THE PLANT WORLD A Monthly Journal of General Botany Established 1897 Edited by FORREST SHREVE Published by THE PLANT WORLD ASSOCIATION Volume 20 OFFICE OF PUBLICATION 2419-21 Greenmount Ave. baltimore, md. EDITORIAL OFFICE TUCSON, ARIZONA 1917 THE PLANT WORLD INDEX TO CONTENTS OF VOLUME TWENTY, 1917 Aase, H C. Megasporophylls of Conifers; Review 263 Absorption and Secretion. -M. H. Fischer; Review 393 Absorption of Carbohydrates by Green Plants. L. Knudson; Review 29 Adkmson, J., et al. Dicotyledonous Woods; Review 191 American Journal of Forestry; Note 66 Around the Year in the Garden. F. F. Rockwell; Note 339 Artificial Osmotic Cell, Observations on a New Type of. J. Rosett 37 Atkins, W. R. G. Experimental Results in Plant Physiology; Review 224 Beginnings and Physical Basis of Parasitism. D. T. MacDougal. 238 Berry, E. W. History of the Willows and Poplars 16 Berry, E. W. Wilcox Flora; Review 127 Bews, J. W. Growth Forms of Natal Plants; Review 299 Boerker, R. H. Germination and early Growth of Forest Trees; Review 64 Book of Forestry. P. F. Moon; Review 262 Bowman, Isaiah. Peruvian Andes; Review 129 Braun, E. Lucy. Vegetation of Conglomerate Rocks of the Cin- cinnati Region 380 Brooklyn Botanic Garden; Note 161 Calvert, A. S., and Calvert, P. P. Natural History of Costa Rica ; Review 395 Cannon, W. A. Rate of Growth of Prosopis is Relation to Soil Temperature 320 Chamberlain, C. J. Prothallia of Lycopodiiim; Review 225 Climatic Conditions as related to Plant Growth. F. T. McLean; Review 158 Comparative Length of Growing Season of Woods. F. W. Haasis 354 Cooper, W. S. Redwoods, Rainfall, and Fog 179 Cowles, H. C, and Fuller, G. D. Work of; Note 364 Cribbs, J. E. Plant Associations of Western Pennsylvania .. . 97, 142 Critical Temperatures for Phytolacca. F. E. Lloj^d 121 Dice, L. R. Work of; Note 95 Dicotyledonous Woods. J. Adkinson et al. ; Review 191 Distillation of Wood; Note 161 Doctorates in Botany; Note 32 .3 55452 Effect of Bordeaux Mixture on Transpiring Power in Tomatoes. J. W. Shive and W. H. Martin 67 Enumeration of the Plants of the San Bernardino Mountains. S. B. Parish 163, 208, 245 Environment of Seeds and Crop Production. B. D. Halsted and E. J. Owen 294 Evaporation and Succession, Recent Investigations on. E. N. Transeau; G. D. Fuller; J. E. Weaver, et al.; Review 357 Experimental Results in Plant Physiology. W. R. G. Atkins; Review 224 Field Study of Osmotic Concentration. J. A. Harris, J. V. Lawrence, and R. A. Gortner; Review 62 Fischer, M. H. Absorption and Secretion; Review 393 Forest Investigations in 1916; Note 192 Gager, C. Stuart. Fundamentals of Botany; Review 93 Ganong, W. F. Text-book of Botany; Review 93, 339 Gates, F. C. Revegetation of Taal Volcano 195 German-English Chemical Dictionary; Note 134 Gennination and early Growth of Forest Trees. R. H. Boer- ker; Review 64 Gnetales, Recent work on. W. P. Thompson; Review 226 Gregory, H. E. Navajo Country; Note 132 Grout, A. J. Mosses of New York; Review 298 Growth-Forms of Natal Plants. J. W. Bews; Review 299 Gurjar, A. M. Truog's Method of Determining Carbon Dioxide 288 Haasis, F. W. Comparative Length of Growing Season of Woods 354 Halsted, B. D., and Owen, E. J. Environment of Seeds and Crop Production 294 Halsted, B. D., and Waksman, S. A. Soil Temperature and Plant Growth; Review 361 Handbook on Algae. G. S. West; Review _ 334 Harper, R. M. Undescribed Prairies in Northeastern Arkansas. . 58 Harris, J. A., Lawrence, J. V., and Gortner, R. A. Field Study of Osmotic Concentration; Review 62 Harshberger, J. W. Pine-Barrens of New Jersey; Review 91 History of the Willows and Poplars. E. W. Berry 16 Howard, A., and Howard, G. L. C. Soil Aeration and Plant Growth; Review 260 Illustrated Flora of Pacific Coast; Note 96 Important Botanical Contributions; Note 264 Indicator Significance of Vegetation for Forest Sites. C. F. Korstian 267 Interpretation and Application of Terms in Classification of Plant Communities. G. E. Nichols 305, 341 Jeffrey, E. C. Structure of Coal; Review 131 Jeffrev E. C, et al. Medullarv Rays; Review 338 Jennings, 0. E. Work of; Note 193 Jones, L. R. Soil Temperatures as a Factor in Phytopathology. . 229 Knudson, L. Absorption of Carbohydrates b}^ Green Plants; Review 29 4 Korstian, C. F. Indicator Significance of Vegetation for Forest Sites 267 Laboratory Manual of Soil Biology. A. L. Whiting; Review.. . . . 159 Lawson, A. A. Work on Psilotum and Tmesipteris; Note 339 Life Histories of Kelps. C. Sauvageau; Review 190 Livingston, B. E. Quarter Century of Growth in Plant Physi- ology 1 Lloyd, F. E. Critical Temperatures' for Phytolacca 121 Local Floras: Note • 133 MacDougal, D. T. Beginnings and Physical Basis of Parasitism. 238 McLean, F. T. Climatic Conditions as Related to Plant Growth; Review 158 Medullary Rays. E. C. Jeffrey et ah; Review 338 Megasporophylls of Conifers. H. C. Aase; Review 263 Moon, P. F. Book of Forestry; Review 262 Mosses of New York. A. J. Grout; Review 298 Murphy, L. S. Seeding Habits of Spruce as a Factor in Com- petition 87 National Forest Receipts; Note 364 Natural History of Costa Rica. A. S. and P. P. Calvert; Review 395 Naturalists Directory; Note 134 Navel Orange ; Note 65 New Zealand Forests; Note 65 Nichols, G. E. Interpretation and Application of Terms in Classi- fication of Plant Communities 305, 341 Node of Angiosperms. E. W. Sinnott; Review 300 North Carolina Trees. W. C. Coker; Note 66 Observations on a New Type of Artificial Osmotic Cell. J. Rosett 37 Osterhout, W. J. V. Tolerance of Fresh Water by Marine Plant's; Review 130 Parishj S. B. Enumeration of the Plants of the San Bernardino Mountains 163, 208, 245 Pentose Sugars in Plant Metabolism. H. A. Spoehr 365 Peruvain i\ndes. Isaiah Bo^\anan; Review 129 Physical Control of Vegetation in Rain-Forest and Desert Moun- tains. Forrest Shreve 135 Physiographic map of United States; Note 162 Pine-Barrens of New Jersey. J. W. Harshberger; Review 91 Pines of the Rocky Mountain Region. G. B. Sudworth; Note 364 Plant Associations of Western Pennsylvania. J. E. Cribbs. . . 97, 142 Plant World; Note 301 Prize in Soil Physics; Note 132 Prothallia of Lycopodium. C. J. Chamberlam; Review 225 Pulling, H. E. Work of 340 Quarter Century of GrO'Wth in Plant Physiology. B. E. Livings- ton 1 Rate of Growth of Prosopis in relation to Soil Temperature. W. A.Cannon ...320 Recknagel, A. B. Working Plans for Forest Organization; Review 299 Redwoods, Rainfall, and Fog. W. S. Cooper 179 t 5 Retting Flax: Note 96 Revegetation of Taal Volcano. F. C. Gates 195 Roberts, Edith A. Root Haii-s; Review 29 Robinson, B. L. Work on BrickelUa; Note 132 Root Hairs. Edith A. Roberts; Review 29 Rosett, J. Observations on a new type of Artificial Osmotic Cell 37 Sandalwood; Note , 35 Sauvageau, C. Life Histories of Kelps; Review 190 Seeding Habits of Spruce as a Factor in Competition. L. S. Murphy 87 Shade Trees. G. E. Stone; Note 162 Shive, J. W., and Martin, W. H. Effect of Bordeaux Mixture on Transpiring Power in Tomatoes 67 Shreve, Forrest, Physical Control of Vegetation in Rain-Forest and Desert Mountains 135 Sinnott, E. W. Node of Angiosperms; Review 300 Soil Aeration and Plant Growth. A. Howard and G. L. C. Howard; Review 260 Soil Temperaturs and Plant Growth. B. D. Halsted and S. A. Waksman; Review 361 Soil Temperatures as a Factor in Phytopathology. L.R.Jones.. 229 Spoehr, H. A. Pentose Sugars in Plant Metabolism 365 Stevenson, Matilda C. Zuni Indians; Note 133 Strawberty Growing. S. W. Fletcher; Note 162 Structure of Coal. E. C. Jeffrey; Review 131 Swiss Phytogeographical Commission; Note 95 Text Book of Genetics. E. B. Babcock; Note 396 Text Books. W. F. Ganong; C. S. Gager; Review 93 Thompson, W. P. Gnetales; Review 226 Tolerance of Fresh Water by Marine Plants. W. J. V. Osterhout; Review 130 Transeau, E. N. Work of; Note 340 Transeau, E. N.; Fuller, G. D.; Weaver, J. E.; et al. Evapora- tion and Succession; Review 357 Trelease, W. Work of; Note 340 Tropical Agriculture. E. V. Wilcox; Review 30 Tropical Forestry; Notfe 227 Truog's Method of Determining Carbon Dioxide. A. M. Gurjar 288 Undescribed Prairies in Northeastern Arkansas. R. M. Harper. . . 58 Vegetation and Climate of Colorado. W. W. Robbins; Note 193 Vegetation of Conglomerate Rocks of Cincinnati Region. E. Lucy Braun \ 380 West, G. S. Handbook on Algae; Review 334 Whiting, A. L. Laboratory Manual of Soil Biology; Review 159 Wilcox, E. V. Tropical Agriculture; Review 30 Wilcox, Flora. E. W. Berry; Review 127 Wilson, Percy. Work of; Note 228 Working Plans for Forest Organization. A. B. Recknagel; Review 299 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Charles Louis Pollabd, Founder Joseph Chables Arthur Purdue University Otib William Caldwell Teacher's College, Columbia University William Austin Cannon Desert Laboratory J. Arthur Harr3 Station for Experimental Evolution Burton Edward Livingston Johns Hopkins University Francis Ernest Lloyd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Trembly MacDougal Carnegie Institution of WaabinstoD James Bertram Overton University of Wisconsin George James Peirce Stanford University Herbert Maule Richards Columbia University Forrest Shreve Desert Laboratory John James Thornber University of Arizona Edqar Nelson Transeau Ohio State University All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without covers WITH COVERS First 100 Additional 100 First 100 Additional 100 Four pages Eight pages $2.6S $0.72 4.32 1.20 4.80 2.00 84.68 11.72 6.32 2.20 Sixteen pages 6.80 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant Worlo, Tucson, Arizona. The subscription price is S2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are 82.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Wdverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. A QUARTER-CENTURY OF GROWTH IN PLANT PHYSIOLOGY! BURTON EDWARD LIVINGSTON The Johns Hopkins University, Baltimore, Maryland Introduction. The two and one-half decades during which the University of Chicago has achieved the remarkable de- velopment that we are here to celebrate, have witnessed a goodly number of notable changes in the status of botanical science in general, but I think no branch of that science has taken longer strides within this interval of time than has plant physiology. It appears that the continuation of this advance may be accelerated if we take some time, now and then, on such occasions as the present one, to pass in review what seem to be the lasting achievements of the past, and to face squarely what seem to be the general needs of the future. To study the happenings of the past as these may be related to one another, seems to offer the only known method upon which rational pre- diction may be founded, and the planning of future researches in our science must depend increasingly upon such prediction. A period of popularizatio7i. The period in question has been characteristically one of the popularization of natural science in. general, at least among the peoples that have been most active in scientific progress. Thanks to increasing education and to the printing of books and papers, the great principles and discoveries, and even much of the philosophy, of science have spread .outward, from their sources in the minds of scientists, so that utter ignorance of these things is now comparatively rare, even among those who do not deal directly with science at all. Gravitation, magnetism, chemical reaction, evolution, the mineral nutrition of plants, fermentation by microorganisms — ^Invitation paper read at the Botanical Session of the Quarter Centennial of the University of Chicago, June 6, 1916. 1 THE PLANT WORLD. VOL. 20, NO. 1 JANUARY, 1917 2 BURTON EDWARD LIVINGSTON these are terms now frequently heard among those who are not scientists, and often encountered in the daily press. Unknow- ingly, perhaps, the world is coming to look more and more to the scientists, for its utilities, for its amusements, and even for its philosophy and practical religion. Although physiology has been one of the last of the sciences to enter upon this phase of popularization, its progress in this direction has, nevertheless, been very rapid, especially since the closing years of the last century. On the animal side mainly through the arts of medi- cine and surgery, on the plant side mainly through those of agriculture and forestry, many of its elementary principles have become incorporated into general knowledge. The popular- ization of a knowledge of the mineral needs of plants, for example, has largely occurred in the period that we are considering. This phase of plant physiological development, based largely on utihtarian desires, has made possible the establishment and rapid growth of many great institutions, such as the United States Department of Agriculture and numerous experiment stations throughout the world, and these, in turn, have furnished opportunity for the carrying out of an ever-increasing number of truly scientific researches on the dynamics of plant processes. There seems to be no limit to this kind of growth, and it is safe to predict that the next quarter-century will produce a still more general and clearer appreciation of both the utilitarian and the philosophical value of a knowledge of what plants do and how and why they do it. Anything that may advance this general appreciation should also hasten the development of the science itself. Turning to the internal growth of physiology, I wish to mention first some alterations in general physiological philosophy that have become especially evident during these twenty-five years, and afterw^ards to direct your attention to a few of what appear to me as important forward steps in the special science of plant physiology. Development of deterministic philosophy. Perhaps the most striking growth, or alteration, in physiological philosophy, to be detected by a comparison of the writings of the '70's and A QUARTER-CENTURY OF PLANT PHYSIOLOGY 6 '80's with those of the last decade, hes in the gradual develop- ment of a more and more thorough-going determinism. The echoes of an age-old struggle between mysticism, vitalism, and so forth, on the one hand, and mechanism or determinism, on the other, are still rolling on our scientific horizon, but the orderly quiet of physical science now extends into almost every phase of physiological thought. As Jacques Loeb has aptly remarked, no matter what may be the emotional attitude of a physiological investigator in these later days, such a one is sure to adopt a deterministic philosophy as soon as he steps into his laboratory and begins an experiment. What we may think or feel about questions that are too complex to be subjected as yet, to experi- ment, is of little consequence in modern science, but rational experimentation is practically impossible without the con\'iction that phenomena are rigidly determined by pre-existing con- ditions. \Miile there may come other periods, as in times of great wars, when the stress of life itself may compel the tem- porary putting aside of reason, in favor of more elemental emotions, yet it may be safely predicted that physiological advancement will always be guided primarily by the mechanistic or detenninistic conceptions that have come to us from the non-biological sciences. Progress has always been in this direction; as Cowles has said, many \dtalistic interpretations have been replaced by mechanistic ones, but the reverse change has not yet occurred. Tentative nature of physiological conclusions. In the twenty- five years here considered, physiology, along with other natural sciences, has undergone a marked alteration in respect to the final value that it places upon its interpretations. It is an in- teresting fact that increased knowledge of plant and animal processes has thus far tended rather to emphasize their extreme complexity than to establish their conditional relations in any final way. During the last quarter-century we seem, indeed,^ to have been mainly engaged in discovering new problems, rather than in solving the problems dealt with by earher workers. In many cases the earher problem has been analyzed into several component problems, each one of the latter appearing as difficult 4 BUETON EDWARD LIVINGSTON now as did the less thoroughly analyzed problem to the writers of a few decades ago. The physiology of the present day has largely to do with the apphcation of physical and chemical principles and methods to the phenomena occurring in organisms, and this application necessitates the analysis of complex processes into their components, as far as this is possible. Meanwhile, physical and chemical science have been advancing with rapid strides and have placed a w^iole world of precise quantitative knowledge in the hands of the^physiologist, so that the latter now requires a far better acquaintance with the litera- ture of the physical sciences than with that of plant and animal morphology. Progress has been so rapid and in so many widely different directions that there results, for the present, a sort of confusion, whereby the same phenomenon may be interpreted in widel}^ different terms by different investigators. This state of affairs has led to a much more tentative attitude of mind among natural scientists in general, and especially among physiologists, than formerly prevailed. We have learned to state our conclusions tentatively, and as limited by certain suppositions, and we are not surprised if they require restate- ment within a few years. Nevertheless, we need not be dis- couraged, for progress clearly lies in just this continued rein- terpretation and readjustment of our knowledge. The outstanding fact, in this connection, seems to be that physiology deals with greater complexity than does any other natural science — since it has to do wdth the most complex mate- rials and processes so far known to man — and the precise state- ment of physiological relations involves a far larger number of dependent variables, or arguments (in the mathematical sense), than are required in the other sciences. In spite of the great progress already made, we must regard physiology as a very youthful science and we must be content that it blunders and stumbles now and then as it moves forw^ard. Complexity of the printed records. One of the greatest changes to which science has been subjected in recent decades hes not so much in the complexity of the things dealt with as in the complexity of our records of scientific knowledge. Of the mak- A QUARTER-CENTURY OF PLANT PHYSIOLOGY 5 ing of printed books there is no end, and each year sees the inauguration of new scientific journals. Physiological literature - — and the literature of science in general — has become such an unwieldy mass that to investigate the records bearing upon any rather Umited subject is now a staggering task in itself. Men have delved into nature, have brought forth the ore of experimental and observational results, have recovered the val- uable metals as interpretations and conclusions, and have stored the latter in the great, hap-hazard store-house of the literature; and now it becomes almost as difficult to find out what is in the store-house and to utilize it as it is to obtain knowledge directly from nature by experimentation. Enormous, confused, hap- hazard, our literature is a veritable muddle, and much of our recorded knowledge will surety be hopelessly lost unless serious attention maj^ soon be directed toward rendering its content practically available. Abstract or reviewing journals and •yearbooks of various kinds are doing their best to help the stu- dent to obtain the references requisite for his work, but they are woefully inadequate, as every physiologist has learned too well. We require a means far more prompt and far more thorough than these, but the future alone can disclose just how such a means may be attained. I have wished here merely to emphasize this feature of recent physiological progress, whereby our science and the sciences related to it seem now tending to smother them- selves b}^ the accumulation of their own products. Rise of general -physiology. With the introduction of physical and chemical methods of experimentation and thinking, the two branches of physiology have been merging very rapidly, so that a true physiological science — of animals and plants together — seems already actually to have been formed. This change has occurred almost entirely within the last quarter- century; witness the fact that the first edition of Verworn's Allgemeine Physiologie appeared in 1894, that the first edition of Pfeffer's Pflanzenphysiologie appeared in 1880 and the second (alrnost entirely rewritten), in 1897. These works have done much toward bringing animal and plant phj^siology together and, at the same time, toward introducing chemical and physical 6 BURTON EDWARD LIVINGSTON conceptions. During the period here specially considered Ver- worn's book has undergone numerous revisions, and similar treatises by other authors have recently appeared. Putter's Vergleichende Physiologie may be mentioned here, and, finally, the very best treatment of the general subject so far available has come from the hand of Bayliss, whose General Physiology was published only last year. From the first editions of Verworn and Pfeffer to Bayliss, is a long way for a science to progress in a quarter of a century, and these books may well serve as land- marks to indicate many aspects of our advance. I should also add that the publications of Jacques Loeb, together with the sometimes acrimonious but undoubtedly clarifying discussions that these have aroused, belong to this period. The writings of this author have been perhaps more influential than those of any other single worker, in the introduction of deterministic conceptions and in the unifying of physiology. At any rate, we have now come generally to realize that the problems, and the methods by which they are to be attacked, are essentially the same, whether our subjects are Protista, or animals, or plants, and it appears now as though physiology might eventually come to have as broad a connotation, as far as the phylogenetic relationships of our subjects for experiment are concerned, as biology has at the present time. Just as biology is the science that deals with all knowledge of living things, so physiology is the science that deals with all the proc- esses or changes occurring in living things, with special reference to the conditions that control the rates at which these processes occur. Physiology is, then, the dynamic aspect of biology. Conditional control. One other noteworthy clarification that has gradually found its way into physiological philosophy, largely during the last three decades, with the development of physical determinism in our science, has had to do with our general conception of causation and causal relations. Less than twenty-five years ago it was still taught in physiological laboratories that the relation of the rate of a given process (such as respiration, absorption, and so forth) to the intensity of any environmental or internal condition (such as temperature, con- A QUARTER-CENTURY OF PLANT PHYSIOLOGY 7 • centration of solutions, and so forth) might be established by maintaining all other conditions constant and causing the intensity of the condition under investigation to vary from experiment to experiment. No attention was apparently to be given to the intensities of the other conditions; they were merely to be constant, or were to vary in the same manner for all comparable experiments. With more knowledge and with deeper thinking we have become aware that the constellation or complex of other conditions frequently exerts a pronounced influence upon the effect produced in the organism by a given difference in the intensity of the one condition studied. For example, if you wished to determine how concentrated must be a solution of copper sulphate in order to kill a wheat seedling, with its roots in solution and its leaves in air, you would naturallj^ make the nutrient solution precisely the same in all of your cultures and you would add different amounts of the poison salt to the respective jars. Also, you would see to it that all jars were alike and that all cultures were subjected to the same tem- perature and light conditions, whether these were to be main- tained constant or allowed to vary with time. From such a series of tests you would arrive at a fairly definite lethal con- centration of the copper salt, and, until recently, you might have published this result with the idea that a generalization, at least for wheat seedhngs of a given age, had been attained. But if you were to take another nutrient solution as foundation for all the cultures, if you were to shade them all or subject them all to another temperature or to a different series of temperature changes, thus repeating the series of experiments, otherwise as before, you would in all probability then estabhsh quite another critical concentration of the poison salt. In short, how much of the poison is required to produce death depends quite clearly upon the other environmental conditions. Failure to realize this, failure to measure and describe all the other effective con- ditions— which were not thought of as being elements of the problem in hand — has frequently given rise to more or less serious polemics between different experimenters, and so to waste of time, energy and accumulated wealth. 8 BURTON EDWARD LIVINGSTON From this conception of multi-conditional control has developed the well-known law of the minimum and of Hmiting conditions, which seems to have been useful in the interpretation of many physiological relations, but this principle is still quite incomplete logically, and its statement will assuredly become much more complex as our science advances. With a score or more of different kinds of conditions acting together to control the processes of our plants, and with an infinite number of possible combinations of the intensities of these various conditions, the prol51em of physiological control assumes almost a hopeless com- plexity. To illustrate, for a given plant, for a given total con- centration of the series of Shive's- three-salt nutrient solutions and for a given set of climatic conditions, there is a certain set of salt proportions that gives the best growth. For another total concentration, however, all other conditions remaining as before, it is quite another set of salt proportions that are most favorable to growth. Adequately to work out the apparently simple problem thus suggested requires literally thousands of cultures. I shall revert to this matter a little later, but I wish now simply to emphasize the point that we can no longer speak of a single condition as being the cause of an observed effect. The next generation of physiologists will have to learn to handle mo]"e than a single variable and to deal with complexes of con- ditions. They will not consider it a scientific statement to say that a certain concentration of poison, in the solution about the roots or in the air about the leaves, results in death, for they will realize that, with different nutrient solutions, with differ- ent rates of transpiration, and so forth, this concentration limit may have any magnitude within a wide range. External and internal conditions. The idea of the conditional control of plant processes has resulted in the rather arbitrary, but very convenient, classification of the effective conditions in question, into two groups, external and internal conditions, ^Shive, J. W., A three-salt nutrient solution for plants. Amer. Jour. Bot. 2: 157-160. 1915. Idem, A study of physiological balance in nutrient media. Physiol. Res. 1: 327-397. 