean; fsi(per'cent)ii. 5. oa seek ne vies 36.3 81.9 66 Normal mean, year (per cent) ..................---- 38.8 85.2 Wind: 68 Normal mean hourly velocity, fs (miles)............. 4.5 1236 Sunshine: 69 Normal total duration; js’ (hours) 2)... 52) 5000-2 2. 2,123 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 98 1,314 wa Normal P/E XT, fs, exponential method............. 906 12,106 72 Normal P/E XT, fs, physiological method............ 1,790 23,652 TaBLE 138.—Climatic extremes for Kallstremia grandiflora. Plate | Temperature: Low. Hygh. 34 Days in normal frostless season (fs) ................ é 189 305 35 TOR Gay STS io PRR UAR Le Se ae eee Un aie eee eee 1204 186 36 Cold dayse sce eae he eee Se ae cate eee 0 0 37 Remainder summation above 32°, year (thousands).... 18.0 coe 38 Remainder summation above 39°, fs (thousands)...... 7.6 10.1 39 Exponential summation, fs (hundreds)............... 6.04 9.0+4 40 Physiological summation, fs (thousands)............. 15.0 20.6 41 FN OSLO AVENE) 60000001, 660! RAM Dene EAE TC eIMER nr UID. ein UR RaI SS —5 +23 43 Normal daily mean, coldest 14 days of year (°F.)..... 354 50 +2 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 78.8+ es 45 Normalidaily mean, year (CR, oo vac ck 2 6 eee eee 60 70+ Precipitation: 46 Normalidalysmean; fs: Gnch).. Y:..406 6 eee eee .020 .060 + 47 Normal No. rainy days (over 0.10 inch), fs........... 0 25+4 48 Normal No. dry days (0.10 inch or less), fs........... 200 — 283 49 Dry days, percentage of total, fs (per cent)........... 80+ 100 50 Days in longest normal rainy period, fs.............. 0 2 51 Days in longest normal dry period, fs................ 1004 283 52 Mean totaly year“ Gnehes) 2.2228 2aeor se. dee ee se 10— . 20+ CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 138.—Climatic extremes for Kallstremia grandiflora—Continued. 477 70 72 Evaporation: Low. Daily mean, 1887-88, fs (inch)...............6..00-- . 1804 Total annual, 1887-88 (inches)...............-...... 704 Moisture ratios: INGER, fares. LORMAN OPIN OW VOR Alia Not hy 1% NOTING a Ply S625 SEE RO UN hit Ae dames .13 IN@rmiali/ EVO ar 56. 52/5530, 2 he Ne ENT ho VEO Ne 12 Vapor pressure: Normal mean, fs (hundredths inch).................. 300 Humidity: Normal mean, fs (per cent).............00000 0c ceeee 36.3 Normal mean, year (per cent)...................06- 38.7 Wind: Normal mean hourly velocity, fs (miles)............. 4.5 Sunshine: Normal total duration, fs (hours) ................... Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 98 Normal P/E XT, fs, exponential method............. 906 Normal P/E XT, fs, physiological method............ 1,790 TaBLeE 139.—Climatic extremes for Cladothrix lanuginosa. Temperature: Days in normal frostless season (fs)................. 142 TOG CAVE pS a NOR OSA fiom ein Ne ua Nee gee Ne thuevest one, eke 113 (COAG Le HE 210 RRS an a Ne ge Ca CT et MR 0 Remainder summation above 32°, year (thousands).... Tes Remainder summation above 39°, fs (thousands)...... 5.5 Exponential summation, fs (hundreds)............... 5.9 Physiological summation, fs (thousands)............. 10.3 AsSOlUtbe) MATTIE: 65 5))5) 5 6s weiss usenet o cihuciele oe whee —29 Normal daily mean, coldest 14 days of year (°F.)..... 27 Normal daily mean, hottest 6 weeks of year (°F.)..... 71.6 Normal daily mean, year (°F.)................00000: 55 — Precipitation: Normal daily mean, fs (inch)...................0000. .020 Normal No. rainy days (over 0.10 inch), fs........... 0 Normal No. dry days (0.10 inch or less), fs........... ies Dry days, percentage of total, fs (per cent)....... ve Days in longest normal rainy period, fs.............. 0 Days in longest normal dry period, fs................ 53 Mean total, ‘year! Gnehes) oss 6 osc ab ck ee oc eee ck 10° — Evaporation: Daily mean,’ 1887-88, fs" Grich):......6. « (Wo. eet e. Godinw .102 Total annual, 1887-88 (inches)....................0. 38.8 Moisture ratios: ING Pe Fa 6 Vy ee. MIRAE RA cotta Ho: aon allti, 12 NOTIN Ss 8 5 i sO ate SRST oh EWS SRN Bi Mk 13 INOCIIGIRE OE ISG AT 6 kia chal e|c's MeN AR Rh. ier eug 12 Vapor pressure: Normal-mean, fs (hundredths inch).................. 300 Humidity: Normal mesn; ys" (per cent)... Py ae. Heeb es 36.3 Normal mean, year (per cent). .........cccccccecucs 38.7 Wind: Normal mean hourly velocity, fs (miles)............. 4.5 Sunshine: Normal total duration, fs (hours) ................0.. 1,700¢ Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 98 Normal P/E XT’, fs, exponential method............. 906 Normal P/E XT’, fs, physiological method............ 1,790 3004 3,000 +4 4,000 +4 2,343 737 6,690 13,926 to 478 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 140.—Climatic extremes for Pectis paposa. Plate | Temperature: Days in normal frostless season (fs) Hot days, fs Cold days, fs Remainder summation above 32°, year (thousands)... . Remainder summation above 39°, fs (thousands) Exponential summation, fs (hundreds) Physiological summation, fs (thousands) Absolute minimum Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily, mean; year CF.).... 2.5. 66S eS Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal 7/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: Normal P/E XT, fs, remainder method Normal P/E XT, fs, exponential method Normal P/E XT, fs, physiological method TaBLE 141.—Climatic extremes for Euphorbia serpyllifolia. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs) ..............+5- 25 334 35 TOGA V SAS ey Ne Lg aia SO Coe po ne el eg 0 218 36 COVGNGAT IS Sess see ody aye cont Pee eae MRR DRS eS ey cpecom ecto 0 158 37 Remainder summation above 32°, year (thousands).... 10.0— 26.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.4 10.3 39 Exponential summation, fs (hundreds)............... Anta 11.3 40 Physiological summation, fs (thousands)............. 2.6 Fei 41 A Dsolitte TMM 3.3 Sacietinse eae casa ee ae —65 +32 43 Normal daily mean, coldest 14 days of year (°F.)..... 0 53 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— 78.84 45 Normaldailyamean, sear: CW)... 254 2s 2 See ee 35 70+ Precipitation: 46 Normaldaily mean\-/s/Gnch)\.5 422508 cee eee ee .009 +.199 47 Normal No. rainy days (over 0.10 inch), fs........... 0 2004 48 Normal No. dry days (0.10 inch or less), fs........... 26 294 49 Dry days, percentage of total, fs (per cent)........... 14 100 50 Days in longest normal rainy period, fs.............. 0 172 51 Days in longest normal dry period, fs................ 11 299 52 Mean total, year Gnehés) .... 3.20 3 0 eae 10— 40+ CORRELATION OF DISTRIBUTIONAL FEATURES. 479 TaBLeE 141.—Climatic extremes for Euphortna serpyllifolia—Continued. Plate | Evaporation: Low. High. 53 Daily mean, 1887-88, fs (inch)...............-.2000- .102 . 349 54 Total annual, 1887-88 (inches)...................+-- 18:4 101.2 Moisture ratios: 58 DVIS Pf bs os a opis eiardlin x x valley 3 RIB: Speliedlapens \s savage .04 3.84 59 POR ANAT PER ISA E s Sin cs sy ouceoraevtie ade niide bie amnkclta es sea are 06 4.48 60 AN ORTITAL REITs VEAL 5's 5s eetela tal sds hee Re, by sith 2 ieyea Braye .09 4.90 Vapor pressure: 63 Normal mean, fs (hundredths inch).................. 183 675 Humidity: 65 Normal mean, fs (per cent) . 2.200 20 cc cc eis cc ceees 22.6 87.5 66 Normal mean, year (per cent)..................00-- ULF 86.8 Wind: 68 Normal mean hourly velocity, fs (miles)............. 3.5 16.4 ; Sunshine: 69 Normal total duration, fs (hours) ..................- LAD7 2,995 Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method.............. 13 1,566 71 Normal P/E XT, fs, exponential method............. 127 11,724 72 Normal P/E XT, fs, physiological method............ 197 13,926 Temperature: Days in normal frostless season (fs) Hot days, fs Cold days, fs Remainder summation above 32°, year (thousands).... Remainder summation above 39°, fs (thousands) Exponential summation, fs (hundreds) Physiological summation, fs (thousands) Absolute minimum Normal daily mean, coldest 14 days of year (°F.)..... Normal daily mean, hottest 6 weeks of year (°F.)..... Normal daily mean, year (°F.)...:.......-.e0020000: Precipitation: Normal daily mean, fs (inch) Normal No. rainy days (over 0.10 inch), fs Normal No. dry days (0.10 inch or less), fs Dry days, percentage of total, fs (per cent) Days in longest normal rainy period, fs Days in longest normal dry period, fs Mean total, year (inches) Evaporation: Daily mean, 1887-88, fs (inch) Total annual, 1887-88 (inches) Moisture ratios: Normal P/E, fs Normal 7/E, fs Normal P/E, year Vapor pressure: Normal mean, fs (hundredths inch) Humidity: Normal mean, fs (per cent) Normal mean, year (per cent) Wind: Normal mean hourly velocity, fs (miles) Sunshine: Normal total duration, fs (hours) Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method C 1,314 71 Normal P/E XT, fs, exponential method 12,106 72 Normal P/E XT, fs, physiological method 23,652 480 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 143.—Climatic extremes for Oxybaphus nyctagineus. Plate | Temperature: 34 Days in normal frostless season (fs) 35 Hot days, fs 36 Cold days, fs 37 Remainder summation above 32°, year (thousands)... 38 Remainder summation above 39°, fs (thousands).... 39 Exponential summation, fs (hundreds) 40 Physiological summation, fs (thousands) 41 Absolute minimum 43 Normal daily mean, coldest 14 days of year (°F.)..... 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 45 Normal aaty menn, year (Ol .) . ooo ac ob eae. ow See Precipitation: 46 Normal daily mean, fs (inch) 47 Normal No. rainy days (over 0.10 inch), fs 48 Normal No. dry days (0.10 inch or less), fs 49 Dry days, percentage of total, fs (per cent)........... 50 Days in longest normal rainy period, fs 51 Days in longest normal dry period, fs 52 Mean total, year (inches) Evaporation: 53 Daily mean, 1887-88, fs (inch) 54 Total annual, 1887-88 (inches) Moisture ratios: 58 Normal P/E, fs 59 Normal z/E, fs 60 Normal P/E, year Vapor pressure: 63 Normal mean, fs (hundredths inch) Humidity: 65 Normal mean, fs (per cent) 66 Normal mean, year (per cent) 68 Normal mean hourly velocity, fs (miles) Sunshine: 69 Normal total duration, fs (hours) Moisture-temperature indices: 70 Normal P/E XT, fs, remainder method 71 Normal P/E XT, fs, exponential method 72 Normal P/E XT, fs, physiological method | oO mOwwnyodo Rho pe TABLE 144.—Climatic extremes for Oxybaphus angustifolius. Plate | Temperature: Tow. High. 34 Daysin normal frostless season (fs)................- 83 331 35 LE LESEN: Leg ike) Pin gees Og ae ge 5, a a gm me ames eke AN a 0 218 36 CONG AUS fS Ee eC ete eres 0 140 37 Remainder summation above 32°, year er erage 10.0— 26.0+ 38 Remainder summation above 39°, fs (thousands) .. 2.4 10.6 39 Exponential summation, fs Gaaniecds) HAS ‘a )o/ MR Peabo 2.4 1 40 Physiological summation, fs (thousands)............. 2.6 21.4 4l Pbeolipe wait. © 20 ee eee ates, oe eres —5l1 +22 43 Normal daily mean, coldest 14 days of year (°F.)..... 9 53 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 78.8+ 45 Normal dary mean: year (SPe)oo 6 oc ke eee 45 — 70+ Precipitation: 46 Norman dany inieaw fs. Gubhyos os 3209 od fv. See ce .025 .129 47 Normal No. rainy days (over 0.10 inch), fs........... 0 257 48 Normal No. dry days (0.10 inch or less), fs........... 32 259 49 Dry days, percentage of total, fs (per cent)........... 14 100 50 Days in longest normal rainy period, fs.............. 0 157 51 Days in longest normal dry period, fs................ 15 2504 52 Med total, year GMches) . ee OF clo cn ch ee oe 10 50 Plate ae 54 58 59 60 63 65 66 68 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 144.—Climatic extremes for Oxybaphus angustifolius—Contin ued. 481 Evaporation: Low. High. Daily imme awe GSS 188s 1S) NCI) 2). cle 0) esalevo aioe lone etenslenels .102 .330 Total annual) 1887-88 (Gnches)'. 2.6. .3s6 0s ea ele eo os a 0 101.2 Moisture ratios: Nominal esas ss 12 1 MPC C EL IG EI AC led) .10 1.01 BN orernnal li sa MEGS 08 8) 2 ante ee rae IIE LEVIN hak 2 52 1.05 Normally PMB Vearin ee si) 2 ante dip ota e manly defor = No Wnysa aia 2 1.16 Vapor pressure: Normal mean, fs (hundredths inch).................. 300 675 Humidity: Normal mean ais (per CEMb) Ss scierc diy cnslietonede We apetubesits in 37.0 i 73.5 Normal mean, year, (per Cent) so. 6h. ae aye ee aeeqeiene Hee 38.8 85.2 Wind: Normal mean hourly velocity, fs (miles)............. 4.5 14.2 Sunshine: Normal) totalidaration, fs (hours) s). a Yeo. bn sees 1,127 2,650 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 58 1,142 Normal P/E XT, fs, exponential method............. 563 10,331 Normal P/E XT, fs, physiological method............ 710 20,570 TaBLe 145.—Climatic extremes for Oxybaphus floribundus. Temperature: Low. High. Days in normal frostless season (fs)................. 94 261 EME CLANS Sirs ee hac as eit gal iia Mictithal EMmeeeu lags ada chia denne 30 173 (CHOU G 128 EERE ATO ESN PN tea eS AOA yc AY AUR an a ES 0 158 Remainder summation above 32°, year (thousands).... 10.0— 18.0+ Remainder summation above 39°, fs (thousands)...... 2.9 8.6 Exponential summation, fs (hundreds)............... 3.0 9.6 Physiological summation, fs (thousands)............. unidl £7.6 PMDOSOMITCS TAPMITIMTIY oc. oiesk eke che 4 a ya ages rebel c Bien leletdteedcl cuatk —65 +19 Normal daily mean, coldest 14 days of year (°F.)..... 8) 46 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 78.8 Normal daily mean, year CE.) so... 6.0.2... ee wee 35 65+ Precipitation: Normal dailyimean.i 7s: G@mela)'s 3 isis lnahaie gens Secs .049 .128 Normal No. rainy days (over 0.10 inch), fs........... 0 182 Normal No. dry days (0.10 inch or less), fs........... 28 203 Dry days, percentage of total, fs (per cent)........... 14 100 Days in longest normal rainy period, fs.............. 0 L172 Days in longest normal dry period, fs................ i 163 Mean total, year Cmehes) occ is scloe ches oe eo ew wee « 20 50+ Evaporation: ‘ DWailyemeamiSS7—S8. fs Gnch) sc. wise y saleee cee ee 101 .200 otaliannwal, T88/—S8 Gnmcehes) ..6...0. 0. c ee cce ecu 22).\1 76.5 Moisture ratios: s INOS EY 27717 ENGR Ae eg MEE SI ay oe ee PRE BE .19 1.23 INV mated ray ere Sis ks ey isla AM Hater MP, ly RoR oak te UN Dott 25 89 Nomi alii wear ck Ciera TURN ome Dekh ot Wat Ue PH AS: 1.30 Vapor pressure: Normal mean, fs (hundredths inch).................. 253 545 Humidity: Nommealimenn, fs (per Gentil ini acta Weil cl Ruderdele x 45.8 73.5 Nonmal menn, vear (per Cemt).. os. k aa. de coke we cs 48.1 74.2 Wind: Normal mean hourly velocity, fs (miles)............. 6.0 14.2 | Sunshine: Normal: total duration, fs (hours). cced.an vu den Mi we 1,127 2,166 Moisture-iemperature indices: Normal P/E XT, fs, remainder method.............. 58 700 Normal P/E XT, fs, exponential method............. 563 6,410 Normal P/E XT, fs, physiological method............ 710 12,977 482 CORRELATION OF DISTRIBUTIONAL FEATURES. TABLE 146.—Climatic extremes for Flerkea occidentalis. Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)............0-- 25 224 35 EV Oui ys an seils cet MUA a dia 8 a cae NS Ch ah 0 105 36 CON arate Ses eh lesa mule ian ENTLY Conkle ohh Bas Ae ck 0 134 37 Remainder summation above 32°, year (thousands) .. 10.0— 11.5+ 38 Remainder summation above 39°, fs (thousands).... Pea 5.4 39 Exponential summation, fs (hundreds)...... Me Gotan 2.8 5.7 40 Physiological summation, fs (thousands)........... 3.1 9.9 41 A bsoliite mmimina mains keh os s3 ee ieia asetent sel Ar oole menu —48 —2 43 Normal daily mean, coldest 14 days of year (°F.)... ive 39 44 Normal daily mean, hottest 6 weeks of year (°F.)... 64.4— 71.6+ 45 Normal idaily mean: year (OFs).)0.02. 5. 6 oe ee. 40 — 50+ Precipitation: 46 Normal daily mean, fs. Gnch): 2). 5 es Soke. .025 .079 47 Normal No. rainy days (over 0.10 inch), fs......... 0 3 48 Normal No. dry days (0.10 inch or less), fs......... 104 216 49 Dry days, percentage of total, fs (per cent)......... 70 100 50 Days in longest normal rainy period, fs............ 0 44 51 Days in longest normal dry period, fs.............. 101 216 52 Mean ‘total: yeariGnehes) . i). 72 bbe ce Ode ae aan 10+ 50+ Evaporation: 53 Daily mean, 1887-88, fs (inch).............. cena Nated .120 . 260 +4 54 Total annual, 1887-88 (inches).................... 34.7 69.0 Moisture ratios: 58 NODE alia PE May simmered amis Sra) eh een .18 .66 59 Normal w/E, fs........ RAR HUT eS Raa ar Le .85 60 INGEMAl LE ME Siyealy etn ede Sica ss ola Cn tae 23 1.30 Vapor pressure: 63 Normal mean, fs (hundredths inch)................ 236 329 Humidity: 65 NormalimeéansifsiQoer Cent) iinscs sss ues) osc ee a soe 45.8 71.4 66 Normal mean, year'(per cent)... 2220 35.0. 22 48.1 75.5 Wind: % 68 Normal mean hourly velocity, ESP CMILES intron ee 4.3 7.5 Sunshine: 69 Normal total duration, js Chours) 22. so. ¢9.00 2. 32" 1,167 1,578 Moisture-temperature indices: 70 Normal P/E XT, s, remainder method............ 66 332 71 Normal P/E XT, fs, exponential method........... 623 3,052 72 Normal P/E XT, fs, physiological method..........| 1,204 3,160 Plate | Temperature: Low. High. 34 Days in normal frostless season (fs)..............00. 108 224 35 HIGticlayayisdics | cieneie olen nen ialaie wil depend Steen Ue Nastia s 0 153 36 Collide fsii2 aes euro eet ee aes Pete oe Ae Pays 0 137 37 Remainder summation above 32°, year (thousands).. 10.0— 18.0+ 38 Remainder summation above 39°, fs (thousands)...... 2.6 7.0 39 Exponential summation, fs (hundreds)............... 3.0 7.9 40 Physiological summation, fs (thousands)............. 2.1 14.4 4] A bsoliate’ raisins j4-o)2 sicko ites sel ees aa ae ule Tes Ole —40 —5 43 Normal daily mean, coldest 14 days of year (°F.)..... 15 40 44 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4 — 78.84 45 Normal daily, mean, year (OH) i 4 cick ayer tes tenes ole 30 60+ Precipitation: 46 Normaldaily mean). fs; Gneh)ieoc Dee Nese envee eee .089 .131 47 Normal No. rainy days (over 0.10 inch), fs........... 26 161 48 Normal No. dry days (0.10 inch or less) fs........... 19 136 49 Dry days, percentage of total, fs (per cent)........... 11 83 50 Days in longest normal rainy period, fs.............. 21 LB wr 51 Days in longest normal dry period, fs................ 4 91 52 Mean totals-vyear Gnehes): 9.050) eae ee ee 30 — 60+ Plate | Evaporation: 53 54 58 59 60 63 65 66 68 69 70 71 72 CORRELATION OF DISTRIBUTIONAL FEATURES. TaBLE 147.—Climatic extremes for Flerka proserpinacoides—Continued. Low. Daily mean, 1887-88, fs (inch)...................6-. .084 Total annual, 1887-88 (inches).............20000000: 20.3 Moisture ratios: IM OEMAl Ee. .e ici eee aa oka Se ee de eo 51 Info coe NW OLS cee See in he, A ee he rar .60 Normal PE) years. 522). shui ditee Ook te len Soak Me Vapor pressure: Normal mean, fs (hundredths inch).................. 345 Humidity: Normal mean, fs (per cent) ............cc cece ccc cecs 65.6 Normal mean, year (per cent)..........--.0+eeeeees 67.5 Wind: Normal mean hourly velocity, fs (miles)............. 5 Sunshine: Normal total duration, fs (hours)................... 1,225 Moisture-temperature indices: Normal P/E XT, fs, remainder method.............. 301 Normal P/E XT, fs, exponential method............. 2,914 Normal P/E XT, fs, physiological method............ 2,747 1,592 483 Plate 34 35 36 ot 38 39 40 41 43 44 45 46 47 48 49 50 51 52 53 54 58 59 60 63 65 66 68 69 70 71 72 TaBLE 148.—Climatic extremes for Trautvetteria grandis. Temperature: Low. Days in normal frostless season (fs)................. 25 18 CONG LER TASUNY ZINA REPT, San Rn EAU opeO EE es N77 Oe Hd etn e 0 RE NAR CAY Sy See o es) ob: 5i'as ahs os g iaison cs: ened outed eae nan ordi 0 Remainder summation above 32°, year (thousands).... 10.0— Remainder summation above 39°, fs (thousands)...... Qe Exponential summation, fs (hundreds)............... 2.8 Physiological summation, fs (thousands)............. 1.9 PAUISOLULES, TANTATUUA TINS: 3. 615. w/o. 0, oro: pserabendveen te Quavoushe tavaienee: «rere —51 Normal daily mean, coldest 14 days of year (°F.)..... 17 Normal daily mean, hottest 6 weeks of year (°F.)..... 64.4— Normal daily mean, year (°PF.).............2000 eee: 40 — Precipitation: Normal daily mean, fs (inch)....................05. .025 Normal No. rainy days (over 0.10 inch), fs...... De as 0 Normal No. dry days (0.10 inch or less), fs........... 72 Dry days, percentage of total, fs (per cent)........... 27 Days in longest normal rainy period, fs.............. 0 Days in longest normal dry period, fs................ 56 Mean total, year Gnches): 0.0. cok ee ec ee eas 20+ Evaporation: Daily mean, 1887-88, fs (inch).................0005- .052 ‘Totalvannual,: 1887-88. GQNCHEeS) ss cjiccierc c'ce seteecsee ee 18.1 Moisture ratios: So Ta A RRL oe ek Oa nee aA a ae 18 AICTE RY C/A] IN a A MRM abe Ue NP alte UMAR aD ly CO .20 NOUN FAME) VOAT 3's SS SS SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST NORTHERN MESOPHYTIC EVERGREEN FOREST (WEST) NORTHERN MESOPHYTIC EVERGREEN FOREST (Eas — Fie. 22. CORRELATION OF DISTRIBUTIONAL FEATURES. 493 Normal daily mean temperature of coldest 14 days of the year (plate 43, fig. 23).—The daily mean temperature of the coldest period of the year is a climatic factor which varies greatly in the various vegeta- tional areas. The lowest value, 0°, is found in the northernmost part of the Grassland area, and minimum values of 5° are found in the Grass- land Deciduous-Forest Transition and in the eastern section of the Northern Mesophytic Evergreen Forest. The highest mean tempera- ture of this coldest period, 69°, is found in the Southeastern Mesophytic Evergreen Forest, and the nearest maximum values approaching it in other vegetations are found in the Desert and Semidesert, where maxima of 54° occur. There is apparently no temperature factor which exhibits greater diversity in its amplitude and extremes in the several vegetational areas than does the mean temperature of the coldest fortnight. The normal daily mean of the hottest six weeks, for which we have used the data elaborated by Merriam, fails to show such a diversity for the vegetational areas (see tables 32 to 40). Normal daily mean precipitation of frostless season (plate 46, fig. 23).— This climatic index exhibits a well-graduated series of differences in the 9 vegetational areas, from its lowest values for the Desert (0.009 inch) and the Semidesert (0.017 inch) to its highest value for the North- western Hygrophytic Evergreen Forest (0.199 inch). Here again the Evergreen Forest areas of group B exhibit greater differences than do the areas of group A. Pronounced similarities exist between the Desert and Semidesert, and between the Grassland Deciduous-Forest Transition and the Deciduous Forest. Similarities which are less Tempcrature. Normat Dairy Mean, co.rpesr 14 pays or Year VEGETATION 0 69 DESERT a SEMI-DESERT EA i 8 «=|. Saal GRASSLAND 3 Fie SE SSRs * FR ae GRASSLAND-DECIDUOUS-FORESTTRANSITION ns = | DECIDUOUS FOREST | NORTHWESTERN HYGROPHYTIC EVERGREEN Forest oo [[_____ SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST (ee "NORTHERN MESOPHYTIC EVERGREEN Forest (West) [__ CT NORTHERN MESOPHYTIC EVERGREEN Forest (East) (__ ey si‘ “‘O;OOO!|}§9NWUUFU€F€F€©€©€©F©F©FTFTUY VEGETATION 009 _y99 DESERT ES SEMI-DESERT ——— =z tti“‘“‘“‘; OS GRASSLAND fone oe ed GRASSLAND-DECIDUOUS-FORESTTRANSITION DECIDUOUS FOREST (OAO0”0VW9._—_ OE NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST a SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST {QeoNoNjETfnNnN--_-?PXnNnN”™’”’"N"vNuvw’w"-".7—T arr NORTHERN MESOPHYTIC EVERGREEN FOREST (Wes?) (oa |) NORTHERN MESOPHYTIC EVERGREEN Forest (East) (ee TATOO 494 CORRELATION OF DISTRIBUTIONAL FEATURES. marked but more surprising exist between the Semidesert and the western section of the Northern Mesophytic Evergreen Forest, and between the Grassland and the eastern section of the Northern Meso- phytic Evergreen Forest. These incongruities probably find their explanation in the differences in the seasonal distribution of rainfall and in the compensating influences of other conditions. The western section of the Northern Mesophytic Evergreen Forest (which is much drier than the eastern section) does not include markedly higher values than does the Desert, a fact which must be considered in con- nection with the temperature and evaporation differences between these two vegetations. Mean total annual precipitation (plate 52, fig. 24).—The graph repre- senting these data is given a conventionalized appearance from the fact that we have used the map prepared by Gannett and have not drawn the extremes from the readings of individual stations, as in the case of most of the other climatic conditions. This graph bears a generic resemblance to the one showing the normal daily mean pre- cipitation for the frostless season. Owing to the smoothed nature of the data on which it is based, it shows an even more pronounced gra- dation between the several vegetational areas. No new features are brought out in this figure, as compared with the one just discussed, and indeed some of the indications of the latter are partially con- tradicted by this one. Owing to the fact that the data from plate 52 are not the readings of individual stations, it is impossible to tell in how far the differences between this figure and the preceding are due to this circumstance and in how far they are due to the fact that the PRECIPITATION. Mean TorTat, Year VEGETATION DESERT Semi-DESERT GRASSLAND GRASSLAND-DECIDUOUS-FORESTTRANSITION DECIDUOUS FOREST NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST NORTHERN MESOPHYTIC EVERGREEN FOREST (WEST) NORTHERN MESOPHYTIC EVERGREEN FOREST ‘EAST? VEGETATION DESERT ; SemI-DESERT GRASSLAND GRASSLAND—DECIDUOUS-FOREST TRANSITION DECIDUOUS FOREST NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST NORTHERN MESOPHYTIC EVERGREEN FOREST (WEST) NORTHERN MESOPHYTIC EVERGREEN FOREST (EAST) CORRELATION OF DISTRIBUTIONAL FEATURES. 495 former is based on the precipitation data of the frostless season and the latter on those of the entire year. Evaporation (plate 53, fig. 24)—The daily mean evaporation for the frostless season reaches its highest values in the Desert region, although some of the stations situated in this vegetation have readings so low as to give the Desert an amplitude of evaporation conditions which is half that for the entire country. The Semidesert and Grass- land have limits and amplitudes which are closely similar. The Grassland Deciduous-Forest Transition exhibits a minimum which is the same as that of the Grassland, but it has a much smaller amplitude of evaporation conditions, nowhere reaching values as high as the lowest ones for the Desert. The Deciduous Forest has a much greater amplitude than the transition region between it and the Grassland, and its highest values are as great as the minimum values for the Desert, corresponding to the southward prolongation of the Deciduous Forest into Texas. The lowest evaporation values are found in the North- western Hygrophytic Evergreen Forest, and relatively low minimum values are found in the Southwestern Mesophytic Evergreen Forest and in the eastern section of the Northern Mesophytic Evergreen Forest. The maximum values of the three areas just mentioned are remarkably similar. The limits and amplitude of evaporation condi- tions for the western section of the Northern Mesophytic Forest are higher than for any of the other evergreen forest areas, and closely similar to the Semidesert and Grassland values. Moisture ratio (plate 59, fig. 25.)—The data here considered are those derived from the precipitation index for the frostless season and the 30 Moisture Ratio. Norma 77/E, F. S. VEGETATION OESERT Semi-DESERT GRASSLAND GRASSLAND-DECIDUOUS-FORESTTRANSITION DECIDUOUS FOREST NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST NORTHERN MESOPHYTIC EVERGREEN FOREST (WEST) NORTHERN MESOPHYTIC EVERGREEN FOREST (EAST) Qs a Ee cana AS) RRR a Humioiry. NoRmaAL Mean, F. Ss. VEGETATION 22.6 DESERT ME. | | SEMI-DESERT |S GRASSLAND OE EE ————————— GRASSLAND~DECIOUOUS-FORESTTRANSITION Min ti: UTR se| iT | DECIOUOUS FOREST VATE MS NORTHWESTERN HYGROPHYTIC EVERGREEN Forest 3 ((_____ OT SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST _ ET TAS en “NORTHERN MESOPHYTIC EVERGREEN Forest (West) [____———————~SC* NORTHERN MESOPHYTIC EVERGREEN Forest (fast) 9 (EEE 496 CORRELATION OF DISTRIBUTIONAL FEATURES. days preceding its commencement, and from the evaporation data for the frostless season. The differentiation of the values of this ratio for the vegetational areas is restricted by reason of the extremely high ratios for the Northwestern Hygrophytic Evergreen Forest. The col- lective amplitudes of the other vegetations cover less than half the total range for the United States. The narrow amplitudes of this climatic feature for all the vegetations except the Hygrophytic Forest are an indication of the importance of the moisture ratio as an expression of the conditions which are critical in determining the distribution of the vegetation of the United States as we have charted it. The five vegetations in group A exhibit progressively higher limits for their values of the moisture ratio. The evergreen forest areas of group B are very dissimilar. The western and eastern sections of the Northern Mesophytic Evergreen Forest stand well apart, the former overlapping with the Northwestern Hygrophytic Evergreen Forest, just as these vegetations merge into one another in their actual occur- rence. The Southeastern Mesophytic Evergreen Forest possesses a greater amplitude than the eastern section of the Northern Mesophytic Evergreen Forest, but embraces almost the whole scale of values found in the latter vegetation. The amplitude of the western section of the Northern Evergreen Mesophytic Forest is covered by that of the Semidesert, again emphasizing the relative aridity of this forest region. The amplitude of the eastern section of the Northern Meso- phytic Evergreen Forest is also covered by that of the Deciduous Forest, which is accordant with the overlapping and intermixture of these two forests. Normal mean relative humidity (plate 65, fig. 25).—The relative humidity values for the Desert are so low that they have the effect of restricting the differentiation of the values for the remainder of the country, just as the Hygrophytic Forest does with respect to the moisture ratios. The lowest humidity is to be expected in the Desert, but the highest readings would be looked for in the Northwestern Hygrophytic Evergreen Forest rather than in the western section of the Northern Mesophytic Forest, as is the actual case for our data. This is doubtless due to the unfortunate circumstance that there are no humidity records available for localities in the most humid portions of the coast or mountains of Washington and Oregon. The maximum value is recorded for Eureka, California, which is situated in the red- wood type of mesophytic forest. The Semidesert greatly exceeds the Desert in the range of its humidities, as would be expected in the con- trasting of arid coastal regions with an arid interior region. The blocks showing the range and amplitude of humidity for the Grassland, Grass- land Deciduous-Forest, and Deciduous Forest overlap in a manner which is quite analogous to the occurrence of these vegetations. The transition region possesses an amplitude of humidities which is nearly CORRELATION OF DISTRIBUTIONAL FEATURES. 497 the same as the overlapping of the Grassland and Deciduous Forest. The total amplitude of humidity conditions in the western section of the Northern Mesophytic Evergreen Forest is half that of the entire United States. The other three evergreen-forest areas have ampli- tudes and limits which are extremely similar, and fall within the range for the western section of the northern forest. The range of humidity conditions which appears to favor the evergreen type of forest also falls within the range for the Deciduous Forest. This indicates that the forest regions of the United States as a whole are to be found under very similar humidity conditions (about 70 to 80 per cent) for the frostless season, and that the diversified types of forest comprised in the western section of the Northern Mesophytic Ever- green Forest extend into regions of both lower and higher humidity, overlapping slightly with the highest values of the Desert Region. Normal daily duration of sunshine (plate 69, fig. 26).