1915. A QUARTER-CENTURY OF PLANT PHYSIOLOGY 9 and recent advance of plant physiology has had much to do with the measurement of the different members of these two groups and with the study of their relations. The morphological study of internal structures led to the consideration of the physiological processes by which these structures came into being, and it looked for a time as though a new branch of botani- cal science might thus arise. Goebel's later writings, on organ- ography and experimental morphology, illustrate this movement. Since, however, experimental morphology is but the morphologi- cal aspect of the physiology of growth and development, it seems undesirable to create a new branch of science for this study, which appears recently to have become merged into certain aspects of ecology and physiology. Nevertheless, the relation of external and internal conditions to growth, as well as to other internal processes, is now occupying the time of many workers, and promises to be an important part of physiology in the future. This study of the sequence of internal conditions or states, as they follow one another in plants growing under natural con- ditions, now embraces all stages from the simply descriptive to the rather precisely quantitative. The more quantitative work along these hnes also necessarily includes careful measure- ment of the controlling conditions. Artificial and, natural conditions. Along with this advance toward a causal intei^pretation of the natural processes of plants there has developed another aspect of the same kind of study, in which the older reverence for natural or ''normal" phenomena has largely disappeared. Not very long ago that which was usual in nature as we knew it was called normal and we were led to think that a knowledge of what occurred in plants under so-called abnormal conditions was nearly useless or even un- desirable. We have learned, however, that the range of con- ditions offered by nature does not generally happen to be great enough to allow adequate experimental interpretation of plant processes, and many kinds of artificial conditions have come to be employed in physiological experimentation. One of the great advantages of artificial experimental conditions lies in 10 BURTON EDWARD LIVINGSTON the fact that we know our conditions much better when we make them than we possibly can when we let nature furnish them to us. The study of plants in the field requires quantitative knowl- edge of natural conditions, however, with all their great com- plexity, and methods for measuring these are being developed with considerable rapidity. This is the study that I have else- where termed physiological ecology, — physiological, because it regards the plant as a complex of processes controlled by physi- cal and chemical conditions; ecology, because its aim is to inter- pret the phenomena of plant life in nature and with reference to natural conditions. These two aspects of plant physiology must go on developing side by side. Ecology requires that natural plant phenomena be interpreted in an etiological way, and physiology itself re- quires that we should appreciate the fundamental principles of plant dynamics. A parallel may be found in the relation between mining and the chemistry of minerals, wherein very precise laboratory studies (with extremely artificial conditions) are just as important as the work of the prospector in the field. For the further advance of physiology, better methods for producing controlled conditions are perhaps the greatest de- sideratum at the present time, and if a student has not a liking and a talent for creating physical and chemical conditions such as never have occurred in nature, he should not cast his lot with plant physiology, for the next generation. Need of facilities for artificial control of conditions. I cannot forbear to dwell a moment longer on the need of controlled con- ditions in physiological work. Having laid aside the older idea that there is something everlastingly right in natural conditions and something almost akin to blasphemy in the employment of artificial ones, the physiologist comes to the same view-point as that held by the modern chemist or physicist, and he employs whatever conditions seem best for the enquiry in hand. Where would the chemist be if he were constrained to study his salts always as they occur in nature? If it is undesirable to study plants growing in quartz sand, is it not just as undesirable to A QUARTER-CENTURY OF PLANT PHYSIOLOGY 11 study sugar solutions in distilled water or to use purified chemi- cals of any kind? Now, if we wish to find out what chemical conditions are best suited to the development of plants it has long been our practice to control the chemical surroundings of our experimental cul- tures, and we have usually allowed the climatic conditions to fluctuate as they would. A very carefully selected plant may be placed in a very carefully washed Jena-glass jar of a very carefully prepared nutrient solution and the culture may be placed, forsooth, in a north window or in a well-lighted greenhouse! This anti-climax suggests the burden of my present plea. Our experimentation is of relatively little value, and we may know that it will soon be all to do over again, so long as we do not attend to the aerial environment of our experimental plants as thoroughly as we do to the nutrient media and the internal conditions as represented by pure strains, similar seeds, and so forth. Obviously, what is needed is properly equipped laboratories, where climates may be made to order as truly as soil solutions are now commonly made. Such laboratories cannot be arranged with slight expenditure in rooms of an architect's building; they must be planned from the ground up, or rather, from the ground down, for I suspect they will be underground, for easy climatic control. A greenhouse used to be what the experimental phys- iologist first asked for, in the future he will demand elaborately equipped chambers, thoroughly protected from the influence of natural conditions. The physical sciences have now placed in our hands all the equipment for such culture chambers, and what we have to do is simply to adapt and arrange such equip- ment. For more than a decade I have watched the improvement in electrical devices for producing light, with the idea that these were the only instz'uments not already suited to our purposes. Very recently the production of nitrogen-filled incandescent lamps has practically filled this gap. The enclosed mercury arc has been available for a longer time and has actually been employed in physiological studies. Temperature and humidity control are now fairly simple; the arrangements for these, as 12 BURTON EDWARD LIVINGSTON needed in our experimentation, are already in use in many manufacturing establishments. The initial expense connected with the sort of laboratory of which I am dreaming will retard the making available of these much needed facilities, but a tardy recognition of the value of plant processes to mankind should eventually place at the dis- posal of plant physiology at least as elaborate apparatus as is now emploj^ed by moderzi astronomy. Almost as little of really lasting value (in connection with higher plants, at any rate) may be expected ol a physiologist in his present laboratory as might be expected of an astronomer compelled to work in an attic room with a dormer window! Internal conditions. Internal conditions, within the plant, have received much attention, from the beginning of physio- logical studies, and the last quarter-century has seen a rapidly increasing interest in these, mainly from the physico-chemical point of view. The whole science of biochemistry, and even its very name, have developed practically within the period since this University was founded. A general physical chemistry of cells, which was new to physiology in the 90's, has broadened and deepened to form a much more special chemistry and physics of physiological solutions, and now the new field of colloid chemistry is rapidly being opened for physiological study. Such words as enzyme, semi-permeable membraiie, protoplasm, as these were first used, are becoming unsatisfactory, as the things that they connote are better understood. These generally descriptive words will be retained, but their meanings to the physiologist of today are vastly different from their meanings to similar students of twenty-five years ago, and future students will read into them much that we do not now suspect. The whole subject of cell membranes, as these influence dif- fusion rates and turgor, is undergoing a thorough overhauhng. I may mention, for example, that the cell wall was regarded as almost always readily permeable to all plant solutes, at the end of the last century; and now we may not discuss semi-permea- bility of plant membranes without considering these walls. Some of the recent studies upon the permeabihty of cell walls, A QUARTER-CENTURY OF PLANT PHYSIOLOGY 13 as you know, have been carried out in the plant physiological laboratory of this University. • If many of the impressive terms of a few decades ago seem to have lost their charm, we still have charmed words, with which to conjure. Hormones, anti-bodies, the determiners of the genet- icists, are examples of these. As our own Professor Barnes used to say, such words are "cloaks for our ignorance," and they may be expected to lose their charm at a still later day, when our ignorance, in these connections, having become somewhat clothed with knowledge, may no longer require a cloak. Relation of plant ecology, agriculture and forestry to plant physiology. In closing, I should like still further to emphasize the intimate relation between plant physiology and ecology. I regard the province of the last-named branch of science as the interpretation, in terms of controlling conditions, of all plant phenomena as they occur in nature. Ecology must, then, in- clude all that is science in agriculture and forestry, for these sciences deal mainb/ with natural conditions. It is of little importance whether seed was sown by wind, by the movements of birds, or by those of man ; it is also of little importance whether the plants growing from this seed are probably destined to be devoured by human beings or by insects and fungi; the funda- mental problems of agriculture and forestry are the same as those of what is commonly called ecology. Ecology may be considered as applied physiology and the arts of agriculture and forestry are largely appUed ecology. For a long time botany, in this country at least, held itself aloof from agriculture and contented itself with "teaching teachers to teach teachers to teach." The plant physiologists of the university laboratories had httle sympathy with the application of their science, and agriculture and forestry were compelled, perforce, to estabhsh their own schools, where the kind of botany they needed might be taught. When ecology arose, only a few years before the founding of this University, it too was almost scorned by many professional botanists. In spite of much disapproval ecology" has grown, however, in these last three decades, to be a wondrously strong and healthy child of the 14 BURTON EDWARD LIVINGSTON scientia amabilis, so that ecological papers now occupy a rather large portion of the jifrograms of our botanical meetings. This vigorous child has introduced into the house of botany a sym- pathy for the problems of agriculture and forestry that was not prominent before, for it has not held itself so completely aloof from agriculture and forestry, there having been a close relation between ecology and these almost from the very start. Plant physiology has felt the ecological movement very strongly, and many workers in this subject have turned a good portion of their attention to field interpretations. With this awakening our science has come into close connection with agri- culture and forestry, and it seems unlikely that this connection will ever be seriously weakened. Our university laboratories of plant physiology still teach teachers to teach, but the hope- less cycle is frequently broken when some of the teachers that have been taught do not teach, but enter into investigation, in experiment stations and other research institutions. The arts of plant production have shown us problems that were worth our serious attention, both scientifically and finan- cially, and they have furnished the facilities for the solution of these problems. . I am sure they will continue to do this more and more, as time goes on, so that the future of plant physiology promises to be as closely linked with the practical questions of agriculture and forestry as is the present of animal physiology with the practical questions of medicine, surgery and hygiene. As rapidly as those who are deeply familiar with plant physiology become able to see the possible applications of their science, new fields will be opened, which will mean much to human wel- fare as well as to the pure science itself. Not only do governmental and endowed research institutions, interested in agriculture and forestry, offer facilities, opportu- nities and money for the prosecution of physiological research on plants, but private corporations and farmers' associations are also entering this field. Perhaps the best example I can give of what pure science can do for the art of plant production, is found in the work of one of our own number, of the doctors of this Department of Botany, who has actually created, out A QUARTER-CENTURY OF PLANT PHYSIOLOGY 15 of a wild species, an exceedingly valuable cultivated crop hither- to miknown in the world. Wliile doing this he has been in the employ of a commercial corporation. There seems to be no doubt that the future of plant physiol- ogy and plant ecology lies with agriculture and forestry. It is these arts that are to supply the elaborate equipment needed for truly scientific studies of the relations between controlling conditions and plant processes. Just as theoretical physics draws upon engineering for its financial support, so must theoreti- cal plant physiology depend upon the arts of plant production. Thus, through its youngest branches, physiology and ecology, the scientia amabilis is becoming also a scientia utilis, but with this great change it will still remain as truly a scientia and as truly amabilis as it has ever been in the past. NOTES ON THE HISTORY OF THE WILLOWS AND POPLARS EDWARD W. BERRY The Johns Hopkins University, Baltimore, Maryland The name willow suggests to most dwellers in temperate climes the graceful pendulous branches of the weeping or so- called babylonian willow or the silky catkins of the pussy- willows collected in the early springs of our childhood days. We associate the gnarled trunks of willows with Carot's paint- ings, or, if we have chanced to live in certain districts, we think of the willow chiefly as a cultivated crop the shoots of which are utilized for the making of baskets, wicker furniture and, willow-ware. Possibly in youthful chemical experiences we have tried to make gun-powder from willow charcoal, or char- coal crayons, and what American boy does not know that wil- low wood makes good baseball bats or that whistles can be manufactured from the twigs. Willow, of course, enters into a great variety of uses, some of which will be enumerated, but probably its oldest use was the plaiting of its shoots into baskets or similar articles. I have no doubt, that the men, or more likely the women, of the old stone age made baskets of willow twigs, since plaiting is part of the culture of the most primitive of existing peoples. Basket willows were cultivated by the Romans, who used the shoots for making bee hives, baskets, garden and vineyard trellises. The light elastic wood they covered with rawhide and bossed with brass for the shields of their legionaries. Pliny mentions four species of willow so used in his day (Salix fragilis, S. purpurea, S. amygdalina, and S. viminalis). During the Middle Ages the basketmakers guilds were of considerable importance particularly in France, Germany and the Low Countries. These sank into insignificance during the 16 HISTORY OF THE WILLOWS AND POPLARS 17 seventeenth and eighteenth centuries when they were replaced by itinerant basket makers, who were sufficient for supplying the local demand. With the advent of the factory system and the simultaneous great increase in trade and communications, the demand for baskets ahd hampers for parcel shipments of all kinds gave a great impetus to basket making, particularly in Europe where labor was so much cheaper than in America. This, coupled with the constantly increasing popularity of wicker furniture, has resulted in a constant and increasing demand for willow shoots. Napoleon's embargo stimulated willow culture in Britain, and considerable areas in our eastern states have long been devoted to this purpose, usually however with little selection as to species cultivated or cultural methods. The willows and poplars, which constitute a separate family and order of plants, are characterized by a number > of well marked morphological features. They have soft light wood, astringent bark, watery sap, scaly buds and deciduous leaves — short stalked in the willows, long stalked in the poplars — arranged alternately and with stipules. The flowers are in the form of catkins which bloom in the early spring in advance of the un- folding of the leaves. These catkins are generally upright in the willows and pendulous in the poplars, and the male and female are borne on different plants. The seeds, which are tufted with silky or cottony hairs, are formed in one celled, two to four valved capsules, and are dispersed by the winds. By reason of their rapidity of growth, tolerance of moisture (the name Salix is said to be derived from the Celtic sal = near and Z^s= water) and their great adaptability to all kinds of soils they occur in a variety of situations and the different members of the family are found from the north polar region to the equa- tor and beyond. They are gregarious because of the ease with which they grow from suckers and sprouts, their great vitality and free formation of shoots and seeds. About the only inimical condition that proves fatal is shade, of which they are very intolerant, hence in the natural growth of the forest they tend to become replaced by slower growing trees which eventually overtop them. Thus in time they become restricted (especially THE PLANT WORLD, VOL. 20, NO. 1 • 18 . EDWARD W. BERRY the willows) to river bars, mud banks, peat bogs, mountain tops and similar unfavorable situations. Both willows and poplars are very fast growers and both are relatively short lived. The majority are not tall trees and the seeds quickly lose their vitality and the trees are much damaged by winds because of their brittle wood. . The willows are far more diversified and more widely dis- tributed than the poplars, and the facility with which hybrids are formed and the trivial specific differentiation of so many of the species makes them a very baffling group for the systematic botanist. Although both willows and poplars come from a very old stock, a stock as old as any of our trees except the conifers, and one much more ancient than that of our familiar warm blooded animals, the willows seem to have reached the zenith of their development in post glacial times, while the poplars on the other hand were more varied and widespread in earlier geologic times. There are about 200 existing species of willows of all grades of stature, and while we think of them as especially chai^acteristic of the North Temperate Zone they are by no means confined to it but range from the Arctic Circle southward across the equatorial regions into the South Temperate Zone. In America there are upwards of 100 species, ranging in size from tiny plants a few inches high under the Arctic Circle to trees 140 feet tall and 4 feet in diameter in more genial situations, as in the bottom lands of the lower Mississippi. About a score of these are trees. They are found from tidewater to the snowline of mountains and from the Arctic through Canada and the United States to the Gulf, and from the Atlantic to the Pacific. They occur in the West Indies and Central America and southward to the Chilean Andes. In the Old World the}^ range from Arctic Europe and Asia southward over both of these continents to Madagascar and South Africa, and from the Himalayan region . southeastward through Malaysia to Java. Aside from the older uses of willow as cover to prevent erosion or for basketry or charcoal, its utilization for lumbering has had a relatively modern development. At the present time low HISTORY OF THE WILLOWS AND POPLARS 19 grades are largely used for box and cooperage material while the higher grades are employed for furniture drawers and back- ing, as well as for refrigerators, cabinet work and cheap furni- ture. Willow planking is satisfactory for purposes where strength is not required, since it does not warp, splinter or check, and this property determines its use for boat parts such as keels, paddles, etc., and for athletic goods, cutting boards, toys, etc. Large quantities are also consumed every year by excelsior mills. The oldest known willows, not certainly identified, are re- corded, along with the early representatives of other dicotyledon- ous plants, from the Lower Cretaceous of Portugal. During the earlier part of the Upper Cretaceous, the time when the remains of the higher or socalled flowering plants first become prominent in the geological record, a great manj^ species of un- doubted willows have been found. Upwards of a score of forms have been described and the ancestral stock during these early daj^s must have possessed some of the ^dtalitj^ that marks the recent forms for it spread rapidly over North America as well as Europe and probably over Asia as well, although there are no known records from the last continent. It should be noted that four-fifths of the known Cretaceous species, are North American and that none have been found in the prolific Cretace- ous plant beds of Greenland, although poplars were abundant at that time in the far north. Botanists are divided in their interpretation of the willow flower, some regarding its simplicity as a primitive character and others regarding it as reduced by evolution from more evolved types. Whichever view is correct the willows undoubt- edly appear early in the geological record and there is absolutely no basis for regarding the terminal wood parenchyma as support- ing the reduction theory, as is done by Holden.^ The oldest Tertiary, or Eocene, deposits have furnished about 25 species of willows, the records including all of the continents of the Northern Hemisphere. Willows had now reached Green- land, where five different species have been discovered. Other 1 Holden, R., Ann. Bot. 26: 17L 1912. 20 EDWARD W. BERRY Arctic lands also shared this invasion, since willows have been found in beds of this age in Alaska, at the mouth of the Mackenzie River, in Iceland and Spitzbergen. The climate of the earth seems to have been warmer during Eocene times since we find many tropical plants in the Mississippi valley and as far north as southern England, and the Arctic lands at this time were clothed with dense forests of a temperate type. The Oligocene, which succeeds the Eocene in the Tertiary sequence, was a time of prevailingly marine deposition in North America so that few fossil plants are known and there is only one willow among them, although doubtless willows still flour- ished since they are common in succeeding deposits. In Europe about half a dozen species are known from the Oligocene rocks. The next period — the Miocene — was a time of great variety and luxuriance of tree growth. Between forty and fifty differ- ent willows are known and the actual number in existence must have been much greater for when we get a glimpse into the past in an otherwise unknown area, like that furnished by the tiny lake basin at Florissant in the Colorado Rockies we find an abundance of willows — five have been described from Florissant. They are equally abundant in the lake beds and elsewhere throughout Europe. A few are known from eastern Asia and in America they occur in Virginia on the East coast and in Oregon and California on the Pacific coast. The Miocene was succeeded by the Pliocene period, a time during which the forests of the Miocene continued practically unchanged. Many willows whose characters foreshadow their existing descendants are known from Asia Minor to Spain, but unfortunately for our history the American Pliocene deposits are for the most part marine marls so that the American Plio- cene plant record is a blank, although we know that the familiar types must have been present since willows are abundant in the next or Pleistocene period. The Pleistocene, or period of continental glaciers, was an epic time for all plants and animals, for it was a time during which ice sheets many feet in thickness gradually accumulated in northern America and Europe and in the more elevated moun- HISTORY OF THE WILLOWS AND POPLARS 21 tains. After fluctuating near a maximum for some thousands of years these ice sheets gradually disappeared and were followed by a long genial interglacial stage. This great accumulation and southward advance of the ice was repeated four times and the last ice sheet has been gone only a few thousand years. During these changing times all life forms were subjected to new competitions and great stresses, hence many forms succumbed. Others shifted back and forth with the shifting climatic con- ditions and still survive. A great many still existing species of willows, as well as other trees, make their appearance in the Pleistocene bogs, lake beds and river terrace deposits and thus serve to record the gamut of changing environments. We find for example the tiny Arctic willows like Salix polaris, which tcdaj^ occurs in the Scandinavian mountains and reaches its southern limits in the tundras along the Arctic coast of Russia, present in the Transylvanian and Swiss Alps, throughout Britain, southern Sweden, Denmark and the north German plain, associ- ated with other plants of the far north such as Dryas and animals like the Arctic fox and lemming. The accompanying sketch map of Europe shows the unusual climatic conditions which enabled this far northern form, now confined to the lined area on the map, to extend southward almost to the Mediterranean. This and other herbaceous or shrubby species of Arctic willows are found at innumerable localities throughout central and northern Europe, where the deposits of this age have been so intensively studied. The conditions were duplicated in North America but as we have devoted so little study to the life of our Pleistocene deposits it is not possible to obtain adequate records of the distribution of our Pleistocene plants. Over twenty kinds of willows have been discovered in the Pleistocene deposits and only two or three of these are extinct species. The details of their present range and Pleistocene occurrences are too extensive for the present sketch so that only a few will be mentioned. One or the other of the four herbace- ous small leafed arctic and alpine species — Salix herbacea, S. polaris, S. retusa and S. reticulata are found in Pleistocene 22 EDWARD W. BERRY deposits as far south as New York state in this country, and Switzerland and Galicia in Europe. Three of them occur in Germany. The northern peat bog species Salix repens and S. myrtilloides are both found in England. The sub-arctic species Salix aurita and S. caprea occur respectively in England and Denmark. The osier or basket willow is recorded from France Fig. 1. Sketch map of Europe showing the limits of the continental ice sheet, the present distribution and the Pleistocene occurrences of Salix polaris (modi- fied from Nathorst, 1891). 