—The sunshine conditions of the frostless season are imperfectly known for the Desert region, where they might be expected to possess their highest values. Much lower minimum values are found in the Desert than in the Semidesert, and in the latter region are the highest known values. The sunshine conditions are very similar throughout the Grassland, Grassland-Deciduous Forest, and Deciduous Forest regions, reaching the lowest value for the United States in the first-named of these regions. The sunshine conditions are very dissimilar in the four ever- green forest areas, reaching a wide amplitude in the Southeastern Mesophytic and western section of the Northern Mesophytic Ever- green Forests. SunsuHine. Normar Dairy Duration, F. S. VEGETATION 1127 2 2995 DESERT + SEMi-DESERT Te PA GRASSLAND ERs =~ — GRASSLAND-DECIDUOUS-FORESTTRANSITION eT = DecipuoUS FOREST (__ EEEEEa- — — NORTBWESTERNIHVGROPHY Tic EVERGREEN) FORES? (22 0 a BP ee eee} SOUTHEASTERN MESOPHYTIC EVERGREEN FOREST | NORTHERN MESOPHYTIC EVERGREEN FOREST (WES)) (ii i i TE TTTTTCSC~:SY NORTHERN MESOPHYTIC EVERGREEN FOREST (EAST) (__ MS COCSSCSCCTTCCTCCCC.T.C.VCCCCCCCSY VEGETATION 197 24265 DESERT | Ci“ CCC SEMI.DESERT OM . | GRASSLAND Oo ee ee GRASSLAND-DECIDUOUS-FORESTTRANSITION See — se DECIDUOUS FOREST Eas — NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST (8 (204s T SEO eS Ee SOUTHEASTERN 'MESOPHYTIC EVERGREEN FOREST (ee ee NORTHERN MESOPHYTIC EVERGREEN FOREST (WEST: CM GSl ee Pe Re NORTHERN MESOPHYTIC EVERGREEN FORest (East) (__ NT TTT TCTTTTCTTTTCTCTCTTTTC™C~—C_ CY Fia. 26. 498 CORRELATION OF DISTRIBUTIONAL FEATURES. Normal moisture-temperature index for the growing-season (plate 72, fig. 26).—This composite climatic feature is remarkable in the fact that it possesses a steep gradient of change on passing from the central to ‘the southeastern part of the United States, and possesses a relative uniformity over the western third of the country. The highest values are consequently to be found in the Southeastern Mesophytic Ever- green Forest and the second highest in the Deciduous Forest, both of which areas show wide amplitudes of this condition. The lowest value is found in the Desert, which is closely approached by the Grassland and the western section of the Northern Mesophytic Evergreen Forest. The last-named vegetation, by reason of its western position, possesses a very narrow amplitude of the conditions expressed by this index. The distribution of the various values of the moisture-temperature index is such as to give closely similar limits and amplitudes to such dissimilar vegetations as Desert, Grassland, Northwestern Hygro- phytic Evergreen Forest, and the eastern section of the Northern Mesophytic Evergreen Forest, with the Deciduous Forest overlapping into this range of conditions. III. CONDITIONS THAT PROBABLY DETERMINE THE GENERAL VEGETATIONAL AREAS. 1. OBSERVATIONS FROM THE CHARTS. The foregoing review of the comparative ranges and intensities of 12 of the leading climatic conditions for the 9 vegetational areas of the United States has served to throw some light on the question as to which of these conditions are most important in controlling the limits of the vegetations. The wide amplitude of all of the temperature conditions has indicated that in the case of many of the vegetations, and particularly those with a wide north-and-south extent, there may be found parallel series of temperature conditions in two cr more vegetations. The moisture-temperature index also fails to exhibit differences between the several vegetational areas such as to give it importance as representing a controlling factor. The precipitation and evaporation data fall much more nearly into groups of intensities | and amplitudes which show dissimilarity throughout the series of vegetational areas. The moisture ratio and the relative humidity also show striking differences between the various vegetations. Figures 27 to 35 give, in diagrammatic form, the limits and ampli- tudes of 17 selected climatic factors for each of the 9 generalized vege- tational areas. These diagrams make it possible to view the correla- tion of climate and vegetation from a different angle to that employed in the immediately preceding pages. Here it is possible to see a diagrammatic picture of the climate of each of the vegetations, to note whether each of the conditions ranges through a series of values which CORRELATION OF DISTRIBUTIONAL FEATURES. 499 are high or low as contrasted with conditions in other parts of the United States, and to observe whether the amplitude of each condition is wide or narrow. The last has already been mentioned as a valuable means of discovering the climatic conditions which are most critica] in controlling the distribution of a given vegetation or plant. It will be fruitful to discuss these diagrams in connection with a comparison between the vegetational boundaries and the isoclimatic lines of the corresponding plates. In this manner it will be possible to test out the indications given by narrow amplitudes of the condi- tions (short blocks in the diagrams), and not only to discover which of the various conditions appear to be the most potent in controlling distribution, but also to find the particular intensity of the condition which seems to be critical in each case. Desert (fig. 27).—Wide amplitudes are exhibited by the Desert with respect to all of the temperature conditions, the number of days in the longest normal dry period of the frostless season, and also the daily mean evaporation for the frostless season. Narrow amplitudes are exhibited by the number of days in the longest normal rainy period of the frostless season and by the moisture ratios and sunshine dura- tion (plate 69). An examination of the 6 plates showing the isoclimatic lines for the temperature conditions used on this diagram (plates 34, 35, 36, 40, 43, 45) will discover that numerous lines cross the Desert region in a northwest-southeast direction, indicating, as we have already been prepared to find, from the wide amplitudes in figures 21 and 22, that the Desert possesses a wide range of temperature conditions, which may also be found to the eastward in three or four other vegetations. TEMPERATURE Days in Norma Frostiess Season (F. S.) Pa ee es | Hort Days, F. S. CO eee Cd Couto Days, F. S. REA ees CS PHYSIOLOGICAL SUMMATION, F. S. ON SS, Normat Daicy Mean, co.oest 14 oars of Year |___— ”t*~“‘“‘(“#(“‘CSC?CXO.WO”t#C(##;#;#C“COMD OOOO ey = 6=6=6=—0COCOCOC*~*~“‘“‘C‘CCSC#S: Normat Daicy Mean, Year ed PRECIPITATION Normat Darcy Mean, F. S. PS NP eS | DAVSIINILONGEST NORMAL RAINY PERIOD, Fu So (MEO r ska a e enn Ia ta ttt. lk ele AnD a SEpDn Tee Prey Days IN LoncesTt Normat Dry Penton, F. S. Mean Torta, Year EVAPORATION Daicy Mean, 1887-8, F. S. (aa Moisture Ratios Normat P/E, F. S. | sR TS Ee ae ee SS ee RE geo ee ee a Normat 7/E, F. S. |___— aT S ee CC , R RS PT ae Normat P/E, Year | __ R STee CRS Se NT ORES RED EET ITT Humioity Normat Mean, & S. DE. SUNSHINE Normat Daicy Duration, F. S. TRESS SESSACETS SSeS 8 8=€=©=— (SERRE LUCERNE eee MoisTurRe-TEMPERATURE INDICES Normat P/E x T, F.S., PHysiotocical Mctxoo a Fria. 27. Climatic extremes for the Desert. 500 CORRELATION OF DISTRIBUTIONAL FEATURES. We may not, therefore, look for any of the factors controlling the dis- tribution of the Desert region in these features of the temperature. The amplitude of the number of days in the longest normal dry period of the frostless season is also great for the Desert (from 127 to 283). This is a case, however, in which even the minimum value for the Desert indicates dry conditions, and the maximum value signifies conditions of extreme aridity. The lower values of this condition may be of importance elsewhere in differentiating vegetation, and the various values within the Desert area may be of importance in connec- tion with the minor vegetational differences of that diversified region. The position of the isoclimatic lines of plate 51 does not indicate that. ' any particular intensity of this condition is critical in limiting the Desert region, which is in accord with the evidence of figure 27. The case of the daily mean evaporation is a very similar one. The number of days in the longest normal rainy period in the frost- less season ranges, in the Desert region, from its minimum value of no days at several stations to a maximum of 10 days. The isoclimatic line of 25 days embraces the entire Desert region and portions of the Semidesert, the Grassland, and the western section of the Northern Mesophytic Evergreen Forest. This factor appears to be an impor- tant one and it is possible that numerous and adequately distributed stations would show that the isoclimatic line of 10 days lies near the boundary of the Desert area. The three derivations of the moisture ratio (plates 58, 59, 60) are very similar here, as they are in all of the vegetations and other botani- cal areas. The narrow amplitude of this condition for the Desert area suggests an importance which is borne out by an examination of the isoclimatic lines. The line representing values of 0.20 for the moisture ratio is roughly similar to the outline of the Desert, and suggests that the isoclimatic line of the ratio 0.25 might be a still closer approxima- tion to the limits of the Desert. The area with values below 0.25 would then include more of western Texas, would separate the Mogollon Plateau of Arizona from the Rocky Mountains, and would extend somewhat further north, thereby coming into still closer agreement with the outlines of the map of generalized vegetation. The bend of the isoclimatic line for 0.20 which extends through the Tehachapi Pass into the San Joaquin Valley of California is in accord with the pro- nouncedly desert character of this valley, which has been included in the composite Semidesert Area. All the evidence which we have been able to bring out in this case points to the moisture ratio as being the climatic condition of most importance in determining the boundaries of the Desert region. Semidesert (fig. 28).—The Semidesert embraces two areas—one in California and one in Texas. These areas are not only diversified within themselves, but are somewhat dissimilar in their vegetation and CORRELATION OF DISTRIBUTIONAL FEATURES. 501 still more unlike in the general character of their climates, particularly with respect to the seasonal distribution of precipitation and other moisture conditions. Ina more detailed study of climatic correlations these two areas would repay separate investigation. The evidence of the amplitudes and also of the position of the iso- climatic lines indicates that temperature conditions are of more impor- tance in limiting the Semidesert than is the case with the Desert. The normal daily mean of the coldest 14 days of the year appears particularly to be of importance, ranging only from values slightly below 45° to 54° for different sections of the region. The amplitudes of the moisture ratios are greater than in the case of the Desert, and the position of the isoclimatic lines corroborates this indication that the conditions expressed by the ratios are not so important in the limitation of the Semidesert. In passing from the coastal to the interior portion of the Texas section of the Semidesert there is a rapid fall in the values of the moisture ratio (plate 59) from 0.81 (Brownsville) to 0.35 (Fort Ringgold). A similar diversity in the California section of the area is indicated by the value 0.10 for Fresno, as compared with the value 0.45 for Los Angeles. The value for Fresno is well above the minimum value for the Desert and the maxi- mum values in each section of the area are well above the maximum (0.27) for the Desert. Grassland (fig. 29).—The longest axis of the Grassland region runs in a north-and-south direction nearly across the United States, with the result that all of the leading temperature conditions exhibit wide amplitudes within its boundaries. The number of cold days in the frostless season runs through the entire gamut for the United States, TEMPERATURE Days in Noamat Frostcess Season (F. S.) es Hor Days, F. S. eee Coto. Days, F. S. BIE eg TT ce nS OE PHYSIOLOGICAL SUMMATION, F. S. a Normat Daity Mean, co.vest 14 oays or Yean [___ ee Normat Daicy Mean, Year PRECIPITATION ; Normat Daicy Mean, F. S. CE — Days IN LONGEST Normal Rainy Peron, F.S. rey DAYS IN LONGEST Normal Drv Perioo, F.S. 9 (RR Mean Torat, Year Sw TE a Ree EVAPORATION Daity Mean, 1887-8, F. S. | Moisture Ratios Normat P/E, F. S. 0) Se ee ee ee ae Normat 7/E, F. S. ee SS Ee ee ee E Normat P/E, Year PL __Ea e e E RSED Humipity Normat Mean, F. S. (Eee SUNSHINE Normat Dairy Duration, F. S. aS ee SS A NE MoisTure-TeMmPerature indices Normat P/E’x T, F.S., PHysiovocican MeTHoo (_ Exe CS Fig. 28. Climatic extremes for Semidesert. 502 CORRELATION OF DISTRIBUTIONAL FEATURES. and the other five conditions shown in figure 29 run through about half the gamut for the country. Although the mean total precipita- tion is both low in amount and narrow in its amplitude for this region, the normal daily mean precipitation ranges through a greater ampli- tude of values and reaches maximum values which are slightly more than half as great as the maximum values for the Northwestern Hygro- phitic Evergreen Forest. This difference points to the importance of the seasonal distribution of rainfall in the Grassland region and to the heavier precipitation of the frostless season. The evaporation index for the frostless season ranges from a daily mean of 0.117 inch, at Moorhead, Minnesota, to 0.275 inch, at Cheyenne, Wyoming, which is nearly half the amplitude for the United States. Numerous isoclimatic | lines cross the central portion of the Grassland, as this would indicate. A comparison of the position of the Grassland (plate 2) with the location of the isoclimatic lines showing the values of the moisture ratio 7/E for the frostless season (plate 59) indicates a correspondence as close as that exhibited for the Desert. The isoclimatic line for the value 0.40 lies slightly to the east of the western edge of the Grassland in Montana, South Dakota, and Nebraska, although very close to it in Texas. The line for the value 0.30 would lie much nearer this boundary along the northwestern edge of the area. The eastern edge follows closely the line for the value 0.60 in Texas and Oklahoma, but crosses rapidly in Kansas and Nebraska to the lines for higher values, and reaches its maximum of 0.117 in western Minnesota. A corre- spondence almost as close is shown between the Grassland and the area, comprising normal mean relative humidities between values of 50 per cent and 65 per cent for the frostless season (plate 65). Along TEMPERATURE Days in Normat Frostiese Season (F.S) as Hort Days, F. S. Cae = =— CdS Cop Davs, F. S. EEE Ne a Oe CRS SO a ea eRe Prysiovocicat Summation, F. S. Ci‘ C™éOSCSCSCCCCOOCOCOC;~;~*;*é*é‘“(‘SNCSCSC#CO#S Normat Daicy Mean, coLogst 14 pays of YeaR ees Normat Daity MEAN, YEAR PRECIPITATION Norma Daicy Mean, F. S. EEE CCCi‘“COSOCSCSC.CC*C‘é Normac Daicy Mean, Year [AN ECR ES | PRECIPITATION Nommat Daicy Mean, F. S. Eee Ss Days im LONGEST Normat Rainy Pisco, F.S. i _ — ) Days in Loncest Normat Dav Penton, F.S. (__— (ees LLL) Man Totat, Year EEE EvaPronation Daiy Mean, 1867-8, F. S. ——————=Z*~—i~aeEeE==|_ Moisture Ratic® Norma P/E, F. S. (SE SE A EE OSS SEL DEE ee ee ET Nonmat 77/E, F. S. eS LT ee Nonmat P/E, Year Se ae ES ee se Humivity Normat Mean, F. S. | ieee Eee! ee SunsHinge Normat Dairy Duration, F. S. EE : Se Te eee Rees Come ea eee MotsTuRE-TEMPERATURE INDICES Norma P/E x T,F. S., Puvsiococicat Mevnco (_ i Fic. 32. Climatic extremes for Hygrophytic Forest. CORRELATION OF DISTRIBUTIONAL FEATURES. 507 to about 45°. Inasmuch as the coldest portion of the year is coincident with the moist portion, this circumstance is of great importance, as indicating that the highest temperatures of the coldest days of the year are still well above frost, while the winter days outside the coldest period present conditions which are favorable for photosynthesis and growth. The normal daily mean temperature of the year ranges from below 50° for the coldest stations to above 55° for the warmest. The whole series of moisture conditions, including evaporation and the moisture ratios, is remarkable in this region for the extremely wide amplitudes exhibited. The highest values for all of these conditions are secured from Cape Disappointment, and the lowest values from Roseburg, Oregon, a town located in the valley of the Umpqua River, in the driest conditions that are to be found in the region. The normal daily mean precipitation exhibits an amplitude which is about five- sixths of that for the entire United States. The values and amplitude of the number of days in the longest normal rainy period of the frostless Season are here very similar to these conditions for the Grassland, while the greatest number of days in the longest normal dry period of the frostless season (198) is greatly in excess of the smallest number of days in this period (127) for the Desert region. The mean total pre- cipitation for the year is not only higher for this vegetation than for any other, but it also shows a greater amplitude than elsewhere. The daily mean evaporation for the frostless season ranges from the lowest value in the United States, 0.052 inch at Cape Flattery, Washington, to a value of 0.143 inch at Roseburg. The values and amplitudes of evaporation conditions in the Hygrophytic Forest are closely similar to those in the Southeastern Mesophytic Evergreen Forest and in the eastern section of the Northern Mesophytic Evergreen Forest. The maximum values for the three vegetations are nearly the same, but the very low values for the Hygrophytic Forest are not found in the two latter regions (see fig. 24). There is a slight overlapping of the evapora- tion conditions with those of the western section of the Northern Mesophytic Evergreen Forest, into which the Hygrophytic Forest merges to the east and south, and with those of the Pacific Semi- desert region, the conditions of which are approached in all of the broad valleys of coastal Washington and Oregon which lie in the lee of the mountains. The values for all three forms of the moisture ratio are remarkable, in the Hygrophytic Forest, for their great amplitude. It has already been seen (fig. 25) that the highest values of the ratios for this region far exceed the maximum values recorded for any of the other vegeta- tions of the United States. The relatively low values of the South- eastern Evergreen Forest and of the eastern section of the Northern Evergreen Forest are completely overlapped in the Northwestern Forest, and the moisture conditions of such localities as Astoria and 508 CORRELATION OF DISTRIBUTIONAL FEATURES. Cape Disappointment are far exceeded by the still more moist condi- tions of Cape Flattery. In short, the difference between the values of the moisture ratios in moderately moist localities in the Northwestern Forest and in the most moist localities is as great as the differences which have already been seen to play such an important réle in deter- mining the distribution of the vegetation in the remainder of the United States. | It is unfortunate that the inadequacy of the climatological data gives this region the appearance of being exceeded in the normal mean relative humidity of the frostless season by the western section of the Northern Mesophytic Evergreen Forest, an appearance that is prob- ably misleading. The sunshine conditions are also imperfectly known for this area. The moisture-temperature index for the frostless season has already been shown to be closely similar in values and in amplitude for this most hygrophytic of the vegetations of the United States and for the Desert. In forming the product by which this compound condition has been secured, the high temperature summation of the desert, together with the low moisture indices, and the low temperature sum- mations of the Hygrophytic Forest, together with its high moisture indices, have given results which are closely identical. Southeastern Mesophytic Evergreen Forest (fig. 33).—In viewing the entire series of blocks drawn to represent the chief climatic conditions of this region, it will be noted that there is, in general, a wide ampli- tude of nearly all conditions, including those of temperature and precipitation, and excepting only the imperfectly exhibited mean annual precipitation and the relative humidity. The amplitude of the moisture ratios is no greater than in the case of the Deciduous Forest TEMPERATURE Days in Norma Fu osTLESs Season (F. S.) Hor Bays, F. S. Cop Days, F. S. Prysio_ocicat Summation, F. S, MoRMAL Da:_ty MEAN, COLDEST 14 Days oF YEAR Norma Daicy Mean, Year PRECIPITATION Normac Daicy Mean, F. S. Days IN LONGEST NORMAL Rainy Perioo, F. S. Days IN LONGEST Norma Dry Periop, F. S. MEAN TOTAL, YEAR EVAPORATION Daity Mean, 1887-8, F. S. Moisture Ratios Norma P/E, F.S. Normat 7/E, F. S. Norma P/E, Year Humipity Normacr Mean, F. S. SUNSHINE Norma. Dairy Duration, F. S. MoOISTURE- TEMPERATURE INDICES Normat P/E x T, F. S., Poysiotocicat MetHoo L_OC—C—COCCidC Fic. 33. Climatic extremes for Southeastern Evergreen Forest. CORRELATION OF DISTRIBUTIONAL FEATURES. 509 and but little in excess of the corresponding amplitude for the Grass- land. The wide amplitude of the temperature and precipitation con- ditions, taken in themselves, might be held to indicate that there is not a close correlation between the distribution of this vegetation and that of any of the important controlling physical conditions. Such a view would have in its support the fact that this vegetation is one that is well known to be closely correlated in its distribution with the extent of the Atlantic Coastal Plain and with the series of soils typical of that physiographic province. However, the types of vegetation which seem _to be strictly controlled by topographic features and by soils in the northern part of the Coastal Plain are not so controlled in the southern part and in the lower Mississippi Valley, where the Coastal Plain is not so sharply defined. In spite of the wide amplitude of many other conditions, the moisture ratios are of a significance with respect to this region which must not be omitted from consideration. In the Southeastern Mesophytic Evergreen Forest all of the leading temperature conditions of the country reach their maximum values, except the number of cold days, which, reciprocally, reaches its mini- mum value. Five of the six temperature conditions represented in figure 33 range in this vegetation through more than half of the ampli- tude found in the United States as a whole, due to the far northward extension of the region along the Atlantic coast. All of these condi- tions overlap with those of the Deciduous Forest region, which is quite to be expected in view of the overlapping and admixture of the vege- tations themselves. A transition region between the Deciduous Forest and the Southeastern Evergreen Forest has been outlined in the detailed map of vegetation (plate 1), and there is considerable evidence (some of which will be discussed) that portions of the Southeastern Evergreen area are of such a character climatically as to support a deciduous forest. The amplitude of the normal daily mean precipitation is nearly equal to that of the Deciduous Forest, but the minimum and maxi- mum values are somewhat higher. The number of days in the longest normal rainy period of the frostless season exceeds even the great amplitude exhibited by this condition in the Deciduous Forest, and reaches, at Cape Hatteras, the highest value for the United States. The number of days in the longest normal dry period exceeds the amplitude of this condition for any of the other forest regions, and is even greater than that for the Grassland and the Desert, although the actual range of this condition is from the lowest value for the country, no days at Cape Hatteras, to 182 days at Key West. The amplitude of evaporation conditions for the Southeastern Ever- green Forest is narrow, and the values are relatively low, being almost equal, as already shown, to the evaporation values for the eastern section of the Northern Evergreen Forest. The amplitudes of the 510 CORRELATION OF DISTRIBUTIONAL FEATURES. moisture ratios have also been seen to be closely similar for these two forests, and their minimum values are almost identical (see fig. 25). There is also little difference between the amplitudes and extremes of the humidity conditions for these two forests and for the Northwestern Hygrophytic Forest as well. The narrowest amplitudes for the South- eastern Evergreen Forest are found in the evaporation, relative humidity, and moisture ratios, and these must be regarded, therefore, as the most important of the various conditions in controlling the dis- tribution of this vegetation, in so far as its control is a matter of climate. A comparison of the position of the isoclimatic lines for the values 0.100 and 0.110 of the moisture ratio based on the conditions of the frostless season and the preceding 30 days (plate 59), with the position of the boundary of the Southeastern Mesophytic Evergreen Forest, shows a close correspondence. This is least satisfactory in the vicinity of Arkansas, where the Southeastern Forest extends into a region with lower values for the ratio. This region, however, is the one in which there are the largest areas of mixed forest forming a tran- sition to the Deciduous Forest region (see plate 1). The moisture-temperature index reaches its highest values in this vegetation, and has an amplitude almost exactly equal to that for the Deciduous Forest. The high values of the physiological summation of temperature are responsible for the high values of this index, when the relatively low values of the moisture ratios are taken into account. The very high values which are rapidly attained by this form of the moisture-temperature index on approaching the southeastern corner of the United States may be taken to signify that this region presents the optimum conditions for plant activity in the entire area studied, as far as climate is concerned. : , Northern Mesophytic Evergreen Forest, western section (fig. 34).—The Northern Mesophytic Evergreen Forest, when considered as a whole, is so widely distributed and so varied in its character and specific com- position that it assumes a unity only when contrasted with the other evergreen-forest areas of the country. The only natural subdivision of this region is that which is made possible in the United States by the geographical separation of the eastern and western portions. In the study of the correlation of this vegetation with the climatic condi- tions it has seemed desirable to determine the climatic extremes separately for the eastern and ‘western sections, which are sharply separated by the northern arms of the Grassland and the Grassland Deciduous-Forest Transition. The most striking feature of the diagram which shows the leading climatic features of the western section of the Northern Mesophytic Evergreen Forest (fig. 34) is the relatively narrow amplitude of the majority of the conditions which accompany this widely and irregularly distributed forest area. There is a particularly strong contrast in this CORRELATION OF DISTRIBUTIONAL FEATURES. 511 respect with the conditions for the Southeastern Evergreen Forest and for the Deciduous Forest, indicating that the western section of the Northern Evergreen Forest is confined in its distribution to a region in which there is a relatively narrow range of physical conditions, in spite of its wide geographical extent. Owing to the mountainous and thinly settled character of most of this region, there is an inadequate series of climatological stations from which data may be obtained. This is particularly true of the southernmost portions in New Mexico, Arizona, and California, and of the portions which face the Desert region on all sides of the Great Basin. The climatic conditions of the western Xerophytic Evergreen Forest (see plate 1) are even more poorly known, and this has been a strong consideration in omitting that vegetation from the generalized map. Its conditions would doubtless be found to be generally intermediate between those of the Desert and those of the western section of the Northern Evergreen Forest. The length of average frostless season ranges from the minimum for the United States to 307 days, a remarkably great amplitude, which is matched only for the Desert region. The lowest values of this condition are recorded for several stations in the Klamath Lake region, where frost has been observed on every day in the year. The shortest normal frostless season outside these stations is 25 days in length, and this has been taken as the minimum for the United States in view of the fact that there is actually, in any given year, a growing-season for plants even in localities where frost is of average daily occurrence, and that the length of this season is at least 25 days even for Klamath Lake stations. The maximum length of frostless season for this vege- TEMPERATURE Days in Nonmat Frost.ess Season (F.S) iE Hor Days, F. S. _—_—————~E_tttttSsSSC—C‘“SCSSCSsSCSCSCSCSC‘C‘®’TNSNNNNNNNNNNN __} Coxo Days, F. S. es ll Prysiococicat SUMMATION, F. S. ET Normat Daicy Mean, covoest 14 oavs of Year (___ TT Normat Daicy Mean, Year CC ee, PRECIPITATION Normat Daicy Mean, F. S. Se ee ee Days IN LONGEST Norma Rainy Peron, F.S. ee Days IN LONGEST Normat Dry Penioo, F.S. 9 (lO E—E—— Mean Torat, Year | EVAPORATION Daity Mean, 1887-8, F. S. RS i Moisture Ratios : . ; Normat P/E, F. S. |___SCREEN Normat 1/E, F. S. fo a Ee SD ee eS Normat P/E, Year a ee eee eee eee Humipity Normat Mean, F. S. | SUNSHINE Normat Dairy Duration, F. S. MT“ |) Moisture-TEMPeRATURE INDICES JE 2 CAR SO SCO ye ae a, a a Fia. 34. Climatic extremes for western section of Northern Mesophytie Evergreen Forest. ne CORRELATION OF DISTRIBUTIONAL FEATURES. tation has been recorded at Fort Bragg, California, where the condi- tions and vegetation of the ocean front are more nearly those of the Hygrophytic Forest than of the western section of the Mesophytic Forest. At stations just inland from Fort Bragg the frestless season is about 100 days shorter. The number of hot days ranges from 0 to 105, which is about one-third of the amplitude for the entire country, and the number of cold days ranges from 78 to 149+, closely approach- ing the maximum values, which occur in the Grassland. The physio- logical summation of temperature has a relatively narrow amplitude, from values approaching the minimum to 9,921 at Grand Junction, Colorado, a station which must be regarded as approximating the conditions of the forests in that vicinity. Much higher values of the physiological summation might be expected for stations located in the more southern extensions of the Mesophytic Evergreen Forest, but our data fail to bear out such an expectation. Santa Fe, New Mexico, is located close to bodies of Mesophytic Evergreen Forest, and is so situated as to enjoy higher temperatures than the forest, yet the sum- mation for Santa Fe is only 5,350, a figure considerably below the maximum at Grand Junction. Flagstaff, Arizona, which is situated in the midst of forest, has the very low summation of 2,652. The cold nights of the mountain altitudes at which the Mesophytic Forest of New Mexico and Arizona occurs are responsible for low daily mean temperatures, and consequently for low values of the summations for the frostless season. The normal daily mean for the coldest 14 consecutive days of the year is a condition ranging through a moderate amplitude and reaching extreme values which are neither very high nor very low, overlapping with the conditions in the Hygrophytic Forest. The normal daily mean temperature for the year is of wide amplitude, but also fails to attain the extremes for the country. When the climatic extremes for the precipitation conditions are compared, as a whole, with those for the temperature conditions, the former are seen to be of narrower amplitude, which points to the limitation of the western section of the Mesophytic Evergreen Forest as being due more largely to moisture conditions than to those of temperature. This is confirmed by the narrow amplitude of the moisture ratios, at least of those which relate to the frostless season only. Although the actual extremes of the moisture ratio 7/E for the frostless season are 0.12 and 0.60, it will be seen by an examination of plate 59 that the major portion of the western Mesophytic Forest is comprised between the lines for values of 0.20 and 0.40. The lowest evaporation values and the highest relative humidities for this region are recorded for the extreme coastal stations of northern California, and they are not typical of the great bulk of the forest, although they permit its occurrence in a form approaching the character of the North- western Hygrophytic Forest. CORRELATION OF DISTRIBUTIONAL FEATURES. 513 No vegetational region exhibits a narrower amplitude of the mois- ture-temperature index than does the western section of the Mesophytic Forest. This derived and complex expression of climatic conditions has been shown to differentiate the evergreen-forest regions of the United States, in spite of its failure to bring out consistent differences between the other regions. Its extremely narrow amplitude for the western section of the Mesophytic Evergreen Forest points to its impor- tance as an expression of the conditions controlling this vegetation. Northern Mesophytic Evergreen Forest, eastern section (fig. 35).—A comparison of the climatic extremes of the eastern and western sec- tions of this forest shows a general similarity of temperature condi- tions, and a dissimilarity of moisture conditions and the expressions derived from them. The length of frostless season is much narrower in its amplitude in the eastern section, ranging from a length of 85 days at Thomaston, Michigan, to 167 days at Fitchburg, Massa- chusetts, values which lie well within those of the western section. The normal daily mean temperature for the coldest 14 days of the year ranges through lower values in the eastern section, as does also the normal daily mean temperature for the year. The only precipitation condition in regard to which the eastern and western sections of the Northern Mesophytic Evergreen Forest are at all alike is the normal annual total. The normal daily mean for the frostless season ranges in the eastern section through values which are well above those of the western section, the maximum of the latter being 0.070 inch and the minimum of the former being 0.091 inch. In accordance with this fact the number of days in the longest normal rainy period of the frostless season is greater in the eastern section than in the western, and the number of days in the longest normal dry period is pronouncedly less in the eastern section. TEMPERATURE Dave in Nonmac Faoer.c9ee Season (F.S.) (a Hor Daye, F. 8. a | er ee Coro Dave, F. S. ee lle Puysiovocicat Summation, F. 8. {ee er ee ee ee ee Nonmat Daicy Mean, cococet 14 cave of Year (_ - ay CC CC~CSSC*dO?; Nonmmat Daicy Mean, Year eee PRECIPITATION Norma Datty Maan, F. S. PS ee — eee Days IN LONGEST Normal Rainy Period, F.S. (i Days In LoNaceT Nonmat Day Penioo, F.S. (CZ Mean Torat, Year Le] $$-é-~ 2 Tae Evaroration Daicy Mean, 1687-8, F. S. Ce ee ee eee Moisture Ratios Normat P/E, F. S. [CRASS Ee See Normat 1/€, F. S. [Ee ee ee ee) Nonmat P/E, Year eS eee) Humioity Nonmat Mean, F. S. RSS ee || Ee Sunsnwine Nonmat Daicy Duration, F. S. ee ee eee) MoisTunc-TEMPERATURE INDICES Nonmat P/E x T,F.S., Pxysiotocica, MeTwoo C= Fig. 35. Climatic extremes for eastern section of Northern Mesophytic Evergreen Forest. 514 CORRELATION OF DISTRIBUTIONAL FEATURES. The amplitude of evaporation conditions is much narrower in the eastern section than in the western, agreeing closely, as already stated, with the amplitude and values for the Southeastern Mesophytic Ever- green Forest. The humidity conditions also exhibit a much narrower amplitude, although they nowhere reach in the East the maximum values that are to be found at the Pacific coast stations of the western section. The moisture ratios all exhibit higher values for the eastern section, and the ratio 7 /E for the frostless season fails to overlap with the range of this condition in the western section (see fig. 25). Here again there is a close correspondence between the Evergreen Meso- phytic Forests of the Northeastern and the Southeastern States. The sunshine values are low and of narrow amplitude for the Northeastern Evergreen Forest, the maximum value for this region being lower than the maximum in any of the other vegetational areas. The moisture-temperature index for the eastern section ranges from a minimum value which is slightly above the maximum for the western section to a maximum which nearly coincides with that for the North- western Hygrophytic Evergreen Forest. The close correspondence between the range of this condition in the last-named region and in the eastern section of the mesophytic forest doubtless affords a means of explaining the features of resemblance between these two vegeta- tions, which are so widely separated in the United States but have a narrow strip of connecting forest in Canada. The Climatic Conditions for Evergreen and Deciduous Forests.—In connection with the inquiry into the climatic conditions characterizing the vegetational areas, a comparison has been made of the climatic extremes for the Deciduous Forest and for the four evergreen forest areas considered collectively. In figure 36 are shown graphs for the TEMPERATURE Days in Nornmac Frostcess Season (F. S.) Hort Days, F. S. Corp Days, F. S. PHYSIOLOGICAL SUMMATION, F. S. Norma Daicy MEAN, COLDEST 14 DAYS OF YEAR Norma Daity Mean, YEAR PRECIPITATION Norma Daicy Mean, F. S. Days IN LONGEST Normat Rainy Peaiop, F. S. Days !IN LONGEST Normat Dry Periop, F. S. Mean TOTAL, YEAR EVAPORATION Daity Mean, 1887-8, F. S. Moisture Ratios Norma. P/E, F. S. Normat 7/E, F. S. Norma P/E, Year HUMIDITY Normac Mean, F. S. SUNSHINE Normac Daicy Duration, F. S. _ MoistuRe-TEMPERATURE INDICES Noamat P/E x T, F. S., Pxysiovocica METHOD == < Fic. 36. Contrasted climatic extremes for Evergreen (black) and Deciduous (shaded) Forests. CORRELATION OF DISTRIBUTIONAL FEATURES. 515 principal features of the climate for these two regions, brought together for ready comparison. The widespread occurrence of evergreen forest, extending into the northwestern, northeastern, and southeastern corners of the United States, gives a very wide amplitude of conditions for this type of forest. In 5 cases the amplitudes of conditions are as great for the collective evergreen regions as for the entire United States, and in 6 cases they are nearly as great. These wide amplitudes are found among temperature and moisture conditions alike. The narrowest amplitude is that of relative humidity, which ranges through the upper half of its scale for the entire country. The importance which humidity is here indicated to have for evergreen forest is borne out by the detailed humidity extremes for each of the evergreen areas (see fig. 25). The amplitude of the conditions found in the Deciduous Forest region is narrower in every case than that of the collective evergreen regions, and for none of the conditions does it approach the, entire amplitude for the country. It is also to be noted that the extremes for the Deciduous Forest are, in nearly every case, well within the extremes for the evergreen regions. In the number of cold days in the frostless season the two have the same minimum, and in the number of days in the longest normal dry period of the frostless season the two have nearly the same minimum. The only case in which the two maxima approach each other is that of humidity. If we disregard the diversities in the evergreen forests which have led us to their separate treatment, it is possible to say that this type of forest in general is capable of withstanding a much wider range of climatic conditions than is the deciduous type. 2. DISCUSSION OF THE OBSERVATIONS. We have now reviewed the observed correlations between the general vegetation areas and some of the leading climatic conditions, both from the point of view of the vegetation and from that of the conditions. In the comparison of the amplitudes and extremes of each single condition, as shown for each of the vegetational areas, it has been possible to see to what extent that condition is unlike in the several vegetations. It is obvious that a condition which ranges through nearly the same values in two vegetations can not be looked upon as one that is important in determining the optimum conditions for each of these vegetations, nor as one that plays an important rdéle in controlling the limit between the two. It is evident, for example, that the physiological summation of temperatures can not be held to play a primary part in establishing the optimum conditions for Grass- land, Grassland Deciduous-Forest Transition, and Deciduous Forest (see fig. 22). If, on the other hand, a given condition exhibits a sliding scale of values for several adjacent vegetations, it is evident that such 516 CORRELATION OF DISTRIBUTIONAL FEATURES. a correlation points to this condition as playing an important part in the existence and distributional limits of these vegetations. This should be true even if there is some overlapping of the values of the condition between the adjacent vegetations, for there is always such overlapping of the vegetations themselves. A comparison of the humidity conditions for Grassland, Grassland Deciduous-Forest Transition, and Deciduous Forest, or a comparison of the moisture ratios for these vegetations and for Desert and Semidesert, shows a progressive change of position of the climatic extremes with respect to the extremes for the entire country (see fig. 25). A comparison of the amplitudes and extremes of all conditions for a single vegetational area makes it possible to discover which conditions tend to exhibit great differences in the various parts of the area and which ones tend to show a relative uniformity throughout the area. We have already seen that this method of evaluating the conditions makes it possible to use their relative amplitude as a measure of their comparative importance in establishing the limiting conditions for the vegetation in question. A cartographic representation of the distribution of vegetation and of the distribution of the various intensities of the climatic conditions makes it possible to compare distributional limits and isoclimatie lines, and to search for correspondence between the two. But such a search is best carried out by the aid of suggestions from the graphs showing the climatic extremes. The use of the three methods of correlation has shown them to be consistent in their indications. If a condition shows a sliding scale of values for a given series of vegetations, it is also found to show ampli- tudes, in each of the vegetations, which are narrow as compared with those of other conditions, and the isoclimatic lines showing the dis- tribution of the intensities of this condition are found to approximate the distributional lines between the series of vegetations. The first two methods serve for the discovery of the relative importance of various conditions in determining distribution, and the third method serves to show the critical intensities of the condition which appear to be important. | In a general review of our examination into the correlations between climatic conditions and the general vegetational areas we find the most salient fact to be the great controlling importance of moisture conditions, embracing precipitation, evaporation, relative humidity, and the moisture ratio, as compared with the small controlling impor- tance of temperature conditions, embracing length of frostless season, number of hot and of cold days, and the temperature summations. The moisture-temperature index partakes strongly of the character of a temperature condition when it is brought into this comparison. In the vegetations of group A (including our series from Desert to Deciduous Forest; see figs. 21 to 26) the temperature conditions show CORRELATION OF DISTRIBUTIONAL FEATURES. 517 particularly wide amplitudes and a pronounced tendency to range through about the same values, except in the case of the length of frostless season and the normal daily mean of the coldest 14 days of the year, in both of which conditions the Semidesert departs from the conditions of the other vegetations of the group. A comparison of the extremes of the temperature conditions for the vegetations of group B (the evergreen forests) shows a much greater dissimilarity, indicating that temperature conditions play a more important role in differen- tiating our evergreen-forest areas than they do in differentiating the other vegetations of the country. This applies to the moisture-tem- perature index, as well as to the purely temperature conditions. It is in the vegetations of group A that the moisture conditions show their greatest differentiation and appear to exert their strongest con- trol. This is shown with diagrammatical clearness by the smoothed data for the mean total precipitation of the year (fig. 24), and it is also shown by the moisture ratio and by relative humidity (fig. 25). There is a much less marked differentiation of moisture conditions among the evergreen-forest areas, as will be seen in the close agreement of the extremes of daily mean evaporation for the Southeastern Mesophytic Evergreen Forest and for the eastern section of the Northern Meso- phytic Evergreen Forest (fig. 24), and also in the similarity of humidity conditions for the above forests and for the Northwestern Hygrophytic Evergreen Forest (fig. 25). The preceding pages have brought out the fact that the moisture ratio 7/E is the most important single expression of climatic conditions with respect to the vegetation as a whole. The nar- row amplitude of this condition in all of the vegetations except the Northwestern Hygrophytic Evergreen Forest, and the distinctness of its extremes for all of the vegetations give an indication of its impor- tance which is well borne out by a comparison of the climatic and vegetational lines of plate 2 and plate 59. The isoclimatic line for the ratio value 0.110 closely follows the limit of the Southeastern Meso- phytic Evergreen Forest from Alabama to New Jersey, and then swings westward in such a manner as to approximate closely the southern limit of the eastern section of the Northern Mesophytiec Evergreen Forest, failing to dip with the vegetation along the Alle- ghenies (where there are no data for this climatic map), but closely following the vegetational line to Minnesota. The similarity of the conditions expressed by the moisture ratio for the evergreen forests of the Southeastern and Northeastern States is indicated in figure 25, but no indication is there given of the closeness with which the inner limits of these vegetations follow a single isoclimatic line. The line for the value 0.80 is an equally close approximation of the inner limit of the Northwestern Hygrophytic Evergreen Forest. The line separating the Grassland and the Grassland Deciduous-Forest Transition is closely followed by the isoclimatic line of 0.60 in the South and by that 518 CORRELATION OF DISTRIBUTIONAL FEATURES. of 0.80 in the North. The area lying inside the line for values of 0.20 is entirely occupied by Desert, which exceeds the line only to short distances in Texas and Washington The importance of the moisture ratio in controlling the case vegetations was shown by Transeau for the eastern United States,! and our investigation has served to confirm his deductions, as well as to extend their application to the entire country. The comparisons which we have made between the vegetational areas and the various other climatic conditions have served to emphasize the importance of the moisture ratio even more than was done by Transeau, since no other single datum has been found in our work to approach it as an expression of the controlling conditions for forest, grassland, and desert. The importance of the moisture ratio is due partly to the fact that it is a combined expression of several other conditions, and still more to the fact that these conditions are ones which have a combined effect upon the physiological processes of the plant. The moisture ratio is, in brief, an expression of the relation existing between the water available for plants and the amount of water lost as a result of atmospheric conditions. The moisture ratio gives us a single numerical expression for the group of conditions which control a single important physiological condition of the plant, namely, its maintenance of a balance between intake and outgo of water. When we secure the product of the moisture ratio and the temperature summation we have a still more comprehensive expression of conditions, the moisture- temperature index. In this index, however, we have no such succinct expression of a set of conditions that are closely coordinated in their relation to the physiology of the plant, in spite of the individual impor- tance of each factor in the product. The moisture-temperature index is correspondingly of less value in interpreting distributional etiology than is the moisture ratio itself. A much more ideal derivation of the moisture ratio is one employing the soil-moisture rather than the precipitation, since it is the former rather than the latter condition that is of immediate relation to the activities of the plant. Shreve has used the ratio of soil-moisture to evaporation in a discussion of the annual march of moisture conditions at Tucson, Arizona,” and also in describing the gradient of conditions from the base to the summit of the Santa Catalina Mountains, in southern Arizona, a range surrounded by desert and capped by heavy forest. For detailed work, and particularly in arid regions or regions with pronounced periodicity of rainfall, the ratio of soil-moisture to evaporation will be found to express the prevailing conditions for 1Transeau, E. N., Forest centres of eastern North America. Am. Nat., 39: 875-889, 1905. *Shreve, Forrest, Rainfall as a determinant of soil moisture, The Plant World, 1'7: 9-26, 1914.— Idem, 1915. CORRELATION OF DISTRIBUTIONAL FEATURES. 519 plants more precisely than the ratio of precipitation to evaporation. In dealing with large areas, however, the soil-moisture is so closely a function of the precipitation that the two expressions frequently approach identity, or at least proportionality. Of course, it is under- stood that in all cases where the soil-moisture content (percentage of soil- moisture on a volume or weight basis) is employed as the index of the soil-moisture condition, great differences in the water-retaining power of the soil in different areas must upset this clear relation. If the soils compared are all clay or all sands, etc., the soil-moisture content itself is probably a relatively good index of the water-supplying power of the soil, but this is not true when sands are to be compared with clays, for a 10-per cent water-content in a sand may be physiologically equivalent to a 50-per cent content in a clay, other conditions being considered as alike. IV. CONDITIONS THAT PROBABLY DETERMINE THE LIFE-ZONES OF MERRIAM. 1. OBSERVATIONS FROM THE CHARTS. In a discussion of the climatic extremes of the life-zones of the United States, as outlined by Merriam, it is necessary for us to dis- regard the Boreal and Tropical Regions, and also the Gulf Strip of the Lower Austral Zone, on account of the very small number of climato- logical stations comprised in those areas. As originally drawn by Merriam, the life-zone map of the United States was in actuality a climatological map, based on a summation of temperatures and slightly modified, particularly on the Pacific coast, by data on the temperature of the hottest 6 weeks of the summer. It is not necessary, therefore, to make correlations of the range of the life-zones with the distribution of the different intensities of the remainder summation of temperatures above 32° for the year (plate 37, which is Merriam’s chart), nor with the normal daily mean of the hottest 6 weeks of the year (plate 44, which is also Merriam’s). In figures 37 to 42 are shown the graphs for the leading climatic dimensions given in tables 33 to 38 for the Transition, Alleghanian, Upper Sonoran, Carolinian, Lower Sonoran, and Austroriparian zones. These 6 subdivisions comprise the western or arid and the eastern or humid subdivisions of the transcontinental zones based on temperature conditions. They represent, in other words, an exact but special sub- division of the country on a basis of certain temperature conditions, together with a rough subdivision on the basis of moisture conditions. The line separating the arid and humid divisions of these zones is drawn by Merriam along the one-hundredth meridian from Oklahoma to South Dakota, departing a little to the eastward at the north and south. This line corresponds rather closely with the isoclimatic line of a value of 0.60 for the moisture ratiow/E. It does not take account, 520 CORRELATION OF DISTRIBUTIONAL FEATURES. however, of the fact that humid conditions exist in the extreme North- west, as shown by the return of the isoclimatic line of 0.60 for the moisture ratio, running from the Upper Columbia River to San Francisco Bay (see plate 59). Transition Zone (fig. 37).—The dimensions of nearly all of the leading climatic conditions exhibit a very wide amplitude in this zone, which embraces the northern Great Plains, portions of the humid Pacific Northwest, and mountain areas throughout the Western States. The length of frostless season and the number of cold days in the frostless season both range through nearly their entire amplitude for the United States. The normal daily mean precipitation and the mean total precipitation of the year likewise range through very wide amplitudes. The amplitude in the number of hot days is not great, and the extremes for this condition are low, ranging from 0 to 105. The physiological temperature summation exhibits a narrow range, as might be expected from the similarity of its derivation to that of the remainder summa- tion above 32°, the use of which in outlining these zones has been mentioned. Evaporation and humidity both show a much wider amplitude in this zone than in any of the vegetational areas that have been discussed, exceeding greatly the amplitude for the western section of the Northern Mesophytic Evergreen Forest, with which this zone has some distributional features in common. The moisture ratios all show wide amplitude for the Transition Zone, P/E and 7/E ranging through about half the total amplitude and P/E for the year through a still greater amplitude of conditions. The Northwestern Hygrophytic Evergreen Forest is the only one of our vegetational areas that exceeds the Transition Zone in the amplitude of the second of these ratios. The entire gamut of sunshine conditions for the United States is to be Temperature Days in Normal Frostiess Season (F. S) a Ee RE TS Hor Days, F.S. / ——————=—E__-t Cop Days, F.S. - ae ere Oe ee ea Se eee Prysiovocicat SuMMaTion, F. S. ae ee See ReReer Norma. Daicy Mean, co.vest 14 cars of Yaar |_- a _ __ __es Norma. Dairy Mean, Year PRECIPITATION Norma Dairy Mean, F. S. Ee) Days IN LONGEST Normat Rainy Periop, F. S.- Days IN LONGEST Normat Day Periop, F.S. 00 (_____ Ea Mean Torat, Year eee oe ee i ee EVAPORATION Dany Mean, 1887-8, F.S. ee Moisture Ratios Norma P/E, F. S. es SSSSC‘“SCSCSC“C“‘(‘“‘C™~*SYS Norma. 7/E, F.S. | Norma P/E, Year aS ee I Humuioity Normac Mean, F. S. aa Pee SUNSHINE Norma Daity Duration, F. S. MoISTURE= TEMPERATURE INDICES Norwa, P/E x T, F. S., Puysiovocitat Metxoo (- EE eee Fic. 37. Climatic extremes for the Transition Zone. CORRELATION OF DISTRIBUTIONAL FEATURES. 5Ft encountered in the Transition Zone. The moisture-temperature index possesses almost as narrow an amplitude as that characteristic of the western section of the Northern Forest region. Alleghanian Zone (fig. 38)—The temperature conditions of this zone, excepting the length of the frostless season, are very similar to those of the Transition Zone, while the precipitation and other moisture conditions are quite unlike. The frostless season ranges from a length of 106 days to one of 211 days, extremes which lie well within those of the Transition Zone. The amplitude and extremes in the number of hot days and the number of cold days are very similar, while the normal daily mean of the coldest 14 days of the year is somewhat higher in its extremes, although very similar in its amplitude. In all of the precipitation and other moisture data the Alleghanian Zone exhibits much narrower amplitudes than those of the Transition Zone, because of the high values characteristic of the portions of the latter zone which lie in the extreme Northwest. In nearly all cases extremes for the Alleghanian Zone lie within those of the Transition Zone, the exceptions being the number of days in the longest normal rainy and dry periods in the frostless season. Owing to the winter occurrence of rainfall in the Northwest, these features indicate more moist conditions for the Alleghanian than for the Transition Zone. The amplitude of sunshine duration for the Alleghanian Zone is much less than that for the Transition, ranging from low values upward through about one-third of the entire amplitude for the country. The moisture-temperature index has a much wider amplitude in the former than in the latter zone, slightly exceeding the amplitude for the eastern section of the Northern Mesophytic Evergreen Forest. TEMPERATURE Days in Norma. Frostiess Season (FS. ((__ Hor Days, F. S. —————=*£{Z£&=~a&«a_—~&& Coto Days, F. S. eRe Tee ee a a eT Pxysiovocicat Summation, F. S. | Normat Dany Mean, cococst 14 oavs OF YOO?) Is Normat Daicy Mean, Year a | PRECIPITATION Nonmac Daity Mean, F. S. Gi =6)hl —s( Fe Te Days !n LONGEST Normat Rainy Penioo, F.S. (es Days IN LONGEST Normat Day Penioo. F.S. (7 Mean Total, Yean Eee) EVAPORATION Daity Mean, 1887-8, F. S. [ESSE Moisture Ratios Norma P/E, F. S. ae) ee ee ES) Normat 7/E, F. S. PSS SS ae Norma. P/E, Year RR Humipity Normac Mean, F. S. DPT = $= seer SUNSHINE Norma Daicy Duration, F. S. 0 CT MoistTurnc- TEMPERATURE INDICES Norma P/E x T,F.S., Paysiovocicat MetHoo (ae Fia. 38. Climatic extremes for the Alleghanian Zone. 522 CORRELATION OF DISTRIBUTIONAL FEATURES. Upper Sonoran Zone (fig. 39).—In this zone are comprised portions of the Desert and more than half of the Grassland region. The ampli- tude of the conditions is not, in general, as great as it is for either of these two vegetations, since the zone does not include the more moist half of the Grassland nor the extremely arid portions of the Desert. This zone is largely one of arid grassland and comprises the Desert- Grassland region of our detailed vegetation map. There is a wide amplitude in length of frostless season and in number of cold days, both seen to be characteristic of the Grassland, and there is a wide amplitude in the number of days in the longest normal dry period. Both the evaporation and humidity conditions range through wide amplitudes, the former from 0.166 to 0.330 inch and the latter from 40 per cent to 80 per cent. The most moist conditions in this zone are to be found in the narrow strip which follows the coast of southern California. Both the physiological temperature summation for the frostless season and the moisture-temperature index show relatively narrow amplitudes for this zone. The narrowest ones, however, are those exhibited by the number of days in the longest normal rainy period of the frostless season and by the moisture ratios. The latter criterion appears to express the conditions which are critical in the limitations of this zone just as it does in the case of the Desert and Grassland. Carolinian Zone (fig. 40).—This zone bears about the same relation to the Upper Sonoran that the Alleghanian does to the Transition. That is to say, the temperature conditions are generally similar in the two, while the moisture conditions are dissimilar. The temperature similarity does not hold with respect to the length of frostless season, as it did not in the case of the Transition and Alleghanian Zones. The TEMPERATURE Days iw Normat Frosturss Season (F.S) EE es or Days, F. S. MAE C~—S—SY Coto Days, F. S. aE ee eed Puysiotocicat Summation, F. S. EEF Norma Daly MEAN, CoLDEesT 14 oars of Year |___—s —- i Ed Normat Daicy Mean, Year eC PRECIPITATION 2 Normat Daity Mean, F. S. i‘ C:;OSOSCSCSC™*™*;*;*~‘;«4 Days IN LONGEST Normat Rainy Periop, F.S. (We Days IN LONGEST Normat Dry Periop, F. S. feeerarscerr oa aS z MEAN Torat, Year eee eee EVAPORATION Daity Mean, 1887-8, F. S. Moisture Ratios Normat P/E, F. S. (EEE wren eesrt sre Ss eee Normat 7/E, F. S. (Cr eee Normat P/E, Year TES Humpty Normat Mean, F. S. a SUNSHINE Normat Daity Duration, F, S. i MoisTURE-TEMPERATURE INDICES / Normat P/E x T, F.S., Paysio.ocica. Mernoo [_—MN OS CCOCOCCCSCSCSCSCSCSCSdS Fig. 39. Climatic extremes for the Upper Sonoran Zone. CORRELATION OF DISTRIBUTIONAL FEATURES. Ze. maximum length is very similar in the two, being 237 days for the Upper Sonoran and 241 days for the Carolinian, but the minimum value for the former is 25 days and for the latter 127 days. Whereas the moisture conditions of the Alleghanian Zone were found to lie well within the extremes for the Transition Zone we have in the case of the Upper Sonoran and Carolinian Zones a more sharp separation of the ranges of these conditions. In every case there is an overlapping of moisture conditions, by which the minimum values of the Carolinian are seen to be lower than the maximum values for the Upper Sonoran. This circumstance is due to the fact that the highest moisture values of the Upper Sonoran are registered on the Pacific coast, while the lowest values of the Carolinian are experienced along the one-hundredth meridian. The minimum sunshine values for the Carolinian and Upper Sonoran Zones are very similar, but the amplitude of the former is only half that of the latter. The moisture-temperature index is higher in its extreme values and wider in its amplitude in the Carolinian Zone, reaching a maximum which is about midway of the amplitude for the United States. Among the relatively narrow amplitudes for this zone should be noted the normal daily mean precipitation for the average frostless season and the number of days in the longest normal dry period within that season. It is of interest to note that the length of the dry period shows a narrow amplitude in the Carolinian Zone, indicating its critical limiting importance, whereas the longest rainy periods are demonstrated to have a critical value for the Upper Sonoran. Con- versely, the length of the rainy period shows a wide, but imperfectly TEmPcRATuRE Days in Noamat Faostcess Season (F. S.) | | Hor Days, F.S. ” | | Coto Days, F.S. .. Ae Oa nee | PrysioLocicat Summation, F. S. CO —_____—— Normat Daicy Mean, covoest 14 cays of Year (_ (“s ~$ Normat Daicy Mean, Year EEE PRECIPITATION Nonmac Daicy Mean, F. S. OEE EEE Days in LONGEST Normat Rainy Pernioo, F.S. (___ - is Days In LONGEST Normat Dry Penioo, F.S. ( _ ————Z—Z_ CCC Mean Totat, Year errr) EVAPORATION ; Daity Mean, 1887-8, F. S. CE) Moisture Ratios Normat P/E, F. S. eee | Noamat 7/E, F. S. TT _——————_E_— Norma P/E, Year TT ———=——E_ Humioity Norma Mean, F. S. EEE SUNSHINE Normat Dairy Dunation, F. S. yy ——E— MoisTure-TEMPERATURE INDICES Normat P/E x T, F.S., Prysiolocical Methoo Cs Fra. 40. Climatic extremes for the Carolinian Zone. 524 CORRELATION OF DISTRIBUTIONAL. FEATURES. determined, amplitude for the Carolinian, and the length of the dry period shows an even greater, but also inaccurately determined, ampli- tude for the Upper Sonoran. The moisture ratios show higher values and wider amplitudes for the Carolinian than for the Upper Sonoran, as was true of their more northern analogues, the indication being that the conditions expressed by these ratios are somewhat less critical in the moister Carolinian Zone than in the Lower Sonoran. Lower Sonoran Zone (fig. 41).—When a coniparison is made between the zones which form the eastern and western halves of a given region, the temperature conditions are found to be similar in the two and the moisture conditions dissimilar. When a comparison is made between the temperature conditions of the Upper Sonoran and Lower Sonoran Zones, the values and amplitudes are found to be dissimilar, whereas the moisture conditions in the two are very much alike throughout, with the exception of the higher range of evaporation in the Upper Sonoran. The length of frostless season in the Lower Sonoran ranges from 106 to 331 days, which is both a wider amplitude and a higher series of values than those found in the Upper Sonoran. Other very wide amplitudes are those of the normal daily mean temperature for the year, the number of days in the longest normal dry period within the frostless season, and the daily mean evaporation for the frostless season. These are all conditions which are likewise of wide amplitude in the Desert region. One of the narrowest amplitudes of this zone is the normal daily mean for the coldest 14 days of the year, for which the amplitude in the Upper Sonoran is great. This emphasizes the importance which TEMPERATURE Days in NoRMAL Frostiess Season (F.S.) (x Es Hor Days, F. S. | Eee SCSC~—CSSC‘« Norma. Daicy Mean, YEAR [ea SS Re 5 PRECIPITATION Norma. Dairy Mean, F. S. DAYS: IN’ LONGEST NGRMAL RAINY; PERIOD, FOS, [2a ee Days IN LONGEST NoRMAL Dry Penion, F. S. Mean ToTAL, YEAR SUE: oR = EVAPORATION s) DaiLy.-Mean, 1887-8, F. S. (____ rs Moisture Ratios | Normat P/E, F. S. (NE 2s eee Norma 7/E, F.S. GEE ss Se eee Norma P/E, Year (ME fossa 5 ee Humipity Normac Mean, F. S. | SUNSHINE Norma Daicy Duration, F. S. ne - lll lc MoilsTURE-TEMPERATURE INDICES Normat P/E x T, F.S., PHysiovocica, MetHoo (— x Fia. 41. Climatic extremes for the Lower Sonoran Zone. CORRELATION OF DISTRIBUTIONAL FEATURES. 