1, vicinity of Edinburgh; 2, localities in Yorkshire; 8, localities in Norfolk and Suffolk; 4, Devonshire; 5, numerous localities in the Alps; 6, localities in Bavaria; 7, localities in Jutland; 8, localities in Zeeland; 9, numerous localities in North Germany; 10, localities in Esthonia, Livonia and Vitebsk; 11, numerous localities in Schonen, Gotland and Jemtland; IS, Felek in Hungary. and Wtirttemberg, and a very similar form occurs in the Pleisto- cene deposits of North Carohna and Kentucky. The white HISTOEY OF THE WILLOWS AND POPLARS 23 willow (Salix alba) and the crack willow {Salix Jragilis) both occur in France and Wiirtternberg. With the amelioration of conditions following the last retreat of the ice the Arctic forms withdrew to the far north with the sub-arctic and cool temperate species in their wake, and these far northern forms are circuni- polar at the present time, although those willows that, attain to the stature of trees and inhabit the Temperate Zone are different in each of the three continents of the Northern Hemisphere. The poplars, while they show their community of origin with the willows, differ from them sufficiently to be readily distin- guishable. They are all" trees and on the whole average larger than the willows. The catkins are pendulous instead of erect; there is a rudimentary perianth or flower envelope, and the bracts of the flowers are toothed or cleft instead of entire as in the willows ; the leaves are usually broad instead of narrow being ovate or deltoid and often cordate, and the leaf-stalks are long and often flattened — a feature well exemplified in the quaking aspen. The generic name Populus is of obscure etymology but was the classical name of the poplar, of which there are several European species. The most important of these is the white, silver poplar or abele (Populus alba), a large tree of the central and southern parts of that continent. The black poplar is also a large tree of central and southern Europe and Asia. An aspen {Populus tremula) occurs in central and northern Europe ranging east- ward to Japan, and there are a number of additional European species, including the downy poplar {Populus canescens) ; Populus monilifera, which furnished the poplar wood of the Romans; and the so-called Lombardy poplar {Populus fastigiata) so often planted in this country as a screen or ornamental tree. The last is probably of oriental origin despite its name, coming originally from the region of the Vale of Kashmir, since it seems to have been unknown in Italy in Pliny's time. Populus euphratica of North Africa, the Altai and Hunalayan region is believed to have been the weeping willow of the Scriptures and its wood along with that of the date palm furnished the rafters for the buildings of Nineveh. The bud gum of the European 24 EDWARD W. BERRY black poplar and of our American balsam poplar has often been employed by herbalists for various medicinal purposes although it has little virtue. There are in all about twenty-five existing species of poplar, of which half are found in North America. Among these the ones known as aspens have an especially wide range, particularly the quaking aspen, Popuhis tremuloides, which covers 112 de- grees of longitude and 41 degrees of latitude, while the European aspen (Populus iremula) covers 140 degrees of longitude and 35 degrees of latitude — the two together nearly encircling the globe. They form dense growths in the north woods and furnish most o'f the drift wood of the Arctic Ocean. Although cut in vast quantities for pulpwood the aspens will probably always form an important element in the more northern forests as they and their ancestors have done during the past three or four million years. They repeat the usual poplar characters of smooth bark, soft weak wood, very rapid growth and sparse broad leafed foliage. They are more gregarious and somewhat smaller at maturity than the other poplars and their long slender leaf stalks cause the lightest summer breeze to set the leaves to quaking or trembling with the characteristic motion and sound that gives them their vernacular names. Other interest- ing poplars are the so-called cottonwoods of the West, where they are almost the only native trees in the river valleys of the prairie country, ranging from Assiniboia to New Mexico. The Cottonwood has narrower leaves than the rest of the poplars v»^hich in the commonest species approaches a willow leaf in appearance. Neither willow nor poplar timber can compete with larger and stronger woods such as pine or spruce or with more durable woods such as oak, cedar, and chestnut. Pulpwood, excelsior, and fuel are their largest uses although for barn floors, boxboard veneer, spools, matches, etc., their qualities of softness, light- ness, ease of working and lack of splintering, render them valuable. The geological history of the poplars is most interesting, there being about 125 fossil species, in. addition to the still existing HISTORY OF THE WILLOWS AND POPLARS 25 Species that are found fossil in the Pleistocene deposits. The oldest known were the contemporaries of the dinosaurs of the closing days of the Lower Cretaceous. One small leafed form is found at this early day in the Potomac River valley and the other, which was for a long time the oldest known dicotyledon, comes from the Kome beds of western Greenland and was named Populus primaeva by Heer, its describer. These first poplars are rare forms but their geographical separation gives us a hint that their abundance was greater in those early days than the records show, and this is also indicated by the abundance and wide distribution of poplars during the Upper Cretaceous, from which about thirty species have been described. They are much less abundant than the willows in the Upper Cretaceous of Europe but, unlike the willows, they are common in Greenland, and they are exceedingly ubiquitous in North America at this time, especially in the West where they appear to have been very common along the borders of the Upper Cretaceous sea that submerged so much of the then low western country. In addition to the American, European and Arctic records a petrified piece of a poplar root has been described from the Upper Cretaceous of Japan, indicating that Asia had its species then as nov\^. During the succeeding Eocene period there were upwards of 50 species, or twice as many as are living at the present time. The rising land of what is now the Rocky Mountain countrj^ shut off the moisture laden winds from the Pacific and the lessening rainfall made of this vast region a quite different country from what it had been during the Upper Cretaceous. In the continental deposits of the Eocene, that is deposits laid down on the bosom of the land rather than in the sea — the deposits of wind blown materials and volcanic dust, laid down in lakes, streams, floodplains, etc — deposits referred to the Fort Union formation, leaves of poplars are the most abundant fos- sils. Poplars appear to have covered at this time all of the plains and mountain country of the West in great variety, extending northward from the western provinces of the United States and 26 EDWARD W. BERRY CajQada to Alaska and the mouth of the Mackenzie River, and encircling the globe in high latitudes. They have been recorded from Greenland, Grimiell Land, Spitzbergen, SachaHn, Siberia and Manchuria. A few are found in central Europe, but the great bulk are American and Arctic, and the climate of more southern lands appears to have been too warm for their presence in any great numbers, for in the abundant Eocene floras of southeastern North America we find no traces of poplars but in their place a subtropical flora of figs, laurels, bread fruit, rain trees and their allies, thatch and date pahns, nutmegs, pond applies, and similar types unfamiliar to dwellers in the Temperate zone. This subtropical flora extends as far north as the mouth of the Ohio in America and a similar warm flora extends to southern England in Europe. During the Ohgocene, which succeeded the Eocene, the scanty records have yielded few poplars. Three species have been described from deposits of this age in the \¥est and four or five are known from central and southern Europe. Southeastern North America was still too tropical in its climate to permit the existence of poplars and although we lack the proof it may be assumed that the numerous Eocene forms lived on in Arctic lands until they were gradually exterminated or driven south- ward by the more severe climate that commenced to prevail in high latitudes before the close of the Oligocene. The poplars are represented during the Miocene period by about thirty species, which are found from Greece westward to Spain in Europe and throughout the western United States and Canada. The Miocene lake of Florissant in the heart of the Colorado Rockies has furnished seven forms of poplar — one a splendidly preserved cottonwood that may well have been the ancestor of the existing forms that are found at the present time in Colorado. Poplars are found at this time along the Pacific Coast, but none are known from the Atlantic or Gulf Coasts. The Pliocene period, which succeeded the Miocene and im- mediately preceded the Glacial period, has furnished about 16 species of poplars, several of which are very close to, if not identi- cal with, still existing European forms such as the European HISTORY OF THE WILLOWS AND POPLARS 27 aspen, the silver poplar and its downj- leafed ally. They are found during this period from Asia ]Minor to Spain, but there are no known American records, since this countrj^ has un- fortunately yielded scarcely any Pliocene plants. The Pleistocene or Glacial period is always of particular inter- est to students of plant history and distribution since the presence of continental ice sheets and the complex physical conditions which their presence brought about played havoc with the uni- formity of development and distribution of the noble races of both animals and plants that had been flourishing for so many thousands of years throughout the Northern Hemisphere. Poplars are represented in the Pleistocene deposits of Europe and America by wood, leaves, bud-scales and catkins. Only two of the ten species recorded from these deposits are extinct and these are both from the earlier Pleistocene of Maryland and are very similar to existing forms. In Europe the black poplar is recorded from Italy; the downy white poplar has been found in both England and France; and the European quaking aspen occurs in peat deposits at a number of localities in Den- mark, Germany, northern Italy, etc. In America the so-called necklace poplar (Populus deltoides) has been found in river terrace deposits in Alabama and western Kentucky, and the balsam poplar or Tacamahac, and the large toothed aspen, have been found in the Interglacial beds of the Don vaUey in Ontario and the former has also been found in the blue clays of Maine. Thus we see that while the life span of both willows and poplars is much shorter than that of most of our forest trees, the stock is a ^drile one and the race an ancient one. While neither have been objects of veneration or worship like the oaks or ginkgoes, or of surpassing utility like so many of our forest trees, both were the associates of our remote ancestors of the Old Stone Age when the last ice sheets were retreating from northern Europe and the Nordic race was being evolved. Both willows and poplars must have been famiUar and useful plants to the Neolithic men that evolved the so-caUed Robenhausian culture of the Swiss lake dwellers (7000-5000 B.C.), the remains of whose d"v^'elhngs, built on piles and found so abundantly throughout 28 EDWARD W. BERRY the region of the Alps and the valley of the Danube, record the time when early man ceased being merely a nomadic hunter and came to occupy fixed abodes and garnered some crops. And when the race passed from lake dwelhngs to fortified and moated habitations in the swamps and along the rivers of southern Europe, the willows must have been one of the familiar and use- ful plants in their immediate environment, during what is called the Terramara period, so that they should have at least a senti- mental interest for the modern race. BOOKS AND CURRENT LITERATURE Absorption of Carbohydrates by Green Plants. — The fact that phanerogams are capable of absorbing by means of their roots a considerable number of organic substances and assimilating them, is not a matter of general knowledge among botanists. A recent memoir by Knudson' brings together the earlier evidence in support of this fact and contributes in addition, a considerable body of data in substantiation of it. Special emphasis is given to certain phases of the problem, namely, the comparative ease of assimilabilitj'' of the several sugars employed and the influence of varying concentration on growth and respiration. Several species of plants including corn, Canada field pea, radish, cabbage, vetch, wheat, timothy, and sweet clover were employed. The seed were germinated and grown for a period of thirtj^ daj^s in tubes containing agar to which a nutrient solution and either glucose, fructose, maltose, or lactose were added. The dry weight of roots and tops was used in the determination of the amount of growth. It was found that not all of the species were able to utilize the same sugar equally well. It was further noted that a certain sugar gave the best growth when the plant was kept in the light while a different sugar exerted the most beneficial effect in the darkness. Respiration was manifestly influenced as early as the fifth day of the experiment. Concentrations of galactose as low as 0.0125% were injurious to vetch, Canada field pea, corn and wheat. This toxicity could be antidoted because of an antagonistic action which was found to exist between galactose and glucose when certain concentrations were em- ploA^ed. — Frederick A. Wolf. Root Hairs. -rRoberts, in a recent contribution from the Hull Bo- tanical Laboratory ,2 reports some results obtained in her study of root hairs. She finds that the ratio between the length of cortical and epi- ^ Knudson, Lewis, Influence of certain carbohydrates on green plants. Cornell Agr. Exp. Sta. Mem. 9, 9-75, fig. 11. 1916. -Roberts, Edith Adelaide, The epidermal cells of roots. Bot. Gaz. 62, 488-506. 1916. 29 30 BOOKS AND CURRENT LITERATURE dermal cells does not determine root hair production. Corn roots were used, and measurements of both smooth and haired epidermal cells were compared with those of adjacent cortical cells. The initial swelling which results in a root hair protuberance is not due to the position of the nucleus, but to the less resistant nature of part of the outer wall as compared with the remainder of this wall, and to the excess of internal pressure of the cell over the opposing pressm'e on the external wall. The internal pressure was found by measurement with sucrose solution to exceed the external pressure by about fom' atmos- pheres. Reduced moisture content of the surromiding air decreased the extensibility of the wall thus retarding root hair development. In- vestigation of the structm'e and composition of the walls of various root hairs (alfalfa, amaranthus, barley, corn, cabbage, daucus, morn- ing-glory, pea, tobacco, tradescantia, and others) showed in every case excepting corn an outer layer of calcium pectate and an inner one of cellulose. Some of the root hairs investigated had in addition to the two layers a callose layer at the tip. Corn root hairs had only a cellulose layer. The pectin layer is closely related to the absorp- tion and retention of water by the hair, and the cellulose layer strength- ens the wall. The formation of cellulose mucilage in corn, and of pectin mucilage in the other root hairs investigated, makes possible the close relation that exists between root hair and soil particles. — J. G. Brow^n. Tropical Agriculture.— Our increasing interest in tropical coun- tries and their development will give a useful place to Wilcox's recent book on the agriculture of the tropics.' A large and well selected series of tropical crops is described with an amount of detail depend- ing upon the commercial importance of each of them. Sugar, rubber, sisal, coffee, the banana, and the coconut, for example, are given an extended treatment covering the botanical description of the plants which yield these products, their propagation, cultivation, harvesting, yield, and preparation for use. The book is sufficiently elementarj^ to enlighten those who still believe that bananas hang from the tree as they hang in the fruit shop, and it- is so full of well arranged material that it is sure to contain a great deal of fresh information for every reader in the temperate zone. No partiality has been shown to any portion of the tropics in the 1 Wilcox, E. v., Tropical Agriculture, pp. 373, pis. 33. New York, D. Appleton and Company, 1916. ($2,50.) BOOKS AND CURRENT LITERATURE 31 selection of a relatively small number of crops and plants from the enormous nmnber involved in the agriculture of the tropics as a whole. The fact that the same plant is often grown in widely separated re- gions means that the selection of universal popular names is impos- sible. Persons with experience confined to the western hemisphere will not recognize in ''kapok" the tree known as "ceiba" in Spanish- America and as ''silk-cotton" in the British West Indies. Other plants with a rich s3^nonomy, such as the dasheen, or taro, are given their entire complement of names. Inasmuch as the volume is designed to give information to the prospective settler or investor, there is considerable importance in the chapters on tropical climate and soils, on the general methods of tropical agriculture and on the economic and social conditions of tropical lands. It is of interest to find the fact getting into print that the tropical cU- mate is not insidiously harmful to the white man if he will take active phj^sical exercise, just as if he were still in the so-called temperate region. — Forrest Shreve. NOTES AND COMMENT About four hundred degrees in botanical science, including some titles in bacteriology and general physiology, have been conferred by American universities during the last decade. This number is about equivalent to the present active membership of the Botanical Society of America, although it is by no means to be taken for granted that all of the doctors are members in that organization. A file of the theses would constitute a special history of research dm-ing the period in question. Great difficulty would be encountered in making a col-' lection of these papers, as some have not been published in their •^^" tirety or under the thesis caption, others have been privately prii^^^^'> and some still repose in manuscript form on the shelves in the library of the institutions which acknowledged their seriousness and value by granting a degree. The galleys of an article discussing the doctorates in all subjects in American universities in 1916 have been received from Prof. J. McKeen Cattell. An examination of this list shows that about 37 are of such character as to be reviewed in botanical journals as compared with 45 in the previous year. About one-half of the subjects are descrip- tive of work done in physiological laboratories. One is in genetics, one in cytology, one in soil physics, two are in bacteriology, and the remainder may l^e apportioned equally among morphology, taxonomy, pathology, and ecology. Many of the papers deal with problems of importance, and appear to deal with the results in a broad way. The character of the list indicates that serious work is expected of the candidate. It is hoped that this attitude also impHes a disposition to annoy the earnest student with fewer formal requirements and super- fluous irrelevant minor courses. COLUMBIA UNIVERSITY Edgar Altenburg. Linkage in Primula sinensis, Clifford Harrison Farr. C>i:okinesis of the pollen-mother-cells of certain dicotyledons. 32 NOTES AND COMMENT 33 CHICAGO UNIVERSITY Sarah Lucinda Doubt. Response of plants to illuminating gas. George Konrad Karl Link. A physiological studj' of Fusarium in re- lation to potato disease. Edith Adelaide Roberts. The epidermal cells of roots. Rachel Emilie Hoffstadt. The 'vascular anatomy of Piper methys- ticum. Millard S. Markle. The root systems of certain desert plants. Mabel Lewis Roe. The development of the conceptacle in Fucus. Charles Albert Shull. Measurement of the sm-face forces of soils. Arthur Gibson Vestal. The phytogeography of the eastern mountain- front in Colorado. Frank Earl Denny. Permeabihty of certain plant membranes to water. Alphaeus William Dupler. The gametoph}i:es of Taxus Canadensis Marsh. Leslie Alva Kenoyer. Environmental influences of nectar secretion. HARVARD UNIVERSITY Sumner Gushing Brooks. Studies on the permeability of plant pro- toplasm. George Gaulterus Stevens. The flora of Oklahoma. THE JOHNS HOPKINS UNIVERSITY Ai'thur Gillett McCall. The physiological balance of nutrient solu- tions for plants in sand cultures. UNIVERSITY OF PENNSYLVANIA Ai'abel Wilson Clark. Seasonal variation in water content and trans- piration of leaves of beech, witch hazel and white oak. CORNELL UNIVERSITY WiUiam Carlyle Etheridge. A classification of the cultivated varieties of oats. Arthur Jackson Mix. Studies on the sun scald of fruit trees. Otis Freeman Curtis. The stimulation of root growth with special reference to the formation of roots in cuttings. Louis ]Melville Massey. The hard rot disease of Gladioh. THE PLANT WORLD, VOL. 20, NO. 1 34 NOTES AND COMMENT James LeRoy AVeimer. Three cedar rust fungi; their hfe histories and the diseases they produce. UNIVERSITY OF WISCONSIN Wilhams Nicholas Steil. Apogamy in Nephrodium hirtipes Hk. Orville Turner Wilson. A study of Pseudopeziza medicoguis (leaf spot of alfalfa). Vive Hall Young. Some factors affecting enzyme formation in certain fungi. UNIVERSITY OF ILLINOIS Fred Wilbur Tanner. A stud}^ of green fluorescent bacteria from water. John Asbmy Elhott. Taxonomic characters of the general Alternaria and Mascrosporium. Ernest Michael Rudolph Lamkey. Absorption and transpiration as affected by temperature and humidity. Rosalie Mary Parr. The response of Piloholus to light. Harry Dwight Waggoner. The viability of seeds as affected by high temperatures and water content. UNIVERSITY OF MICHIGAN Reed Oshea Brigham. Assimilation of organic nitrogen by higher plants and its mocUfication by the action of Bacillus sub- tilis. UNIVERSITY OF CALIFORNIA Arthur Hugo Ayres. The influence of the composition and concentra- tion of the nutrient solution on plants grown in sand cultures. Robert Percy Brandt. Notes on the Californian species of Trillium L. Seasonal changes in Trillium species with reference to the reproductive tissues. Robert Humphrey Forbes. Certain effects upon crop plants of cop- per in irrigating waters. Pierre Auguste Boncquet. Bacillus Morulans, n. sp., a bacterial or- ganism which inhabits the sieve tubes of sugar beets and related plants; its characters and significance. UNIVERSITY OF MINNESOTA John Ernst Weaver. A study of the vegetation of southeastern Wash- ington and adjacent Idaho. NOTES AND COMMENT 35 UNIVERSITY OF MISSOURI John Herman Winkler. An investigation of the relation between vegetation and reproductive activity in plants. — D. T. MacDougal. The sandalwoods of Hawaii form the subject matter of a bulletin of the Hawaiian Board of Agricultm-e and Forestry, prepared by Mr. Joseph F. Rock. Nine species and two varieties of Santalum are in- digenous to the islands, where they appear to have formerly com- posed a very important part of the dry lowland forests. It is stated that all of the Hawaiian species are parasitic upon the roots of other trees, although they are not obUgate parasites. The principal source of sandalwood has been the forests of Santalum album in southern India, but a nmnber of other species, as well as some members of other genera and famihes have been of coimnercial importance. This famous wood, the mention of which is so famiUar in all south sea tales, is still in demand for cabinet work in tropical comitries, because of its im- munity from the attacks of termites, it is used as a source of dyes and oil, the wood is largelj^ used in the orient for carving, because of its odor, and it is burned by the Chinese as incense. The report of the Chief of the Division of Publications of the De- partment of Agriculture states that a total of 39,098,239 Ixilletins, pamphlets, circulars, and reports were issued by the Department dm- ing the last fiscal year. Nearly one-fourth of this number consisted of reprints of earlier pubHcations, while about one-third of the total was made up of Farmers' Bulletins. A recent fascicle of the first volume of the Puget Sound Marine Station Publications contains eleven papers based on work done at the station at Friday Harbor. These are all devoted to the mor- phology, distribution, or physiology of the algae of the northwestern coast. OBSERVATIONS ON A NEW TYPE OF ARTIFICIAL ^^^ OSMOTIC CELL .■ 'i. .^a^o » .^ I L I B ^ A " JOSHUA ROSETT \.-..-\ Baltimore, Maryland ' \r^» INTRODUCTION Students in plant physiology are familiar with what is called Traube's' artificial cell — one of the means by which osmotic pressure and some of the properties of precipitation membranes are frequently demonstrated to elementary classes. It will be remembered that these cells are formed by placing a frag- ment of CUSO4 in a weak solution of K4Fe(CN)6, that a brown membrane of copper ferrocyanide is instantly formed about the mass, and that the cell thus formed enlarges for a considerable time, this enlargement being due to repeated osmotic ruptures of the membrane and subsequent closings of these openings by new precipitation. The writer has been interested in the osmotic and chemical phenomena involved in this sort of ''osmotic growth," and has been able to improve the technique so as to bring out several new details of the processes involved. Some of the results should be of interest to physiologists as furnishing examples of certain physico-chemical and colloid-chemical phenomena that may need to be considered in connection with the analysis of the growth processes of living cells. Aside from serving as simple illustrations of certain general phenomena that are ap- parently very roughly paralleled in the tissues of organisms, these artificial growths also furnish opportunity for the deeper study of the phenomena themselves. But it must always be borne in mind, in such studies, that the processes of enlargement ^ Pfeffer, W., Physiology of plants, translated by A. J. Ewart, vol. 1, p. 106. Oxford. 1900. For the original work on precipitation membranes, see: Traube, M., Experimente zur Theorie der Zellenbildung und Endosmose. Arch. Anat. Physiol. 1867: 87-165. 1867. 