525 the temperatures of the coldest periods of winter assume on passing to a warm subtropical zone in which there are no cold days in our sense. The number of days in the longest normal rainy period of the frostless season appears to be of narrow amplitude in the Lower Sonoran Zone, although this is not accurately determinable. Its values and ampli- tudes are doubtless very similar to those of the Upper Sonoran Zone, as indicated by a comparison of figure 39 and figure 41. While, in other words, there is a sharp contrast between the conditions in the Upper and Lower Sonoran Zones with respect to one of the most critical temperature conditions of the latter, there is a similarity with respect to a moisture condition which is not critical in separating these zones, but is critical in separating them from their eastern humid analogues. The moisture ratios, which show narrow amplitudes for this zone, are also very similar in range and amplitude to the moisture ratios of the Upper Sonoran Zone. Austroriparian Zone (fig. 42).—The temperature conditions of this zone show less similarity to those of the Lower Sonoran Zone than is shown by a comparison of Upper Sonoran with Carolinian or Transi- tion with Alleghenian. The amplitude of the length of the frostless season is relatively narrow, and that of all the other temperature con- ditions is narrower than in the Lower Sonoran. There are rather wide limits, however, within which the temperature conditions of these two zones overlap. The normal daily mean precipitation ranges through a wide ampli- tude in the Austroriparian Zone, exceeding its amplitude in the Caro- linian. The number of days in the longest normal rainy period of the frostless season also reaches much higher maximum values in the former zone than in the latter. With these exceptions, there is a general “ Temperature Days in Nonmat Frosticee Season (F.S.)0 (a Hot Davs, F. S. CEL PEE Coto Days, F. &. [| RS eS ee Oe eR SO See | PHysioLoaicaL Summation, F. S. Pit iéé $i i$i.é« Pewee Nonmac Datty Mean, cocoest 14 pays or Year (TT) Nonmat Daicy Mean, Year La ? Mean Torat, Yan MMI SL ES EVAPORATION Daity Mean, 1687-8, F. S. SS eee Moisture Ratios Normat P/E, F. S. CT —E—————=—=Z=Z_— Normat 7/E, F. S. EEE Nonmat P/E, Year eS Mumioirty Normac Mean, F. S. SRL TTT = ; SUNSHINE Normat Dairy Duration, F.S. | CAC |= tS MoisTune-TemPcrarure Invoices Nonmat P/E x T, F. S., Paysiovocicat MeTHon (a Fig. 42. Climatic extremes for the Austroriparian Zone. 526 CORRELATION OF DISTRIBUTIONAL FEATURES. correspondence of limiting values for the moisture conditions in the Austroriparian and Carolinian. There is a very strong dissimilarity between the moisture conditions for the Austroriparian and the Lower Sonoran. The daily mean evaporation of the frostless season ranges from 0.96 to 1.69 (?) in the former zone and from 104 to 273 in the latter, thereby overlapping to a considerable extent. Several of the temperature conditions exhibit narrow amplitudes in this zone, notably the number of cold days and the number of hot days. A narrow amplitude is also exhibited by the number of days in the longest normal dry period of the frostless season, and in the imperfectly determined data for the mean total precipitation for the year and the normal mean humidity for the frostless season. It is apparent from this evidence that the Austroriparian Zone is differ- entiated from the adjacent zone on the north by temperature condi- tions and from the adjacent one on the west by moisture conditions, the greatest importance in this differentiation attaching to the con- ditions of narrow amplitude which have been mentioned. 2. DISCUSSION OF THE OBSERVATIONS. It is impossible to undertake a logical discussion of the correlation of climatic conditions with the areas occupied by the life-zones, because of the climatic basis on which these zones were originally outlined by Merriam. The boundaries running, in general, in an east-and-west direction were determined by the remainder temperature summation above 32°, and the boundary running north and south along the one- hundredth meridian was selected because it is a pronounced climatic line, separating what would otherwise be very irreconcilable faunal and floristic regions. From these considerations it may be seen that we should be able to predict the nature of the conditions which limit these areas. An examination of figures 37 to 42, indeed, shows that we encounter marked differences in all of the temperature conditions on passing southward from the Transition Zone, through the Upper Sonoran to the Lower Sonoran, or in passing from the Alleghanian Zone down through the Carolinian and Austroriparian, barring a rather strong similarity between these conditions for the Alleghanian and Carolinian Zones. A comparison of Transition Zone with Alle- ghanian, of Upper Sonoran with Carolinian, and of Lower Sonoran with Austroriparian, exhibits a similar marked difference of moisture conditions. If the humid Transition of Washington and Oregon is considered separately from the remainder of the Transition, this con- trast becomes more striking in the first of these comparisons. As far as possible we have made use of Merriam’s maps of the remainder summation of temperatures above 32° F. and of the normal daily mean temperature for the hottest 6 weeks of the year, but we have been prevented from making as full use of these maps as their CORRELATION OF DISTRIBUTIONAL FEATURES. 527 importance warrants on account of Merriam’s failure to publish the numerical data on which they were based. The climatic extremes have been read from these maps, however, for all of our botanical areas. A consultation of the tables of climatic extremes will show that the absence of the readings for individual stations, and the mere possession of the values for the isoclimatic lines, has made the climatic extremes for these maps (plates 37 and 44) very general in their nature, and has resulted in giving the same extremes for areas which are widely sepa- rated or very unlike. The physiological summation of temperatures appears to be a more natural method of securing a measure of the cumulative effects of this factor on plants than either of the remainder summations which we have used, and its resulting figures should bear a closer relation to distributional facts than the figures derived from any other mode of summation thus far suggested. The four charts showing summations by the different methods (plates 37, 38, 39, and 40) have a generic resemblance so far as concerns the general sweep of their isoclimatic lines, although the actual values represented by the lines differ. The amplitude of the conditions expressed by the physiological summation is not great for any one of the 6 life zones, although it is not so narrow, in any case except the Transition Zone, as to indicate that it expresses one of the conditions of most vital importance in controlling the position of the limits between the life-zones. When the remainder summation above 32° has been found to have such apparent impor- tance as a controlling condition as to form a leading basis for the delineation of life-zones, it is a matter of surprise that the more logical physiological summation does not show a high degree of importance when correlated with the life-zones. This. discrepancy might be attributed to the fact that the boundaries of the zones were partly determined by the temperature of the hottest 6 weeks, particularly in the western or arid zones, if it were not for the fact that it is these zones in which there is the strongest indication that the physiological summation is of importance as a controlling condition. It is at least true, from the indications of our data, that the physiological summa- tion appears to be more important in controlling the zones than is any other temperature factor that we have used, except in the Austro- riparian Zone, where several others are of equally narrow amplitude. As we proceed from the northern toward southern zones the mean temperature of the coldest 14 days of the year is seen to be a controlling condition of increasing importance. With a single exception, the moisture conditions of the western and eastern subdivisions of Merriam’s transcontinental zones show a very different range of values, as would be expected from the fact that the subdivision was made on a basis of the differences in these conditions. The one exception is the case of the Transition Zone, in which the 528 CORRELATION OF DISTRIBUTIONAL FEATURSE. humid northwestern region gives the moisture conditions both higher and lower extreme values in the Transition than they exhibit in the Alleghanian. With the same exception the moisture ratios have a much narrower amplitude in the western zones than in the eastern ones. They are clearly to be looked upon as expressing the most important controlling condition in the Upper Sonoran and Lower Sonoran Zones, but their amplitudes are relatively wide in the eastern zones. The moisture-temperature index is also of narrower amplitude in the western zones than in the eastern ones. While it is sufficiently narrow in the Transition Zone to be regarded as an expression of important conditions in the limitation of this zone, ihis is not the case with the other zones. In the three western zones this index has the same minimum value, but increases in amplitude on passing southward, so that its maximum values are progressively higher and consequently its amplitudes increasingly wider. In the eastern zones the extremes become progressively higher on passing from north to south, and the amplitudes become greater. | From the preceding discussion, and from considerations presented in Part II, it appears that the system of life-zones worked out by Merriam and now rather widely used in a descriptive way, especially by the United States Biological Survey, will require much modification before it may become at all satisfactory to a serious student of etio- logical plant geography. It is extremely unfortunate that the actual data on which this system was originally based, and on which its appli- cations are based in current descriptions, do not exist in the published literature. Neither Merriam nor any of his followers has thus far attempted to present the actual basis for the system in form such that a critical study of its good and bad features may be undertaken. Perhaps this may be a main reason why the who.e subject of the climatic relations of floral and faunal areas has received so little atten- tion at the hands of students who are able and willing to undertake the complex analyses which are involved in such a subject. The pub- lication of the charts without the data on which they were based, together with the general and official adoption of the system by the United States Biological Survey, have given this important problem the appearance of having been satisfactorily solved—of being a closed subject. Those who have employed this zone system have either refrained from any discussion of its good and bad characteristics, or else they have merely taken the standpoint of advocates, and the lack of the numerical data that are absolutely necessary for a critical study has tended strongly to discourage such inquiries. Also, a sort of authoritative atmosphere that seems to hang over government pub- lications in general, together with the apparent authority and dog- matism that invariably go with well-printed (and especially colored) CORRELATION OF DISTRIBUTIONAL FEATURES. 529 charts, to the exoteric reader, tend in the same direction, to retard real progress. Ecological students should realize that this is not by any means a closed subject, but that it is in a very early, formative stage, and that it requires vastly more critical and original study than has ever been accorded it. Merriam’s work formed an excellent beginning and he opened up a new and very important field, but his presentation of the matter was hurried and incomplete, and the later work of his followers has consisted in drawing zonal boundaries on a finer scale on biological evidence without any effort to extend the investigation of the climatic basis of the scheme. The work of Merriam should be regarded as a beginning and the whole field opened by him assuredly deserves elaborate critical study at the hands of ecologists. We do not wish to attempt to substitute any other dogmatic scheme of cli- matic provinces in place of this one, but we do wish to emphasize the fact that some other and much better scheme is to be expected when this subject receives attention such as it deserves. V. CONDITIONS THAT PROBABLY DETERMINE THE DISTRIBUTION OF GROWTH-FORMS AND THE ECOLOGICAL DISTRIBUTION OF INDIVIDUAL SPECIES. 1. GROWTH-FORMS. The fundamental vegetational data for use in any study of climatic conditions in relation to the relative abundance of a particular growth- form should be based on a knowledge of the réle played by this growth- form in the vegetation of the region involved. Such knowledge is in hand for certain small areas, but is lacking for the great bulk of our region. We have therefore fallen back upon the best obtainable sub- stitute, namely, the securing of distributional data for each of the various species belonging to these growth-forms, and the plotting of their cumulative distribution. The distribution of all evergreen broad-leaved trees and of all microphyllous trees of the United States have been superposed so as to show the regions in which these growth-forms are represented by the greatest number of species. The resulting maps doubtless come near to showing the relative importance of these forms in the vegetation, as well as their numerical representation in the flora. The distribu- tion of the eastern deciduous trees has been treated by superposing the ranges of a group of the most common and widespread species, rather than by an attempt to use all of the very numerous trees of this growth- form. The resulting area does not coincide with the Deciduous Forest region of plates 1 and 2, but it comprises the region in which deciduous trees are known to reach their maximum abundance, size, rate of growth, and speed of reproduction, as well as the regions in which they are abundant and successful in the optimum habitats. 530 CORRELATION OF DISTRIBUTIONAL FEATURES. The ecological distribution of two species, Liriodendron tulipifera and Bulbilis dactyloides, has been investigated, as exemplifying the methods that it would be highly desirable to extend to a much larger number of species if the data were available for doing so. The aim of securing the climatic data for the areas of relative abundance has been to determine the optimum conditions for these species, as con- trasted with the conditions existing where they are not so well repre- sented in the vegetation. The relatively narrow amplitude of condi- tions exhibited by the central areas of ecological distribution points in each case to the conditions of these areas as the optimal ones. In all five of the following cases our effort has been the same, whether concerned with the ecological centers for growth-forms or for individual species. The former have been determined entirely from floristic data in the case of the evergreen broad-leaved and microphyllous trees, from floristic data on ecologically important species in the case of the decid- uous trees, and from purely vegetational data in the case of Lirioden- dron and Bulbilis. Evergreen broad-leaved trees—Owing to the complicated nature of the areas in which different numbers of trees of this group are found, it has been impossible to construct a satisfactory figure to represent graphically the limiting conditions for the several areas. By a com- parison of the map showing the cumulative distribution of this group of trees (plate 3) with the various climatic maps, it is possible, however, to determine some of the conditions upon which an abundant repre- sentation of evergreen broad-leaved trees is apparently dependent. Both in the West and the Southeast these trees are seen to be almost wholly confined to the region with an average frostless season of more than 180 days, and with no cold days in our sense. The Desert region between Texas and southern California is nowhere occupied by more than 10 species of evergreen broad-leaved trees, and extensive stretches of it are occupied by less than 5 species or by none at all, although the temperature conditions are analogous to those of the adjacent regions to the east and west in which there are 10 or more species. The eastern boundary of this group of trees is mainly formed by the limit of Ilex opaca, while the boundary for 5 or more species is formed by several intersecting limits. The position of the latter boundary corresponds roughly with the line for a frostless season of 240 days, while in the West and the East the areas with 5 or more species are so situated as to have a daily mean of 40° or more for the coldest 14 days of the year. The physiological summation of temperature appears to have a slight correlation with the cumulative distribution of this group of trees in the Southeastern States, but such correlation is not borne out on the Pacific coast, where the region with 10 or more species encounters the same values of the summation as those found in the Northeastern CORRELATION OF DISTRIBUTIONAL FEATURES. 5A | States, where no evergreen broad-leaved species occur. Although the length of the frostless season is evidently a condition of great impor- tance for the rich representation of trees of this type, it is apparent that the temperature conditions of the frostless season itself are not so important as are the conditions insuring a mild winter. In parts of the California coast with a physiological summation of 5,000 to 7,500 there are over 10 species of evergreen broad-leaved trees, while in Georgia and Florida the same number of species are to be found in a region with summations of 15,000 to 17,500. In each of these cases the frostless season is between 240 and 300 days in length. In spite of such great differences in temperature summation between regions with frostless seasons of so nearly the same length, we have, on the other hand, an absence of cold days in both regions and daily mean temperatures in both places that are above 45°, or even above 50°, for the coldest 14 days of the year. The rapid increase in the total number of evergreen broad-leaved trees encountered in passing from the central Eastern States into peninsular Florida is paralleled by a rapid increase in the number of hot days, by an increase in the physiological temperature summation, by an elevation in the mean temperature of the coldest fortnight to 60° and above, and by increasing values for the moisture-temperature index. In none of these conditions does the coast of California approach the high values of southern Florida, except in the case of the mean temperature of the coldest 14 days. The long frostless season and the mild winter, which favor the abundance of broad-leaved evergreens, do so only in regions of high moisture conditions. In the Southeastern States the region with 5 or more species exhibits moisture ratios of 1.00 or above, except in extreme southern Florida. On the Pacific coast the greatest abundance of evergreen broad-leaved trees is in a region with moisture ratios of 0.40 to 0.60. This marked difference must be interpreted in connection with the much lower summations of temperature for the frostless season which characterize the Pacific coast. Between coastal Cali- fornia and eastern Texas the number of evergreens rises above 5 only in the mountain ranges of southern Arizona and western Texas, where the local conditions are not elucidated by our climatic data. In the correlation of moisture conditions with the cumulative dis- tribution of the evergreen broad-leaved trees, it should be borne in mind that our moisture data are chiefly elaborated for the frostless season, and that the moisture conditions of the winter (even where it is reduced to a length of less than 9 weeks) are surely of great importance to these trees. The low moisture ratios of the frostless season on the coast of California must be interpreted in the light of the fact that the short frost season is there the time of the principal rainfall. Microphyllous trees —The cumulative occurrence of this small group of trees characteristic of the subtropical desert regions has been 532 CORRELATION OF DISTRIBUTIONAL FEATURES. shown on the same map with the cumulative occurrence of the ever- green broad-leaved trees (plate 3), in order to demonstrate the manner in which the former group fills the break in the distribution of the latter. The region of maximum occurrence is in extreme southern Texas, while 5 or more species are found in the Texas Semidesert, along the lower Rio Grande, and in southern Arizona. The maximum occurrence of microphyllous trees is in a region with © a frostless season of 300 days or more, and the areas with 5 or more species are confined to regions with a season of from 240 to 300 days. Nowhere does the occurrence of as many as 5 species encounter any cold days nor a mean temperature for the coldest fortnight that is lower than 40° (or for the largest areas, 50°). The physiological sum- mation of temperature is above 15,000 for 5 or more species and above 20,000 for 10 or more. The moisture ratio for the region of maximum occurrence of micro- phyllous trees falls rapidly from 0.80 on the Gulf coast to 0.40 in the interior, and for the region of 5 or more species it falls from values above 0.60 to values below 0.20. Dry periods of 75 days are experienced on the Texas coast, of 100 days and more along the Rio Grande, and of 250 days and more in southern Arizona. In spite of the occurrence of the maximum number of trees of this type in the relatively moist climate of extreme southern Texas, as many as 5 species of the group are able to withstand the extremebe arid conditions of the desert near the mouth of the Colorado River. The encountering of rainy periods of 25 days (or of 50 days in Texas) appears to limit the western and eastern occurrence of 5 or more species. While the microphyllous trees are confined longitudinally by mois- ture conditions, their latitudinal range is restricted by temperature conditions. The continuity of the region of 5 or more species from California to Texas is broken only by the highlands of the Conti- nental Divide near the Arizona-New Mexico boundary, where all temperature conditions are relatively severe. Eastern Deciduous trees (fig. 43).—The 13 most common and wide- spread deciduous trees of the eastern United States are all found in a region stretching from Massachusetts and New York to Delaware and Ohio, and southward to northern Alabama. The region with 8 or more of the 18 embraces southern New England, southern Michigan, eastern Iowa, the whole of Arkansas, and nearly the whole of South Carolina. The region with from 1 to 7 species embraces all the remain- ing States east of the one-hundredth meridian, barring southern Florida (see plate 5). An effort has been made to show the climatic extremes of these three areas graphically and in such a way as to make their direct com- parison easy, and the result is shown in figure 43. In this figure we have a rough means of determining the optimum conditions for deciduous CORRELATION OF DISTRIBUTIONAL FEATURES. 533 trees, not on the ideal basis of the ecological distribution of all species of that type, but on the only basis which is now practicable—the geographical distribution of the most abundant species. It will be noted that there are a number of cases, particularly among the temperature conditions, in which the upper climatic extreme grows higher as we pass from the center (with 13 species) through the subcenter (with 8 or more species) into the fringe (with 1 to 7 species). Thus, the number of species of deciduous trees grows less as the frost- less season grows longer, as the number of hot days increases, as the number of cold days increases, etc. In several cases the extremes are nearly the same for the center and the subcenter, or for the subcenter and the fringe. In the case of humidity we have no deciduous trees srowing in the lower half of the gamut of this condition; with increasing humidities above 53.2 per cent we have an increasing number of deciduous species; on approaching the region with highest humidities we first leave the fringe, then the subcenter, and finally the center. Rather wide amplitudes characterize all of the temperature condi- tions, and in most cases the conditions of the subcenter and fringe shade off very gradually from the conditions of the center. The minimum number of cold days is the same for all three areas, inasmuch as all of them range into the region with no cold days. A much more irregular set of relations is exhibited between the extremes for the moisture conditions of the three areas. The shortening of the longest rainy period brings us rapidly from the center to the limit of the entire group. Increasing evaporation also brings us, within very narrow limits, from the center to the edge. TEMPERATURE Days in Normat Frostcess Season (F. S.) Hor Days, F. S. Co.p Days, F. S. PHYSIOLOGICAL SUMMATION, F. S. Normat Daitv Mean, COLDEST 14 Days OF YEAR Luss Normat Dairy Mean, YEAR PRECIPITATION Norma Daicy Mean, F. S. Days IN LONGEST NorMaAt Rainy Periop, F. S. Days iN LONGEST Norma Dry Periop, F. S. { ‘alain chbaahatatiate 111 LLL LED MEAN TOTAL, YEAR EVAPORATION Daicy Mean, 1887-8, F. S., Moisture Ratios Norma P/E, F. S. -Normat 7/E, F. S. Normat P/E, YEAR Humipirv Norma Mean, F. S. SUNSHINE Norma Daicy Duration, F. S. MoIstTuRe- TEMPERATURE INDICES Normac P/E x T, F. S., PHYsiotocicaL METHOD Fig. 43. Climatic extremes for eastern Deciduous trees; center of distribution (black), subcenter (shaded), fringe (dotted). 534 CORRELATION OF DISTRIBUTIONAL FEATURES. The narrowest amplitudes for the center are in the three moisture ratios and in the number of days in the longest dry period; and in all four of these cases a slightly wider amplitude of conditions brings us to the extremes for the fringe. A comparison of plate 5 with plate 59 shows that the whole region occupied by the center, subcenter, and fringe is very nearly confined between the isoclimatic lines for mois- ture-ratio values of 0.60 and 1.10, although the fringe enters regions with higher values. The range from 0.80 to 1.10 is scarcely exceeded by the center. The isoclimatic line for dry periods of 50 days is close to marking the western limit of the fringe of deciduous trees. In the center the extreme range is from 4 to 56 days, values above 50 being extremely local in this region, however. Figure 43 should be compared with figure 31, which shows the climatic extremes for the Deciduous Forest region. The extremes for the Deciduous Forest lie, in general, outside those of the center of the 13 common species and inside those of the fringe. Inriodendron tulipifera (fig. 44).—The area in which this tree is of commercial importance may well be regarded as its ecological center, while the region in which it occurs too infrequently to have such importance may be designated as its fringe (plate 9). The center for Liriodendron lies almost wholly within the center for the 13 decid- uous trees just treated, and its distributional limit is similar to that of the subcenter of the deciduous trees, although not.extending quite so far west. The conditions for the center and fringe of Liriodendron have been shown by pairs of graphs in figure 44. The region of greatest abundance for Liriodendron is one of the very few botanical areas investigated in which the edge lies entirely within the United States and is nowhere formed by a coast-line. The fact Days in Nommat Frostiese Season (F. S099 (rr Hot Days, F. S. ee OO Cotp Days, F. S. nO —=————EE | PHYSIOLOGICAL SUMMATION, F. S. ee ——————————————— | Normat Daicy MEAN, COLDEST 14 Days oF YeaR (rrr reg Normat Daicy Mean, Year | Precipitation Normat Daity Mean, F. S. ee _ Days In LONGEST NORMAL Rainy PERIOD, F. S. perros I SN Days in LoNGest NormaL Dry Perioo, F. S. (IRIN a Mean Torat, Year rrr a EvaPoration _ Daiy Mean, 1887-8, F. S. — — ———— es | Moisture Ratios Norma P/E, F. S. Ba EE——EEEEE Norma 7/E, F. S. (ee NN, es | Norma P/E, Year aa |_| Humipity Normac Mean, F. S. ——————EEE———————— SuNSHINE Normat Daity Duration, F. S. —— | Moisture- TEMPERATURE INDICES Noamat P/E x T, F.S., PHYSIOLOGICAL METHOD [——————— ree Fig. 44. Climatic extremes for Liriodendron; upper blocks for center, lower for fringe. CORRELATION OF DISTRIBUTIONAL FEATURES. 535 that the fringe completely surrounds the region of greatest abundance makes this a case in which it is of interest to compare the character of the two sets of amplitudes. The amplitudes of conditions for the center are narrow in all cases, except the number of cold days. The ampli- tudes for the fringe are wide in a number of cases, notably the number of cold days, the annual daily mean temperature, the length of the longest rainy period, and the moisture-temperature index. In every case the amplitude of the conditions for the center is less than that for the fringe, and the extremes for the center lie within those for the fringe in all cases except those of evaporation, humidity, and the moisture ratios. The geometrical centers of the blocks representing the extremes for the region of greatest abundance lie within the blocks for the extremes of the fringe in every case except that of evaporation. This means that for all of the conditions except evaporation it is possi- ble to find a locality in the fringe which possesses climatic values that are near those of the absolute ecological optimum of the species. The fact that a straight line laid down across any portion of the map of the United States passes through localities showing for long dis- tances a progressive change in the values of each climatic condition is responsible for the maximum and minimum values of so many con- ditions being respectively greater and less in the fringe than in the center. The conditions which are favorable to Liriodendron in the region of greatest abundance are, in some cases, still more favorable to it in the northern part of the fringe, and in other cases still more favorable in the southern part of the fringe. The center exhibits the favorable constellation of conditions designated as the ecological optimum. When a given condition shows minimum and maximum values for the fringe which are not respectively lower and higher than the extremes for the center (fig. 44, plates 53, 57, 59, 60, and 65), it is probably an indication that the condition involved is not an important one in determining the location of the center and fringe, however narrow the amplitudes involved may be. The comparative uniformity in the amplitudes of all temperature conditions for the distributional center of Liriodendron indicates that these conditions are of nearly equal weight in determining the limits of the center, with a slight indication of preponderant importance for the mean temperature of the coldest 14 days. The daily mean pre- cipitation and the number of days in the longest normal dry period appear also to be conditions of importance in limiting the center. The narrow amplitude of the moisture ratios for the center is largely to be attributed to the low values which characterize the Ohio Valley (see plate 59). An adequate series of evaporation and precipitation sta- tions in the heart of the southern Alleghenies would doubtless give maxima for the center nearly or quite as high as those for the fringe (see values for Pisgah Forest, North Carolina, table 16). The west- 536 CORRELATION OF DISTRIBUTIONAL FEATURES. ward extension of Liriodendron does not carry it far beyond a mean annual rainfall of 40 inches, nor into the region with more than 25 days in the longest dry period. Bulbilis dactyloides (fig. 45).—The areas of relative abundance for Bulbtlis (plate 10) have been charted in an effort to depict the virgin conditions of the distribution of this grass, using all available sources of information, but the resulting map is probably less faithful to the facts than the map of Lirtodendron or the map of the relative abun- dance of Pinus teda. The areas of the latter are unfortunately so small that they frequently comprise no climatic stations whatever, thereby rendering an adequate discussion of them impossible. The range of Bulbilis crosses the United States in a broad belt between the ninety-fifth and one hundredth and sixth meridians, extending from the Canadian boundary in North Dakota to southern Texas. In the North the distributional area is narrower than the Grassland, not reaching to its western edge; in the South the distribu- tion is more extended than that of the Grassland, reaching eastward to Louisiana and westward into the Desert-Grassland Transition region. The only limits of the geographical distribution of this species that fall within the United States are the eastern and western ones. The center of ecological distribution extends from South Dakota to northern Texas, and the subcenter of ecological distribution is only from 100 to 200 miles in width, surrounding the center. Both of these areas lie entirely within the United States (see plate 10). . TEMPERATURE Days in NORMAL FRostTLess Season (F. S.) Hot Days, F. S. Coup Dars,.F. S. PHYSIOLOGICAL SUMMATION, F. S. Normat Daity MEAN, COLDEST 14 DAYS OF YEAR Normat Daicy MEAN, YEAR PRECIPITATION Norma. Daicy Mean, F. S. Days IN LONGEST NorRMAL Rainy PeRiop, F. S. Days IN LONGEST Norma Dry Perioop, F. S. MEAN TOTAL, YEAR EVAPORATION Daicy Mean, 1887-8, F. S. Moisture Ratios Norma. P/E, F. S. Normat 7/E, F. S. Normat P/E, Year Humipity ‘NorMaL Mean, F. &. SUNSHINE Normat Daicy Duration, F. S. MoisTURE=-TEMPERATURE INDICES Norma P/E x T, F. S., PHysiotocicat Metuopo [7/7 ane — 577 ? f A i ERS Seen ROeTnAE NA SEERRITAS Sy WM = UU AA RD aT : [eS ee Ee EE EL ER OO [= WL TA oS eee Ea LLL os si LEED EE CLE LLEL LAE A E T EERIE er ZZ 8 =< MMM Fic. 45. Climatic extremes for Bulbilis; center of distribution (black), subcenter (shaded), fringe (dotted). CORRELATION OF DISTRIBUTIONAL FEATURES. 