37 THE PLANT WORLD, VOL. 20, NO. 2 [•EBRUARV, 1917 38 JOSHUA ROSETT here encountered are not to be considered as the same as those called vital. Because a Traube's copper ferrocyanide cell enlarges in much the same general manner as does a germinating Vaucheria zoospore, this is not to be taken as evidence that the zoospore with its resulting filament is composed of a copper ferrocyanide membrane with a solution of copper salt on the inside! It is clear that the chemical substances involved in the living cells are entirely different from those of the artificial model, and yet the latter does unquestionably serve to illustrate some of the physico-chemical principles that are probably effective in cell formation. Failure to emphasize this point in an adequate manner — the point that artificial precipitation cells are like living ones only with regard to the general nature of certain forces involved, and to certain superficial characteristics of their mechanical structure — seems to have been to blame for some features of the present attitude of cytologists toward the study of these artificial growths. Opposed on the one hand by the vitalists, with their slogan of ignorabimus, as far as the molecular physics and energetics of protoplasmic phenomena are concerned, and on the other by the extreme mechanists, who are forever attempt- ing the explanation of protoplasmic phenomena in terms that are far too simple, the study of these interesting and suggestive processes has had but few followers. They lie in a realm still almost unentered either by physico-chemistry or by physiology. Such writers as Leduc,^ for example, by emphasizing inordinatelj^ the likenesses and ignoring the unlikenesses between the "won- derful" phenomena of organic growth and the equally ' 'wonder- ful" ones of physico-chemical growth, have done much to in- culcate the current prejudice of biologists against this promis- ing line of study. On the other hand, the dense ignorance of molecular physics that still prevails among writers in experimental biology — the ^ Leduc, S., Th6orie physico-chimique de la vie et generations spontanees. English translation by W. Deane Butcher, entitled The mechanism of life. New York, 1911. See also an article by W. Deane Butcher in Archives de Plasmologie G^nerale, Brussels, 1912. AN ARTIFICIAL OSMOTIC CELL 39 vagueness that remains evident in these circles, about osmotic phenomena, for instance — seems to render some acquaintance with the plant-Uke and animal-like growths of precipitation cells almost a prerequisite for constructive research in proto- plasmic physiolog^^ If the phenomena of cell growth in organ- isms are ever to be stated in physical and chemical terms, the principles to be worked out for artificial growths will surely be of great value in the formulation of such a statement. The osmotic growths hitherto studied^ have been of the form of closed tubes or cells, open to the outside only momentarily (as in the case of Traube's ferrocyanide cell), and their walls have been soft and unstable. They have been irregular in form, bending or breaking at points impossible to foresee; and it has beea almost impossible to regulate the direction of growth and the production of branches, so as to make them capable of careful study. The osmotic growth about to be described is offered as a modification of those hitherto produced, which lends itself easily to regulation and to study. The tubes are of firm and stable composition, so much so, that specimens have been kept for eighteen months without change, and there is no reason to think that they may not be kept much longer. They are always open at the growing end and are filled with a watery solution. The diameter of the tube is nearly uniform through- out, and the direction of growth may easily be controlled by defi- nite conditions in the surroundings. Except under certain defi- nite conditions no branches are produced, but they may be pro- duced at will. Unlike the growths hitherto studied, these may be grown to a great height, specimens nearly 2 meters high hav- ing'been produced with ease; the limit of growth in these experi- ments is only the height of the available vessel. They are extremely sensitive to many variations in their surroundings and react to them promptly and definitely. 3 Bottger, R., Ueber Erzeugung Baum-und strauchartiger Vegetationen. Jour. Prak. Chem. 101: 295-296. 1867. Quincke, G., Ueber unsichtbare Fliissigkeitsschichten und die Oberflachen- spannung fliissiger Niederschlage bei Niederschlagsmembranen, Zellen, CoUoiden und Gallerten. Annal. Physik. 7: 589-631, 701-744. 1902. 40 JOSHUA ROSETT METHOD AND OBSERVATIONS The conmiercial solution of sodium silicate (specific gravity about 1 : 40) is mixed with a watery solution of sodium salicylate (concentration about 1:10), one volume of the salicylate solu- tion to from ten to twenty volumes of the silicate solution; the solutions should be mixed gradually to prevent the formation of a coagulum. Fragments of potassimn permanganate are dropped into the mixture thus formed, and the osmotic growth begins. As soon as the fragment of KMn04 comes in contact with the liquid medium, some of the salt of course passes into solu- tion. This solution is acted on by the medium and a precipi- tate (probably the oxides of manganese and sihca) is formed around the fragment of the salt. This precipitate forms as a rather rigid layer or membrane, which constitutes the initial osmotic sac, and which bars the entrance of both the silicate and salicylate but allows the entrance of water. The exact nature of the chemical reactions by which this first membrane is formed and by which subsequent growth is accomphshed h3,s not been worked out, but the first step appears to be a reduction of the KMn04 so as to give manganese oxides and probably silica compounds. The action of the salicylate is not clear; it may be catalytic. As water enters the sac, on account of the osmotic action of the saturated KMn04 solution within, additional quantities of the salt pass into solution. As long, therefore, as there re- mains a supply of undissolved KMn04 there can be no relief of the osmotic pressure, and the sac expands. Within a period of less than a second it becomes about a third larger than the origi- nal salt fragment (see fig. 1, A). The smaller sacs are either ovoid or spherical; the larger sacs are more nearly of the shape of the original crystal, but with rounded angles. The solution outside of the sac being of a higher specific gravity than that within it, the highest point of the sac becomes the point of least resistance, and the sac, having expanded to its full capacity, bursts open at this highest point. Through the rupture a stream of KMn04 solution pours forth and comes in direct con- AN ARTIFICIAL OSMOTIC CELL 41 tact with the surrounding medium. The process of growth proper now begins. The opening in the sac, which is at first irregular, rapidly becomes round. It is then seen to be raised upon a protuber- ance which turns from a translucent red-bro^^^l (the color of the osmotic sac) to an opaque black. This protuberance be- comes elongated into a stem whose thickness is uniform except at the end, where it tapers into a tall cone, open at the apex. This conical end of the stem retains throughout growth the trans- lucency and red-brown color of the original protuberance. The entire process, from the moment the crystaj is dropped into the medium until the formation of a perfect stem, occupies (at room temperatVu'e) about one minute. The stem consists of an outer, a middle and an inner layer. During the process of growth no sharp hne of demarcation can be seen between the sohd tip of the stem and the solution in which it is bathed (see fig. 1, B). The first discoverable struc- ture is at the upper edge of the inner surface of the stem and consists of minute refractive colorless sphericaJ bodies which become irregular as they coalesce to form a continuous surface. This structure, which constitutes the thin lining of the lumen of the stem, may be observed in prepared microscopic specimens as a yellow band passing along the entire length of the stem. Where the refractive bodies have formed a continuous surface, this surface becomes covered externally with a translucent red- brown coating, which constitutes the thin outer covering of the stem. When fully developed this layer appears perfectly homogeneous. During the process of growth, however, it can be seen to be formed by the conglomeration of a vast number of minute spherical bodies of a red-brown color. Between these two layers a third, thin black layer, now makes its appearance, which thickens, until at the junction of the cone-shaped tip and the body of. the stem, it outstrips in thickness both the in- ner and outer layers. The formation of the middle layer after the formation of the outer and inner ones accounts for a state of tension which exists in the outer layer. This tension is mani- fest from the fact that when a stem is removed from the solu- 42 JOSHUA ROSETT tioii, washed with water and dried, the outer layer bursts and peels off. If it is wished to produce tall specimens, a glass tube 8-12 mm. is emplo3'ed, and it should be sHghtly inclined, in order to permit the growth to approach the wall and chmb along it. In such cases, too, the fragment of KMn04 (compressed tablets may be used) should be placed at some distance above the bottom of the glass tube. This may be accomplished in the following manner: Previous to filling the tube its wall is mois- tened with the solution at the desired point and the fragment applied. The salt will attach itself to the glass in a few seconds, after which the lower end of the tube is stoppered and the tube is filled. Specimens for microscopic study are obtained as follows: Glass microscope shdes are moistened with the solution and the fragment or fragments apphed. The sUdes are then lowered into the solution in a shghtly inchned position, the fragments being attached to their lower surfaces. When growth has taken place to the desired height, the specimens may be prepared in either of three ways. (1) The solution is permitted to dry upon the sUdes. In this case the stems will crack in a number of places, affording a \TLew into their interior. (2) The slides are washed with water and the preparation is mounted in gly- cerinated gelatine. (3) The slides are washed with water and dried, after which the growths are brushed away. In the last case traces of the iimer lining of the stems and of their outer covering adhere to the glass and give a very clear picture of their physical makeup. The actual process of growth may be studied in two ways. Specimens may be growTi in a very narrow space, as between a slide and a cover glass, joined by a frame of cardboard or paper. In this case the preparation is placed on the stage of the micro- scope inclined about 10 degrees from the vertical, in order to permit the growth to apply itself to the coyer glass. The other way is as follows: The slide is moistened with the solution and fragments of the salt are strewn upon it. The preparation is then held over a vessel filled wdth water and a few drops of AN ARTIFICIAL OSMOTIC CELL 43 the prepared solution are placed upon it. After the desired amount of growth has taken place, the slide is lowered into the vessel, moved briskly, to wash off the solution, and allowed to remain in the water until all the KMn04 is washed out of the osmotic sacs. The preparation may then be mounted in glyceri- nated gelatine. A series of such preparations, with different Fig. 1, A. Diagrammatic representation of various stages in the formation of osmotic sac and tube. B. Representing the manner of growth at the tip of the tube. Inside are shown small separate bodies, which became joined to form the inner layer. The middle layer is shown in black, and the outer by shading. C. General appearance of growth at surface of solution (floroid). D. Micro- scopic appearance of the central part of the floroid, showing the closely crowded open canals. Magnification 33 diameters. E. Bending of tubes toward wall of vessel and beginning of annular formation. amounts of growth, constitutes a consecutive record of the changes occurring in the process. As long as the stem is immersed in the solution and there is a supply of KMn04 within, its upward growth continues. Ar- rived at the surface of the solution — not too near the wall of the vessel — a number of branches are formed, which grow hori- 44 JOSHUA ROSETT zontally in all directions, forming by their confluence a flattened cup with an irregular, fringed border. I have called this type of growth the floroid (see fig. 1, C). These horizontal tubes are open above, where they do not come in contact with the medium. In other words, the formation on the surface of the medium consists of a number of convoluted and anastomosing grooves and each groove is extended outward as one of the branches. All three layers of the stem are represented. The middle and outer layers are, however, much thicker than in the stem, especially toward the center of the cup. In that situa- tion the outer coats of neighboring canals coalesce, and the appearance is that of a solid surface traversed by grooves (see fig. 1, D). The diameter of the structure varies with the num- ber of stems participating in its formation. A single stem may produce a floroid as large as 2.5 cm. in diameter. When the upward-growing stem reaches the surface of the solution near the wall of the vessel, it divides into two or more branches, which proceed horizontally toward the wall, at which point each branch bifurcates (see fig. 1, E and fig. 2, A and A')- The new branches grow along the wall, in opposite directions, at its junction with the surface of the liquid, until they meet again at the opposite side of the vessel. The ring thus formed continues to thicken until growth ceases. This ring-like growth consists of a number of parallel canals situated at different levels, and in cross section has the appearance of a honeycomb (see fig. 2, B). I have called it the canalicular formation. While the stem is immersed in the medium, the surplus of KMnO^ — that part not used up in the growth of the stem — es- capes from the open tip of the stem, is partly reduced, is changed in color to a red-brown solution, and rises to the top. "When the stem has reached the top of the medium, however, this surplus accumulates unchanged, either upon the flat cup of the floroid or within the parallel canals of the annular formation. The surface structure may therefore be removed from the vessel and dried, after which it may again be placed in the solution, with the result that new stems sprout forth from it and the whole process is repeated. As the KMn04 is more protected from AN ARTIFICIAL OSMOTIC CELL 45 contact with the medium in the canalicular formation than upon the floroid, the former produces the more certain re-growth. After a well-developed surface growth has formed, if a fresh supply of mediuni is poured into the vessel, new stems regularly sprout forth from the old surface formation thus submerged. By adding solution each time to the height of only 2 or 3 cm. in a test tube, it is possible to produce a number of surface formations, both canalicular and floroid, one mounted upon the other (see fig. 2, C). A structure resembling the floroid described above may be obtained on a glass slide. Crystals are placed upon the bottom of a suitable vessel, brimful of the medium, and the stems are allowed to grow upward, toward the surface, in the usual way. The glass slide is laid across the top of the vessel, thus being in contact with the solution. Upon reaching the surface of the slide, the stems branch out laterally and continue to grow on the glass to which they adhere. The slide may be removed, and the preparation thus obtained may be treated like the slide preparations described above. As the stem grows upward, in the regular way, it is observed that a brownish fluid continuously issues from its tip, rises, and becomes dispersed in the upper layer of the medium. If part of the medimn be removed so as to expose the stem for a centimeter or two, and if water is then added until the stem is once more covered, it is observed that instead of the brownish fluid a clear solution of KMn04 issues from the tip of the grow- ing tube. At the same time growth is suspended. If the tip of the stem be exposed and a glass capillary tube be placed over it, the glass tube soon fills with a concentrated solution of KMn04. When the stem is grown in a space about 0.1 mm. in width (somewhat less than the diameter of the stem), as betw^een a slide and a cover glass joined by a frame of cigarette paper, the opposite sides of the osmotic growth — those m contact with the glass — are imperfect. It can then be plainly seen that the canal of the stem is filled with an upward flowing solution of KMn04, and that the solution, as it issues from the tip of the stem and comes in contact with the reducing medium, turns brown. -l^' 46 JOSHUA ROSETT As growth proceeds, the upper layer of the medium becomes thin and about the color of port wine. The salt is dissolved in the water taken up by the osmotic sac, and propelled upwards to the growing tip of the stem. There part of the salt in solu- tion is used up in growth, and the remaining dilute solution is set free and, partially reduced, rises to the top of the medium. INFLUENCE OF INTERNAL AND EXTERNAL CONDITIONS UPON THE RATE OF GROWTH The stem varies in thickness from 0.24 to 0.12 mm. The diam- eter of its lumen is from 0.08 to 0.04 mm. The height of the stem depends upon the total amount of KMn04, upon the height of the column of liquid within the container, and upon the amount of water available for bringing the salt into solu- tion within the osmotic sac. For some time it seemed impossible to grow stems taller than about 38 cm. Upon investigation it was found that after some hours of growth the osmotic sac, resting upon the bottom of the vessel, became surrounded by a highly concentrated zone of the colloid solution. Water had been taken up by the sac from the solution immediately sur- rounding it, and, the supply of water having become exhausted, growth of the tube above had been stopped. This condition was obviated when the crystal was supported at some distance above the bottom of the vessel. The concentrated zone of the colloid solution being of a higher specific gravity, then sank to the bottom and was replaced by fresh solution of a lower specific gravity. Specimens have thus been grown nearly 2 meters high, in glass tubes, as has been mentioned. The rate of elongation of the stem is greatly influenced by temperature. Chemical processes are more active, and the osmotic pressure of a substance in solution increases, as the tem- perature rises. These facts partly explain the relation. Thus while growth is more active at the tip of the stem with every rise in temperature, a greater supply of KMn04 is at the same tim6 furnished by the increased osmotic pressure of the KMnO, solu- tion within the canal of the stem and the osmotic sac. At a temperature of 0°C. the stems grow at the rate of 2.5 cm. in AN ARTIFICIAL OSMOTIC CELL 47 ten hours. At 42°C. they grow at the rate of 2.5 cm. per hour during the first twenty-four hours and at the rate of 30 cm. per day during succeeding days. Growth is more rapid when the stem clings to the side of the vessel than when it is surrounded on all sides by the solution. The vessel wall (or glass plate, etc.) supports the inner layer of the stem as it is formed. The outer and middle layers are not then formed, as has been remarked; that is, the side of the stem in apposition to the solid surface is imperfect. Thus not so much KMn04 is used in forming the wall, and a more rapid rate of growth is the result. When stems are crowded in a limited space to the extent of interfering with each other's growth, this factor — the economy of substance — makes for the persistence of the stems situated in apposition to a foreign body, at the expense of others, which cease growing. This question will be further discussed under a separate heading. Rapidity of growth being in direct proportion to the degree of osmotic pressure within the sac, it is necessarily less rapid when a number of stems arise from the same sac than when only a single stem is formed. DIRECTION OF GROWTH When the conditions of the environment are the same on all sides of the stem, its direction is vertically upward, this being due to the fact that the solution within is less dense than the surrounding medium. If, in the course of growth, the vessel be tilted, turned on the side, etc., the stem bends and still pro- ceeds to elongate upwards. In this manner a stem may be made to assume almost any linear figure (see fig. 2, D). If a horizontal obstacle be placed above the vertically growing stem, the latter will branch out laterally along the under sur- face of the obstacle, until one of the branches will have reached its edge, when it will continue vertically upwards again. When the stem is surrounded on all sides by the solution, it is rarely perfectly vertical. This is due to the extreme sensi- tiveness of the stem to differences in temperature on opposite sides. After the stem has been formed, it does not respond to 48 JOSHUA ROSETT temperature differences, but the new increments of the grow- ing stem are added so as to produce a bending toward the warmer side of the container. Stems were grown in rectangular vessels 25 by 15 by 3.75 cm. The broad sides of the vessels were of glass, the narrow sides of tin. In such vessels heat conduction 'f\i Fig. 2, A. Microscopic appearance of beginning of annular formation. A. A stem bifurcating into two horizontal branches at junction of glass slide and top of solution. A', the interior of A. The glass slide upon which the specimen was grown was first photographed, then the growth brushed away and the slide photographed again. Magnification 24 diameters. . B. A canalicular forma- tion in cross section. The lining of vertical canals of stems and openings of horizontal canals only appears, the opaque parts of the growth having been brushed away before being photographed. Magnification 24 diameters. C. Repeated canalicular formations, one above another. The lowest is al- lowed to form at the surface of the solution, then more solution is poured in, a second is allowed to form, etc. D. A linear figure produced by turning the glass plate, to which the growth adheres, a number of times in the solution. E. The effect of heat upon the stems. Actual size 25 by 15 by 3.75 cm. The broad sides of the vessel ai-e made of the glass, the narrow sides, the bottom and the chim- ney passing through the center are made of tin. A small flame burned in the chimney while the stems were growing. F. Showing the thickening of the stem below an outgrowing branch and its bending in a direction opposite to the side from which the branch arises. The lining of the canals only is shown, the opaque parts of the stem having been brushed away from the glass slide. Magnification 100 diameters. AN ARTIFICIAL OSMOTIC CELL 49 s is greatest along a line of the long diameter. To produce ver- tical steins in such vessels, in the winter, in a room heated in the ordinary manner, is impossible. The inclination of the stems in such cases is always toward the source of heat in the room. A vessel of the type above described was placed under conditions where the temperature on all sides of it were as nearly equal as I could make them. The room (in the winter) was unheated, and the vessel, well isolated with towels, was placed in the central compartment of the bottom drawer of a desk and left there undisturbed overnight. In the morning it was found that the stems were inclined toward a vertical line passing through the center of the vessel. The temperature of the room had fallen during the night, while the stems were growing, a little over one degree, and the center of the vessel has there- fore become the warmest point. The direction of the stems is, however, not continuously toward the warmer side. It is at first toward, then away from it; then again toward, then again away; and so on in a series of upward curves. Stems were grown in a vessel of the type de- scribed above, except that it had a tin chimney passing vertically through its center, in which was placed a small flame. The re- sult was a series of regularly symmetrical curves on each side of the chimney, as will be seen in figure 2, E. So far I have no adequate explanation to offer for the formation of these curves. When the stem has reached the top of the solution, and the source of heat is definite, as from a Bunsen burner, the direction of horizontal surface-branches is definitely toward the warmer side of the vessel. A similar bending toward the source of strong illumination is also observed, but this may be another instance of heat effect. THE PRODUCTION OF BRANCHES When the stem has been compelled, b}' the turning of the vessel, to make a number of sharp bends, it ceases to grow. Instead a new stem shoots out either from the osmotic sac or from the side of the old stem. It has already been remarked that the 50 JOSHUA ROSETT interposition of a horizontal obstacle in the course of the verti- cally growing stem produces a branching of the stem on the lower surface of the obstacle. These branches pass laterally in all directions until at least one of them reaches the vertical side of the obstacle, when it will continue upwards, while the rest of the branches stop growing. If the tip of the stem is covered with wax, or some other material so as to close up its opening, it stops growing. In a few seconds, however, it is found that a new stem grows either from the side of the old stem or from the osmotic sac. If the tips of the branches are in their turn closed up with wax, new branches shoot out either from the old branches, from the main stem, or from the osmotic sac. In this manner any number of branches can be produced at will. When a branch grows from the side of the stem, the part of the stem between the osmotic sac and the branch, thickens and bends in a direction opposite to that where the branch arises (see fig. 2, F). A breach in the weakest point of the stem wall,, or sac, consequent upon the rise of pressure within the stem and sac when t*he outlet is closed, explains the growth of branches under these conditions. The pressure of the fluid within the stem must rise when it is bent at sharp angles a number of times, and this condition, too, accounts for the outgrowth of branches. The same increase of pressure within the stem, forcing the per- manganate solution through its wall, possibly accounts for the thickening of the stem between the sac and the outgrowing branch. The wall of the stem opposite to that from which the branch grows, must be subjected continually to greater pres- sure from within than that which bears the branch (the latter having an outlet, the former having none — the principle of the revolving garden-sprinkler), and this fact may account for the bending of the stem between the sac and the branch in a direc- tion opposite to that from which the branch grows. Thus it apparently happens that the same factor which causes the out- growth of a branch (the rise of osmotic pressure within) also, enables the stem to withstand the increased weight occasioned bj'' the new outgrowth. ^ AN ARTIFICIAL OSMOTIC CELL 51 REACTIONS OF THE GROWTH TO UNFAVORABLE CONDITIONS \\Tien the fragment of KMn04 is dropped into the solution, it is seen that one or more gas-bubbles adhere to it. Microscopic observation reveals the fact that a gas-bubble always appears in the situation where a stem is about to sprout forth (see fig. 3, A). Not infrequently it happens that this gas-bubble is caught in the open tip of the stem (see fig. 3, Bl). Growth takes place around the gas-bubble, the stem showing a protuberance in that point, the wall of which is sometimes thinned out so that the bubble can be plainly seen through it (see fig. 3, B2). If sufficient space is left between the inner wall of the stem and gas-bubble for the free onward-flow of the solution within, no other reaction occurs (see fig. 3, B4). If the space is too nar- row, a branch shoots out from the stem (see fig. 3, B3). At a temperature of about 56°C. the fluid within the tip of the stem coagulates. The pressure within the stem forces out this coagulum, which appears in the form of a fine, convoluted thread about the upper part of the stem. The increased pres- sure within the stem, however, soon causes the outgrowth of branches. The coagulation of the fluid within the tips of these branches results in the outgi'owth (from the branches) of finer branches. The finer branches, in their turn send out still finer branches, until the growth appears like a thick mass of matted threads (see fig. 3, C). When a stem is entirely broken off, a new conical tip rapidly forms upon the stump and growth proceeds as before. Advan- tage was taken of this fact to obtain successive crops of stems without replanting the crystals, until the osmotic sacs were exhausted of the contained KMn04. A somewhat modified reaction occurs when the stem is broken so as to retain the broken part on a line with the stump. The latter may be accomplished in the following manner: Stems are grown upon glass slides, as directed above. When grown to some length, they are cut across with a knife and the slides again immersed in the solu- tion, as far as possible in the same situation as before. A few minutes after the cut stems have been immersed, it is found 52 JOSHUA ROSETT that the loss of substance has been bridged over by new growth and that the stems are much thickened in that situation. Exami- nation of the interior of this thickening shows two canals (see Fig. 3, A. A sketch from a photograph of an osmotic sac. Gas bubbles are seen to adhere. Below and to the right is seen an aborted beginning of a stem enclosing a gas bubble within its opening. Fig. B. Sketches made from photo- graphs. 