537 The graphs showing the climatic extremes for Bulbilis (fig. 45) have been drawn in such a way as to show the maximum and minimum values for the center, only such maximum and minimum values for the subcenter as lie outside those for the center itself, and only such extreme values for the fringe as lie outside those for the subcenter. The ecological center exhibits several climatic conditions with narrow amplitudes, notably the number of hot days, the physiological summation, mean annual precipitation, evaporation, humidity, and the moisture ratios. The position of the isoclimatic lines for the physiological summation would indicate a somewhat wider amplitude (5,000 to 15,000) for this condition than that based upon the readings of the minimum and maximum stations and given in table 71. The widest amplitudes are those of the number of cold days, the daily mean temperature, and the daily duration of sunshine. For the ecological center, then, we may state that the amplitudes are narrow for all of the moisture conditions and are partially narrow and partially wide for the temperature conditions. An examination of the graphs for the climatic extremes of the sub- center and fringe shows that the amplitudes are wide for all of the temperature conditions, even for those that show narrow amplitudes for the center. With respect to the moisture conditions, however, the amplitudes of the subcenter and fringe are not so greatly in excess of those for the center, except in the cases of evaporation and humidity. The moisture ratios show narrow amplitudes even for the fringe. These facts indicate that the location of the Bulbilis areas as a whole is chiefly determined by moisture conditions, and this is particularly true of the center. The position of the zones of abundance is deter- mined on the east and west by small but significant differences in the moisture conditions, and on the north and south by temperature conditions. 2. SPECIES. The climatic extremes for all of the individual species treated in the following pages will be found in tables 77 to 151. Some 31 species have been selected from a total of 75 for the presentation of the climatic extremes in graphic form (figs. 46 to 74). These have been chosen so as to represent all types of plants and all types of distribution represented among the larger number. The relation of climatic con- ditions to the distribution of these species will now be discussed. Tsuga heterophylla (fig. 46).—This tree occupies an area in which the conditions are similar to those of the Northwestern Evergreen Hygro- phytic Forest, with differences due to the extension of the limits of Tsuga into northern Idaho and Montana, well to the east of the Hygro- phytic Forest. The number of cold days in the frostless season endured by the easternmost individuals of this species reaches a maximum of 538 CORRELATION OF DISTRIBUTIONAL FEATURES. 120, whereas no cold days are experienced within the Hygrophytic Forest. The normal daily mean temperature also ranges to lower values for the tree than for the vegetation in which it is most charac- teristically developed. The temperature conditions encountered by Tsuga in northern Idaho and Montana are otherwise very similar to those in coastal Washington and Oregon. The precipitation condi- tions for the area occupied by 7J'suga are very similar to those of the Hygrophytic Forest, at least with respect to the frostless season. Higher intensities of evaporation are encountered in Idaho and Mon- tana and higher values for humidity in northern California, making the amplitudes for both of these conditions somewhat greater than they are for the Hygrophytic Forest. The remarkably wide amplitude of the moisture ratios which is characteristic of the last-named forest is also shown for the area of Tsuga. The narrow amplitude in the number of hot days in the frostless season and in the physiological summation of temperature would indicate that these conditions are important in the limitation of Tsuga heterophylla, and the position of the isoclimatic lines also suggest that the precipitation conditions are of critical importance, in spite of the wide amplitude which they exhibit within the distributional area jof this tree. TemPcrarune Days in Norma: Frosticse Season (F.S) [iS Hor Days, F. S. SI 2 ee ee Coip Days, F. S. Puysiovocica Summation, F. S. I eee Normat Dairy Mean, coLorst 14 cavsor Year (iD Norma Darcy Mean, Year ee 0 FE PRECIPITATION Norma Daity Mean, F. S. EEE PE EE DEEP OL ET ES Days IN LoncesT Normat Rainy Perio, F.S. (___ ssh Days IN LONGEST Normat Dry Penioo, F.S. 0 (CE Mean To7at, Year (eee EVAPORATION Oaiy Mean, 1887-8, F. S. EE —__CSCSC‘“CSC“‘“‘“‘S;WCC) Moisture Ratios ‘Normat P/E, F.S. (RE AO AOE SPREE OSE OP NRE Sh Sy a ae Normat 7/E, F.S. (i RT TS Se ee ee an Norma P/E, Year (ES ES ORE 6 Ue Br i Re OO eT Humiory Nonmar Mean, F. S. CS SUNSHINE Nonmac Daity Duration, F. S. Sar + MoisTuRe-TEMPERATURE INDICES Normat P/E xT, F. S., Puysiotocicat Metxoo (_ i Fig. 46. Climatic extremes for Tsuga heterophylla. Pseudotsuga mucronata (fig. 47).—The range of this tree covers all of the Northwestern Hygrophytic Evergreen Forest and a large part of the western section of the Northern Mesophytic Evergreen Forest. The climatic extremes for it exhibit some of the features of each of the vegetations with which it is coextensive, and in several cases the CORRELATION OF DISTRIBUTIONAL FEATURES. 539 graphs exhibiting these extremes are such as would be secured by a superposition of the graphs for the two vegetations. In spite of the great north-and-south extension of the range of Pseudotsuga, it encounters a narrow amplitude of conditions in the number of hot days in the frostless season and in the physiological summation of temperature. Further climatological data from stations situated within the range of this tree at some of its most southerly localities might broaden the amplitude of these conditions, giving values more nearly like those for the western section of the Northern Evergreen Forest, which area is drawn in a more generalized manner. With respect to all of the conditions involving precipitation or atmospheric moisture, the amplitudes are very wide, being in many cases a superposition of the amplitudes for the two forest areas men- tioned. The fact that this tree is so nearly coextensive with the southernmost areas of Mesophytic Evergreen Forest may be taken to mean that the constellations of conditions by which its range is limited are very similar to those limiting this forest. The lowest normal daily mean precipitation, the highest values for evaporation, and the lowest ones for the moisture ratios are all to be regarded as important in limiting the southward range of this tree. Although the lower limit of Pseudotsuga in the mountains of Arizona and New Mexico is slightly higher than the lower limit of the pines which form the edge of the Mesophytic Forest, the data from the few stations in that region show a close correspondence in the extremes just mentioned. The number of hot days and the value of the physiological summation of tempera- TEMPERATURE ~ Days in Nornmat Frostiess Season (F. S.) Hort Days, F. S. Coto Days, F. S. PrysioLocicat Summation, F. S. Normat Daicy Mean, co.pvest 14 pays of YEAR Normat Daicy Mean, YEAR PRECIPITATION Normat Daicy Mean, F. S. Days In LONGEST Normat Rainy Perion, F. S. Days in LONGEST Normat Dry Perioo, F. S. Mean ToTat, Year : EVAPORATION Dairy Mean, 1887-8, F. S. Moisture Ratios Normat P/E, F. S. Norma 7/E, F. S. Normat P/E, Year Humipiry Norma Mean, €. S. Sunswine A i a eee ie in Minne. Pa eee ee a > (—_— es (eS Pe EER PES CRT ENGST ER UIT TE ES | RES Se OTP RC SRS RE SLE (—E — — Nonmar P/E x T, F. S., PHysiovocica METHOD Be vad Wormac Dany Duration, F. S. MoisTure-TEMPERATURE INDICES Fia. 47. Climatic extremes for Pseudotsuga mucronata. 540 CORRELATION OF DISTRIBUTIONAL FEATURES. ture are the two conditions which appear to be most critical in the limitation of this species with respect to its entire range. There are few localities in its distributional edge, however, in which the moisture conditions would fail to be of importance in connection with the tem- perature conditions just mentioned. Pinus ponderosa (fig. 48).—The range of Pinus ponderosa is similar to that of Pseudotsuga, but is somewhat more extended from Colorado northward to the Canadian boundary, where it exceeds the eastern limit of the western section of the Northern Mesophytic Evergreen Forest, and is less extended in the extreme northwest, where it fails to enter the Northwestern Evergreen Hygrophytic Forest. Except for the slightly narrower amplitude in length of frostless season, the temperature conditions are similar for Pinus ponderosa and for the western section of the Northern Mesophytic Forest. The number of hot days and the physiological summation of temperature again appear to be factors of importance in limiting this tree. On account of its extension into the western edge of the Grassland, the moisture values of Pinus ponderosa are of somewhat wider ampli- tude than those of the forested area in which it is so abundant. This species does not, however, encounter such low evaporation values nor such a high range of humidities as does the forest itself. It is doubtful if the former of these facts would be confirmed by data from a larger number of critically located stations; the latter is due to the absence of Pinus from the extreme coast of northern California. The conditions expressed by the moisture-temperature index appear to be of considerable importance in limiting this tree, together with the moisture ratios, the number of hot days, and the physiological summa- tion of temperatures. TEMPERATURE Days In Normat Frostiess Season (F. S) (EE Hot Days, F.S. # es = eee Coin Days, F. S. (EE Eee Pxysiotocicat SumMATION, F. S. eer Normat Dairy MEAN, corDest 14 pavsor Year [=I z ea : Normat Daity MEAN, YEAR eee ees PRECIPITATION Norma Daicy Mean, F. S. I Eee Days IN LONGEST Normal Rainy Perion,F.S. Ey . ©... 4 Days IN LONGEST Normal Dry Perioo, F.S. ([ ES Mean Tota, YEAR ON EVAPORATION Daity Mean, 1887-8, F.S. NN Moisture Ratios Normat P/E, F. S. ES 23 ere Norma 77/E, F.S. CE ee en ee Norma P/E, Year a ee ee ee HumIpDITY Normar Mean, F. S. NS SUNSHINE Normat Daity Duration, F. S. a _—ee MOISTURE-TEMPERATURE INDICES _ Norma: P/E x T, FS Pavstovocica: Metnon [EEL 22 ene Se en ee a 2 Fic. 48. Climatic extremes for Pinus ponderosa. CORRELATION OF DISTRIBUTIONAL FEATURES. 541 Pinus contorta (fig. 49).—The range given for this tree is based on the view that it is identical with Pinus murrayana, and comprises the regions that are occupied by the two forms—the northern Pacific coast, the Sierra Nevada, the northern Rocky Mountains, and the Black Hills. The extremes and amplitudes of conditions for this tree are very similar to those for Pseudotsuga mucronata. It encounters a slightly greater number of hot days, and a greater value for the physiological temperature summation, with a lower maximum value for the number of days in the longest dry period. Pinus contorta is like Pseudotsuga in encountering a wide amplitude of nearly all of the conditions here studied, its strongest control appearing to lie in the number of hot days and the values of the physiological summation of temperatures. It will be noted that both the eastern and western evergreen needle- leaved trees are confined to ranges which exhibit a narrow amplitude in the number of hot days. The amplitude of the physiological summa- tion is narrow for all except the species that are found in the South- eastern Evergreen Mesophytic Forest (for example Pinus echinata). With respect to both of these conditions there is a marked contrast between the evergreen needle-leaved and the deciduous broad-leaved trees. TEMPERATURE Days in Nonmat Frostiess Secon (F.S) ee =~ Hort Davs, F. S. eR aaa aR TEE ETT Corp Days, F. S. ara ee er ee eT Am Kee Puysio.ocicat Summation, F. S. ER oscars ee ee Normat Datty MEAN, COLDEST 14 pays oF YEAR Normat Daicy Mean, Year Cea oF ? PRECIPITATION Normai Dairy Mean, F. S. EE Se IS GCSES ee ee OS Days in LONGEST Nornmat Rainy Perio’, F.S. xn | 4} Days In LONGEST Normat Drv Perioo, F.S. ([__ [i Mean Tortat, Year EVAPORATION Daicy Mean, 1687-8, F. S. Moisture Ratios Normat P/E, F. S. Normat 7/E, F. S. Normat P/E, Year Humuioiry Normar Mean, F. S. SUNSHINE Normar Daicy Duration, F. S. MoisTurRe-TEMPERATURE INDICES Normat P/E x T, F.S., PHysiococicat MerHoo (_ Ee Fig. 49. Climatic extremes for Pinus contorta. Pinus echinata (fig. 50).—The range of this tree occupies all of the Southeastern Evergreen Mesophytic Forest except a strip along the Gulf of Mexico and peninsular Florida, and also the southern half of the Deciduous Forest region. It therefore exhibits amplitudes and extremes which lie between those of the two vegetations in which it 542 CORRELATION OF DISTRIBUTIONAL FEATURES. occurs, and is remarkable in having a number of relatively narrow amplitudes for a tree of such wide distribution. Its widest amplitudes are in the number of days in the longest normal rainy period and in the moisture-temperature index. The number of hot days and the number of cold days appear to be of about equal importance in limiting the range of Pinus echinata. The number of days in the longest normal dry period and the mean total precipitation of the year appear to be still more important as limiting conditions, while the amplitude of relative humidity is also comparatively narrow. TEMPERATURE Days in Nornmat Faostiess Season (F.S) (_ i z_ 7 UU) Hort Days, F. S. Om Coup Days, F. $. EEE rr PHYSIOLOGICAL SumMaTioN, F. S. Normat Daity MEAN, CoLoestT 14 pays or Yeah [_——S———CCCSaXKF __—s Cas es Norma Daity Mean, Year a ez oie + PRECIPITATION Mormat Daicy Mean, F. S. Days in LONGEST NormaAL Rainy Periop, F. S. Days IN LONGEST Normat Dry Periop, F. S. Mzan TOTAL, YEAR EVAPORATION Dairy Mean, 1887-6, F. S. Moisture Ratios Norma P/E, F. S. Norma 7/E, F. S. Norma P/E, Year Humipity Normac Mean, F. S. SUNSHINE Normat Daity Duration, F. S. MolSTURE-TEMPERATURE INDICES Normat P/E x T, F.S., PHysiotocicat METHOD (nae Fic. 50. Climatic extremes for Pinus echinata. Pinus strobus (fig. 51).—The distribution of Pinus strobus is coex- tensive with that of the eastern section of the Northern Mesophytic Evergreen Forest, and exceeds it to some extent toward the south and west, carrying the tree into the Deciduous Forest region and into the Grassland-Deciduous Forest Transition region. The conditions in the area of Pinus strobus are therefore similar to those of the vegetational area in which it reaches its greatest abundance. The southernmost extension of the tree carries it into a region with longer frostless season and with no cold days, in our sense of this term. A slightly greater value for the physiological temperature summation and a greater normal daily mean temperature are also encountered by Pinus strobus in its extension toward the Atlantic Coastal Plain and southward to Georgia. The number of days in the longest normal rainy period and the number in the longest normal dry period both reach maximum values which are greater for this tree than for the Evergreen Forest, although the minimum values are the same for the two. There are no very narrow amplitudes for thispine. The narrowest, however, are those for the moisture ratios and for relative humidity, CORRELATION OF DISTRIBUTIONAL FEATURES. 543 and those for the number of hot days, the normal daily mean pre- cipitation, the physiological temperature summation, and the number of days in the longest normal dry period. From a comparison of the distributional limit with the positions of various isoclimatic lines, the southward range of Pinus strobus appears to be determined by temperature conditions, of which the physiological summation and the number of hot days in the frostless season are the most important, while its westward range appears to be determined by moisture conditions, of which the normal daily mean precipitation and the number of days in the longest normal dry period are the most important. The position of the isoclimatic lines for the moisture ratio, r/E, would indicate that this compound factor is one of strong importance in determining both the southern and the western limits of this tree. Temperature Days in Normat Frostiess Season (F. S.) TE” C‘“C™SOSCSCSC™*™*™*~*~‘< Hor Days, F. S. Corp Days, F. S. oo a eh by te aa ei eek ead Soe a eas a a ade id eee ig ae PHYSIOLOGICAL SUMMATION, F. S. Li i | Jj Normat Daicy Mean, covoest 14 oavs of Veen ee Normat Daicy Mean, Year Rae PRECIPITATION Normat Daity Mean, F. S. (22am ee Days In LonGesT Normat Rainy Perio, F.S. (— x J Days IN LONGEST Norma Day Perion, F.S. (ry Mean Torat, Year i ae aa : e : EVAPORATION Dairy Mean, 1687-6, F. S. I eee MorstureE Ratios Nonma. P/E, F. S. (Geer a ee ee Norma. 77/E, F. S. (Gs eee ey Norma. P/E, Year Humipity Normat Mean, F. S. Grosiesaqeinen a ee) SuNSHINE Normat Daity Duration, F. S. Es) MoiSTURE-TEMPERATURE INDICES Noamac P/E x T, F.S., Paysiococica, MeThoo (___ es Fig. 51. Climatic extremes for Pinus strobus. Quercus alba (fig. 52).—This oak is found throughout the eastern United States, with the exception of northern Minnesota and Michigan and peninsular Florida. In keeping with its wide distribution it encounters a very wide range of practically all of the climatic condi- tions, exceeding in a number of cases the extremes for the Deciduous Forest region, in which it finds its greatest development. The nar- rowest amplitudes for Quercus alba are those of the number of days in the longest normal dry period, the normal mean relative humidity of the frostless season, and the moisture ratios. The first and last of these conditions appear to be responsible for the western limit of distribu- tion. This edge is roughly paralleled by the line for 25 days in the longest dry period and by the line for a value of 0.60 for the moisture 544 CORRELATION OF DISTRIBUTIONAL FEATURES. ratio. Owing to the extension of the northern edge into Canada it is impossible to speak regarding its probable controls in that direction. TEMPERATURE Daye tn Nornwat Frostiess SEAson (F. S.) (Cl ec er Hor Days, F. S. i a Cop Davs, F. S. Nite Toei ties pike wil See ee a Bae Puysiotocicat Summation, F. S. OB Normat Day Mean, cocoest 14 oavs of Year (es — Normat Dairy Mean, Year : PRECIPITATION Normat Dairy Mean, F.S. Eee Dave in concestT Nonmat Rainy Peron, F.S. (xp anRR es Dave im Loncest Normat Day Penyoo,F.S. UU) Mean Tora, Year {CS | Evaroration Daicy Mean, 1687-8, F. S. CS OM i _ Ee See (eee Cees | Morsrure Ratios ‘Nonmar P/E, F. 5. Nonmar r/E, F,S. Normat P/E, Year Humioity Nonmar Mean, F. &. SunsHine Nonmac Dairy Curation, F. S. MoisTURE- TEMPERATURE INDICES Norma. P/E x T, F.S., Puysio.ocicay MeTHoo (iia Fic. 52. Climatic extremes for Quercus alba. Quercus falcata (fig. 53).—This tree is found throughout the Atlantic Coastal Plain and the southern Mississippi Valley, reaching its greatest abundance in the Southeastern Mesophytic Evergreen Forest, but ex- tending well into the Deciduous Forestregion. Itencountersextremely TEMPERATURE Days in Norma Frostiess Season (F. S.) OE EEE Hort Days, F.S | eee Cotp Days, F_S. _——k—~—~—~—~—~_= °°» °°» ©} Puysiotocicat Summation, F. S. (ee Cas ee ee, Nonrmac Dairy MEAN, COLDEST 14 Days oF YEAR Normmat Daicy Mean, Year (OS EE EEE PRECIPITATION Normat Daiy Mean, F. S. CC, | Days In LONGEST Normat Rainy Periop, F.S. (_____—=—=d Days.In LonGesT Normat Dry Perico, F.S. Mean ToTAt, YEAR Ree ea ae RN EVAPORATION Daity Mean, 1687-8, F. S. ( Moisture Ratics Norma P/E, F. S. (ree Normat 7/E, F. S. (rr Normat P/E, Year SS sn 2 eee HumibiTy Norma Mean, F. S. a ee | SUNSHINE Normat Daicy Duaation, F. S. OMUMNN Mo!IsTURE-TEMPERATURE INDICES ON NoAMAL P/E x T, F. S., PHysiocrocicat MetHopo Fic. 53. Climatic extremes for Quercus falcata. wide amplitudes of all but one of the temperature conditions here dealt with, and its diminishing occurrence in southern Florida is coincident with the maximum values for these conditions. This is one CORRELATION OF DISTRIBUTIONAL FEATURES. 545 of the cases already mentioned in which the southernmost limit of plants in Florida is not well known, so that it is impossible to state just how far Quercus falcata may fall short of extending into the region of the temperature conditions represented by Key West. The one temperature condition for which Quercus falcata shows a narrow ampli- tude is the number of cold days, due to the fact that its range barely extends into the region in which any cold days are experienced. The moisture conditions in the area of this oak are very similar to those of the Southeastern Evergreen Forest, except in the case of the number of days in the longest normal dry period. While the Evergreen Forest withstands a maximum of 182 days (the reading for Key West), Quercus falcata has its maximum at 63 days, at the southwestern edge of its range. The normal dry period, the moisture ratios, and the relative humidity of the frostless season appear to be important con- ditions for the limitation of Quercus falcata. Its distributional area may be defined as the region in which the frostless season is more than 180 days in length, the moisture ratio greater than 0.80, the humidity ereater than 70 per cent, the normal number of cold days in the year less than 30, and the number of days in the longest normal dry period not more than 63. Quercus macrocarpa (fig. 54).—The area occupied by this oak covers the Northeastern States, omitting the Coastal Plain, and extends as far west as eastern Montana and central Oklahoma. Its southern limit is roughly coincident with the northern limit of Quercus falcata, and its northern limit is in Canada. Quercus macrocarpa is like Q. alba in exhibiting broad amplitudes for nearly all of the climatic condi- tions. It encounters approximately the lower half of the scale of Lie Frosr.ese Season (F. S.) MOU = ee Hor Daye, F. S. Coco Days, F. S. PHystococicat SUMMATION, F. S. nn || Normat DAity Mean, cococst 14 vavs of Yea? ET (CS Normat Daity Mean, Year Es = = = PRECIPITATION Normat Daicy Mean, F. S. EEE Days IN LONGEST Normal Rainy Period, F.S. (es Days IN LonGesTt Normat Dry Periop, F. S. _ See aay J MEAN TOTAL, Yan ___——_ ness EVAPORATION Daity Mean, 1887-8, F. S. EE — Moisture Ratios Normat P/E, F. S. OM Normat 7/E, F. S. eee Normat P/E, Year eee Humiorry Normac Mean, F. S. OC SUNSHINE 7 Noamat Daity Duration, F. S. EE ——-_ — MoIsTURE> TEMPERATURE INDICES Norma P/E x T, F.S., Pxysiovocicac MeTHoo (__ a Fic. 54. Climatic extremes for Quercus macrocarpa. 546 CORRELATION OF DISTRIBUTIONAL FEATURES. amplitudes of temperature conditions for the United States, but reaches areas with the maximum number of cold days. One of the narrowest amplitudes among the moisture conditions is found in the case of the number of days in the longest normal dry period, for which the extreme values are 9 and 88 days. A previous allusion was made to the western limit of this tree as showing the manner in which wholly — distinct conditions cooperate in controlling the ranges of plants. It will be seen by a comparison of plate 52 (dry days) with plate 18 (dis- tribution of Quercus macrovarpa) that the longest dry period encoun- tered at the western edge of this tree in Oklahoma is less than 50 days, whereas the maximum number encountered near the Canadian boundary is 88 days. The potence of this moisture condition is evi- dently modified by the differences in temperature conditions which are encountered along the western limit of the tree. The values of the moisture ratio (7/H) encountered in Oklahoma are about 0.60 and those encountered in Montana are about 0.40. An ability on the part of Quercus macrocarpa to withstand the same values for these two con- ditions in the latitude of Oklahoma that it does in Montana would carry the tree to the eastern borders of New Mexico with respect to the moisture ratio, and well into the borders of that State with respect to the longest dry period. These two conditions, as modified in their influence by temperature conditions, may be regarded as setting. the limit of the westernmost occurrences of this oak, which (like the western limits of so many deciduous trees) are to be found in alluvial bottoms characterized by moisture conditions which are higher than those of the adjacent upland. The southern limit of Quercus macrocarpa corresponds roughly with the isotherm of 120 hot days (see plate 36), and this condition, possibly in conjunction with closely related conditions, may be regarded as probably controlling the southern edge of the distributional area. The mean temperature of the hottest 6 weeks is apparently one of the most important of these related conditions, as the isotherm of 78.8° lies near the southern limit (see fig. 45). Ilex opaca (fig. 55)—The occurrence of this [ler is rather closely confined to the Atlantic Coastal Plain throughout all but a small part of its range, where it extends into the Piedmont and mountain sections of Georgia, Alabama, and Tennessee. This range is characterized by wide amplitudes of the temperature conditions, reaching the maximum values in all cases except the number of cold days. With respect to the latter condition, the amplitude is relatively narrow and the maximum is 55 days, encountered only at the northernmost attenuated limit of occurrence, in Massachusetts. The moisture conditions for the area of Ilex are nearly those of the Southeastern Mesophytic Evergreen Forest, the amplitudes being Eg WMD apne hea a SS ee en ee eS ee! eT. CORRELATION OF DISTRIBUTIONAL FEATURES. 547 wide in all cases except the imperfectly determined mean annual pre- cipitation. Although this plant encounters a wide range of the condi- tions expressed in the moisture-temperature index, there is still a close correspondence between its limit and the isoclimatic line of 11,000 for this index. At the localities where it occurs in southern Illinois and Indiana it encounters index values of only 7,000, and at its northern limit in Massachusetts it encounters its minimum value of 5,193. Numerous isoclimatic lines have such a direction as to indicate that there are belts of relatively similar climatic conditions extending parallel to the Atlantic coast for long distances (see plates 46, 50, 53, 59, 65, and 72). The conditions of the southern part of the Missis- sippi Valley, which is technically a part of the Coastal Plain, are almost always different from those of the coastal strip of this physiographic province. Numerous plants occur throughout the Coastal Plain from New Jersey or Virginia to Georgia or Mississippi, but fail to range coextensively with it in the southern Mississippi Valley, and terminate their distribution before reaching the mouth of the Rio Grande. Ilex opaca, Pinus teda, Itea virginica, and Quercus falcata are all examples of this type of distribution. In all of these cases we undoubtedly have to do with three sets of limiting conditions; those operating in the Atlantic coast region, those in the Mississippi Valley, and those deter- mining the extreme southern limit in Texas. In at least the first of these regions we have to reckon with the modifications of climatic conditions which are due to the soil. | ‘Vamperatune Davs 1” isonmar Frost.ess Season (F. S.) Hort Days, F. S. Coup Davs, F. S. Prysiotocica, Summation, F. S. Norma Daicy Mean, coLoest 14 avs of YEAR Normat Dairy Mean, YEAR PRECIPITATION Normat Dairy Mean, F. S. Days IN LONGEST Normal Rainy Peaioo, F. S. Days IN LONGEST Normat Drv Penion, F. S. Mean Totat, Year EVAPORATION Daitv Mean, 1887-8, F. S. Moisture Ratios NormMAL P/E, F.S. Normat 77/E, F. S. Normat P/E, Year. Humioity Normat Mean, F. S. SUNSHINE Normat Daicy Duranion, F. S. MoIsTURE- TEMPERATURE INDICES Noamat P/E x T, F. S., PHYsioLocicat MeTHoo (_________ SEE Fig. 55. Climatic extremes for Ilex opaca. 548 CORRELATION OF DISTRIBUTIONAL FEATURES. Magnolia grandiflora (fig. 56).—The distribution of this magnolia covers only the portion of the Coastal Plain between Cape Fear and the Trinity River, and south of the northern boundary of Louisiana. This is a region with no cold days, in our sense, and with high ranges for all of the temperature conditions studied. It is also a region with a high normal daily mean precipitation, although the amplitude of this condition is not great. The amplitude in number of days of both the wet and the dry periods is very wide, and those of evaporation, humidity, and the moisture ratios are narrow. The range of Magnolia is remarkable from the fact that its limit corresponds with a large number of isoclimatic lines, giving the follow- ing indications regarding the conditions which it encounters: a frostless season of 240 days or more, a normal daily mean temperature of 45° or more for the coldest 14 days of the year, an annual mean temperature of 65° or more, a mean relative humidity in the frostless season of 65 per cent or more, and a value for the moisture-temperature index of 15,000 or more. None of the isoclimatic lines for moisture conditions coincide, even roughly, with the limit of Magnolia, although the narrow amplitudes of evaporation, moisture ratios, and humidity indicate that this tree encounters only a small part of the total range of these conditions for the United States. The limit of Magnolia corresponds rather closely with the line to the south of which are found 5 or more species of evergreen broad-leaved trees (see plate 3), and the climatic characteristics just mentioned may be taken as defining the region which is favorable for the abundant occurrence of trees of this type. TEMPERATURE Days im Norma Faostiess Season (F. S.) EEE Eee Hor Days, F. S. (ee ee Coin Days, F. S. [E30 ee Prysio.ocicat Summation, F. S. Te Norma Daity Mean, cocogst 14 vars or Year (_CC“‘“‘($;CCOC#*#C(#WNNNNNN¥NWNKNN._____ Es Normat Daity PAEAN, YEAR a SE ET PRECIPITATION Norma Dairy Mean, F. S. SS Days IN LONGEST Normat Rainy Perioo, -.S. (es Days IN LONGEST Normal Dry Pesioo, F.S. (i s ) Man Torat, Year: Se eer. EVAPORATION Daity Mean, 1887-6, F. S. SS ey a ae Morsture Ratios Nonmat P/E, F. S. EE EEE eeeE—E—Eeeeeeeeeeeee Normat 7/E, F. S. EE ee ee Nonmac P/E, Year = EE. eee Humipiry Normac Mean, F. S. SS OPEL E SCLEROSIS SUNSHINE Norma Daity Duration, F. S. | NS MOoIsTURE-TEMPERATURE INDICES Norma P/E x T, F.S., Puysiovocicat MetHop (ee Fic. 56. Climatic extremes for Magnolia grandiflora. CORRELATION OF DISTRIBUTIONAL FEATURES. 549 Serenoa serrulata (fig. 57).—Only the extreme edge of the southern Atlantic Coastal Plain is occupied by this palm, from southern South Carolina to the eastern border of Texas. It occupies the warmest and moistest portion of the area which has just been stated to be favorable for the development of evergreen broad-leaved trees, with which it may be classed. Considering the small area occupied by Serenoa, it encounters a wide range of conditions in both temperature and pre- cipitation, together with narrow ranges of evaporation, humidity, and the moisture ratios. It encounters a frostless season of 231 days or more and no cold days, in our sense. Its limit coincides closely with the line of 50° for the normal mean temperature of the coldest 14 days of the year, although the palm does not follow the region of these tem- perature conditions into southern Texas. The encountering of the conditions expressed by a moisture ratio of 1.00 appears to be respon- sible for the westward limitation of a plant which is elsewhere con- trolled by temperature conditions. TEMFEZRATURE Dava in Normat Frosrcces Season (F. S$.) Hor Days, F. S. Corp Days, F. S. PHYSIOLOGICAL SUMMATION, F. S. Normat Daicy Mean, covogst 14 oays of Year (_ Norma Daicy Mean, YEAR PR ea ee PRECIPITATION ‘Nonmat Dairy Mean, F. S. a Days iN LONGEST Nonmat Rainy Penioo, F.S. (__ ss CCCCtC—C“‘édCrC Days In LONGestT Norma: Dav Psnioo, F.S. (_ i Mean Totat, YEAR Hie ee ae ee i ee a EVAPORATION Daity Mean, 1687-8, F. S. CREE) — ID TS MAL ee EE Moisture Ratios Normat P/E, F. S. {eet mor 2 ET oe see eee ee eee Norma 7/E, F. S. (ase ee ee ey Normat P/E, Year es ES ee ee Humipity Normat Mean, F. S. ia ee Ta Ta re) eae SUNSHINE Normat Daicy Duration, F. S. Cy MoisTuRe-TEMPERATURE INDICES (ee Te) es - . | Fig. 57. Climatic extremes for Serenoa serrulata. Cephalanthus occidentalis (fig. 58)—The distribution of Cepha- lanthus is remarkable from the fact that it is one of the very few woody perennials of the southern United States which has a nearly trans- continental distribution. It is very infrequent west of the one-hun- dredth meridian, apparently being absent from New Mexico, but appearing again in southern Arizona and in the San Joaquin Valley of California. A‘distribution which is so extensive both latitudinally and longitudinally naturally encounters a wide amplitude of conditions, both with respect to temperature and moisture. None of the ampli- tudes of conditions for Cephalanthus are sufficiently narrow to give any 550 CORRELATION OF DISTRIBUTIONAL FEATURES. suggestion of their importance as limiting the plant. Its distributional edge, extending from central Michigan to the mouth of the Colorado River, is 2,300 miles in length, which in itself suggests that very-dis- similar constellations of conditions are involved in its limitation in different sections of this line. In a plant of palustrine habitat it is not surprising to find that the normal moisture conditions of upland habitats have no apparent importance. We find Cephalanthus occur- ring in localities where the moisture ratios approach their minimum values for the United States, and extending from there halfway through the gamut of values for this compound condition. It also encounters extremely low values for the normal daily precipitation and high values for the number of days in the longest dry periods. These con- ditions, however, have no apparent influence on the plant in the habitats where it occurs, although they are probably responsible for the fact that there are very few favorable habitats for it in the localities where these extremes are registered. In the San Joaquin Valley the atmospheric conditions are extremely arid, but there are numerous areas of moist soil, and Cephalanthus is there abundant. It is by no means true that all palustrine or swamp plants are able to withstand extremely arid atmospheric conditions if they are supplied with an abundance of soil-moisture, and only a relatively small number of the plants associated with Cephalanthus in the southeastern United States are found growing with it in southern Arizona and the San Joaquin Valley. It is in the eastern half of its range that Cephalanthus encounters the greatest amplitude of temperature conditions. It is there found in localities with no hot days, as many as 137 cold days, where the TEMPERATURE Days in Normat FrRosTLess Season (F. S.) Hor Days, F. S. Cot Dave, F. S. niall Bat pee oe eee i AS A Days IN LONGEST Norma Dry Peniop, F. S. EVAPORATION Dairy Mean, 1887-8, F. S. Moisture Ratios Norma P/E, F.S. Normat 7/E, F.S. Norma P/E, Year Humipity Normac Mean, F. S. SUNSHINE Norma Daicy Duration, F. S. , Motsture-TemPerature Indices Normat P/E x T, F.S., Paysiovocicat MetHoo (cers Fic. 58. Climatic extremes for Cephalanthus occidentalis. CORRELATION OF DISTRIBUTIONAL FEATURES. ool physiological summation is as low as 2,100, and where the normal daily mean of the coldest 14 days of the year reaches 11°. Some of these conditions may, indeed, be exceeded at the extreme limit of this plant in Canada. Much more complete information regarding Cephalanthus will be needed before it is possible even so much as to suggest some of the conditions that may be keeping it from spreading into other parts of the United States, if indeed it is not now making secular movements to the west and north. A knowledge of its relative abundance in different parts of its area and of the character of the habitats which it occupies throughout the edge of its distribution might aid in solving the problem which it presents. It seems to be a plant that would be well worthy of a thorough ecological study. Decodon verticillatus (fig. 59).—This is an aquatic or palustrine shrub found throughout the States east of Wisconsin, Missouri, and Louisi- ana, with the exception of southern Florida. The temperature condi- tions which it encounters are almost as wide in amplitude as those encountered by Cephalanthus. The amplitudes of the moisture condi- tions are somewhat narrower than in the case of that plant, but the only condition that can be regarded as having a significantly narrow amplitude is the number of days in the longest dry period, which reaches a maximum value of 78 days. The isoclimatic lines for the latter condition indicate that the area of Decodon is roughly limited by the line for 25 days in the longest dry period. Another line approxi- mating the limit of Decodon is that for a mean annual precipitation of 30 inches, the distribution of the plant extending over the region in which the rainfall is greater than that amount. TEMPERATURE Days in Normat Frostress Season (F. S.) (eee es | Hor Days, F. S. a fat Seal Tear! marian rt on see ote See Carey Pa Cotp Days, F. S. PHYSIOLOGICAL StsmmarTion, F. S. Normat Daity Mean, coLpest 14 pays of Year —————————— Norma Daicy Mean, Year PRECIPITATION ' Normat Dairy Mean, F. S. | i Days IN LONGEST NoRMAL Rainy PERIOD, F. S. (__ SRSA es Days IN LONGEST Normal Dry Periop, F.S. (Sey Mean Torat, Year (es) EVAPORATION Daiy Mean, 1887-8, F. S. EE EEE—E——EEEEX=_ —— Moisture Ratios Normat P/E, F. S. EEE) Norma 7/E, F. S. =a ne eee ee Norma. P/E, Year = . i .# .}» #2]. eRe Humipity Normat Mean, F. S. | PT STEER SUNSHINE Normat Daicy Duration, F. S. L$ MoisTure-TeMPERATURE INDICES Normat P/E x T, F.S., PHysiococicat MeTHoo (aaa Fia. 59. Climatic extremes for Decodon verticillatus. ~~ 552 CORRELATION OF DISTRIBUTIONAL FEATURES. The palustrine and semipalustrine shrub Itea virginica (see plate 23) has a more restricted range than Decodon, very similar in its general outlines to that of Ilex opaca, and apparently limited, like the latter, by high values for temperature and moisture conditions. Artemisia tridentata (fig. 60).—This plant is the dominant element of the vegetation of the Great Basin, and it extends in diminished abun- dance eastward to the edge of the Great Plains, upward into the moun- tains, southward to northern New Mexico and Arizona, and still more sparingly into southern California. The map of its distribution (plate 22) is not drawn to indicate the mountain areas from which it is absent. When these breaks in the distribution are taken into account the shrub is found to occupy an area which is much more homogenous in its climatic conditions than its wide extent would seem to indicate. The amplitude for Artemisia is wide with respect to the number of days in the average frostless season, the number of cold days in the year, the normal daily mean for the coldest 14 days, and the normal daily mean for the year. With respect to the number of hot days and the physiological summation of temperature the amplitudes are nar- row, however. The precipitation conditions also exhibit narrow ampli- tudes, with the exception of the number of days in the longest dry period. The amplitude of evaporation and humidity conditions is made to appear wide because of the extension of its area to the Pacific coast, where the plant is extremely rare, its most westward abundant occurrence being in the Cuyamaca Mountains, 40 miles from the coast. The values for the moisture ratios exhibit narrow amplitudes, reaching, in two cases, the lowest values for the country. It is manifest that the southern limitation of Artemisia is not solely a matter of its inability to withstand extremely arid conditions, since sive Nene ecoe eee BEI ee PrysioLocicaL SUMMATION, F. S. Normat Daicy Mean, cotoest 14 cays of Yean |__s—“ (sti‘“‘(Cr:”;*Cr ee Normac Daicy Mean, Year PRECIPITATION Normat Daicy Mean, F. S. —ZZ—*=Z2aEZ———_ CC‘ DAYs IN LONGEST Normat Rainy Penioo, F:S. Li "ss ee ee Days IN LONGEST Normat Dry Perioo, F.S. [eee a eee Mean Torat, YEAR EVAPORATION Daity Mean, 1887-8, F. S. Moisture Ratios Normat P/E, F. S. Normat 7/E, F. S. Normat P/E, Year Humipity Norma Mean, F. S. SUNSHINE Normac Dairy Duration, F. S. fA OISTURE- TEMPERATURE INDICES Normat P/E x T, F. S., PHysiotocica MetHop Bara Fic. 60. Climatic extremes for Artemisia tridentata. CORRELATION OF DISTRIBUTIONAL FEATURES. 593 it encounters the lowest normal daily mean precipitation (Reno, Nevada), the highest evaporation (Winnemucca, Nevada), and the lowest moisture ratio (Winnemucca, Nevada). The most trying con- ditions with respect to these three important moisture conditions are, therefore, not found near the southern edge of the distribution of Artemisia, but well within the region of its greatest abundance. The narrow amplitude of the number of hot days suggests that this may be a condition of importance in limiting this plant at the south, and the maximum of 118 hot days for its area is close to the value of the isoclimatic line of 120 days, which is seen to approximate the dis- tributional limit in Arizona and Nevada. The amplitude of the physiological summation of temperature is also narrow, and the maxi- mum value encountered by Artemisia is 8,400. The evidence would indicate that these and associated temperature conditions are respon- sible for the southern limit, or else that they cooperate with the low moisture conditions in rendering the deserts along the lower Colorado and Gila Rivers untenable for this plant. The eastern limit of Artemisia appears to be set by some of the several moisture conditions which present isoclimatic lines closely paralleling its course. The indications of these correlations are that the plant nowhere encounters a mean annual rainfall of more than 20 inches, reaches no areas in which the longest normal rainy period is more than 25 days, nor the moisture ratio more than 0.40, and that it is accustomed to normal longest dry periods of at least 75 days in length. It is more than probable that the northern limit of Artemisia is set by conditions similar to those that appear to be responsible for its eastern boundary, with the possible cooperation of low temperature conditions. Low temperatures accompanied by arid atmospheric conditions appear to permit the northward extension of the plant into Canada, but low temperatures accompanied by more humid conditions appear to keep it from the northern Rockies and the Coast Range, as well as from the higher slopes of the Sierra Nevada. Covillea tridentata (fig. 61).—The range of Covillea extends from southern Nevada and interior California through southern Arizona and New Mexico to the lower part of the valley of the Rio Grande. The area which it occupies in the United States is less than half of its total range in North America, which extends southward through the deserts of central Mexico. No cold days, in our sense, are encountered by Covillea, and the amplitude of the normal daily mean temperature of its area is rela- tively wide. In other respects the temperature conditions present nar- row amplitudes, especially when compared with those for Artemisia. The data for moisture conditions reveal the extremely arid conditions under which Covillea exists, showing that it also extends into regions 554 CORRELATION OF DISTRIBUTIONAL FEATURES. with much more favorable conditions, particularly with respect to the longest dry periods, daily mean evaporation, and normal humidity. The distributional area of this plant contains few climatological sta- tions, and it is certain that the conditions actually met by it include the lowest values of normal daily mean precipitation, the longest normal dry periods, and the lowest mean total precipitation o the year. In the vicinity of Death Valley and in the arm of the Mojave Desert which stretches southeast toward the Colorado River are to be encountered the most arid areas in the United States, and in them Covillea is one of the most ubiquitous plants. The narrow amplitude of the moisture ratios indicates here, as in the case of Artemisia, that conditions of greater general favorableness with respect to this condition are either directly inimical to Covillea, or else that they are accompanied by associated conditions which are of importance in limiting its range. The extremely narrow amplitude in number of days in the longest rainy period signifies that there is a great importance in this factor, probably having to do with the effect of prolonged wet periods in making the conditions of soil aeration injurious to Covillea. The distributional boundary lies close to the northern limit of the area in which there are no cold days, and this condition, with its associated conditions of low winter temperatures, is undoubtedly of great importance in controlling the northward limitation of the plant. Covillea appears, in brief, to be confined to a region in which there are no prolonged periods of rain and no severe periods of cold. The narrow amplitude of the physiological summation of temperatures for the frostless season indicates importance for this condition, but the fact that Covillea is an evergreen points to the low temperatures of winter having a greater significance in its limitation than do the summations for the growing season. ” Temperature Days 1n Normat Frostiess Season (F. S.) ne: Hot Days, F. S. PE a i $$$iééé« i =<. Corp Days, F. S. | am eA = Ko ge NTT ow mE SG Puysiotocicat Summation, F. S. - $— eee Normac Daisy Mean, coLoest 14 pays of Year (_—C—C“‘;CNC™”™”””CC ES) Norma Daicv Mean, YEAR [eeu eaas Pa Se aw ee : E See PRECIPITATION Normat Daicy Mean, F. S. CE ||} DAYs In LONGEST NORMAL RAINY PEniobd, F..S. (Eo Days IN LONGEST Normal Dry Perioo, F.S. 9 (_——SCSCSCSCSCSC=C | Mean Torat, Year i ian EE ne oye mRne mE nE eee EVAPORATION ; Daity Mean, 1887-8, F. S. ND Moisture Rarios Normat P/E, F. S. ar 5 Normat 77/E, F. S. ee ee Normat P/E, Year Wl re a Humipity Normac Mean, F. S. ee SUNSHINE ' Norma Daity Duration, F. S. Ci ii niente | MoisTURE=-TEMPERATURE INDICES Normat P/E x T, F. S., Puysiovocica, MerHo> es Fic. 61. Climatic extremes for Covillea tridentata. eee CORRELATION OF DISTRIBUTIONAL FEATURES. 55D Silphium laciniatum (fig. 62).—The range of this plant extends from Texas to South Dakota and from Alabama to Pennsylvania, but itis mostabundant in the Grassland Deciduous-Forest Transition and in the Grassland. The distributional area is such that the plant encounters only 140 cold days in the frostless season. The amplitudes are relatively wide in all of the temperature conditions and are also wide in all of the moisture conditions except the number of days in the longest normal dry period. The moisture ratios are also relatively narrow in amplitude, the extremes for 7/E in the frostless season being, minimum 0.47, maximum 1.32. The eastern limit of Silphiwm is very roughly approximated by the isoclimatic line of 0.80 for the moisture ratio 7/E, isotherms of 45° and 50° for the annual daily mean temperature, and is closely followed by the isotherm for a physiological summation of 7,500°. The western limit is closely approximated, at least in part, by the isoclimatic lines of 20 inches annual mean total precipitation, 75 days in the longest normal dry period, 25 days in the longest normal rainy period, and a moisture ratio of 0.40. Although the extreme values of the moisture ratio for Silphium are 0.47 and 1.32, nevertheless the location of its entire range with respect to the isoclimatic lines for this condition indicates that the plant is found mainly where the moisture ratio is between 0.40 and 0.80. The northward extension in the area pre- senting this range of conditions is apparently controlled by tem- perature conditions, among which the physiological summation is most important. The central location of the range of Silphiwm laciniatum gives it a distributional edge about 3,300 miles long, with only its southern limitation formed by the ocean. These circumstances make it a par- TEMPERATURE Days in Nornmat Frostiess Season (F. S.) a ey Hor Days, F. S. Coup Days, F. S. PHysiotocicat Summation, F. S. I Normat Daity Mean, covoest 14 pays or Year (___—s§s LE TE Normat Daicy Mean, Year LER EIS PRECIPITATION Normat Dairy Mean, F. S. i Days IN LONGEST Normal Rainy Perioo, F.S. (_ in Sd Days IN LONGEST Normat Day Perioo, F.S. (ees Mean Torat, Year ea EVAPORATION Daity Mean, 1887-8, F. S. ESS > Moisture Ratios Normat P/E, F. S. (aaa ND Sen ee ee ey Normat 7/E, F. S. (= oer ee Normat P/E, Year (eee ay Humipity Normat Mean, F, S. | SUNSHINE Normat Daicy Duaation, F. S. SO, —e MolsTURE-TEMPERATURE INDICES Normat P/E x T, F. S., PHYSIOLOGICAL MeTHoo (SSS ep a TS Fira. 62. Climatic extremes for Silphium laciniatum. 556 CORRELATION OF DISTRIBUTIONAL FEATURES. ticularly favorable subject for fuller investigation. Its ability to with- stand a considerable range of temperature conditions between Missis- sippi and South Dakota and its ability to range through dissimilar moisture conditions from Ohio to Texas should be investigated in terms of the habitat requirements of the plant in the various portions of its range. From such information as is available, this plant seems to be confined to the most arid situations on the eastern edge of its area and to relatively moist situations or seasons on the western edge, so that it would be particularly valuable to have parallel series of data for the local conditions met by the most widely separated colonies. Bouteloua oligostachya (fig. 63).—This abundant and characteristic grass of the Great Plains is found throughout the Grassland, in the western part of the Grassland Deciduous-Forest Transition, and in the southeastern part of the Desert. It is most abundant in the Grassland and the Desert-Grassland Transition, becoming infrequent at the southeastern and southwestern corners of its area. The temperature conditions encountered by Bouteloua are those of the Grassland, but with slightly higher maxima in each case (except number of cold days). The amplitude of the precipitation conditions | is much greater for Bouteloua than for the Grassland, the maxima being higher and the minima lower. With respect to the length of the longest normal dry period particularly, Bouteloua exhibits its ability to range from the conditions of the Grassland far into those of the Desert, enduring 283 days in the vicinity of Phoenix, Arizona. Like many other perennial grasses, it is able to withstand prolonged and severe conditions of drought in its resting condition and to take advan- tage of moist periods of relative infrequency. TEMPERATURE Days in Normat Frostiess Season (F. S.) a ee Hort Days, F. S. a eee Coup Days, F. S. Cr a Ee See TE ORE PRR oon oer OAS Rae PHYSIOLOGICAL SUMMATION, F. S. nes | Normat Daicy MEAN, COLDEST 14 DAYS OF YEAR NN Normat Daity Mean, YEAR PRECIPITATION Normat Daicy Mean, F. S. Days IN LONGEST Normat Rainy Penton, F. S. a I I SE SO NTS ES Days IN LONGEST Normat Dry Peaioo, F. S. Mean Tora, YEAR EVAPORATION Dairy Mean, 1887-8, F. S. Moisture Ratios Normat P/E, F. S. Norma 7/E, F. S. Norma P/E, Year HumiIpiTy Normat WMiean, F. S. SUNSHINE Normat Daity Duration, F. S. Ps | MOoISTURE-TEMPERATURE INDICES Normat P/E x T, F. S., PHysiovocica, MetHoo | SaaS eR Sd Fig, 63. Climatic extremes for Bouteloua oligostachya. CORRELATION OF DISTRIBUTIONAL FEATURES. 557 The minimum conditions of evaporation and the maximum condi- tions of humidity are very similar for Bouteloua and the Grassland region, indicating that conditions which determine the eastern limit of the Grassland also limit one of its most characteristic plants, and this is also true of Bulbilis dactyloides and Bouteloua hirsuta. The maximum conditions of evaporation and the minimum conditions of humidity, however, are respectively higher and lower for Bouteloua than for the Grassland. The moisture ratios for the frostless season are very similar for this plant and for the Grassland as a whole, although the minimum values for Bouteloua are lower. The eastern limit of Bouteloua, like that of many of the grasses associated with it, is apparently set by some one of the moisture con- ditions, or by a combined operation of several of them. Neither the area of Grassland nor that of Boutelowa extends very far into the region with more than a daily mean precipitation of 0.100 inch with more than 75 days in the longest rainy period, or with a mean annual precipitation of more than 25 inches. The position of the western boundary of Bouteloua indicates that it is there again limited by mois- ture conditions. Although we have presented no data bearing directly on the seasonal distribution of precipitation, it is apparent that this grass is unable to penetrate far into the portion of the Desert, in which the summer rainfall is ight. The ability to withstand dry periods of as much as 283 days has enabled it to range as far as the area of uncer- tain summer rains in the lower Colorado Valley. It is not able, how- ever, to extend its area into the region in which there is frequently no summer rain for many successive years. Agropyron spicatum (fig. 64).—This grass is found throughout the Grassland north of Oklahoma and New Mexico and in the outlying portions of that vegetation which fringe the northern edge of the Great Basin Microphyll Desert. Although withstanding the entire amplitude of cold days this grass encounters lower and narrower amplitudes of the other temperature conditions. It has a relatively low maximum (125) for the number of hot days and a low maximum (11,600) for the physiological temperature summation. With respect to precipitation it shows wider amplitudes than those of the Grassland, and this is true of evaporation and the moisture ratios for the frostless season. Agropyron appears to have its eastern limit set by the same con- stellation of moisture conditions that controls the Grassland and other grasses, but it does not follow the conditions favoring Grassland.as far as the southern limit of that vegetation. Nowhere does it encounter more than 100 to 120 hot days, nor does it range into regions with a physiological summation of temperature greater than 12,500. These and associated temperature conditions appear to be responsible for its southern limitation. 558 CORRELATION OF DISTRIBUTIONAL FEATURES. The failure of Agropyron to extend farther into the northern part of the Great Basin Desert is apparently due to the moisture conditions of that region. A more precise correlation of its distribution with that of the moisture ratio (7/E) would probably show that it does not occur where the values of this ratio are lower than 0.20, the same value that limits it in Arizona and New Mexico. The actual moisture-ratio conditions of the areas occupied by Agropyron in Utah and northern Nevada are poorly exhibited by our data, which are from stations located in the valleys. TEMPERATURE Oavs in Normat Frostiess Season (F. S.) Hor Days, F. S. Caco Days, F. S. Prvsiorocicat Summation, F. S. Norma Daicy Pcan, cotogst 14 pays or VEar NORMAL Daity Mean, YEAR PRECIPITATION Normac Daity Mean, F. S. Days in LONGEST Norma Rainy Peniop, F. S. Days IN LONGEST Normat Dry Peniop, F. S. Mean Torat, Year EVAPORATION Dairy Mean, 1887-8, F. S. Moisture Ratios Norma P/E, F. S. Nonmat 77/E, F. S. Normat P/E, Year Humipity ‘Norma Mean, F. S. Mi SunNsHINE Noamat Dairy Duration, F. S. \ MoistuRe-TEMPERATURE INDICES Norma P/E x T, F.S., Pxysiovocica, McTHoo (ain 7?) Fic. 64. Climatic extremes for Agropyron spicatum. Hilaria jamesis (fig. 65).—This is a characteristic grass of the Desert- Grassland Transition region, ranging from western Texas to southern Nevada and northward to extreme southwestern Wyoming. All of the climatic conditions exhibit narrower amplitudes for Hilaria than for the Grassland, with the exception of the number of days in the longest normal dry period. The narrowest amplitude among the temperature conditions is that of the normal daily mean for the coldest 14 days of the year, which ranges from 27° to 45°. At few points does the limit of Htlaria extend north of the isoclimatic line for 25° as the daily mean of the coldest fortnight, and the correspondence of these lines would indicate that this condition is an important one in limiting the northward distribution of the grass. The eastward extension of Hilarta in Texas is such that it nowhere encounters moisture ratios (7/E) higher than 0.40, nor rainy periods of more than 25 days. These are the same conditions that appear to limit the eastward range of other grasses, but different intensities are involved in the case of Hilaria from those mentioned in connection with Bouteloua. si at ar at a a ee CORRELATION OF DISTRIBUTIONAL FEATURES. 559 With respect to the westward range of Hilaria, it appears that the same limiting conditions are operative that have been mentioned in connection with Bouteloua oligostachya. Extremely long normal dry periods, in excess of the 250-day maximum for Hilaria, are inimical to it as to all other perennial grasses. Temperature Dave in Nonmat Frostices Scason (F.S) (es Hor Davs, F. S. CO E—E EE ————————— Coup Dara, F. S. Po ——eeeeeeeeeee Prysiovocicat Summation, F. S. Ts °° &# #&# # — 4 Norma Daicy Mean, cocogst 14 oavs of Year (_—‘“C;C;C;‘ ‘iC TY Norma Daity Mean, Year (__ ene) . Pagciritation Normat Day Mean, F. S. EEE C—C—C“‘“OSOC;!O CCS Days In LONGEST Normat Rainy Perion, F.S. BME Davs In LonGest Norma. Day Penioo, F.S. (_ [ii es ‘@ean Torat, Year Caine tees 7 0 aa ea EVAPORATION Daiy Mean, 1887-8, F. Ss. Le Moisrune Ratics Norma P/E, F. S. {I renee ee Normar 7/E, F.S. CE Saisntcernmne env ae Tae ee ey Nonwar P/E, Year (CUE eesnenmnmnrsssiatreniinss ele Humioity Normat Mean, F. S. Tl” EEE) Sunsnine _Nonmat Daity Duration, F. S. ee) Moistune- TEMPERATURE INDICES Nonmat P/E x7, F.S., Puysiotocicat MeTxoo (_ SY > Fia. 65. Climatic extremes for Hilaria jamesii. Sparganium americanum (fig. 66).—Sparganium is widely distributed throughout the eastern United States, except in peninsular Florida, and from its westward extension in Canada it reappears within our limits in Washington. A considerable number of northern plants exhibit distributions of this type, Dulichium arundinaceum being another example (see plate 27), with a range closely like that of Spar- ganuum. The range of another palustrine plant, Siwm cicutefolium, is of an analogous character (see plate 28), its limits being far enough south, however, for it to present a continuous area within the United States. The distribution of each of these palustrine plants is such that they are absent from the arid and semiarid regions, where they might find localities with suitable soil-moisture conditions, although much more widely separated than in the moist regions. The western edges of the ranges of Sparganium and Dulichium in the Eastern States run parallel to the isoclimatic lines for moisture conditions. Although these are plants of wet habitats, there is here a suggestion of their inability to extend into the regions with very high evaporation. In other words, the conditions expressed by the moisture ratio are of importance to them even when the numerator of the ratio is constant and of high value. Their ability to withstand lower moisture ratios in eastern Washington than they endure along their western edge in the Central States is doubtless due to the interaction of temperature con- ditions. 560 CORRELATION OF DISTRIBUTIONAL FEATURES. Wide ranges are exhibited by Sparganium for both temperature and moisture conditions, due to its extended north-and-south range in the Eastern States, and to its occurrence from the Atlantic coast to the arid interior of Washington. Its climatic extremes are of interest in comparison with those of Siwm, which shows the broadest amplitudes of any of the plants that we have selected for investigation. The dis- tribution of Siwm indicates that it is able to withstand the entire gamut of temperature conditions for the United States, excepting those encountered in peninsular Florida, and that it is excluded only by the lowest conditions expressed by the moisture ratio (0.40 or lower). Sium, Dulichium, and Sparganium are apparently alike in being unable to withstand the highest intensities of evaporation, in spite of the saturated substrata in which they are invariably found, apparently belonging to that already well-known group of plants in which the transfer of water from absorbing to transpiring organs is internally limited. TEMPERATURE Dave in Ronwac Frostites Season (F.S) (SS Hort Daves, F. S. BO Coto Dars, F. S. a a ee Oe EE Sa Prysio_ocica: Summation, F. S. BO Normat Oaity (ean, coocer 14 cays of Vean Ses SS) Normat Daicy Mican, Year SEA OL OR ETT PRECIPITATION Nommat Dairy Mean, F. S. SN nc i i ee Daye IN LONGEST NORMAL Rainy PERico, F. S, SmaI StS peri a a it aan tn nOny nti te ee es Days In LONGEST Normat Dry Period, F.S. i _ EL Mean Tora, Year Saas a8 - EvarPcrarion Daity Mean, 1687-8, F. S. a | Moisture Ratios Norma P/E, F.S. EE ERE EE DE IO A ee ee ES ED, Norma 7/E, F.S. RS SE SE I I Ly PET PY ED Normat P/E, Year EEE PEI STEED DS OE ET DE CS Fe Humioity Normar Mean, F. S. Oc SUNSHINE Normat Daity Duration, F. S. eee MoisTuRe-TEMPERATURE INDICES Normat P/E x T, F.S., Pysiovocicat METHOD (aziz ata=S Fic. 66. Climatic extremes for Sparganium americanum. Arceuthobium americanum (fig. 67).—This mistletoe is found throughout the Rocky Mountains and the mountains of the Great Basin and its western edge. Its actual occurrence is limited to the forested portions of the area indicated for it in plate 29 (see plate 1). A number of the climatological stations located within the area credited to it are not in situations actually occupied by Arceuthobium, and consequently some of the moisture conditions, in particular, are higher than indicated in figure 67. Arceuthobium americanum is chiefly confined to Pinus contorta (including P. murrayana) as a host, but appears to be absent from it in Washington, Oregon, and California east of the Cascade Mountains. CORRELATION OF DISTRIBUTIONAL FEATURES. 561 The area of Arceuthobiwm is therefore closely similar to that of Pinus contorta, with the exception of its absence from the northern Pacific coast. The area of the mistletoe (plate 29) has been drawn in a more generalized manner than has that of Pinus contorta (plate 16), because less information is available regarding the occurrence of the former. The climatic extremes for Arceuthobium are very similar to those for Pinus contorta, except with respect to the high conditions of precipita- tion, moisture ratios, and humidity encountered by the host in the Pacific-coast part of its range. This is a case in which a sap parasite is not able to accompany its host throughout the entire range of the latter, apparently as a result of the operation of limiting climatic con- ditions upon the parasite. The well-known xerophytic character of the mistletoes apparently brings their distributional behavior into accordance with that of other xerophytic plants in their inability to invade regions of high moisture conditions. The only mistletoe that is found in Washington west of the Cascade Mountains is a locally abun- dant form of Arceuthobium douglasti growing on T'suga heterophylla. Temperature Dave in Nonmat Faostices Scacon (F.S) Ey Hor Davs, F. S., | Coto Days, F. S. LO PrysioLogicat Summation, F. S. CE 2 Normat Daity Maan, coLornest 14 cays of Yean [__ TF Nommat Daity Mean, Year Cs PRreciriTation Normat Daicy Mean, F. S. a Days in toncest Noamay Rainy Penide, F.S. MB} Davs in Lonaesy Nqnmat Day Pemion, F.S. 00 (es | ‘Mean Torac, Year ares, Evaporation Daity Mean, 1887-6, F. S. (__ ee Ee EE a eee ee Molsture Ratios Norma P/E, F. S. GR ein ere Normat 7/E, F. S. Mt ea ee LL ies the et De ae Se Normat P/E, Year DR Humioity Normat Mean, F. S. ME SUNSHINE a Normat Dairy Duaation, F. S. ————~—E——— = CC“‘“‘($SNSN’N’N’NN’N’NNN ‘J MoisTURE-TEMPERATURE INDICES Normat P/E x T, F.S., Paysiococica Metho0 ee Fig. 67. Climatic extremes for Arceuthobium americanum Phoradendron flavescens (fig. 68)—A remarkably wide range is exhibited by this plant and its varieties, extending from coastal Oregon, through California and the extreme southwest, to Texas, Florida, Indiana, and New Jersey. The species itself is found from New Jersey to Louisiana, variety orbiculatum in Arkansas, Oklahoma, and Texas, variety pubescens in Texas, variety macrophyllum in Arizona, and variety villoswm in California and Oregon. Both the species and the varieties of this mistletoe are found on a number of different host trees, so there is no such restriction of its range as that shown for Arceuthobium americanum. Little is known 562 CORRELATION OF DISTRIBUTIONAL FEATURES. regarding the water-supply of sap parasites and the relation between the seasonal conditions of the host and the maintenance of the tran- spiration-stream in the parasite. It is safe to assume, however, that the water-supply for mistletoe is not subject to as sharp nor as pro- nounced fluctuations as that of most autonomous plants rooted in the soil. The influence of precipitation and soil-moisture conditions is exerted very indirectly on the mistletoes, and we may regard them, for the purposes of our investigation, as somewhat analogous to palus- trine plants. Phoradendron encounters wide ranges of all temperature conditions, except in regard to the number of cold days. The wide range of mois- ture conditions which it meets is to be anticipated from its independ- ence of these conditions as they affect autonomous plants. The extremely wide amplitudes of evaporation conditions through which it ranges apparently indicate that it is able to secure supplies of water sufficient for the maintenance of high rates of transpiration. In the most arid parts of its range, however, Phoradendron flavescens var. macrophyllum is found only on trees that occur in relatively moist situations, and not on the small microphyllous trees, in which the maintenance of the transpiration-stream is precarious. The temperature condition which appears to be most potent in limiting the range of Phoradendron is the number of cold days. A very small part of its area lies inside the region in which cold days are encountered, and in this part (the Ohio Valley) it reaches the maximum of 44 days for this condition. TewmPenatuae Davs im Nonmat Frostices Season (F. S300 (nS Hot Days, F. S. Pee Ly ee ER a TT ae Coio Days, F.S. _——_—_——_—————~—L_ °° °° °° °° © 4} Prysiococicat Summation, F. S. TSS Sr ea yaa a aa IT Nonmat Dairy Mean, coLoest 14 pavs of Yeam [_____C~*~C*i‘“C*‘*idi Normat Dairy Mean, Year LLL PRECIPITATION Normat Daicy Mean, F. S. ea aa oe RE ORE UEE PE) = Days iW LONGEST Normal Rainy Penson, F. S. Saas | Days iw LONGEST Normat ODay Penton, F.S. (aE Mican TOTAL, YEAR EVAPORATION Daity MEAN, 1887-8, F. S. aE EE RE I TTS CTE Moisture Ratios Norma P/E, F. S. Pa |) Normat 77/E, F.S. Norma P/E, Year ; Bee Humipity Normac Mean, F. S. a SUNSHINE Hornmat Dairy Duration, F. S. SS MOoisSTURE-TEMPERATURE INDICES Nonmat P/E xT, F.S., Prvsiococicat MetHon [apa SES OI ei gg OP Fic. 68. Climatic extremes for Phoradendron flavescens. Daucus pusillus (fig. 69).