1, Gas bubble caught in the open tip of the stem. 2, The thickening of stem at the point where the gas bubble is held. 3, The outgrowth of a branch beneath the obstructing gas bubble. 4, The lining of the canal of the stem enclosing a gas bubble. Magnification of 1, 2, 3 36 diameters, magnification of 4 150 diameters. C. The effect of high temperature upon the osmotic growth. D. Showing a thickening at the point where repair has taken place after fracture. The black patches to the right of 1 are chips from the fracture which adhered to the slide while it was photographed. 2, The interior of 1, showing the exact site of fracture where the canal is interrupted. The new canal arises from the side. Magnification 36 diameters. AN ARTIFICIAL OSMOTIC CELL 53 fig. 3, D). The old canal is on a line with the stump, the new somewhat to the side. Further growth is along the line of the latter canal. When the medium is too thin, the osmotic pressure within the stem forces the KMn04 solution through the wall of the stem, with the result that the latter becomes surrounded by a brownish precipitate. Growth under these conditions is tardy, the stems remaining stunted. MUTUAL INTERFERENCE A number of osmotic growths crowded together in a limited space, affect each other's growth in several interesting ways. To elucidate the facts in this connection, a series of experiments was carried out, as follows: Various numbers of fragments of KMn04 (as nearly as possible of the same size) were planted in test tubes (also of the same size), filled with the solution to the same height, and placed as far as possible under the same conditions of temperature, etc. After a certain number of hours the solution in the test tubes was replaced by water and the stems grown were counted and measured (through the glass). Following are two typical tables of the results obtained. TABLE 1 Stems were permitted to grow for eight hours in six test tubes, each 20 cm. in height and 1.5 cm. in diameter, with the following results p c; a a i H H a H f" 5 e S f- W d. O ^ < z a CO a; It ^ i. 2 a i^ s i. _ •< «5 Q t; S « fa H to s fag H RESPECTIVE LENGTHS OF STEMS iH H &! " ^ O a! O H &.6 0 Z §5 (in centimeters) o z 02 to to p H ag n « S fc. D S rt cj ^1 go H O JO*: < « P3 is J p W H % z i5 Centin neters 1 3 11.8, 0.6, 2.5 3.0 19.9 19.9 11.8 2.5 2 4 11.25, 10.6, 9.3, 6.25 2.0 37.4 18.7 11.25 6.25 3 6 13, 12, 8.5, 8.5, 5.6, 2.5 2.0 50.1 16.7 13.0 2.5 4 9 11.5, 10.5, 8.75, 8, 6.5, 6.8, 5.5, 2. 5,2 2.25 62.05 15.51 11.5 2.0 5 9 12.8, 11.5, 11, 10, 6.5, 6.5, 6, 6, 1.8 1.8 72.1 14.4 12.8 1.8 10 13 12.5, 10.6, 9.5, 8, 7, 7, 7, 7, 5.6, 5, 3 '> 1 1.3 85.2 8.52 12.5 1.0 THE PL.\NT WORLD, VOL. 20, NO. 54 JOSHUA ROSETT A study of table 1 shows that, on the whole, there is a dispro- portion between the number of fragments of KMn04 planted in each test tube and both the number of stems and the total stem-length (the sum of the lengths of all the stems in the test tube) produced; that while the single fragment in the first test tube had produced 3 stems — had produced a total length of growth of 19.9 cm. — a similar fragment in the last test tube had produced only 1.3 stems of a total length of only 8.52 cm. On the other hand the table shows that notwithstanding the total diminution of the product as the crowding of the fragments increases, taller specimens are, on the whole, to be found there than where the crowding is least; and in contrast to this, the shortest specimens as well are found where the crowding is greatest. TABLE 2 Stems were permitted to grow for twenty-five hours in 12 test tubes, each 35 cm. in height and 2.5 cm. in diameter. The test tubes were filled to within 2.5 cm. from the top. Number of fragments of KMNO4 test tube in Number of stems which arrived at the top of the solution Al canalicular formation completely (C) encircles the wall of the test tube at its junction with the top of the solution, or, (1), incom- pletely 3 0 0 6 1 1 9 1 1 12 3 C 15 4 C 18 4 I 21 4 C 24 3 C 27 8 C 30 7 C 33 8 C 36 Table 2 shows that the chances for re-growing the stems from the KMn04 deposited at the surface of the solution are greater where the crowding of the fragments is greatest. Of the stems grown in the test tube containing three fragments of KMn04, none reached the top of the solution, consequently no canalicular formation was produced, and therefore no KMn04 was deposited. The canalicular formations in the test tubes contairfing a fewer number of fragments, are, on the whole, incomplete, and there- fore contain less KMn04 than the complete canalicular forma- tions in the test tubes containing a larger number of fragments. AN ARTIFICIAL OSMOTIC CELL 55 To sum up. Crowding affects the growth in the five follow- ing ways: (1) By a diminution of the number of stems produced by the average fragment of KMn04. (2) By a diminution of the total length (the sum of the lengths) of the stems produced by the average fragment. (3) By the appearance of very tall specimens. (4) By the appearance of very short specmiens. (5) By a larger deposit of KMn04 wdthin the surface-canals. There is a sixth way, which does not appear from the tables. The stems, with the exception of the very tall ones, are not as clear-cut and regular where the crowding is beyond a certain point. They are matted together; they cling to and twine around each other. The circumstances which, when the growths are crowded, result in the better development of a few at the expense of the greater number, may be summed up briefly as follows: 1. A situation of the fragment of KMn04 where a large area of its surface comes in contact with the medium. As the osmotic sac continually dehydrates the medium, and becomes surrounded by a concentrated zone of the colloid solution, the higher it is situated above the bottom of the vessel, the better will be the growth. For the concentrated solution around the osmotic sac being of a higher specific gravity, continually falls downward and, is replaced by a solution containing a larger amount of water upon which the osmotic sac draws for its supply. 2. A situation of the fragment near the wall of the vessel. As has been remarked, the apposition of the stem against a foreign body makes for economy of substance, and the less substance is required to form it, the faster will it grow. Owing to the fact that the stem grows towards the warmest point, the shape of the vessel and the material of which it is made will have a bearing in bringing a stem to or away from the vessel- wall. When a stem is situated on the cooler side of a circular vessel, made of a poor heat conductor, such as glass, it will move toward the center of the vessel,, where the heat-rays are focussed. When a stem is situated, on the other hand, near the warmer side of the vessel, it will approach the wall, cling to it, and proceed to grow at an advantage. 56 JOSHUA ROSETT 3. When the solution is poured upon the crystals, or when the crystals are thrown into the solution, they become neces- sarily somewhat displaced from the position assumed by them upon their first contact with the liquid. The manner in which this displacement occurs will have a bearing upon the persistence of some of the stems and the cessation of growth of others. Growth begins immediately upon contact of the KMn04 with the medium. If, now, after stems have sprouted forth from the fragment, the fragment becomes displaced, the stems which arose originally from its highest point, come to arise from its sides or bottom, and must make an abrupt bend in order to proceed upward. If the bend is too abrupt, the increased pres- sure at the highest point of the osmotic sac will cause a rupture, with the consequent outgrowth of a stem. The flow of the KMn04 solution being unimpeded within the lumen of this stem, it will grow faster than the older, bent stems. The flow of the fluid within the more advantageously situated stem moreover, accumulates momentum under the incident force of the osmotic pressure at the expense of the flow of the fluid within the less advantageously situated stems. The stagnating KMn04 solu- tion in the open tips of the latter stems becomes reduced by contact with the medium, clogging their openings with the precipitate formed, with the cessation of growth of these stems as the result. 4. When several fragments of KMn04 lie close together in the solution, they adhere to each other and form one sac par- titioned on the inside into as many compartments as there were fragments. The KMn04 of those compartments from which no stems grow, or those whose stems have ceased growing, serves as a supply for the growth of the more advantageously situated stems. Thus not only does the better situated fragment pro- duce the taller growth, but the growth which it produces is at the expense of the worse situated fragments. AN ARTIFICIAL OSMOTIC CELL 57 CONCLUSION In conclusion it should be again remarked that the resem- blances between this osmotic growth and the growth phenomena of living things are very grossly superficial. The phenomena of these precipitation tubes are of interest mainly because they lead to a kind of physico-chemical thinking that is surely re- quired in the analysis of many physiological processes. If it is worth while for the beginner in cell physiology to attempt to interpret the behavior of Traube's artificial cell, it is perhaps worth while for him also to see this other form of artificial growth. SOME UNDESCRIBED PRAIRIES IN NORTH- EASTERN ARKANSAS ROLAND M. HARPER College Point, New York In The Plant World for February, 1914, attention was called to the large prairies in the alluvial region east of Little Rock, Arkansas, which seem to be unique in several respects. In the latter part of August, 1915, while spending a few days in Craig- head County, 80 or 90 miles northeast of the prairies previously described, I was shown some smaller prairies in the same gen- eral region (the coastal plain west of Crowley's Ridge), which may have had a similar origin, but differ considerably in their vegetation from those of Prairie and adjoining counties. The first (fig. 1) is about a mile and a half southwest of Gilker- son (a station on the Cotton Belt Route at the foot of Crowley's Ridge), and is an opening in alluvial hardwood forests, covering only a few acres. The vegetation is fairly dense and about knee- high, but the flora is very meager, the only plants identified at the time being Crotonopsis linearis and Ambrosia hidentata, with a sprinkling of Vernonia fasciculata (?), Baptisia leucantha (?), Aristida sp., Fimbristylis autumnalis, and Diodia teres. Scat- tered around the edges of the opening, and showing plainly in the illustration, are trees of Quercus palustris, while a little farther back in the forest Quercus pagodaefolia, Ulmus alata and Quercus Phellos prevail. Grasses, and plants with wind- distrihuted seeds, are much scarcer than in the average prairie, and the mode of dissemination of the two commonest herbs is not certainly known. Fire is probably a rare occurrence here. In Georgia the Crotonopsis is chiefly cojifined to rock outcrops, where fire is almost impossible, and the Diodia is also found in similar habitats, though more common as a roadside weed.i 1 In this connection see Bull. Torrey Bot. Club 40: 390 (footnote). August, 1913. .58 PRAIRIES IN NORTHEASTERN ARKANSAS 59 About 9 miles southwest of Jonesboro (the county-seat) a considerably larger prairie, perhaps fifty acres in extent (fig. 2), with similar surroundings but much richer flora, was visited the next morning, but rather hurriedly, for the man w^ho took Fig. 1. Small prairie near Gilkerson, Arkansas. palustris. August 24, 1915. The trees are mostly Querciis me there in his automobile had to be in his office in Jonesboro by 8 a.m. The following plants were noted, the herbs being arranged in approximate order of abundance: TREE.S QiLercus palustris (around edges) SHRUBS Sassafras variifolium Rhus copallina HERBS Ambrosia hidentata Laciniaria scariosa Crotonopsis linearis Sarothra Drummondii Vernonia fasciculata? Baptisia leu^anthaf Chamaecrista fasciculata Panicum virgatum Panicum capillar ef Paspalum sp. Diodia teres Euthamia sp. Eupatorium semiserratum? Cracca Virginiana Boltonia diffusa Juncu^ hrachycarpus Morongia sp. Lespedeza Virginica? Aristida gracilis? Laciniaria spicata? Cv^cuta sp. Buchnera elongata Galactia sp. 60 ROLAND M. HARPER This vegetation is more like that of the Grand Prairie of Prairie County, and if that region were visited at the same season prob- ably nearly all these species could be found there. Plants with wind-borne seeds are evidently more abundant here than in the small prairie first mentioned, a fact probably correlated with the larger size of this one, which exposes it more to the wind. Some of the plants in the last list have thick rootstocks or corms, and probably would not be injured by an occasional fire; and it is very likely that the frequency of fire in prairies is roughly proportional to their size. No estimate of the bulk Fig. 2. Prairie about 9 miles southwest of Jonesboro, Arkansas. Laciniaria scariosa conspicuous in foreground. August 25, 1915.. of the vegetation per unit area was attempted at the time, but from comparisons with other types of herbaceous vegetation that have been studied since I should judge that it would produce at least three or four tons of hay per acre annually. Although the soil is of a comparatively recent alluvial forma- tion, the area is not subject to overflow now, and it may have experienced a slight uplift at a very recent geological epoch. A mile or two from the larger prairie, and apparently on the same level, is a roadside gully about five feet deep, showing PRAIRIES IN NORTHEASTERN ARKANSAS 61 about two feet of brown silty loam resting on stiff mottled clay. The soil looks fertile enough, but there must be something about it unfavorable to vegetation, for I was told that the farm- ers were not able to make any use of it until rice culture was introduced in this section a few years ago. Rice fields now threaten the obhteration of these prairies, as of the Grand Prairie. There are probably other prairies in the neighborhood, and an early investigation of them is greatly to be desired, for the opportunities are growing less every year, on account of the ''pernicious activities" of the farmers. The colored map in Bulletin 494 of the United State Geological Survey, and some of the recent government soil surveys of counties in northeastern Arkansas and southeastern Missouri, will assist materially in locating them. *■? \ BOOKS AND CURRENT LITERATURE Field Study of Osmotic Concentration. — Whenever a step is taken which makes it possible to secure data on any aspect of the physiological behavior or condition of plants under field conditions, an important contribution is thereby made to the advancement of plant ecology in one of its most important and fruitful directions. The technique which has been worked out by Harris for securing the sap of plants and determining its freezing point has been simplified and perfected in such a manner that he has been enabled to secure a very considerable quantity of data on the osmotic concentration of plant saps. Following a preliminary paper in Science^ Harris, Lawrence, and Gortner have published the results of their determinations of concen- trations for plants growing in the vicinity of Tucson, Arizona.^ From one to four sets of determinations were made for each of some 124 plants, and figures are published for the depressions of freezing point and for the osmotic concentrations in atmospheres. The work was done in March and April, when vegetative activity is high and the moisture content of the soil is neither at its highest nor its lowest values for the year. Plants of every vegetative type were used, and sets of determinations were secured in five localities which differ in the physi- cal and moisture conditions of the soil. Sap was secured only from the leaves, and usually from plants in flowering condition. The lowest values were secured in the annuals, Calypiridium exhibiting 8.3 at- mospheres, Calycoseris 9.1, Parietaria 9.5, and Galium 9.6; and in the climbing root-perennial Cissus, which exhibited a value of 8.6 atmos- pheres. High values were secured for the leguminous tree Olneya, 29.7, for Covillea, 34.2, for Yucca, 37.4, for the buxaceous shrub Sim- mondsia, 40.6, for Atriplex growing in a salt spot, 52.0, and for the evergreen celastraceous shrub Mortonia, 57.2. A comparison of the various vegetative types of plants shows that the trees and shrubs ^Harris, J. A., Lawrence, J. V., and Gortner, R. A. On the osmotic pres- sure of the juices of desert plants. Science, 41: 656-658, 1915. 2 Harris, J. A., Lawrence, J. V., and Gortner, R. A. The cryoacopic con- stants of expressed vegetable saps, as related to local exivironmental conditions in the Arizona deserts. Physiol. Res., 2, No. 1, pp. 1-50, 1916. 62 BOOKS AND CURRENT LITERATURE 63 have, in general, a higher sap concentration than the dwarf shrubs, and the latter a higher concentration than the annuals and root-peren- nials. The only true trees worked on were Olneya, which grows away from water courses, and shows a concentration of 29.7, and Fraxinus, which grows only near streamways and shows a concentration of 16.7 to 19.6. The semi-succulent Dasylirion has a concentration of 35.0 and the leaf-succulent Agave of 11.1, while the deciduous Fouquieria varies from 10.4 to 14.4. The material used by Harris and his collaborators was taken in five habitats differing in physical conditions and in vegetation. These were the floor of a canon, the rocky slopes of a hill, bajada slopes (tilted detrital plains), a sandy arroyo, and a salt spot. The osmotic con- centrations were averaged for all of the plants of each vegetative type that were gathered in each habitat. These are lowest for the arroyo, slightly higher for the canon, still higher for the rocky slopes, again higher for the bajada, and highest for the salt spot. These results indicate that there is an appreciable difference in sap concentration for each type of plant in each of these habitats, which are among the most marked that may be seen at desert elevations in the Tucson region. However much the extraction of sap by Harris's method may obscure the conditions under which many of the foliar functions are carried on, it gives nevertheless a means for securing an average expression of the physico-chemical condition of the juices of the plant, which he terms ''both the product and the environment of the activities of the pro- toplast." However much our conception of the importance of osmotic phenomena in plants may be modified by the results in colloidal chemis- try which are now beginning to accumulate, nothing can minimize the importance of the physico-chemical condition of the sap of plants as related to environmental conditions, and particularly to the intake and loss of water. The facts that Harris's results are accordant with our knowledge of the physical conditions of the habitats in which he worked, and with what we know of the seasonal behavior of the plants which he used, are in themselves a confirmation of the physiological soundness of his work, as well as a stimulus to the study of physiological phenomena in connection with field work. The results that have been secured by Harris in his subsequent work in Florida, Jamaica, and Arizona will be awaited with interest. — Forrest Shreve, 64 BOOKS AND CURRENT LITERATURE Germination and Early Growth of Forest Trees. — In a recent paper', Boerker presents what is perhaps the first American. pubHcation on the scientific side of forest nursery practice, the work being based on the greenhouse germination and growth of many American forest tree species. The work is divided into three parts : the effect of habitat factors on germination; the effect of habitat factors on stem and root development, and the relation of the size of seed on germination and development. The author finds that from the germination in three different soil moistures he is able to divide the trees of each region into three classes. The xerophilous species germinated in all three soil moistures, the xero-mesophilous group in the two moister soil cultures, and the meso- philous species germinated only in the soil containing the most moisture. In general, the drier the soil the longer germination was delayed, though the total length of the germination period is decreased as is the final germination per cent. Shade affected the germination by decreasing the time necessary for its initiation and by increasing the length of the germinating period. In all three groups germination began first in the dense shade and last in full light with the longest germinating period and highest germination per cent in the dense shade. Sand gave a more rapid germination, a higher final germination per cent, and a longer period of germination than did either gravel or loam. Sand and gravel accelerate germination while loam retards it, due more to the lack of oxygen than to a difference in soil moisture. The larger sized seeds of Pinus ponderosa and Pseudotsuga taxifolia gave a higher germination per cent and produced larger seedlings than did the smaller sized seeds. From east to west, the seeds of these species germinated earlier, the rapidity factor was greater and the germination period was shorter, while in the case of P. ponderosa the size of the seed increased. In this discussion of the habitat factors on stem and root develop- ment, the author brings out no points that are unfamiliar to the forest nurseryman and practitioner, and the results attained with four species are too conflicting for definite conclusions. While the work is interest- ing from many standpoints to foresters and well worth a perusal by students of plant life the data are too meager and the number of seeds on which the work is based too few, especially in such species as Liboce- drus decurrens, to eliminate errors and to warrant adopting in toto the conclusions which are brought forward. The germination curves which accompany the text are very instructive. — Edw. N. Munns. 'Boerker, Richard H., Ecological Investigations upon the germination and early growth of forest trees. Diss. Univ. Neb. Lincoln, Nebraska, 1916. NOTES AND COMMENT The navel or seedless orange, which is so extensively grown in Cali- fornia, has been in existence little more than a .hundred years, and its cultivation in this country can be traced to several small saplings brought from Brazil only forty-five years ago. A recent study of the fruit made in its native home near Bahia, Brazil, by representatives of the Department of Agriculture, has eliminated much of the mystery that surrounded its introduction into the United States and has added much interesting knowledge in regard to its origin and its present culture. The results of this study have recently been published as Department of Agriculture Bulletin 445. The evidence points to the fact that the variety of navel orange grown in this country first came into existence near Bahia early in the nineteenth century, as a sport from the Selecta orange. The latter variety is still grown extensively in Brazil, and some of the trees show a marked tendency at times to produce fruit with well-developed navels. Almost the entire present planting of navel oranges in California can be traced directly back to two of the trees sent there by Mr. Saunders in 1873, from stock secured by a missionary in Brazil. The navel orange as it occurs near Bahia is large, varying from 3| to 4 inches in diameter, is yellow green in color, and extremely juicy and sweet. The Brazilian fruits have a consider- ably lower percentage of peel than the California fruits and somewhat less fibrous matter or ''rag." The California orange, however, has a much larger percentage of both citric acid and sugar. The forested portions of the public domain of New Zealand are administered by the Department of Lands and Survey, with an approxi- mate expenditure of £40,000 per annum and an income which has fluctuated in recent years between £30,000 and £60,000 per annum. No definite forest policies have been formed and there are no trained foresters in the service of the Dominion. At a meeting of the recently formed New Zealand Forestry League an address was made b}^ Mr. D. E. Hutchins, in which the forest conditions were described and a plea was made for the early establishment of a department of forestry under thoroughly scientific management. The substance of this 65 66 NOTES AND COMMENT address, together with much interesting information about New Zea- land's forest resources, was pubHshed in recent numbers of the Journal of Agriculture. Mr. Hutchins has been engaged in practical forestry work in British possessions for over forty years. He was engaged in the demarcation of forest reserves in India as early as 1872, — twenty years before the setting aside of the first reserves in the United States, under President Harrison. He has since been active as Conservator of Forests in Cape Colony and British East Africa, and during the past year has been making a preliminary survey of the forests of New Zealand and preparing a report upon them. AVith the beginning of the present year an amalgamation was effected between the Proceedings of the Society 'of American Foresters and the Forestry Quarterly, resulting in the appearance of the American Journal of Forestry. Dr. B. E. Fernow is Editor-in-Chief and Mr. Raphael Zon is Managing Editor, assisted by a group of seven associate editors representing different phases of forest work. The new journal will appear eight times a year, and will contain from 800 to 1200 pages of original articles, notes, reviews, personals, and reports of society affairs. The subscription price is $3 per annum. Dr. W. C. Coker and Mr. H. R. Totten, of the University of North Carolina, have recently issued a booklet on The Trees of North Carolina. It contains untechnical descriptions of the 166 species of trees com- prised in the flora of that state. A less conservative treatment would have included about a dozen more hawthorns, another dozen of shrubby forms which occasionally reach the size of small trees, and a few" trees which have escaped from cultivation. The University of Chicago Press announces the preparation of a volume entitled The Living Cycads, by Dr. C. J. Chamberlain, and another on Mechanics of Delayed Germination in Seeds, by Dr. William Crocker. THE EFFECT OF SURFACE FILMS OF BORDEAUX MIXTURE ON THE FOLIAR TRANSPIRING POWER IN TOMATO PLANTS JOHN W. SHIVE AND WILLIAM H. MARTIN New Jersey Agricultural Experiment Station, New Brunswick, New Jersey The use of Bordeaux mixture as a fungicide has given rise to many problems of physiological interest and importance. Fre- quent reports of increased and prolonged vitahty in plants, and greater crop yields resulting from the use of this spray mixture, in the absence of all disease producing organisms, have aroused widespread interest and have led to many investigations in an effort to determine the nature of the influence of this fungicide upon healthy plants. During the past twenty years an exten- sive literature has accumulated dealing with questions of the influence of Bordeaux mixture upon various plant physiological processes, as well as upon plant structures. The results de- rived from the experimental work on the influence of this spray mixture on the rates of water loss by transpiration from sound plants, have led to conflicting opinions among investigators. Studies of the influence of Bordeaux mixture on the rates of transpiration have been stimulated by the belief that prolonged vitality and greater yield from crop plants, such as the potato, following the use of this spray, are the result of a decrease in the rates of water loss, due to the presence of the spray material on the leaves. An explanation of this apparent conservation of the moisture in the leaves of the potato plant in dry seasons has been offered by Clinton, ^ upon the theoretical ground that the stomata and water pores of the leaves are clogged wdth the sediment of the spray, thus checking the loss of moisture by transpiration. The shading influence of Bordeaux mixture has 1 Clinton, G. P., Spraying potatoes in dry seasons. Conn. Agr. Exp. Sta. Report, 1909-10: 729-752. 