—This annual herbaceous plant ranges from the coastal region of Washington and Oregon through California op) CORRELATION OF DISTRIBUTIONAL FEATURES. 563 and the extreme Southwest to Oklahoma, Mississippi, Florida, and North Carolina (see plate 31). The relation of Daucus to the climatic conditions of its wide range requires interpretation in terms of its seasonal behavior in different sections of the range. In the States east of Texas it is an early summer plant, reaching maturity in July or later; in the Desert region it is an early spring plant, reaching maturity in March or April; on the Pacific coast it is a late spring or early summer plant, reaching maturity from May (in southern California) to July (in Washington). In order to evaluate properly the conditions under which it actually lives in these sections of its range, we should take into account only those climato- logical values in each section that refer to the period of its activity. A separate investigation of Daucus and other plants of the same facul- tative seasonal habits would yield results of great value. The wide amplitudes of moisture conditions shown in figure 69 would thus doubtless be greatly narrowed and the temperature amplitudes would be made somewhat narrower also. Whereas this plant appears at first to encounter a remarkable gamut of conditions through its range, nearly 4,000 miles in length, a study of the conditions in its particular seasons and in the habitats which it occupies would undoubtedly show that it grows only under a relatively limited set of conditions. The northern (and eastern) limit of Daucus follows certain of the isothermal lines so closely as to indicate that its controlling conditions are to be looked for in the temperature series. The danger of attempt- ing a final explanation of distributional limits by correlational methods alone is shown vety clearly in the case of this plant. The distributional limit is closely parallel to the line for a length of growing-season of 240 days, but the length of this season is obviously of no direct importance TEMPERATURE ays IN NORMAL Frostiess Season (F. S.} ‘oy Days, F. S. Corp Days, F. S. PrysioLocicat Summation, F. S. Normat Daitvy Mean, covocsr 14 oars of Year Nonrmat Dairy Mean, Year Precipitation Normac Daicy Mean, F. S. Days IN LONGEST Norma Rainy Penion, F. S. Days in LONGEST Normat Day Prion, F.S. Mean Tortat, Year EVAPORATION. Daitvy Mean, 1887-8, F. S. Moisture Ranrios Norma P/E, F. S. Normat 7/E, F. S. Normat P/E, Year Humipity Normat Mean, F. S. SUNSHINE Normat Dairy Dunarion, F. S. MoisTURE-TEMPERATURE INDICES Normat P/E x T, F. S., Pxysiovocical Metnoo (__ Fia. 69. Climatic extremes for Daucus pusillus. 564 CORRELATION OF DISTRIBUTIONAL FEATURES. to an annual plant which uses only a portion of the season in any part of its range. There is also a close correspondence between the dis- tributional limit of Daucus and the line for a daily mean temperature of 40° for the coldest 14 days of the year, but here again there is obviously no significance for this plant in the temperatures that super- vene while the entire race is represented only by seeds. There is nevertheless a parallelism between the different phases of any climatic condition, as has been remarked before, and this may well mean that there are other indices of temperature conditions critical for Daucus which have not been elaborated in our work, and the isotherms for these may be parallel to the ones mentioned above. It may also be true that there is an unsuspected importance for this plant in the length of the total frostless season and in the low temperatures of winter. Spermolepis echinatus and Parietaria debilis have ranges which are similar to that of Daucus, although not so extended either to the northwest or the east. These plants are also annuals which have different seasonal habits in the different sections of their areas, and the remarks made about Daucus will apply also to their relation to climatic conditions. Oxybaphus floribundus (fig. 70).—This herbaceous root-perennial ranges throughout the central United States between the Deciduous Forest region and the Rocky Mountains and north of central Texas. It encounters the entire amplitude for the country, of cold days, and relatively wide amplitudes of the other conditions, both of temperature and moisture. The narrowest amplitude is that of the moisture ratio (r/E), which ranges from 0.25 to 0.89. Temperature Days in Normat Frostiess Season (F. S) Her Days, F. S. Cop Days, F. S. PHYSroLosicaL SUMMATION, F. S. Normac Daity Mean, CoLpest 14 Days oF YEAR Noarmat Daicy Pecan, YEAR PRECIPITATION Normat Daity Mean, F. S. Days In LONGEST Normat Rainy Peniop, F. S. Days in LONGEST Normat Dry Peniop, F. S. Mean Totat, Year EVAPORATION Dai_y Mean, 1887-8, F. S. Moisture Ratios Normat P/E, F. S. Normat 1/E, F.S. Normat P/E, Year Husmiviry Normac Mean, F. S. SUNSHINE | Ih Normar Dairy Duration, F. S. MoistTurne-TEmPeRATURE INDICES Normat P/E x T, F.S., Pxysiotocical MeTHO> | EMME Fic. 70. Climatic extremes for Oxybaphus floribundus. CORRELATION OF DISTRIBUTIONAL FEATURES. 565 The area of Oxybaphus is somewhat similar to that of Siaphium laciniatum with respect to eastern and western limits, but the latter plant is definitely limited at the north, failing to reach the Canadian boundary, while Oxybaphus is limited at the south, failing to reach the Gulf coast. The eastern and western limits of Oxybaphus, like those of Silphium, appear to be set by definite constellations of moisture conditions, while the southern limit must apparently be sought in the temperature conditions. The western edge of the distribution of Oxybaphus is set by the lines for dry periods of 75 to 125 days, according to the latitude, and nowhere does this plant enter regions with a moisture ratio of less than 0.20. Its eastern limit is like that of Solidago missouriensvs (see plate 25), in being located along the western boundary of the Deciduous Forest more nearly than along any of the climatic lines. The actual ecological conditions for these plants of the open prairies are more radically changed on passing from the Grassland Deciduous-Forest region into the Deciduous Forest than the data of ordinary climatological stations are capable of showing. A normal mean relative humidity above 70 per cent and rainy periods of more than 100 to 125 days doubtless serve as limiting intensities of important conditions for these plants in a much more precise manner than is indicated by the positions of the isoclimatic lines as shown on our charts. At its southern edge Oxybaphus does not enter the regions with more than 200 to 240 days in the frostless season, does not encounter more than 180 hot days, and grows at no place with a physiological summa- tion of more than 17,500. Trautvetteria grandis (fig. 71) and Trautvetteria carolinensis (fig. 72).— These closely related species are the only North American representa- Temecnatuac ‘ Days in Norma Faosticse Season (F.S) EPS Hor Days, F. S. a Cou Dars, F. S. ET) ST TOT ET Puysiovoaicat Summanion, F. S. ee ae eS aT -Nonmat Daity MEAN, coLocsT 14 oave of Year (7 Nonmat Day Mean, Year ‘y PRECIPITATION Nonmat Daity Mean, F. S. PT TPE Days In LONGEST Normat Rainy Period, F.S. ey Days IN LONGEST Normat Dry Perioo, F.S.00 (Ee Mean Total, Year ee ee EvaPoraTIon Daitv Mean, 1887-8, F. S. fe SS > Moisture Ratios Normat P/E, F. S. (FE EL SPER AE oh ts RT PS Nonmat 7/E, F. S. (ES SE OC SOE ESS TES TU Norma P/E, Year | RRS aN eT Humiprry Normat Mean, F. S, | SUNSHINE Norma Dairy Duration, F. S. 1 “EE TE EE MorstTurRe-TEMPERATURE INDICES Norma P/E x T, F.S, Pxysiotocical MetHoo (i EEE Fig. 71. Climatic extremes for Trautvetteria grandis. 966 CORRELATION OF DISTRIBUTIONAL FEATURES. tives of a genus of Ranunculaceze which is found elsewhere only in eastern Asia. They are herbaceous root-perennials of moist situa- tions, and neither of them is common nor characteristic of very exten- sive plant communities. The ranges of both the eastern and western species are based on a very small number of known localities of occur- rence, and are so broadly drawn that they comprise climatological stations near which the plants are doubtless absent. Here, as in many other cases, 2 much more detailed study should be given to the dis- tribution of the plants involved and to the nature of the climatic condi- tions before attempting to apply the methods of a general study of this character to an investigation of the climatic controls involved. It is, nevertheless, of interest to make even a broad comparison between the conditions under which these related but geographically segregated species exist. The amplitude of the climatic conditions for the area of Traut- velteria grandis is wider than for that of 7’. carolinensis in all cases except the number of hot days, physiological summation, and the number of days in the longest normal rainy period. The former species exhibits a very narrow range in number of hot days, from 0 on the coast of Washington to 57 at Sante Fe, New Mexico (near one of the southernmost stations for the plant in the Sante Fe Mountains). This condition appears to be an important one in determining the limits of the western species. Trautvetterra carolinensis encounters from 63 to 160 hot days, and also has a relatively narrow amplitude of conditions with respect to the length of the frostless season, 145 to 231 days. The amplitudes of the daily mean precipitation and of the mean annual precipitation are much narrower for Trautvetteria carolinensis TamecraTuRe Dave in Nonmat Faosrizes Stason (F.S) 00 (a Hor Davs, F. S. * CT EEE Coro Dave, F.S. ———EE Puysiotocicat SumMATION, F. S. TE Norma Dairy Mean, coLoret {4 oave of Yean (i ) Nonmat Dairy Mean, Year “” ERATE ea PRECIPITATION Norma Daicy Mean, F. S. eT EE EEE) Davs in Loncest Normat Rainy Peniop, F.S. (es Days in LoNGesT Nonmat Day Pemioo, F.S. (= Mican Torat, Year Pare Tye eee ee EvaPoration Daity Mean, 1887-8, F. S. SS eee Moierture Ratios Normat P/E, F. S. } ee ee ee Normat 7/E, F.S. (CE ce on TS (Norma. P/E, Year SN ee EY Ds Houmipity \Nonwac Mean, F. S. CA, = feel SUNSHINE Nonmat Daicy Duration, F. S. a 8£&8£8§8= iii Eee eo Moistune-TEmPrcraTune invices Norma P/E x T, F.S,, Paysioocica Meteo (i — Fic. 72. Climatic extremes for Trautvetteria carolinensis. CORRELATION OF DISTRIBUTIONAL FEATURES. 567 than for the western species, but are comprised in the wide amplitudes of the latter. The amplitudes of the rainy periods and the dry periods, on the other hand, are such as to indicate that the two species have almost nothing in common with respect to these conditions. The occurrence of Trautvetierta grandis over both interior and coastal regions in the Northwest is responsible for wide amplitudes of evapora- tion, humidity, and moisture ratios, for all of which the amplitudes are narrow for the eastern species. Climatological data from such locali- ties as Helena, Boise, Walla Walla, and Spokane are not suited, however, to giving an accurate conception of the conditions for this plant. The moisture conditions of those stations are doubtless much more severe than those of the southernmost mountain localities for Trautvetteria grandis in New Mexico. Even though our graphs may indicate conditions of evaporation that are too high for Trautvetteria grandis and conditions of humidity and moisture ratio that are too low, there remains, nevertheless, a marked difference between the amplitudes of these conditions for the eastern and western species, since the low range of evaporation and the high range of humidity and moisture ratios are the conditions in which the western species is most abundant. In this case our climatological stations are located in the midst of the conditions in which it actually grows. The differences in the extremes and amplitudes of the principal climatic conditions for the two species of T’rautvetierva are sufficiently great to indicate that it would be difficult to grow either of them throughout the range of the other. The distinctive conditions under which the two species now grow, together with their complete geo- graphical segregation, must be taken to mean that they are neither recent nor immediate derivatives from a common ancestral stock. Populus balsamifera and Sapindus marginatus (fig. 73).—A ready comparison of climatic extremes for these two trees has been made possible by placing the blocks for the two on the same diagram. Sapin- dus is a@ tree of southern range, extending from central Texas and southern Kansas to Florida. Populus is a tree of northern range, extending from Connecticut to North Dakota, and through Canada to the northern Rocky Mountains, where it occurs in a form which has been recently regarded as a distinct species (see plate 19). Since the distributional areas of these two trees are quite separate and yet are nowhere less than 400 miles apart, it is not surprising that the ranges of temperature conditions are so unlike as to overlap only in the case of the length of the frostless season, where the maximum for Populus is slightly in excess of the minimum for Sapindus. The pre- cipitation conditions for these two trees are such that there is a con- siderable range of precipitation values common to both of them, although the extremes are by no means the same. The amplitudes of evaporation and humidity are much greater for Populus than for 568 CORRELATION OF DISTRIBUTIONAL FEATURES. Sapindus, but the values of all three of the moisture ratios are nearly the same. The amplitudes of sunshine duration do not overlap at all, and those of the moisture-temperature index are very dissimilar. The southern limit of Populus balsamifera and the northern limit of Sapindus marginatus have such a direction as to indicate that both trees are controlled by temperature. The edge of the area of the former corresponds closely to the line for 30 hot days in the normal year, although the tree extends far enough south to encounter 88 days at the edge of its range, at Toledo, Ohio. The area of Sapindus is limited in central Kansas by an average frostless season of slightly less than 180 days, by slightly more than 60 cold days, and by a physio- logical summation of 10,000. The position of the northern limit of Sapindus is so placed, however, as to indicate very clearly that its range is determined by the interaction of temperature and moisture conditions in such a manner as to require a detailed investigation based on a more accurate knowledge of the distribution of the tree than is yet available. The arid conditions of the Grassland and Desert regions apparently limit the western extension of both Populus and Sapindus. TEemMPrcmaTuREe Dave in Nonmat Frost.ess Season (F. S) Hor Days, F. S. Coro Days, F. S. PHYSIOLOGICAL Summarion, F. S. Nonmac Daitv Mean, corvest 14 pays or Year Nommat Daicy Mean, Year E PRECIPITATION _ Norma Daicy Mean, F. S. Days In LONGEST Normal Rainy Periop, F.S. Days im Loncest Normat Dry Peniop, F. S. Mean ToTat, YEAR EVAPORATION Daity Mean, 1687-8, F. S. MoistTure Ratios Norma. P/E, F. S. Ronmat 7/E, F. S. Normat P/E, Year Humipity Normat Mean, F. S. SUNSHINE Nonmat Darcy Duration, F. S. MoistTure-TEMPERATURE INDICES Noamat P/E x T, F.S., PHYsiovocicat METH ot ESL SD Fic. 73. Climatic extremes for Populus balsamifera (shaded) and Sapindus marginatus (black) Cornus canadensis and Spermolepis echinatus (fig. 74).—These plants are examples of species with northern and southern transcontinental distributions, respectively, and their climatic extremes have been placed together in the same diagram for comparison. Cornus ranges from northern California and the Sierra Nevada through the Rocky Mountains and the Black Hills to the extreme Northeastern States, being nearly coextensive with the Northern Mesophytic Evergreen Forest (plate 30). Spermolepis ranges from central California through southern Arizona and western Texas to Arkansas, western Tennessee, and western Florida (plate 31). CORRELATION OF DISTRIBUTIONAL FEATURES. 569 Wide amplitudes are exhibited by both of these plants for a number of the temperature conditions. Cornus shows a narrow amplitude for the number of hot days and the physiological temperature summation, and Spermolepis shows narrow ones for the number of cold days and for the annual daily mean temperature. The region with less than 60 hot days coincides roughly with the area of Cornus, except in the Great Basin region, where the plant is absent. The isotherm for a physio- logical summation of 5,000 corresponds in a striking way with the limit of Cornus, from the Pacific to the Atlantic. Spermolepis nowhere encounters a daily mean temperature of less than 55°, and barely enters the region with cold days. These temperature conditions are manifestly the strongest determinants operating to limit the ranges of these two plants. _ Both of the plants under comparison exhibit wide ranges for all of the moisture conditions, and in most cases their amplitudes overlap to a considerable extent, or even show closely similar extremes. The moisture ratios for Spermolepis show much narrower amplitudes, and much lower maxima, than those for Cornus. The sunshine conditions are more nearly wholly dissimilar than any other condition, even than those of the temperature series. These plants are of particular interest as exhibiting the influence of temperature conditions in controlling the distribution of individual species. Such plants as these and Arenaria lateriflora, Parietaria pennsylvanica, and others of transcontinental distribution are able to range through widely diversified conditions of precipitation, evapora- tion, humidity, and moisture ratio at the same time that they are strongly controlled by temperature conditions. » Tempenaturc Dave in Nonmac FrRost.ess Season (F. S.) Hor Days, F. S. ,Coro Days, F. S. “PnysioLoaicat Summation, F. S. 'Nommat Daicy Mean, coLoest 14 cays or Year EZ Nonmat Daicy Mean, Year Prccipitation | NORMAL DaiLy Mean, F. S. | Days IN LONGEST Normat Rainy Penton, F. S. | Days in Loncest Nermat Day Peron, F. S. Mean TorTat, Year EVAPORATION Daity Mean, 1887-8, F. S. ‘ Moisture Ratios Normat P/E, F. S. Normat 7/E, F. S. ‘Norma P/E, Year Humioity Normat Mean, F. S, SUNSHINE |Normat Dairy Duration, F. S. MoisTure-TemPeraTure Indices (NORMAL P/E x T, F.S., PHYSIOLOGICAL MCTHOD Stitt Fig. 74. Climatic extremes for Cornus canadensis (shaded) and Spermolepis echinatus (black). 570 CORRELATION OF DISTRIBUTIONAL FEATURES. Among such species of northern transcontinental range we find chiefly herbaceous and shrubby plants of the evergreen forests, while among those of southern range we find herbaceous plants of facultative seasonal habits, or else palustrine and aquatic forms. We see, there- fore, in each group a set of circumstances which apparently tend to equalize the moisture conditions for these plants—the northern species are subordinate associates of the evergreen forests; the southern species are active in different portions of the frostless season, according to the seasonal distribution of rainfall, or else they occupy perpetually moist situations. VI. CORRELATION OF VEGETATIONAL AREAS WITH GENERALIZED CLIMATIC PROVINCES. 1. INTRODUCTORY. The generalized climatic provinces roughly defined from the results of our climatic studies should be of value in comparing the geographic distribution of vegetation with the distribution of different degrees of intensity and duration of climatic conditions throughout the country, and we have therefore carried out such comparisons between the vegeta- tion charts (plates 1 to 33) and the generalized climatic graphs of figures 18 to 28. Of course, it is not to be expected that any vegeta- tional area will be found to correspond perfectly with any climatic area. Probably the only method by which close areal correlations may be attained lies in the employment of several climatic conditions, as in our two-dimensional systems of climatic provinces. A number of cases have been discovered, however, in which the correspondence between areas of plant distribution and simple climatic provinces is very good. The mention of these will be valuable in the formation of a conception of what sort of plants may be expected to occur in the various climatic provinces. Owing to the complexity of the conditions to be compared and to the varying degrees of precision with which the climatic zones can now be defined—as well as to our own limitations, no doubt—these correlations are but preliminary and very tentative. The first observation to be made in beginning these comparisons is one that might have been expected on general grounds, namely, that relatively few of the vegetational areas show any pronounced corre- spondence with any single climatic province, defined by whatever method. The second observation is perhaps a little surprising, after all, considering how crude are our climatic charts, namely, that a num- ber of good agreements have been found. As has been previously mentioned, it appears that correlations between moisture provinces and vegetational areas are more frequent than those between tempera- ture provinces and the same areas. This may perhaps be due to the fact that the range of moisture conditions in the United States is very great (from very arid to very humid), while the range of temperature CORRELATION OF DISTRIBUTIONAL FEATURES. BA conditions is relatively not nearly as great. If the humidity of our most humid areas were to be increased (within the limits set by world climate), little or no alteration in the vegetation would be expected. Nor would any great alteration in the vegetation of our most arid areas be expected from increased aridity, excepting that vegetation would finally be prohibited altogether. On the other hand, if the intensity or duration factor of the temperature conditions of our warmest provinces were increased, or if that of our coldest provinces were decreased, great changes in vegetation would be expected. Both north and south of the area of the United States the same humidity conditions are concomitant with very different vegetation characters, and this difference is to be related mainly or entirely to temperature differences. We present below some of the most definite cases of concomitancy, considering first the temperature provinces, then the moisture prov- — inces, then the provinces based on the temperature-moisture product, and finally the two-dimensional provinces based on temperature and moisture. 2. TEMPERATURE PROVINCES. Two charts of temperature provinces have been employed for these comparisons, the one based on the average frostless season (plate 34) and the one based on physiological summation indices (plate 40). It will be convenient to consider the comparisons in the order of the vegetation features as these have been presented in plates 1 to 33. As has been mentioned several times, there is no primary correlation between temperature conditions and the general types of vegetation as shown by plates 1 and 2, and a comparison of these plates with those of the temperature provinces emphasizes this statement once more. In the case of plate 3, if the evergreen broad-leaved trees and the microphyllous trees are taken together as a single group (characterized by relatively low transpiring power), it is found that the geographic area occupied by this group very nearly corresponds with the area of the very warm, warm, and medium temperature provinces as brought out by the chart of the average frostless season. Near the Pacific and Atlantic coasts the correspondence is not good when the chart of physiological summations is employed. The two eastern palms, Sabal palmetto and Serenoa serrulata, occupy nearly the same area as does the very warm temperature province on either of the two temperature charts here employed. On plate 29, Phorodendron flavescens shows an area of distribution that closely agrees with the form and extent of the combined very warm, warm, and medium temperature provinces, as shown on the frostless-season chart. As in the case of the broad-leaved and micro- phyllous group of trees, the correlation is not good with the physiologi- cal summation chart. 572 CORRELATION OF DISTRIBUTIONAL FEATURES. Parietaria pennsylvanica, and, to a less extent, Arenaria lateriflora (plate 30), generally agree in their distributional area with the area of the very cool and cool temperature provinces, based on the length of the average frostless-season. On plate 31, Daucus pusillus is shown to occupy an area that corre- sponds, in a very satisfactory manner, with an area composed of the very warm and warm climatic provinces, taken with the warmer half of the medium province, as shown on the frostless-season chart. Other correspondences are suggested by our charts, but these are the most satisfactory. The generalization is at once suggested that the length of the period of the average frostless season (plate 34) exhibits much more striking correlations to vegetational areas than does the chart based: on physiological summations (plate 40). The results of these comparisons are shown graphically by the following scheme: Temperature provinces based on frostless season. Sabal palmetto Serenoa serrulata Daucus pusillus Broad-leaved and microphyllous Parting: pemsylyames 91). 8-1: 2 cts. f- Se arc}. hese. SP. eee 3. MOISTURE PROVINCES. For these comparisons with the vegetation charts we have employed four charts showing moisture provinces: (1) mean daily normal pre- cipitation (P, plate 46); (2) mean daily evaporation, 1887-88 (E, plate 53); (8) precipitation-evaporation ratio (P/E, plate 57); and (4) mean normal relative humidity (H, plate 65). The main cases of agreement brought out by these comparisons are given below. The generalized vegetation chart of plate 2 shows many coordina- tions with the charts of moisture provinces. The best correlation occurs with the moisture-ratio chart (P/E), which alone will be con- sidered here, although a study of the other moisture charts is well worth while in this connection. Desert occupies approximately the arid province. Northwestern Evergreen Forest occupies about the humid and semihumid provinces, western subdivision. Western Evergreen Forest: occupies the western and northern subdivisions of the semiarid and semihumid provinces. Grassland occupies most of the eastern subdivision of the semiarid province, extending eastward approximately to the line joining western Hudson Bay with western Gulf of Mexico. Deciduous-Forest Grassland Transition (the so-called prairie type of vegetation) occupies the more arid portion of the eastern subdivision of the semihumid province, merging imperceptibly into the next type. . . | CORRELATION OF DISTRIBUTIONAL FEATURES. 573 Deciduous Forest occupies the remainder of the eastern subdivision of the semihumid province, so that if the two last-named vegetation types are grouped together they occupy the whole eastern subdivision of the semihumid province. Northeastern Evergreen Forest occupies very nearly the northern portion of the eastern subdivision of the humid province, but this vegetation type extends southward in the Appa- lachians, which is not shown for the corresponding climatic area by the precipitation-evaporation ratio; but this southward extension of the northeastern humid conditions is shown by the line for 140 on the evaporation chart (plate 53, figs. 3 and 22). Southeastern Evergreen Forest occupies nearly the same area as the southern portion of the eastern subdivision of the humid province. This agreement is about as close as could be hoped for in work of this kind, and the correlations are very nearly what might have been expected. Two apparently important features require brief mention: (a) the relation of the Deciduous Forest area to that of the Deciduous- Forest Grassland Transition, and (b) the relation between the climatic conditions concomitant with the Northeastern and Southeastern Ever- green Forests. (a) It will be noticed that no one of the climatic maps shows any line that may be considered as approximating the position of the boundary between the deciduous forest and the prairie. While this boundary, like the other lines of plate 2, does not represent a sharp line of demarcation, nevertheless it is one of the most pronounced and clearly recognizable vegetational boundaries presented by the United States. It is actually a simple matter—for example, in Minnesota, Indiana, or Illinois—for an observer to step, within a very few meters, from what is clearly and unequivocally decid- uous forest into what is just as unquestionably prairie. This is not nearly so easy in the case of the other vegetation boundaries as actually encountered in the field; deciduous and evergreen forest usually mingled near their common margins, and desert, grassland, and prairie usually intergrade quite imperceptibly, so that their bound- aries frequently have to be regarded as bands or zones many kilo- meters wide, even by an observer in the field. Furthermore, various species of trees have recently been introduced upon the upland of the prairie region, which originally was forested only on the flood-plains of the streams, while the deciduous forest of Pennsylvania, Ohio, ete., has been largely removed, so that the general aspect of the country is now much the same as in Iowa or eastern Kansas and Nebraska. This fact has led many students to regard the prairie region as potentially a deciduous-forest region, as far as climatic conditions go, and various non-climatic conditions have been suggested as explaining the original absence of trees from the prairie uplands. Looked at from the dynamic standpoint, it seems clear to us that the difference in environmental conditions that has to be postulated as 574 CORRELATION OF DISTRIBUTIONAL FEATURES. related to the difference in vegetation here considered must be rather recondite and subtile in its nature. We are, however, strongly inclined to maintain that this environmental difference will prove to be a cli- matic one, though probably not measurable in terms of any of the simpler climatic indices. Here is a problem that is well worthy of much deeper study than we have been able to give it. We wish to suggest one possible dynamic explanation on climatic grounds. If our charts showing mean daily evaporation (plate 53, figs. 3 and 22) be once more examined, it will be recalled that the eastern sub- division of the semiarid moisture province here exhibits a great eastern lobe reaching from Oklahoma to Pennsylvania. This general phe- nomenon is shown or suggested on other moisture charts, and may be tentatively regarded as of climatic significance, until more thorough- going studies of the aerial moisture conditions become possible. Now, this penetration of semiarid conditions into the center of the great eastern area of the semihumid province suggests that the explanation of the vegetational transition before us is probably largely related to evaporation. The same conclusion is suggested by the relative air- humidity chart (plate 65, figs. 17 and 24). Just how atmometric or air-humidity data should be treated in order to obtain a moisture index that may bring this point out in a satisfactory way, if it be true, can not, of course, be predicted. In support of the general probability that evaporation is the main climatic feature to be called upon to explain this vegetational transition, it should be remarked that small local prairies were of frequent occurrence in Indiana and Ohio when these regions were still under forest, so that the tension zone between forest and prairie was apparently very broad in the region south of the Great Lakes. It should also be mentioned that the evaporation data used for these studies all refer to a single year (Russell’s data, 1887-88) and it is suggested that a normal evaporation chart may show an iso-_ atmic line approximating the position of the prairie-forest boundary here in question. (b) The Northeastern and Southeastern Evergreen Forest types of vegetation are well known to be very distinct, at least floristically; yet. they are to be regarded (along with the Western and Northwestern Evergreen Forests) as physiologically or ecologically rather similar, being dominated by evergreen, needle-leaved trees. It is therefore important to note that the climatic conditions that seem to correspond to the Northeastern Evergreen Forest are no more continuous with those corresponding to the Southeastern Forest than is the actual dis- tribution area of the former forest itself with that of the latter. This point is clearly shown on the three charts for E, P/E, and H (plates 53, 57, and 65; figs. 2, 3, and 17, and 21, 22, and 24), and a still more CORRELATION OF DISTRIBUTIONAL FEATURES. 