67 THE PLANT WORLD, VOL. 20, NO. 3 MARCH, 1917 68 JOHN W. SHIVE AND WILLIAM H. MARTIN been considered in this connection by Schander,^ who suggests that decreased rates of transpiration from plants sprayed with Bordeaux mixture are to be expected, since the spray material must exclude from the leaf certain rays which in the unsprayed leaf tend to accelerate the process of transpiration. An attempt to verify this theoretical conclusion by a study of leaf tempera- tures met with but little success. As early as 1894, Frank and Krliger,^ as the result of investi- gations in which they employed quantitative methods, reached the important conclusion that Bordeaux mixture, when applied to the leaves of plants as a spray, exerts an accelerating influence on the rates of water loss by transpiration. Very convincing evidence in support of these observations has recently been presented by Duggar and Cooley^- ^ in two publications. These authors have demonstrated quantitatively that the normal rates of transpiration of abscised leaves of the castor bean {Ricinus communis, L.) are very materially increased by a surface film of Bordeaux mixture. With potted plants of the tomato {Ly- copersicum esculentum, Mill.) and of the potato {Solayium tubero- sum L.) they have shown also that as a result of an application of this spray mixture the transpiration rates were markedly in- creased in comparison with the rates from similar unsprayed plants. In a series of quantitative experiments which have just been published, Martin^ has confirmed the work of Duggar and Cooley with abscised castor bean leaves and with potted tomato plants, and has extended his tests to include eight species of abscised leaves and five species of potted plants. 2 Schander, R., Ueber die physiologische Wirkung der Kupfervitriolkalk- bruhe. Landw. Jahrb. 33: 517-584. 1914. ' Frank, A. B. and Kriiger, F., Ueber den direkten Einfluss der Kupfervitriol- kalkbruhe auf die Kartoffelpflanze. Arb. d. deut. landw. Ges. 1894: 1-46. ^ Duggar, B. M. and Cooley, J. S., The effect of surface films and dusts on the rate of transpiration. Ann. Missouri Bot. Gard. 1: 1-22. 1914. * , The effect of surface films on the rate of transpiration: Ex- periments with potted potatoes. Ann. Missiouri Bot. Gard. 1: 351-356. 1914. ® Martin, W. H., The influence of Bordeaux mixture on the rates of transpira- tion from abscised leaves and from potted plants. Jour. Agr. Res. 7: 529-548. 1916. EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 69 Up to the present time, investigations dealing with the prob- lem of the influence of surface films on rates of transpiration have been confined almost etirely to experiments with detached plant parts and with potted plants. Of the several methods available for the determination of the rate of water loss from plants or plant parts for any given set of conditions, the one most frequently employed by workers in this field is that of weighing the plants and their containers at stated intervals and determining the water loss in weight for each interval. The methods employed for the quantitative determination of water loss by transpiration can not be used with plants rooted in the soil under natural conditions. For such plants, therefore, abso- lute transpiration quantities cannot be determined. The ability of plant leaves to give off moisture to their sur- roundings has been called their transspiring power. ^ This foliar characteristic can be measured directly through the power of the leaf surface to give off water to a standard water-absorbing surface. If the surrounding conditions remain the same and the degrees of the transpiring power vary from time to time, these variations must be due to internal conditions, and the various degrees of the transpiring power should be directly proportional to the rates of water loss. It has been pointed out that the quotient of the transpiration rate for a given time period divided by the evaporation rate from some standard evaporating surface for the same period, should be a measure of the effective internal conditions of the plant in question. The quotient here referred to has been called by Li\dngston^ the rela- tive transpiration ratio, and corresponds to the transpiring power, which may be measured by m.eans of hygrometric methods. Two such methods have been devised, by means of which the relative transpiring power of leaves may be measured. The two methods are the same in principle, but differ in the kind of materials composing the absorbing surfaces. The one em- ^ Livingston, B. E., The resistance offered by leaves to transpirational water loss. Plant World 16: 1-36. 1913. '^ Livingston, B. E., The relation of desert plants to soil moisture and to evapo- ration. Carnegie Inst. Wash. Publ. 50. Washington. 1906. 70 JOHN W. SHIVE AND WILLIAM H. MARTIN ploys the horn hygroscopeof Darwin,^ the other the hygrometric paper of Stahl.^'' It is the latter method as improved by Living- ston and Shreve,ii which has been employed in the present study. It was the purpose of the experiments here recorded to meas- ure, at different hours of the day, by means of standardized cobalt chloride paper, the transpiring power of leaves which had previously been covered with a film of Bordeaux mixture, and to compare the values thus obtained with those derived from similar measurements made at the same hours upon un- treated leaves of the same plant and of different plants. It was thought that such a comparison might give some indication of the relative rates of water loss from treated and untreated plants grown under agricultural conditions, a consideration of some importance in connection with the study of crop pro- ductions in general. The experiments further served as a practical field test of an improved method of cobalt chloride paper when applied to studies involving the effect of surface films on the loss of moisture from plant surfaces; studies which heretofore have been confined almost wholly to detached plant parts or to potted plants grown under artificial conditions. It is a pleasure to acknowledge indebtedness to Dr. Byron D. Halsted for his kind consent to the use of a field plot on the experiment grounds of the Department of Botany of the New Jersey Agricultural Experiment Station, where the field tests were carried out. METHODS The method employed for the tests with cobalt chloride paper is essentially the one described by Livingston and recently improved by Livingston and Shreve, as already stated. The improved method makes use of composite paper slips consist- 8 Darwin, F., Observations on stomata. Phil. Trans. Roy. See. Lend., B. 190: 531-621. 1898. 1° Stahl, E., Einige Versuche tiber Transpiration und Assimilation. Bot. Zeit. 52: 117-146. 1894. 11 Livingston, B. E. and Shreve, Edith B. Improvements in the method for determining the transpiring power of plant surfaces by hygrometric paper. Plant World 19: 287-309. 1916. EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 71 ing of a cobalt chloride paper slip and slips of two permanent color standards' 2 firmly joined together into a composite slip which can be manipulated as a single piece. The permanent color standards are both blue, one being a Httle less intense in color than is thoroughly dry cobalt chloride paper, while the other is just faintly but perceptibly blue. By means of the composite slips, the two color standards and the cobalt chloride paper are brought to the leaf surface simultaneously. When the hygrometric paper is dry it has a slightly more intense blue color than the dark blue standard, but the color becomes less intense as moisture is absorbed. The test is begun when the color of the hygrometric paper just matches that of the more intensely colored standard. As the cobalt paper gradually becomes less intense in color, due to the absorption of wacer, a point is finally reached when its color just matches that of the pale blue standard. WTien this point is reached the test is considered ended. A test consists in determining the length of time elapsing between the occurrence of a fixed dark blue color and that of an equally fixed pale blue color. Since the two color standards are permanent, they furnish these two fixed points. In making a test, some error may, of course, occur from a failure to judge the exact time when the colors are correctly matched, either at the beginning or at the end of the test. In making the composite sUps, the cobalt chloride paper and the two color standards were cut into 5 mm. squares. To join these together firmly very thin, black, water-proofed, gummed-cloth tape 2 cm. wide, was used. The tape was cut into 2 cm. squares. Two of these squares were placed together with the gimimed face of the one against the cloth surface of the other, and the two were cemented together along one edge to prevent them from shpping out of place. Three circular holes, each 4 mm. in diameter were cut through this double tape square by means of a cork borer. The holes were so cut that each was about 1.5 mm. distant from the other two, thus forming a triangular arrangement. One layer of the double ^^ The permanent standard blue papers, as well as the cobalt chloride paper, were secured from The Plant World, Tucson, Arizona. 72 JOHN W. SHIVE AND WILLIAM H. MARTIN square was then folded back and over one of the openings was placed a slip of cobalt paper, over the second and third openings were placed slips of the dark blue and pale blue standards, respec- tively. After this the squares of tape were cemented together with the paper slips between, thus allowing each of the three paper surfaces to be exposed only through the circular openings in the tape. Each finished composite slip was permanently mounted (by means of the free gummed surface of the tape) upon a small cover glass cut to a suitable size (about 1.2 cm. by 1.5 cm.), and the margins of the slip were trimmed to the edges of the cover glass. Thus each composite slip was exposed to the leaf, always with the same surface, the observations being made through the cover glass. This feature of mounting the com- posite slips on cover glasses does not interfere with the stand- ardization nor with the drying of the slip, and it reduces the possibility of the influence of the lateral leakage of moisture upon the time required for the color change of the cobalt chlo- ride paper, when the slip is in contact with the leaf surface. Repeated tests with single mounted slips, over the standard water surface, showed less variation in the time required for the color change of the hygrometric paper than did similar tests with unmounted slips. The Livingston method of applying the slips of hygrometric paper to the plant surface makes use of a spring wire cUp, the movable ends of which are extended by two small glass plates which lie face to face when the clip is closed. The clip used in the present work differed from the usual form by having a small metal plate soldered to one of its free ends, the other free end resting against the face of the metal plate at right angles to its surface when the clip is closed. In making a test, the leaf is held between the metal plate and the mounted slip, the free end of the wire clip resting upon the cover glass of the slip and near its center. The pressure exerted by the spring of the clip is, therefore, imparted to the composite slip in such a way as to secure uniform contact between the slip and the leaf. The composite shps were dried over an electric hot-plate and EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 73 were then placed in small desiccators to retain them in the dry condition until used. The desiccators consisted of glass \dals about 7.5 cm. long and about 2 cm. in diameter, fitted with paraffined cork stoppers. The desiccators were filled to about' two-thirds of their capacity with anhydrous calcium chloride, which was covered with a thin layer of absorbent cotton held in place by a thin, perforated cork disc. The composite hygrometric paper shps used for these tests were standardized once for all in the laboratory by the method employed by Trelease and Livingston, ^^ and presented in detail by Livingston and Shreve. This method is based upon the assumption that the time required for the color change of the hygrometric paper over the standard evaporating surface is inversely proportional to the maximum vapor pressure of water, corresponding to the given temperature. Accordingly, if the time T required for the color change of a slip of hygrometric paper over the standard water surface at the known tempera- ture t, is determined experimentally, it should be possible to calculate approximately the time for the same slip for any tem- perature t' , the calculation being made by means of the fol- lowing formula: ^ _ ^ or r. - ?^' in which P, represents the maximum vapor pressure of water for the temperature at which the actual laboratory test was made with the standard evaporating surface, and P/ represents the vapor pressure corresponding to the temperature t'. The values of Pt and P/ are obtained from pubhshed tables of aqueous vapor pressures. In making the calulations, it is under- stood, of course, as has been pointed out by Bakke,-^ that the only condition external to the hygrometric paper itself which can 1' Trelease, S. F., and Livingston, B. E., The daily march of transpiring power as indicated by the porometer and by standardized hygrometric paper. Jour. Ecol.4: 1-14. 1916. " 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. ■A?^»^f^ 74 JOHN W. SHIVE AND WILLIAM H. MARTIN influence the time of color change over the standard water sur- face, is the temperature. For each of the hygrometric paper sHps here used, ten tests of the time response were made in the laboratory, all at approxi- mately the same temperature. The air temperature in the im- mediate vicinity of the standard water surface and that of the standard water surface at the time when the tests were made, were here considered to be the same. The average time re- sponse for each sUp, for the temperature at which the tests were made, was calculated, and the value thus obtained was used in the calculation of the time response of the slip in question (over the standard water surface) at field temperatures. In the standardization of the composite slips, all the precautions sug- gested by Livingston and Shreve were cao-efully observed, so that the calculations of the time response over the standard evaporating surface at field temperatures should be fully as satisfactory as actual field tests themsleves. It has been asserted bj^ the last-named authors'^ that "it is practically certain that calculations for field temperatures, made from the average of a large number of tests in the laboratory, will prove to be more nearly correct than most single field tests, or even averages of a number of the latter." The time required for the color change of the hygrometric paper from the dark blue to the light blue of the two color stand- ards, upoji the leaf surface, was determined by means of a stop watch. The time period in question will be designated by T?, and the time period for the corresponding color change over the standard water surface will be termed T^, following a similar usage of these symbols by Trelease and Livingston. The ratio of the calculated time period (TJ required for the color change over the standard evaporating surface at field temperature, to the time period (T^) required for the corresponding color change over the leaf at the same temperature, has been called by Liv- ingston the index of transpiring power of the given leaf surface. T This index, ~, is a measure of the relative capacity of the leaf I; " Livingston, B. E. and Shreve, Edith B., 1916, p. 303, I. c. EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION /O surface to give off-water vapor, in terms of the standard evaporat- ing surface blanketed by one millimeter of air. The determination of the indices of transpiring power in plants, by the method of standardized hygrometric paper, are made upon the supposition that the temperature of the leaf and that of the paper* slip at the time when the tests are made, is the same as that of the surrounding air. A certain amount of error may here be introduced, as Trelease and Livingston have pointed out, since leaf temperature and air temperature at any given moment are seldom exactly the same. It is scarcely probable, however, that the difference in temperature between the leaf and the surrounding air is ever sufficient to render the results obtained from a series of tests very different from what they would be if the supposition were entirely true. MEASUREMENTS AND RESULTS As has already been stated, the tomato plants used for these tests were grown under agricultural conditions in the open field. The plants were about 80 cm. tall, profusely branched, and in full bloom when the tests were made. Two plants, growing side by side, with an intervening space of about one meter, were chosen for each days' experimentation. The leaves on about one-half the branches of one plant were sprayed on their upper and lower surfaces with Bordeaux mixture (4-4-50 for- mula of agricultural practice), care being taken to secure a complete covering with a fairly uniform fihn of the spray mate- rial. The leaves were sprayed on the day preceding that dur- ing which the tests were made. The leaves on the second plant remained unsprayed. In selecting leaves to be tested, care was taken to choose only those of approxunately the same age, on branches having about the same relative position on the stem. It has been pointed out by Bakke and by Bakke and Livingston'^ that leaves of dif- ferent ages, and occupjdng different positions on the stem may ^^ Bakke, A. L. and Livingston, B. E., Further studies on foliar transpiring power in plants. Physiol. Res. 2: 51-71. 1916. 76 JOHN W. SHIVE AND WILLIAM H. MARTIN differ markedly in their transpiring power, as this is measured by the method of standardized hygrometric paper. Prelimi- naiy tests, however, made with leaves chosen as indicated above, gave very uniform results. Nearly simultaneous tests with standardized hygrometric paper were made throughout the day upon three sets or groups of leaves: (1) upon sprayed leaves; (2) upon unsprayed leaves on the same plant as the sprayed leaves, and (3) upon leaves of the second unsprayed plant. For the sake of convenience in presenting the data, the three groups of leaves will be desig- nated as series A, series B, and series C, in the order given. Three tests were made upon both the upper and lower foliar surfaces, of different but apparently similar leaves of each of the three groups. The observations, made at intervals of one hour, were begun early in the morning (5.00 a.m.) and were con- tinued until sunset. Owing to a heavy dew on the morning of August 18, observations were not begun on this date until 9.00 a.m. Since the data for this day's tests are, therefore, not so extensive as those for August 10 and for August 14, they are given in full in table 1, where the hours are numbered consecu- tively in the day. The tests were made, of course, within the stated hour, usually within the first twenty or thirty minutes of that hour, for the lower leaf surfaces. A somewhat longer period of time was required for. the tests on the upper leaf sur- faces where the stomata are less numerous than on the lower surfaces; the number of stomata per square millimeter on the upper and lower surfaces of the leaves of tomato plants being estimated by Duggar'^ to be 12 and 130, respectively. The temperatures given were read, at the beginning of the hour in- dicated, from thermometers suspended among the leaves of the plants. In table 1 are given, for each hour indicated, the three individual time coefficients and the corresponding individual indices of transpiring power, for upper and for lower leaf sur- faces, for each series, as are also the averages of these. The last line of each horizontal section of the table presents, in fuU- 1^ Duggar, B. M., Plant Physiology. New York. 1915. EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 77 face type, the indices of transpiring power for the entire leaf surfaces, these being derived by taking the mean of the aver- age indices for the upper and lower foliar surfaces. These are followed on the same line in the last two columns of the table, by the ratios of the indices for the entire leaf surfaces of series A to the corresponding indices of each of the other two series. It wall be observed from the last two columns of table 1 that the ratios of the index values for entire leaf surfaces of the sprayed leaves (series A) to the corresponding values of each of the other two series (series B and series C), while by no means constant, show comparatively small differences. The average indices of the relative transpiring power of the sprayed leaves (series A) may, therefore, be considered roughly proportional to the corresponding indices of each of the other two series (series B and series C). The average of the values of the first of the two sets of ratios here considered is 1.21, 'and of the other it is 1.18, as given at the end of the last two columns of table 1. The indices of transpiring power of the sprayed leaves average, therefore, 21 per cent, higher than the corresponding indices of the unsprayed leaves of the same plant, and 18 per cent, higher than the corresponding indices of the leaves of the unsprayed plant, for the day during which the tests were made (August 18). The average nmnerical data for the tests made on August 10 and on August 14 are brought together in table 2, where the individual time coefficients for the two leaf surfaces and the corresponding individual indices are omitted. On August 10, readings were taken on the upper and lower foliar surfaces of the leaves of a sprayed plant and of an unsprayed plant, only. Series B, therefore, does not appear in the table for this date. Each index of transpiring power for both upper and lower leaf surfaces, as given in table 2, represents the average value of three individual indices, and was obtained in precisely the same manner as were the average indices in table 1. The ratios pre- sented in the last two columns of the table correspond to those which appear in the last two colimins of table 1. The ratios given in the last two columns of table 2 are quite as uniform in value as are the corresponding ratios in table 1. TABLE 1 Dale of relative transpiring power {by standardized cobalt chloride paper) for upper, lower, and for entire foliar surfaces, of leaves of tomato plants. Series A, sprayed leaves; series B, unsprayed leaves of the same plant as the sprayed leaves; series C, leaves of an unsprayed plant. August 18, 1916. ■z e K B o < o a „ RATIO OF H "o^ INDICES FOR P. B O . ENTIRE FOLIAR » s E B "^ S a ^ OBSERVED riME FOR COLORI INDEX OF TRANSPIRING POWER SURFACES, t'-— ^z'^ CH.\NGE ON LEAF (.SEC.; SPRAYED TO B O «p m s K a H u s 3 n ^ 0 M K -V ,, OBSERVED CHANGE ( TIME FOR COLOR 3N LEAF (sec.) INDEX OF TRANSPIRING POWER ENTIRE FOLIAR SURFACES, SPRAYED TO T7NSPRATED o O Eh ^ •< O -< ta o ■< J o z &< •^ 0 H & J O 00 [0 LEAVES It D O a Series A Series B Series C Series A Series B Series C A B A C u 325 580 378 0.092 0.052 0.079 u 376 540 410 0.084 0.056 0.073 u 405 519 545 0.074 0.058 0.055 13 28.5 29.9 Av. 0.083 0.055 0.069 L 57 78 82 0.507 0.383 0.365 L 59 67 78 0.490 0.447 0.383 L 68 91 88 0.425 Av. 0.478 E 0.280 0.328 0.386 0.220 0.340 0.363 0 216 1.27 1.29 U 425 790 670 0.071 0.038 0.045 U 310 510 595 0.097 0.059 0.050 u 424 550 628 0.071 0.055 0.043 14 29.0 29.1 Av. 0.080 0.050 0.046 L 63 82 84 0.462 0.356 0.347 L 66 74 71 0.441 0.394 0.411 L 81 73 77 0.360 Av. 0.421 E 0250 0.399 0.383 0.216 0.378 0.412 0.229 1.16 1.09 U 560 770 710 0.053 0.039 0.042 u 600 756 810 0.050 0.040 0.037 u 550 730 740 0.055 0.041 0.040 15 28.5 29.9 Av. 0.052 0.040 0.039 L 87 104 83 0.344 0.288 0.360 L 74 86 92 0.404 0.348 0.325 L 82 102 101 0.365 Av. 0.371 E 0.212 0.293 0.310 0.175 0.296 0.327 0.188 1.21 1.13 U 687 660 1030 0.046 0.048 0.032 U 660 716 812 0.048 0.044 0.039 u 660 880 865 0.048 0.036 0.042 16 27.5 31.7 Av. 0.047 0.042 0.035 L 149 225 167 0.211 0.140 0.189 L 165 230 150 0.191 0.137 0.250 L 140 300 180 0.225 Av. 0.209 E 0.128 0.105 0.128 0.085 0.175 0.205 0.122 1.51 1.05 80 JOHN W. SHIVE AND WILLIAM H. MARTIN TABLE 1- -Continued 2; 1 OS a » ■< o W H RATIO OF f- H fc. > 7 r, O f" INDICES FOR > OBSERVED TIME FOR COLOR ENTIRE FOLIAR 'i^ CHANGE ON LEAF (sec.) INDEX OP TRANSPIRING POWER SURFACES, SPRAYED TO a 0 od a ii 0 H B (S H TJN8PRATED h se^ HO^ g LEAVES O ^w § o Z fe S o f< P ^ u m m o P Series Series Series Series Series Series A A o m CO H o A B C A B C B C U 650 1245 1380 0.052 0.030 0.028 U 655 900 1270 0.051 0.042 0.031 U 840 1185 1080 0.044 0.032 0.037 17 25.0 34.7 Av. 0.049 0.034 0.032 L 260 254 220 0.133 0.137 0.158 L 225 320 295 0.154 0.108 0.117 L 300 338 250 0.116 Av. 0.134 E 0.091 0.103 0.116 0.076 0.138 0.134 0.083 1.21 1.10 U 960 1330 1270 0.038 0.028 0.029 U 1080 1390 1440 0.034 0.027 0.026 U 1200 1275 1430 0.031 0.029 0.026 18 23.5 36.8 Av. 0.034 0.028 0.027 L 260 290 400 0.141 0.127 0.094 L 285 420 360 0.129 0.087 0.104 L 330 250 350 0.111 Av. 0.127 E 0 080 0.147 0.120 0 074 0.107 0.102 0 065 Av. 1.08 1.21 1.23 1.18 * The letters U, L, and E here denote upper surface, lower surface, and entire surface, respectively. The low value indicated in the last column of the table for the seventh hour, August 14, is not explained. The average value of the ratios of indices for entire leaf surfaces of the sprayed leaves (series A), to the corresponding indices for the leaves of the unsprayed plant (series C), for August 10, is 1.25. The indices of transpiring power for the sprayed leaves average, therefore, 25% higher on this day than the corresponding in- dices for the leaves of the unsprayed plant. The average ratio value of the indices of the sprayed leaves (series A) to those of the unsprayed leaves on the same plant (series B), for August 14, is 1.23. The corresponding average ratio value of the sprayed leaves to the leaves of the unsprayed plant for the EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 81 TABLE 2 Average data of relative transpiring power (by standardized hygrometric paper) for upper, lower, and for entire foliar surfaces, of leaves of tomato plants. Series A, sprayed leaves; series B, unsprayed leaves of the same plant as the sprayed leaves; series C, leaves of an unsprayed plant 1 a INDEX OF TRANSPIRING POWER OF FOLI.IR SURFACES R.