575 marked climatic difference is shown between these two areas on the chart for P (plate 57, figs. 16 and 23). Turning now to the more detailed vegetation charts, the area occupied by Pinus palustris (plate 6) nearly corresponds to the south- eastern humid province, as shown by P (plate 46, figs. 2 and 21). Pinus divaricata (plate 7) occupies about the same area as the north- eastern humid province, as shown by E (plate 53, figs. 3 and 22); its area, also somewhat nearly corresponds to the same province on the charts for P/E and H (plates 57 and 65, figs. 16 and 23, 17 and 24). Bulbilis dactyloides (plate 11) shows an area of distribution nearly corresponding with the eastern subdivision of the semiarid province and the most arid portion of the eastern subdivision of the semihumid, as shown by P/E and H. The line from Hudson Bay to the Gulf of Mexico passes nearly through the north-south axis of its area. Pinus edulis (plate 14) occupies nearly the arid province, as shown by #. Picea sitchensis (plate 14) occupies about the northwest humid province, by P/E, and Tsuga heterophylla (plate 14) covers about the northwestern humid and semsthumid provinces by the same index. Quercus falcata (plate 18) has an area of distribution nearly corre- sponding to the southeastern humid province, as shown by P. Less satisfactory agreements with this same province are exhibited by Sapindus marginatus (plate 19) and Itea virginica (plate 23). In all these cases the distribution area extends farther north in the Missis- sippi Valley than does the climatic province as shown. Populus balsamifera (plate 19) occupies the northern part of the eastern subdivision of the humid province, by EH. It extends farther south than this climatic area, as shown by P/E. The climatic charts are not sufficiently detailed in the Northwest to show a correspondence to the northwestern area of the species. Decodon verticillatus (plate 23) has an area of distribution nearly conforming with that of the eastern subdivision of the humid province, together with all but the most arid portion of the eastern subdivision of the semehumid province, as shown by P/E or H. Phorodendron juniperinum (plate 29) has an area of distribution roughly corresponding to the arid province, by P/E and H. Oxybaphus nyctagineus (plate 33) occupies the more humid part of the eastern semiarid province and the more arid part of the eastern semihumid province, as shown by P/E, the distribution area of this form being much like that of Bulbilis dactyloides (plate 11). The schematic presentation on page 576 shows the relations just described, for the individual species considered. 576 CORRELATION OF DISTRIBUTIONAL FEATURES. Moisture provinces, by P, E, P/E and H. Humid. Semihumid. Semiarid. North- | South- eastern. , eastern. —_—_—_——_—_ ee | | [| | J Western. Western.| Eastern. | Western.| Eastern. Picea sitchensis (Bis PY PEPIN ifs Ekg AS ee INO 8 et eer Tsuga hetero- pO en L EI O20 110) et SEES SESS MEME pet iatoe [Oyen oa cg ye Seine IRIS A iy Pa Quercus falcata Tis cs a A Er cs rr as TESTA i te ee eee nul Sty Ora Goce ive Mute 2a a rr rrr Decodon verti- cillatus(P/E, 1 3 i ea je ROM panes resents (SE REARS FU Aer PRP ME PMR Bulbilis dactyl- oides (P/E, Oxybaphus nye- tagineus(P/E, Phorodendron juniperinum Pinus edas!| (EB) ss eee ce hile ee Slee eke Boas «ell Be wicel ols bl aea cn tue ee 4. TEMPERATURE-MOISTURE PROVINCES BASED ON THE PRODUCT INDEX. It will be recalled that our three moisture-temperature charts (plates 69 to 72) show a form of climatic zonation that is very similar to that shown by the chart based on the mean aqueous-vapor pressure for the period of the average frostless season. For comparison with the vege- tational areas, only the generalized chart of moisture-temperature indices using the physiological temperature summation (plate 72, figs. 18 and 25) has been employed. To avoid confusion, it is first necessary to point out that certain climatic provinces are shown as practically the same by the moisture- ratio chart (plate 58, figs. 16 and 23) and by the one here considered (plate 72, figs. 18 and 25). The arid province corresponds very well with the province of very low moisture-temperature values. The semiarid province represents much the same area as the province of low product values, but the north-south boundary of the latter province lies much farther west at its southern end (Texas), and farther east at its northern end (South Dakota). This line on the moisture-ratio chart is practically the Hudson Bay-Gulf of Mexico line, as has been noted, while the north-south line just mentioned has a very different position. Also, the eastern projection of the province of low product values is not represented on the chart of moisture-ratios; it roughly CORRELATION OF DISTRIBUTIONAL FEATURES. 577 corresponds to the northeastern portion of the humid province, as shown on the latter chart. The northwestern areas of medium and high product values correspond, to a degree, with the similar semihumid and humid provinces on the moisture chart. The eastern half of the product chart resembles a temperature chart in its zonation, as has been mentioned, and shows no clear rela- ‘tion to the moisture-ratio chart, excepting that the southeastern area of very high moisture-temperature values may be considered as corre- sponding to the southeastern humid area in the latter case. Only this eastern half needs, therefore, to be specially compared with the vegeta- tion charts, and in this comparison the southeastern area (of very high products and of high moisture ratios) may be left out of account. The comparison brings out the fact that there are but two cases where any striking agreement in form and position of areas is to be detected. Quercus alba (plate 18) occupies, roughly, the provinces of medium, high, and very high product values, but this species does not extend nearly as far westward in the southwestern part of its area as does the province of medium moisture-temperature products. Also, this tree does not occupy peninsular Florida, which includes the highest product values. Quercus alba may be said mainly to correspond, in its dis- tributional area, with the region having moisture-temperature indices ranging from 4 to 22, but in the southwestern portion of its area it extends westward only about as far as index-value 17. This is not to be considered a very satisfactory agreement. The other case where an apparent agreement between moisture- temperature product zones and vegetation areas is to be detected is that of the cumulative distribution of southeastern deciduous trees (plate 4). In this case the agreement is more nearly perfect than for Quercus alba, but here, also, the vegetation area does not extend south in Florida far enough to include the very highest product value. These 15 trees, considered together, occupy the provinces of high and very high product indices, except the very highest, and with the further exception that they extend much farther westward in Texas than does the province of high index values. These trees may be considered as occupying the region having moisture-temperature indices ranging from 7 to 23, but they extend to index-value 2 in Texas. On the whole, we are once more led to the conclusion that the mois- ture-temperature products do not furnish a criterion of great general value, as far as the discovery of distributional correlations is concerned, at least for the vegetation areas that we have charted. Of course, many areal correlations not here mentioned are to be found between our vegetation charts and the chart here considered, but most of these represent cases where this chart agrees, in its zonation, with the mois- ture charts, and a number of such correlations have been noted in connection with those. 578 CORRELATION OF DISTRIBUTIONAL FEATURES. 5. TWO-DIMENSIONAL CLIMATIC PROVINCES. Although a number of the various vegetational areas shown on the charts of plates 2 to 33 have been shown to be more or less precisely comparable with geographically corresponding climatic areas, it never- theless appears that such satisfactory correspondence is the exception rather than the rule. The climatic conditions concomitant with the vegetation areas that fail to show such simple correlations as have been mentioned in the preceding paragraphs require a more complex mode of description, at least until the proper simple climatic indices may be discovered. The most thoroughgoing subdivision of the country into climatic provinces, which has been attempted in our studies, is that based on the two-dimensional provinces. The use of these smaller climatic areas makes it possible to describe any vegetation area not simply correlated with either moisture or temperature prov- mees alone, in terms of both moisture and temperature conditions together. Such a description is clearly climatic and may lead to further correlations, but this method soon encounters limitations, since, as has been pointed out, there are frequently several two-dimensional provinces with the same dimensions or characteristics, and these can not as yet be simply distinguished on a climatic basis alone. For the present, and in the comparisons mentioned below for illustration, it seems best to fall back upon geographical terms, in order to distinguish such climatically similar but geographically distinct areas. This method frankly begs the entire question of correlations; it furnishes, wherever it is employed, nothing more than a geographical description of the details of configuration with which it deals. It is, however, not to be resorted to until the climatic description of the vegetational area in question is as complete as possible, so that the resulting description always bears much more climatic information than would a purely geographic description. The latter sort of description is quite useless, as far as our purposes are concerned, for it merely states that the given plant or vegetation type occurs where it is. In the following paragraph we present descriptions of several vege- tational areas, following the method just outlined. For the two- ~ dimensional climatic provinces we shall here employ only the chart formed from the length of the average frostless season and from the precipitation-evaporation ratio (fig. 19). The cases considered are set forth here simply to illustrate the use of this method of interpreta- tion; we have not yet proceeded far enough with this more complicated aspect of the subject to be able to arrive at any very promising general- ization. The distribution areas chosen for discussion here are taken from eastern forms among those that fail to show intelligible relations to the simple climatic provinces of moisture and temperature. In the case of the evergreen broad-leaved and microphyllous trees (plate 3), attention has been called to the fact that the distribution of CORRELATION OF DISTRIBUTIONAL FEATURES. 579 this group may be very satisfactorily described in terms of the tem- perature provinces alone, but neither temperature nor moisture conditions alone are adequate to bring out any climatic correlations that may suggest an explanation as to why the broad-leaved trees occur only west and east, while the microphyllous ones occur in an intermediate region. Comparing plate 3 with figure 19, it becomes at once apparent, however, that the broad-leaved trees occur mainly in the very warm humid province (Florida and Louisiana) and that they occur in smaller number of species in the warm and medium humid and in the warm and medium semihumid provinces. Especially in California they occur in the warm and medium semihumid provinces. The microphyllous trees occur mainly in the warm and medium arid, and they occur as fewer species, especially in Texas, in the warm and medium semiarid. The two-dimensional provinces are thus fairly satisfactory in corre- lating the distribution of these two groups of trees with the two primary groups of climatic conditions. The distribution of the eastern deciduous trees (plate 5) must be described, first, in geographic terms. They occur east of the line joining Hudson Bay with the Gulf of Mexico, and they are absent from all climatic provinces west of this line. In the area thus demarked their area of greatest density lies within the cool and medium semi- humid provinces. This area does not correspond to all of the area of these provinces, but it does not significantly overlap any of the humid provinces. Itoccupiesabout theeastern half of the cool semihumid prov- ince (Kentucky to Massachusetts), and the northern marginal portion of the eastern half of the medium semrhumid province. For the most part, these trees may be said to occur in greatest number of species with the more humid and warmer conditions of the cool semihumid province. The distributional area of Lirvodendron tulipifera, one of the eastern deciduous trees, is also not‘ possible of description in terms of our climatic provinces alone. It must first be stated that this tree occurs only in the East. Its area occupies most of the eastern half of the cool semihumid province, not reaching the boundary of the cool humid on the north and extreme northeast. It occupies about the eastern two-thirds of the medium semihumid and all of the medium humid provinces. It also occupies the eastern lobe of the warm semihumid and a portion of the warm humid (Georgia, etc.). It does not extend into the very warm temperature province. The area of greatest frequency for this tree, which may be considered as its geographic and climatic center of distribution, lies practically in the center of the distributional area just described. This smaller area may be defined as occupying the southeastern triangular lobe of the cool semehumid province and the northern half of the central por- tion of the medium semihumid, which adjoins that triangular lobe at the southwest. Thus, this center of distribution occurs with cool- 580 CORRELATION OF DISTRIBUTIONAL FEATURES. medium temperature conditions and with the more humid conditions of the semihumid moisture province. It does not extend to the bound- ary of the humid province at any point. Silphium laciniatum (plate 25) shows a clearly outlined geographical area of distribution, occupying the Missouri-Mississippi-Ohio Valley as far north as the Grand River in Michigan, as far west as western Kansas, and as far east as the Appalachian Mountains. It does not occur either in the West or east of the Appalachians. Within these geographical limits the distributional area of this plant corresponds to the following two-dimensional climatic provinces: (a) Warmer two-thirds of the cool semihumid, west of Appalachians. (6) Small portion of cool semiarid, the warmer, more humid part of this province. (c) Medium semihumid, west of Appalachians. (d) Eastern (more humid) half of mediwm semiarid. (e) Most of warm semihumid (all but a small area in Georgia). (f) Coolest portion of warm semiarid (Texas). (g) Western half of warm humid (Louisiana to Florida). This Silphium appears not to extend into the very warm temperature province to any considerable extent. It occupies the more arid part of the semihumid and the more humid part of the semiarid, within the warm and medium provinces and the warmer part of the cool province. Many other examples might be given showing the use of two-dimen- sional climatic provinces, supplemented by geographical data, in climatically describing vegetational areas for purposes of comparison. Indeed, any vegetational area may be so described after the requisite two-dimensional chart has been once prepared. But the four cases considered above should be sufficient to demonstrate the investiga- tional value of this general method. If the relations holding between climatic conditions and plant activity receive the attention that they deserve from ecologists and climatologists, this method, with improve- ments, should prove very useful. Especially should this be true for studies of agricultural and forest climatology, which is just beginning to attract serious attention in this country. CONCLUSION. The work presented in this publication has fallen under three heads: (1) giving the facts as to the distribution of certain types of vegetation and certain species of plants of the United States; (2) giving the data to show the intensities of the leading climatic conditions in the United States; (3) correlating these two bodies of facts in such a man- ner as to learn the exact range of conditions under which each plant or vegetation lives with respect to each of the climatic elements. The botanical facts lead to the subdivision of the vegetation into a small number of natural areas, delimited on a purely vegetational basis, to the outlining of regions in which particular ecological types are most abundant, and to the presentation of the distributional areas of a number of important species in the vegetation. The climatological data have been selected or elaborated with respect to the conditions which are of most importance to plants, with the aim, wherever possible, of devising new expressions for the climatic conditions that might be suited to the botanical problems in hand. ‘The correlation of the dis- tribution of plants with the distribution of various numerical values or indices of the several climatic conditions has been carried out with the full realization that such correlations do not carry conclusive proof of the existence of causal connection. It is only by careful elimination of possibilities and by comparison of results, that these correlations can be used as more than a source of suggestions. The existence of a causal relation between the climatic conditions and the vegetation of any given region is so well known as to have become practically axiomatic. A relation between climate and the distribution of the common species which dominate the principal vegetations is likewise well-established fact. But the relations between climate and the distribution of the generality of individual species is indirect and is obscured by many considerations. In an investigation of the réle that is played by the various climatic conditions in determining the optimum activity of a plant or the limitation of its distribution, it is necessary to bear in mind that the conditions operate collectively and that their influences are often interdependent. The rdéle of each condition changes with the changed values of the other conditions. In attempting to determine the relative importance of several climatic conditions as determinants of a given distributional phenomenon, it is seldom possible to do more than speak in general terms. It may be possible to state, for example, that temperature conditions are more important than moisture conditions in a given case, without its being possible to determine, on the same evi- dence, which of the several aspects of temperature is most important. The problem of the réle of climatic conditions in determining plant distribution is essentially a physiological one, since it rests, in ultimate analysis, upon the influence exerted by environmental conditions on the 581 582 CONCLUSION. activities of individual plants. The attack upon this problem must, however, be made by methods quite different from those employed in purely physiological investigations. The conditions must be measured rather than controlled, and the plant material must be examined throughout its range of occurrence, much as a large series of experi- mental cultures is scrutinized for the discovery of the effect produced by controlled conditions. The methods that must be employed hinge very largely upon the interpretation of a vast series of uncontrolled experiments under the varying conditions of natural environment. It is to the geographical aspects of the problem that we must ascribe many of its complexities and much of its difficult nature. Although the results secured in this investigation are only general in their applicability, we have endeavored to develop and make use of methods which are specific and definite enough to warrant more extended use. The basic data, both as to climate and vegetation, are scanty in many cases, and the methods used could well be employed to greater advantage with fuller data, or for the investigation of similar problems in smaller areas. The presentation of vegetational data that has been given takes no account of the minor plant communities that occupy relatively small areas in all plant formations, and owe their existence to the modifica- tion of the fundamental conditions of climate through differences in what might be designated as the response of soils to the climatic condi- tions. No account has been taken of the developmental changes of vegetation in regions with rapidly shifting topography, since these changes depend mainly on differences in the character of the soil, or on changes of environment due to the plant covering. All develop- mental changes in vegetation are due to changes of environmental con- ditions, and it is only rarely, or over very long periods of time, that these changes are in the nature of definite alterations of the general climate of the region. Our presentation of climatic conditions has been limited chiefly to thosé elements of the climate that are commonly measured, as it is impossible to secure well-distributed series of data for other conditions, although many of these are well known to be of great importance to plants. A departure from the customary climatological procedure has been made in securing many of the data on temperature and mois- ture conditions for the period of the average frostless season as well as for the calendar year. The length of the average frostless season has been determined for each of the stations from which other climatic data have been used. The data for the summation of temperature have been worked out by three methods, in addition to the one used by Merriam. It seemed advisable to give this promising means of secur- ing additive temperature data a thorough test, and to attempt to arrive at a method with fewer objections from a physiological standpoint than could be urged against the older methods. CONCLUSION. 583 The determination of the ratio of precipitation to evaporation, which was first applied to distributional problems by Transeau, has been made for the entire United States, and has been derived by three methods. So great is the importance of the “‘moisture ratio,” as this has been designated, that it is greatly to be hoped that our maps showing the distribution of the ratios may soon be redrawn upon the basis of much fuller evaporation data. A further attempt has been | made to secure composite expressions of groups of important climatic conditions by determining the products of the moisture ratios and the summations of temperature. A cartographic method of approaching the same end has been employed for the determination of the areas included between the isoclimatic lines for the moisture ratio and those for the physiological summation of temperature. The result is a series of climatic provinces which are based upon the two expressions of climatic conditions that are probably the most fundamental ones dealt with in this work. The correlation of climate and vegetation has been carried out in three ways: The maximum and minimum values of each climatic condition have been determined for each vegetational area or for the distributional area of each species. A comparison has been made between the amplitude of the conditions in each botanical area and the amplitude in the United States as a whole, in order to discover how small or how great a portion of the whole range of climatic conditions is eccupied by the vegetation or plant in question. Comparisons have been made between the positions of isoclimatic lines and the lines drawn to show the limits of botanical areas, for the purpose of discovering close correspondences. The detailed results of these methods of correlation are given in the preceding pages; they do not lend them- selves to being summarized. The parallelism that exists between the distribution of many of the closely related climatic conditions makes it difficult in some cases to determine which of the several aspects of a given condition is of the greatest importance in controlling a particular plant or vegetation. The methods used rarely fail, however, to demonstrate whether it is the temperature group of conditions or the moisture group that pos- sesses the greater importance. With respect to the generalized vegetation areas of the United States, one of the most clear-cut evidences of a fundamental correla- tion exists in the correspondence between the position of the vegeta- tional boundaries and the position of the isoclimatic lines expressing certain values of the moisture ratio for the average frostless season. The composite character of the moisture ratio, and the fact that it is derived from such an important group of climatic conditions, give it a value of the first rank in dealing with the physical conditions determin- ing the distribution of vegetation. 584 CONCLUSION. With respect to the distribution of individual species it is to be noted that most of those which are characteristic and abundant in important vegetations are, like the vegetation itself, controlled by moisture con- ditions. In fact, the distributional limits of such species frequently lie just within or without the limits of the vegetation in which they are dominant. The limits of distribution of many herbaceous and palus- trine plants lie parallel to the isoclimatic lines for temperature condi- tions. For palustrine plants the topographic conditions make the soil-moisture nearly alike at all times and in all places, and the dis- tribution of these plants is therefore subject to temperature control. The aim of our studies has been to bring forward certain types of the methods that may be employed in studying the etiology of plant distribution and to present some of the climatological data necessary to such work in the United States. Thesubject is large and complex, but it offers promising fields for further investigation, and it is to be hoped that many more workers will be attracted to it in the early future. The growth of our knowledge of plant physiology will bring with it the need of obtaining measurements of new features of the environ- mental complex, or the need of determining new phases of the climatic elements for which we already have data. The progress which is being made in the study of light and its influences upon plants may well lead to the discovery that this group of conditions plays a more important rdéle in the distribution of plants than has heretofore been suspected. ‘The whole field of the influence of . temperature on plant distribution needs to be approached with regard to the temperature requirements of each phase of the life-history of the plant. A much more detailed analysis of temperature effects is needed, and a much more elaborate system of recording temperature data. The physical conditions of the soil need much more detailed investi- gation from the point of view of their dependence on general climatic conditions. The geographical aspects of soil-moisture and soil-tem- perature conditions have been neglected. by reason of the local com- plexities that they present. There is great need of the investigation of these and other soil conditions at a large number of well-distributed localities. An elucidation of the local conditions of each place would throw light on the relation of climatic conditions to the conditions of the soil, would increase our knowledge of important aspects of the soil, and would give a basis for learning the geographical range of the intensities of these conditions. The methods used in this publication and the climatic data presented may be used to investigate the controlling conditions for other plants than those we have taken up. A marked improvement in methods would doubtless follow a truly thorough investigation of the ecological distribution and controlling conditions of any one plant. To have its greatest value, such an investigation should be made with reference to the ecological center for the plant and with reference to all parts of the edge of its distributional area. CONCLUSION. 585 The work of distributional etiology must be carried on in close coordination with the work of plant physiology. A knowledge of the fundamental physiological features of a plant should go hand in hand with an effort to investigate the features of physiological and ecological behavior that do not lend themselves to laboratory experimentation. A substantial advance in the investigation of the etiology of plant dis- tribution would provide facts and methods of inestimable value in the practice of agriculture, horticulture, and forestry. EXPLANATION | Lower Sonoran Zone (western area). Austroriparian Zone (eastern area). Eareal Region. | | encta a Supteds Lean fe a Gulf Strip of Lower Austral Zone. ] Upper Sonoran Zone (western area). = n Carolinian Zone (eastern area). neal Tropical Region. + a =p PS pe =i fe ~ Sea emeT TaN 7 ——— SEE = oh SS ee ee ae ee ae 10s bet Toe _ er 3 r ES ar Ge aa a Salalior BASE FROM U.S, GEOLOGICAL SURVEY MAP SHOWING THE LIFE ZONES OF THE UNITED STATES, AFTER MERRIAM. Gt 1 ee 1 ct em amore 4pm 6 om onemnanti-ameaiiade LITERATURE CITED. ABBE, CLEVELAND. 1905. A first report on the relations between climates and crops. U. 8. Dept. Agric., Weather Bur. Bull. 36. Apams, C.C. 1902. Southeastern United States as a center of geographical distribution of flora and fauna. Biol. Bull. 3: 115-132. Bascock, 8. M. 1912. Metabolic water: Its production and rdle in vital phenomena. . Wisconsin Agric. Exp. Sta. Bull. 22. Baxxke, A. L. 1914. Studies on the transpiring power of plants as indicated by the method of standardized hygrometric paper. Jour. Ecol. 2: 145-173. Berry, Epwarp W. 1916. 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' =e ye > aia drivel Phyheiet 4 . , i : « iddi Nyy : ‘ ‘me! , . , , rt f ew : ¢ ; AN Wer ; ; ot} ay *; +) i . . a y tyt : ' i] iy “ > = ~ ‘ * ‘ $ p - 5 t ‘ 4 é + y : t ' } 4 $ j ‘ i * vile td , Witt ' - a is ‘ ‘ , . 5 : fb 4 . ‘ yo Bt 5° ‘> Li a ' J ’ 4 “7 ae Li + | . 4 ' = . ‘ ’ . ; ‘ { ‘ i ; ‘ ? > 7+ ‘ r ‘ a . } i & +e thal 3 +48 2 8 wid . ei) ; yi at i ae : ¥ ‘ uy = - . ~ ‘ ‘ & ‘ via e 1 i : up { ‘ y a: ~ = “5 J ; ; *® : i A ‘ . - ‘ J ( i r 5 x i: : i’ S ‘ M4 * 4 ’ 7 ar i ‘ + : . fn) ot . ; ‘ . 5 zy i P 3 i) ; us ° * iis , ‘ . ‘ at ' q +? - : » ; ‘ i t i ' J ‘ . ' / F Nay ; t Vr tad ; ‘ A ete 2s ; reel 5 ett e ‘ L848 ; ' 4 skal ‘ ’ 4 : : dd = r& SA 7 i ' . ol - bf * oy ' ey < : ; ‘ . * ’ i = . ‘ t ier =f - : 4 id » - j ' t 4) es + ‘4 - ' ‘ 4 : = % : ‘ : % ‘ ; * ; ' 4 iv . i 2 ' A ‘ ’ * . Ae bal, * ‘ ; Pid § ‘ . ‘ s th fi ' ’ ~ 4 TTA ao ER at PS ch A a - e & ee ia ial , ‘ i ‘ . , i 4) i . . RAL i “ ; OV ia i fs