^TIO OF AVERAGE INDICES FOR EN- CO a o &. ^ ° 2 a ^ o > s Series A Series B Series C FACES, SPRAYED TO UNSPR.4YED LEAVES U* L* E* U L E U L E A B A C 5 0.078 0.188 0.133 0.051 0.161 0.106 . — 1.25 6 0.123 0.129 0.171 — — - — 0.077 0.199 0.138 — 1.24 7 0.092 0.363 0.228 — — ■ — 0.077 0.321 0.199 • — 1.15 8 0.112 0.545 0.329 — — — 0.071 0.443 0.257 — 1.28 9 0.268 0.659 0.463 — — — 0.135 0.642 0.388 — 1.19 10 0.287 0.790 0.538 — — — 0.205 0.598 0.401 ■ — 1.34 August 11 0.287 0.851 0.569 — ■ — ■ — 0.185 0.642 0.414 — • 1.37 10 12 0.220 0.922 0.571 — • — — • 0.164 0.723 0.443 — 1.29 13 0.154 1.022 0.587 — — ■ — 0.132 0.942 0.537 — 1.09 14 0.130 0.741 0.435 — — — 0.117 0.641 0.379 — 1.15 15 0.177 0.642 0.409 — — — 0.116 0.438 0.277 — 1.47 16 0.111 0.539 0.325 — — • — 0.105 0.381 0.243 — 1.34 17 0.098 0.323 0.210 — — • — ■ 0.089 0.248 0.168 — • 1.25 ■ 18 0.078 0.176 0.124 " " " 0.067 0.163 0.115 Av. 1.08 1.25 r 5 0.038 0.198 0.118 0.160 0.046 0.173 0.110 1.07 6 0.072 0.219 0.146 0.046 0.228 0.137 0.051 0.201 0.121 1.07 1.21 7 0.073 0.178 0.126 0.037 0.171 0.104 0.064 0.198 0.131 .21 0.97 8 0.094 0.192 0.143 0.043 0.191 0.117 0.075 0.193 0.134 22 1.07 9 0.087 0.292 0.190 0.048 0.307 0.178 0.038 0.225 0.132 07 1.44 10 0.107 0.378 0.234 0.045 0.325 0.185 0.086 0.346 0.216 26 1.08 August 14 11 0.096 0.573 0.340 0.044 0.476 0.260 0.060 0.397 0.227 31 1.49 12 0.089 0.448 0.267 0.043 0.385 0.214 0.058 0.340 0.199 25 1.34 13 0.098 0.321 0.210 0.063 0.311 0.187 0.076 0.285 0.181 12 1.16 14 0.069 0.253 0.161 0.048 0.250 0.144 0.044 0.191 0.118 12 1.36 15 0.059 0.236 0.148 0.037 0.212 0.125 0.033 0.206 0.120 18 1.23 16 0.055 0.227 0.141 0.045 0.151 0.098 0.036 0.161 0.099 44 1.43 17 0.040 0.208 0.124 0.032 0.137 0.085 0.037 0.190 0.114 46 1.09 18 0.043 0.124 0.084 0.032 0.099 0.066 0.033 0.122 0.078 Av. 1 27 23 1.08 1.29 * The letters U, L, and E, here denote upper surface, lower surface, and en- tire surface, respectively. 82 JOHN W. SHIVE AND WILLIAM H. MARTIN same day is 1.29. This indicates that the indices of transpiring power for the sprayed leaves average 23% higher than for the un- sprayed leaves of the same plant (series B), and 29% higher than for the leaves of the unsprayed plant (series C). A comparison, similar to the one made here, of the ratio values derived from the data of August 18, considered in connection with table 1, shows that the indices of transpiring power for the sprayed leaves average 21% and 18% higher than the corresponding indices for the unsprayed leaves of the same plant (series B) and for the leaves of the unsprayed plant (series C), respectively. It is interesting to note in this connection the results obtained by Duggar and Cooley'^ with potted tomato plants. In an experiment extending over a time period of more than three weeks, during which quantitative measurements of transpira- tion were made, these authors found the water loss per gram of green substance from ten plants sprayed with strong Bordeaux mixture (4-6-50 formula of agricultural practice) and from ten similar plants sprayed with weak Bordeaux mixture (2-3-50 formula) to be 25% and 13% higher, respectively, than the cor- responding water loss from ten similar unsprayed plants. In a similar experiment extending over a time period of sixteen days, Martin'^ found the water loss per gram green substance and per gram dry substance from six potted tomato plants sprayed with Bordeaux mixture (4-4-50 formula) to be 7% and 9% higher, respectively, than the corresponding water loss from six similar unsprayed plants. While the results noted are not strictly comparable with those here obtained by means of the method of standardized hygrometric paper, it appears that such a method as the one here employed with plants under cultiva- tion, may be expected to yield results which are in entire ac- cord with those obtained by means of the quantitative methods usually employed. The three separate series of hourly index values for entire foliar surfaces, given in tables 1 and 2, are represented graphically in figure 1. Here the abscissas indicate the hours (numbered i« Duggar, B. M. and Cooley, J. S., 1914, p. 19, /. c. "Martin, W. H., 1916, p. 546, I. c. EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 83 consecutively in the day) at which the tests were made, and the ordinates represent the index values for entire leaf surfaces. The heavy black line indicates the march of the transpiring power of the sprayed leaves, the narrow unbroken line and the broken line represent the march of corresponding indices for the .35 - .30 - .25 .20 .15 - .10 - .05 August 18 August 14 9 iO 11 12 13 14 15 15 17 18 -I I I I I 1 I I I I Fig. 1. Graphs showing the march of average foliar transpiring power of sprayed and unsprayed leaves of tomato plants, from hour 5 to hour 18, of August 10 and 14, and from hour 9 to hour 18, of August 18. Series A, sprayed leaves; series B, unsprayed leaves on the same plant as the sprayed leaves; secies C, leaves of an unsprayed plant. THE PLANT WORLD, VOL. 20, NO. 3 84 JOHN W. SHIVE AND WILLIAM H. MARTIN unsprayed leaves of the same plant (series B) and for the leaves of the unsprayed plant (series C), respectively. Inspection of the graphs shows that the index values for the sprayed leaves are, with only one exception, greater than are the corresponding values for the unsprayed leaves, whether on the same plant or on a different plant. The single exception, to which reference has already been made, is given for the seventh hour, August 14. Here the index value for the leaves of the unsprayed plant (series C) is slightly higher than the corre- sponding value for the sprayed leaves. The various graphs show slight irregularities, . but there is a marked tendency for the same irregularities to occur at cor- responding points on the three graphs (two for August 10) of a set. This is particularly striking for the graphs representing the indices for the sprayed and unsprayed leaves of the same plant. The three sets of graphs show clearly that the foliar transpiring power, as measured by the method of standardized hygrometric paper, rises to its maximum about the middle of the day, falls somewhat abruptly for several hours, and then more slowly to the low values attained late in the day. It will be observed that the maximum index values for the three sets of graphs are here indicated at different hours of the day, but the maximum for each graph of a single set appears at the same hour. The maximmn transpiring power of the leaves of each series on August 10 was attained at the thirteenth hour. The maxima for August 14 and for August 18 were reached at the eleventh hour and the twelfth hour, respectively. It is to be noted that the indices for entire leaf surfaces of series A and series C, on August 10, are, with only one exception, much higher in value than are the corresponding indices on either of the other two days. This striking difference in the values of corresponding indices is not at once made apparent from a casual inspection of the graphs, since the graphs of in- dices for August 10 are plotted on a different scale than are those for the other two days. The difference here indicated may be due to the fact that for several days preceding August 10, a rainy season prevailed, so that the moisture content of the soil EFFECT OF BOKDEAUX MIXTURE ON TRANSPIRATION 85 in which the plants were rooted was very much greater on this day than was the case on either of the other two days. The graphs here presented possess all the characteristics of the t^Tpical graphs of foliar transpiring power thus far pub- lished, and in addition to this, they bring out very clearly the influence of a surface film of Bordeaux mixture upon the trans- piring power of the leaves of the tomato plants here employed, for the particular sets of conditions under which the tests were made. Whatever may be the nature of the influence of a film of Bordeaux mixture, effective in producing higher indices of transpiring power, it is clear that this influence is just as effec- tive to increase and to maintain these indices when their values are low as it is when their values are high. It should be stated that the data here presented involve the tests of comparatively few of the total number of leaves of a single plant. As has already been pointed out, the leaves chosen from each plant for these tests were neither very old nor verj' young, and may, therefore, be considered to be representative of the leaves of the plant as a whole. Had it been practicable to make simultaneous tests, similar to these, upon a large num- ber of leaves at various stages of growth and maturity, or upon all the leaves of each plant here employed, it is questionable whether the average data thus obtained would show the results to be essentially different from those here presented. It was not the purpose here to inquire into the causes under- lying the modification of the indices of transpiring power through the agency of Bordeaux mixture, but merely to determine the effect of surface films of this spray material on the transpiring power of tomato plants under cultivation in the open field, by the improved method of standardized hygrometric paper. SUMMARY The results obtained from these tests demonstrate clearly enough that the method here employed furnishes an adequate and simple means of studying the transpiring power of plants which have been treated with surface films of Bordeaux mixture. 86 JOHN W. SHIVE AND WILLIAM H. MARTIN and it is here suggested that the method is equally applicable to similar studies involving the use of other spray materials. The method may also be found useful for the investigation of the transpiring power of diseased plants, or of diseased plant parts: a matter of considerable importance in coim.ection with certain pathological, as well as physiological studies. For each single day, the average values of the indices of trans- piring power of the leaves treated with films of Bordeaux mix- ture may be considered to be roughly proportional to the cor- responding values of the untreated leaves of the same and of different plants. The indices of transpiring power of the treated leaves, for August 14 and 18, show values averaging 23% and 21% higher, respectively, than the corresponding index values of the un- treated leaves of the same plant. In like manner, the index values of the treated leaves, for August 10, 14, and 18, average 25%, 29%, and 18%, higher, respectively, than do the corre- sponding indices of the leaves of the untreated plants. The graphs showing the march of foliar transpiring power, indicate that the maximum indices occur near the middle of the day. The graphs of each single set, representing the index values of the three groups of leaves here considered, all agree in indicating their maxima at the same hour of the day, although the ma,xima of the three different sets of graphs occur at differ- ent hours on different days. The influence of Bordeaux mixture effective in producing higher indices of transpiring power, of the plants here employed, under the particular sets of conditions prevaihng when the tests were made, is just as effective when these indices are low as it is when they are high. SEEDING HABITS OF SPRUCE AS A FACTOR IN THE COMPETITION OF SPRUCE WITH ITS ASSOCIATES LOUIS S. MURPHY U. S. Forest Service, Washington, D. C. I wish to make it entirely clear at the outset that my contri- bution to this discussion is chiefly by way of suggestion, and that the observations on which my paper is based were hardly sufficient to justify too positive a conclusion. Yet, I take it that you are not averse to having brought to your attention pre- liminary findings which point the way to promising new fields of research. Doubtless many, if not all, of you are familiar with the fact that red spruce (Picea ruhens) bears a full crop of seed only at infrequent intervals, which vary from four to seven years. This in itself is a considerable handicap, and is indeed generally so ac- cepted in accounting for the paucity of spruce reproduction as compared with that of balsam fir and the hardwoods with which it is associated, most of which are annual seeders. Other causes commonly assigned to this failure of spruce to maintain itself in the young growth with species with which it is able to compete so successfully in later life are its exacting demands on seed bed as to moisture, texture, and acidity of the soil, and its extremely slow growth in early life even under most favorable circum- stances. Still another factor, however, the early dispersal and germina- tion of spruce seed, may also be concerned. It is this factor hitherto apparently unnoticed which I wish to present for your consideration. My observations on this point were made in the fall of 1910 and the spring of 1911 when I was engaged in a study of the growth and development of spruce stands, particularly "second growth," or "old pasture," stands. It so happened 87 88 LOUIS S. MURPHY that 1910 was also a full seed year for spruce in the northern New Hampshire and adjoining Maine regions and weather con- ditions favored early maturity and dispersal of the seed. During the latter half of September an examination of the for- est floor under the normal cover of even-aged spruce stands re- vealed a large quantity of germinated spruce seed which must have been from the recently ripened seed crop, since only the seed leaves were developed, and in many cases even the seed- coat still enveloped the tips of the embryonic leaves. These spruce germinates were so thick in places as to make it impos- sible to place a finger on the ground without crushing several. Balsam fir seedlings were also found with them, but these were remotely scattered as single individuals and were almost without exception spring germinates with well developed stems and permanent leaves. One and two year old balsam seedlings were also present. Spruce of this age was entirely lacking and seed- lings of the previous spring's germination were also only spar- ingly represented. Balsam seed trees were not very numerous, so that this condi- tion did not of itself indicate much with relation to the behavior of that species ; but subsequently a stand of almost pure balsam within a short distance of the spruce plot just mentioned was examined. Here, although the site was not quite the same, the density of the cover was very similar, and in places conditions were more favorable to germination and early growth than in the spruce stand. A close examination of the humus and light moss cover failed to disclose more than a scattering of balsam fall ger- minates, although the presence of new sound seeds in considerable quantity was observed. Balsam seedlings from spring germi- nates were plentiful, occurring as individuals, while one and two year old seedlings were also numerous. In contrast to this condition spruce in the young growth of open pastures was observed to be much more prevalent than balsam. In explanation of this apparent reversal of the repro- ductive capacities of the two species it seems entirely probable that in the fall soil moisture and general climatic conditions are, in the open, much less favorable to germination of spruce SEEDING HABITS OF SPRUCE 89 than in the forest. Furthermore, the principal seed distribu- tion of spruce in the open, except in the immediate vicinity of seed trees, doubtless occurs later in the season from seeds subse- quently dislodged from the cones by the winter storms. Thus in the open a relatively larger percentage of spruce seeds would lie over for spring germination than in the forest with a corre- spondingly better chance of becoming permanently established As to the less favorable showing of balsam in the open, this was unquestionably due in part to the smaller production of balsam seed, since there were fewer balsam than spruce seed trees in the particular locality where conditions were observed. Then too, balsam seeds are heavier than spruce, so that they would not be carried so far by the wind, and balsam seedlings are also browsed by cattle much more than spruce. If this behavior of spruce and of balsam in regard to time of seed disbursal and germination is typical of the two species, it can be readily seen that even with a smaller proportion of fertile seed than spruce, balsam would have a considerable advantage. The fall germination of spruce would subject the very young seed- lings to a material reduction in numbers and vitality during the first winter as a result of winter killing, while the loss to balsam from this cause would be comparatively insignificant. Concerning spruce competition with hardwoods, observation made in Waterville, New Hampshire, the following spring (1911), in connection with the five year remeasurements of sample plots of spruce reproduction under hardwoods, showed a considerable number of spruce germinates under the hardwood leaf litter shed the previous fall. Many of these, however, were either wilted or had already succumbed to '^damping-off." Others were bleached almost white, and the stem and leaves were turgid and succulent, but without vigor, doubtless from too humid growing conditions and lack of sufficient light. This was particularly noticeable under moosewood and young hardwood brush with large coarse foliage. The absence of any one-year or two-year spruce on these plots was also noticeable. A marked contrast to this condition was found where any part of these plots hap- pened to be protected from the heavy hardwood leaf fall by a 90 LOUIS S. MURPHY group of suppressed spruce, or small balsams, or a pile of slash. Here there would be a generous number of spruce germinates and one and two-year seedlings as well. In fact, reproduction appeared to be entirely satisfactory. Here again the early seed dispersal habit of spruce very proba- bly works to the disadvantage of its reproduction. Whether fall germination takes place in these circumstances or not the seeds, or germinates, will be covered with a thick layer of hard- wood leaves. In the spring the warm rains and sun start fermen- tation of the mulch, and while this at first affords conditions ex- ceedingly favorable to the germination of the spruce seed, the young seedlings are unable to survive the continued heat and humidity and the general smothering effect of the hardwood leaf litter. The trouble thus seems to be not that the seedlings are unable to get their roots into mineral soil or other suitable mate- rial as is usually claimed but that the heavy mulch prevents them from getting their shoots up into the needed light and air. BOOKS AND CURRENT LITERATURE Pine-Barrens of New Jersey. — Probably no region in North Amer- ica is more famous from a botanical standpoint than the New Jersey Pine-Barrens. Situated as it is at the very threshold of New York and Philadelphia, this barren wilderness of pines, so strikingly different from the deciduous forest areas to the west both in the general aspect of its vegetation and in the unique nature of its flora, has been a happy hunt- ing-ground for local collectors since the earliest days of botanical study in America. Several local floras, dealing with portions or all of the area, have been published at various times, and the most recent of these, by Witmer Stone,' leaves little to be desired along floristic lines. Stone was perhaps the first writer to clearly outhne the boundaries of the pine-barrens, as delimited from other parts of the New Jersey coastal plain. It has remained for Harshberger to discuss their vegetation from the ecological point of view.- The subject matter in the present work can be grouped for the most part under one of three heads: (1) Origin and present distribu- tion of the pine-barrens ; (2) Ecology of the vegetation as a whole (syne- cology); (3) Ecology of individual plants (autecology). In attempting to explain the origin of the pine-barrens Harshberger urges the very reasonable theory, which he himself first suggested^ but which later was worked out in detail by Taylor,-* that the vegetation of this area repre- sents an isolated relict of an ancient Miocene coastal plain flora, the present distribution of which is practically coextensive with the Beacon Hill (geological) formation of New Jersey and whose perpetuation may be attributed to the fact that the area which it occupies, in contrast to surrounding portions of the coastal plain, has been uninterruptedly out of the water since upper Miocene times. That the ecologically more advanced deciduous types of forest which prevail in regions farther 1 Stone, Witmer, Ann. Rep. N. J. State Mus., pp. 22-828, pis. 1-129 + map. Trenton, 1911. 2 Harshberger, J. W., The Vegetation of the New Jersey Pine-Barrens, pp. 1- 329, figs. 1-284 + map. Christopher Sower Company, Philadelphia, 1916 ($5.00). 3 Harshberger, J. W., Phytogeographic Survey of North America, pp. 219-221. Leipzig, 1911. * Taylor, Norman, Torreya 12: 229-242, 1912. 91 92 BOOKS AND CURRENT LITERATURE west have been unable to displace the relatively primitive type found here is thought by Harshberger, on the basis of his studies of the soils of the region (chapter 4) and of the distribution of the subterranean or- gans of pine-barren plants (chapters 16 and 17), to be due largely to the fact that the dominant plants are superfically rooted perennials, whose roots and root-stocks are so intricately matted and interlaced, and whose reciprocal relations are so intimate that "no alien plant has a chance of establishing itself in an area where the original vegetal covering has remained unbroken." Nine types of natural plant formations (sic) are distinguished: the pine-barren, cedar swamp, deciduous swamp, savanna, marsh, pond, river bank, bog, and plains formations. In addition to these there are four successional plant formations (sic) : the cranberry bog., scrub oak, oak coppice, and mixed pine-oak formations. These latter arise second- arily, due to the disturbing of the primary associations. The natural formations are discussed in detail, but only the more prominent of these need be mentioned further here. The Pine-Barren Formation, which occupies most of the territory outside of the swamps, comprises a fairly open stand of (mainly) Pinus rigida, associated with which, and forming five or six more or less definite strata of vegetation, are various smaller trees, especially Quercus marilandica and other species of oak, shrubs and herbs. Three distinct facies of the pine-barren for- mation are distinguished: high pine-barren, flat pine-barren and low or wet pine-barren, all of which are treated in some detail. The Plains Formation occupies an elevated tract of country about twenty-five square miles in area, its vegetation consisting of a scrubby forest of Pinus rigida and Quercus marilandica only a few feet high. Because of the abundance here of Corema Conradii, elsewhere absent, this for- mation is designated the Coremal. The causes of the development of this peculiar type of forest have been variously explained. Harsh- berger advances the view, based on an extensive series of cultural experi- ments with the soils of the area, that the character of the vegetation is in large part correlated with the presence of a stiff, impervious subsoil or hard-pan, similar to the Ortstein of the Germans. In connection with the description of the pine-barren and plains vegetation, attention is called to parallel formations in Long Island, Nantucket, and Ger- many. The Savanna Formation presents one of the most unique types of the region. It embraces flat, grassy tracts which occupy low stream terraces and may be miles in extent. In wet savannas, which are more or less arbitrarily separated from swamps, the dominant vegetation BOOKS AND CURRENT LITERATURE 93 consists of grasses and sedges, and trees may be practically absent. Dry savannas differ in aspect from wet savannas primarily in the presence of scattered trees or clumps of trees (mostly Pinus rigida). It is in these savannas that Tojieldia, Abama, and several other distinctive pine- barren plants are found. The Cedar Swamp Formation represents the common swamp type. Such swamps are extensively developed in shallow depressions and low grounds along the sluggish streams of the region. The character tree is Chaniaecyparis thyoides. Due to lum- bering operations and other causes many former cedar swamps have been superseded by deciduous swamps, but it should be noted that many of the latter are apparently natural. The distribution of the pine-barren, plain, savanna, and cedar swamp formations is indicated in colors on the large map which accompanies the volume. The last half of the book is largely devoted to matters of autecologi- cal interest. Among other things, there is a chapter (15) on the phyto- phenology of the pine-barren vegetation, in which the flowering or fruit- ing periods of practically all the pine-barren species are presented in tabular form; a chapter (16) on vegetative propagation and the gross structure of the shoot and root in typical pine-barren species, illustrated by nearly fifty line drawings; a chapter (18) on leaf-forms of pine-bar- ren plants, and another (19) on the microscopic leaf structure of more than fifty species, all of which are figured in cross-section; a chapter (20) on cone and seed production of the pitch pine, and viviparity in Quercus marilandica; and finally a chapter (22) on pine-barren plants from an evolutionary standpoint. Altogether the book probably rep- resents the most comprehensive treatment of a relatively small area from an ecological viewpoint that has ever been attempted in this country. — George E. Nichols. Recent Text-books. — Two new text-books of botany have recently come out which make very distinct appeals for recognition — the one' by a college teacher of long experience and acknowledged success, the other- by the efficient director of a botanical garden the main purpose of which is to teach. In covers and contents the books are surprisingly different from each other. The four hundred pages of Ganong's book are bound in stiff boards, are abundantly illustrated from nature, the ' Ganong, W. F., A Text-book of Botany for Colleges. New York, The Mac- millan Company, 1916 ($2.00). * Gager, C. Stuart, The Fundamentals of Botany. Philadelphia, P. Blakis- ton's Son and Company, 1916 ($1.50). 94 BOOKS AND CURRENT LITERATURE authorities, and the diagrammers, and present a scholarly and therefore conservative statement of the main facts of botanical science today. The six hundred and forty pages of Gager's book, which would occupy no more space than Ganong's if trimmed to the same size, are bound in flexible covers, are equalty illustrated but from sources not so immedi- ately recognized, and not only present the facts but reflect the fashions in botanical science today. Both are designed to interest the student who has no intention of becoming a botanist (unless perchance he may become that best of applied botanists — a farmer), furnishing him with palatable information and giving him such mental discipline as may help him as an "educated" citizen to think a little more clearly and to conclude a little more correctly. In Gager's book one meets a distinct novelty in the small portraits of the most eminent contributors to the science of botany. To the ad- vanced student, the faces of Ingen-Housz, Priestly, and others, have a very human interest, and to many other students this human interest may also appeal. The faces are of men whom one would gladly have known; they make the famous names more real. But does the casual student care enough to justify the cost of space? Probably not, but also it is not the casual student of whom much can be made by any means whatsoever; and the reviewer is not sure that the botanical facts which might have filled the space of these figures would make any more desirable impression. In Ganong's book one finds the usual botany expounded most unusu- ally well. In Gager's the newer and more immediate relations of plant life and plant study to human life find more direct and thorough treat- ment. Botany as an intellectual pursuit, as a source of interest and satisfaction, has long been recognized: but botany as a vital, practical interest is comparatively new. The intimate relation of the study of plants to the economic condition of mankind is not generally acknowl- edged, if generally recognized at all. When the world of men realizes — not merely vaguely knows — that all its food is produced by plants, that most of its conveniences and comforts come from plants, and that its health is dependent upon plants, it will turn to a much more intense and much broader study of plants, their workings, and their conditions of work, than is now the case. Books which emphasize these relations to readers whom they have interested have a new and valuable reason for existence. These two are such books and are correspondingly com- mendable; they are excellent text-books, human, intelligent, and in- forming.— George J. Peirce. NOTES AND COMMENT It frequently happens that the published results of zoological field work give so much attention to the physical conditions and the vege- tation of the areas studied that they are of interest even to those botan- ists who have a deaf ear and a closed eye for all of the phenomena of animal life. Dr. Lee R. Dice, of the Kansas State Agricultural College, has published a paper on the Distribution of the Land Vertebrates of Southeastern Washington (University of California Publications in Zo- ology) which gives some information regarding the vegetation of that region and a few excellent illustrations of it. The field of his work ex- tended from the sagebrush region along the Columbia River, through the grassy plains drained by the Walla Walla River, to the Blue Moun- tains. It is interesting to learn from this paper that the dissatisfaction with the life zone system, which has been prevalent among botanists for some time, has also appeared among field zoologists. One of the strongest defences of Dr. Merriam's scheme of life zones has been the plea that it is biological, and that the primary role of temperature as a controlling distributional factor is more strongly played in the animal kingdom than it is in the vegetable kingdom, where moisture relations are highly important. Dr. Dice states, ''It has not yet been estab- lished that small differences of temperature of the degree supposedly separating some of the life zones are as important barriers to distribu- tion as are some of the more marked differences due to variations in rainfall and humidity." He even goes further and states that " . . . it cannot be considered proved that the temperature relations estab- lished by Merriam are the particular ones which determine the limits of distribution of any species of animal." The Swiss Phytogeographical Commission has issued a program of prospective work on the geobotany of Switzerland, containing a list of works relating to the vegetation of that country and numerous titles of papers dealing with the study of environmental conditions. The admirable and ambitious plans of the Commission provide for exact distributional records, the securing of meteorological data both in ex- tenso and in parvo, the devoting of greater attention to cryptogams, the 95 96 NOTES AND COMMENT harmonizing of the work with economic interests, and the utiHzation of physiological methods in the study of environmental influences upon plants and plant associations. The members of the Commission are Dr. E. Rubel, Prof. C. Schroter, and Dr. H. Brockmann-Jerosch. The Textile World Journal describes a new process invented by Prof. James Rossi, of the College of Agriculture at Naples, for retting flax, ramie, china grass and other fibre plants by means of bacterial action. The method is more rapid and dependable than any of the chemical processes now employed, and is superior to earlier methods of bacterio- logical retting in the nature of the organism employed and in the has- tening of its action by the introduction of currents of air into the ves- sels employed. The precautions used for securing complete asepsis are almost as exacting as those of a surgical operation. It is announced that arrangements have been made for the prepara- tion of an illustrated flora of the Pacific Coast, similar in character to Britton and Brown's Illustrated Flora of the Northeastern States. The execution of the plan is in the hands of Prof. LeRoy Abrams, who will engage the assistance of other Western botanists. The flora will be published in four volumes by cooperation between Stanford Univer- sity and the New York Botanical Garden. Meetings of the Pacific Division of the American Association and of the Western Society of Naturalists will be held at Stanford University on April 4 to 7. A special program will be devoted to papers on evolu- tion and genetics. The last day of the meeting will be devoted to an excursion and a visit to the Field Laboratory of Zoology which has just been established by Stanford University. PLANT ASSOCIATION OF WESTERN PENNSYLVANIA WITH SPECIAL REFERENCE TO PHYSIO- GR.APHIC RELATIONSHIP J. E. CRIBBS Grove City College, Grove City, Pennsylvania The development of the vegetation of any given region is subject to a number of important factors. The variation of one or more of these may suffice to initiate very noticable changes in the composition of the vegetation. The water content of the soil, for instance, is the most import- ant single factor influencing plant development; and other conditions being equal, will determine whether the vegetation will be of a desert, prairie, open forest, or mesophytic forest type. The increased available supply of soil moisture, up to a certain point, always affords a proportional increase in the rich- ness and abundance of vegetative development. There are always additional factors, however, which in conjunction with this one, give rise to a wide range of habitats. Of these tem- perature, exposure to wind, exposure to sun, and soil composi- tion, are of most significance. One of the striking features which occurs is the close relation- ship between these physical factors and the local topographical conditions, so that it is customary to encounter a similar com- bination of factors in like physiographical situations (e.g.: in the ravine, valley, or on the bluff, or flood plain). This general likeness in the combination of factors encountered under similar conditions, produces habitats in which are found characteristic types of vegetation. These vary as the factors vary; but never- theless there is a striking resemblance noticed when the vegeta- tions of these positions are compared. Western Pennsylvania may be divided into two general areas; (1) the glacial drift, and (2) the unglaciated clays. The THE PLANT WORLD, VOL. 20, NO. 4 APRIL, 1917 98 J. E. CRIBBS former of these regions occupies a zone extending from a point approximately forty miles north of Pittsburg, northward to Lake Erie. It is about thirty miles wide in the central part and gradually diverges northward, following very closely the course of the Allegheny River. The topography is of a rolling morainic character, and the soil a mixture of glacial boulder clays. The latter region borders this on the east, and extends eastward to the Allegheny Mountains, forming the Allegheny Plateau. The soil here is predominantly of yellow clay and the topography very much broken up into rough, irregular, hills and valleys. The altitude of the glaciated region ranges from 573 feet at Lake Erie to 1350 feet in Mercer County, while that of the unglaciated area extends from about 715 feet at Pittsburgh to 1840 feet in southern Warren County. The following climatic data, compiled from Grove City Col- lege records, is worthy of notice since it bears a direct relation to the type of flora developed there as a climax. The table below shows the average rainfall during the months of April to November inclusive. This is the period of the year during which the soil is not frozen and hence retains large quantities of water which become available for vegetative growth. • inches inches April 4.12 August 3.61 May 3.60 September 3.91 June 3.52 October 3.03 July 4.73 November 2.05 The average annual rainfall is 41.7 inches. The average rainfall for above eight months — 28.63 inches. The average annua' snowfall is 58.26 inches. The following average temperatures are given for the months during which the greatest vegetative development occurs. April 49.53°F. August.? 67.10°F. May 57.40° F. September 63.60° F. June 67.70° F. October 51.65° F. July 70.00° F. The average temperature for these seven months is seen to be 61°, while that of the five months of comparative inactivity PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 99 is 31.18°. While the average summer temperature is favorable for rich vegetative growth, it is at once evident from the average of the colder months, that conditions are unfavorable for other than a deciduous type of flora. In accordance with the annual precipitation, its relatively equal distribution through the months of greatest growth, and the favorable temperature during these same periods, there is developed a climax mesophytic forest for this region. It is also typically deciduous; an adaptation suitable to the low average temperature for the five months of dormancy. It will not be within the scope of this paper to treat exhaustively the various exceptions occasioned by pecuhar combinations of physical factors, and the corresponding features in the vegeta- tion. An attempt will be made, rather, to correlate the vegeta- tion of the most important physiographic features to their habitats; to define the generic composition; and to observe the sequence of development. The specific forms enumerated from time to time as components of particular associations in the various series are not exhaustive, but include in each instance the forms which dominate or are of considerable ecological importance. THE SWAMP SERIES LOWLAND SWAMPS The distribution of swamps in western Pennsylvania is limited largely to the glaciated region. Here the irregular, rolling topography frequently includes small glacial lakes and ponds. The smaller of these have been wholly or partially reclaimed by the natural development of vegetation, so that various stages may be seen from the open swamp to the dense swamp forest. In Mercer County the area occupied by these is relatively great. The land lies at an altitude ranging from 1100 by 1350 feet and the numerous swampy depressions serve as headwaters for the small streams which flow south, east, and west into the Shenango and Allegheny Rivers. Many of these included lakes and ponds have long since de- veloped beyond the early stages of reclamation, but are pre- 100 J- E. CRIBBS vented from a rapid advance to a more mature stage by the seepage of water into them from the surrounding morainic clays, or because they are fed by springs. Upon the unglaciated area east of the Allegheny River the topography is rugged, the gradient, steep, and the drainage system more efficient. Hence the development of swamps there is quite uncommon. Glacial lakes which have not advanced far in the process of reclamation frequently show four distinct stages of development, namely — the Aquatics, the Open Swamp, the Shrub Stage, and the Swamp Forest, the last exhibiting Deciduous and Evergreen Types. While these more or less distinct regions are arranged horizont- ally and in a concentric fashion, they really represent successive phases in the vertical sequence of the plant series. The Aquatics The aquatic species are the first to infringe upon both lakes and streams. Because of their habit of growth they may be subdivided into three groups, namely — Submerged Aquatics, Floating Aquatics, and Aero- Aquatics. These are regularly distributed in zonation, in the order given; and constitute an assemblage of plants well adapted, because of their abundant developeent, to fill up shallow water to a stage which admits of the entrance and development of aerial species. Submerged Aquatics. The submerged aquatics advance far out into the lake. They are attached species with vegetative structures entirely beneath the water surface, but with flowers which develop at the surface. They are mostly annuals, and because of this fact, by their decay in the fall, add yearly to the humus, which by gradually collecting on the bottom raises it's level to a position near the water's surface; thus affording a condition which is conducive to the entrance of the succeeding stages. Among the species encountered here Elodea canadensis is the most characteristic both because of it's early entrance and prolific development. The following species are also promin- ent members in this stage: Najas flexilis, Najas guadalupensis . Myriophyllum heterophyllum, Ceratophyllum demersum, Nitella, and Ranunculus aquatilis. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 101 Floating Aquatics. The zone of submersed aquatics, which constitutes the pioneer stage, is not usually sharply defined from that of the floating-aquatics but overlaps it to a con- siderable extent. To this latter group belong not only the few species which float freely upon the surface such as Spirodela polyrhiza, and Lemna minor, but also those which develop with roots or rhi- zomes anchored at the bottom and send up leaves which spread out flat upon the water, permitting the direct exchange of gases through their upper surfaces. Many of this assemblage bear two kinds of leaves, the second type being submerged and more finely divided, or smaller than the floating ones. To this zone, besides those already cited, belong the following members: Nymphaea advena, Potamogeton natans, Potamogeton amplexi- folius, Potamogeton angustifolius, and Polygonum amphibium. Always in association with these, there are found some of the submersed species which persist in the shallower water. Aero- Aquatics. Following the stage which is dominated by aquatics with floating leaves, occurs a region which is variable in extent — the aero-aquatic zone, or marsh. This stage appears in very shallow water, and the characteristic members develop aerial vegetative leaves which rise from roots or rhizomes that are commonly submerged. Many of the forms developmg here are quite xerophytic in texture and general appearance. This is in part due to the intensity of the light, both incipient and reflected; partly to the exposure to desiccating winds, and partly to the lack of cor- relation in root and shoot development. Among the species commonly encountered here may be mentioned, Typha latifolia, Scirpus americana, Scirpus validus, Polygonum Hydropiper, and Slum cicutaefolium. The Open Swamp The marsh stage is seldom sharply defined but grades off into the open swamp which more commonly occupies extensive areas. In fact the larger number of western Pennsylvania swamps have advanced beyond the aquatic stages, but retain the open swamp 102 J. E. CRIBBS formation for a long period of time. This phase in development is commonly referable to one of three causes: (1) Because of frequent burning. Burning strongly inhibits the development of many shrub and tree species. (2) Partial Submergence. This follows the melting of winter snows and the occurrence of heavy spring rains. (3) Raising of the water table. This is commonly caused by the seepage of water from adjacent regions, or by the presence of springs. It is especially the latter two of these conditions which are responsible for the retention of the open swamp phase. A very noticable feature of these stages is the development of two types of vegetation; one characteristic of the spring and early summer, and the other of late summer and autumn. The vernal and early summer type is composed primarily of aero- aquatics and species adapted to growing in low muddy or marshy situations. This is made necessary by the great abundance of water present over the area during this season. In the compo- sition of this vegetation there are a number of species which may be considered typical, but as in all plant associations, they vary in different localities, chiefly because of local limits to migration. Among the most representative of the species may be mentioned, Typha latifolia, Scirpus americana, Caltha palus- tris, Senecio aureus, Polymonium reptans, Polygonum amphibium, Polygonum Hydropiper, Symplocarpus foetidus, Aspidium The- lypteris, Onoclea sensibilis, Sphagnum, Cicuta bulbifera. Ranun- culus septentrionalis, Veratrum viride, Viola cucullata, Saxi- fraga pennsylvanica, etc. Later in the summer the habitat may be greatly changed by the evaporation and gradual drainage of the surplus water, so that the water table is lowered and conditions become much more xerophytic. The relative abundance of vegetation is greatly reduced; and that which remains is, because of its greater openness, subject to very desiccatmg influences such as intense heat and light exposure associated with a low water content in the soil. These in conjunction with the acidity and low soil temperature initiate the changes in floral composition. The autumn flora is usually strongly represented by the rushes PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 103 and sedges. The following species are typicsX :—Eriophorum gracile, Eriophorum callitrix, Scirpus sylvaticus, Scirpus atro- virens, Scirpus polyphyllus, Carex gijnocrates, Carex tenella, Carex diandra, Carex Frankii, Carex aquatilis, Typha latifolia, Aster puniceiis, Spiranthes cernua, Eupatorium perfoliatum, etc. Many of the rushes develop hummocks which are always typical of the open swamp. It is upon these that the seedlings of invading species usually first appear. Fig. 1. The open-swamp stage in which Typha latifolia dominates. This stage is being replaced by the entrance of Alnus incana, Betula Lenta, and Acer rubrum. The Shrub Stage The open stage very commonly has scattered patches of 'ow shrubs which develop upon the hummocks. These invade from a surrounding zone where this type is dominant in the vegetation. Of these pioneers the most common are Rosa Carolina and Cornus stolonifera. There is frequently a well defined bomidary betw^een the open swamp and shrub stages. In the latter the soil has become more 104 J. E. CRIBBS stabilized, but the depressions between the hummocks are commonly flooded in the spring and may remain so for most of the summer, in which case vegetation is limited almost exclus- sively to the hummocks or is composed of aquatics. The species at this stage of the series include, Rosa Carolina, Cornus stoloni- fera, Ilex verticillata, Rhamnus alnifolia, Chamaedaphne caly- culata, Pyrus arbutifolia, Salix lucida, Salix Candida, Benzoin aestivale, Ruhus hispidus, Aster puniceus, Sphagnum, Ranun- culus septentrionalis, Caltha palustris, Aspidium Thelypteris, Aspidium cristatum, Osmunda cinnarnomea, Osmunda regalis, Onoclea sensihilis, Symplocarpus foetidus, Veratrum viride, Viola cucullata, Ranunculus, recurvatus, etc. The species which occur in the depressions are most variable, since they are subjected to the greatest variation in conditions of environment. Frequently Alnus incana forms dense stands occupying large areas, and when present usually dominates. It is especially characteristic of swamps which are traversed by small streams, or of undrained areas upon relatively unstable humus. Its most common position is the low boggy humus on either side of swamp streams where it differs from the other members of the shrub stage in that it is not necessarily associated with hummocks. This cool wet situation is somewhat different from the more removed portion of the swamp for there is a greater circulation of the soil water, and hence a lower acidity. There are associ- ated with this habitat a few forms which are relatively uncommon outside this situation, namely ; — Cardamine pennsylvanica, Helen- ium autumnale, Sium cicutaefolium, Polemonium reptans, etc. The Forest Stage Deciduous Swamp Forest. Previous to the establishment of the swamp forest there may be considerable instability of the soil. This is due to its being built up from a depth of several feet by the accumulation of a loose humus which has undergone only partial decomposition ; and because of its texture and high water holding capacity. Because of this origin the mucky sub- stratum is frequently found to quake in the various stages up PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 105 to and including that occupied by the shrubs. This condition however has passed and the soil become more compact before the development of the forest stage upon it. The pioneer trees like their predecessors the shrubs, advance, occupying positions upon the hummocks, while the depressions m.ay remain quite unoccupied for a time. These, however, are eventually reclaimed, the first occupation being made by her- baceous species. Among the earliest of the tree entrants, Fraxinus nigra, Fig. 2. A late stage in the reclamation of an upland depression, which was formerly a pond. It is occupied here by a pure stand of Quercus bicolor. Beiula lenta, and Acer rubrum are most conspicuous. Fraxinus develops abundantly while young but when well matured, it almost invariably dies, giving a characteristic appearance to this stage by the scattered trunks of the dead and dying trees. The explanation of this behavior is quite uncertain, but it apparently lies in the relation of the root system to the wet swamp soil. So long as the roots of the seedlings are confined to the hummocks the development is quite rapid, but when once the stem has developed so far that the root system must extend itself into the wet boggy humus of the depressions, there generally occurs a 106 J. E. CRIBBS reaction upon the stem and foliage, and the tree either fails to develop further or gradually dies. , The pioneer tree species are, as a rule, the dominant ones throughout the deciduous stage, especially when it is succeeded by an evergreen one. Accompanying these may also be found, Betula lutea, Larix laricina and Ulmus americana. The latter form being found here but rarely and then usually associated with slight elevations. The undergrowth of shrubs and tree seedlings is commonly very dense, and may make passage through this stage quite difficult. The essential forms represented here are; — Rhus vernix, Rhus toxicodendron, Hamamelis, virginiana, Vaccinium corymbosum, Cornus stolonifera, Rhododendron canadense, Rosa Carolina, Prunus virginiana and Alnus incana. With these occur the seedlings of Betula, Fraxinus and Acer. The herbaceous representatives include, Viola cucullata, Viola pollens, Caltha palustris. Sphagnum, Cirsium muticum, Lactuca spicata. Polygonum sagittatum. Polygonum arifolium, Symplocarpus foetidus, Arisaema triphyllum, Veratrum viride. Ranunculus septentrionalis, Ranunculus recurvatus. Ranunculus abortivus, Senecio aureus, Polemonium reptans, Mnium, etc. These are characteristic of the depressions while upon the broad hummocks of the same area are found Rubus idaeus, Medeola virginiana, Trillium erectum, Mitella diphylla, Cypripedium parviflorum, Dentaria diphylla. Polygonum biflorum, Maianthemum canadense, Osmorrhiza longistylis, Circaea lutetiana, Aspidium spinulosum, Aralia nudicaulis, Osmunda cinnamomea, Osmunda Claytoniana, Onoclea sensibilis, Aspidium cristatum. Geranium maculatum, etc. Larix laricina, which belongs to the deciduous zone, although of the coniferous type, commonly assumes a position on the inner edge of the zone, adjacent to the true evergreen species. When Larix is strongly represented there rarely occurs any deciduous swamp forest of the broad leaved type, except possibly a narrow fringe of more or less scattered forms. This means that Larix infringes upon the shrubs, and that the position occupied by Fraxinus, Betula and Acer is, in this instance, largely taken by the tamarack. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 107 Evergreen Swamp Forest. The deciduous type of swamp forest is replaced by one which is predominantly evergreen. It. occupies the outer borders of the swamp and constitutes an association which is more persistent than those already described. It is common to encounter a few scattered individuals of Fagus grandifolia, Castanea dentata, and Prunus virginiana here, but these are limited to elevations and represent entrants from the morainic forests without. The coniferous forest persists as long as does the swamp itself, and cannot be replaced naturally until the true swamp conditions have passed; therefore it may be considered as the climax stage of the swamp series. If succeeded eventually by another stage, it is the deciduous climax forest. There are two essential tree members of the evergreen forest, Tsuga canadensis, and Pinus Strobus. Tsuga is of much greater abundance than Pinus, and follows the Betula-Fraxinus-Acer stage more commonly than the Larix. It begins as seedlings upon the hummocks. These it eventually broadens and greatly enlarges, thus affording more ample space for the development of herbaceous species which are not adapted to the heavy wet soil of the depressions. Pinus is most abundant in Sphagnum bogs where it regularly succeeds Larix. It likewise is associated with hummock development. In contrast to the deciduous swamp forest the evergreen stage is readily penetrable, so far as undergrowth is concerned, since the close stand excludes almost all direct light; thus forbidding the luxurious development of the lower forms. The undergrowth is likewise essentially evergreen, or largely so. Especially is this true when one considers that which is associated with the hummocks. Here the chief species include Taxus canadensis, Coptis trifolia, Lycopodium lucidulum, Lyco- podium ohscurum, Aspidium spinulosum, Porella, Mitchella repens, Gaultheria procumbens, Sphagnum, Trientalis, americana, Cypripedium acaule. Viburnum alnifolium, Osmunda cinnamo- mea. Viburnum acerifolium, Epipactus repens, Trillium erectum, Maianthemum canadense, etc. The depressions at* this stage are frequently carpeted with 108 J- E. CRIBBS Sphagnum or Mnium, but may contain herbaceous species which persist from the preceding deciduous stage, especially such as can develop in poorly lighted situations. It should be noted that the large majority of the species represented in the conifer- ous swamp zone, which are not evergreen, are vernal forms. These develop in greatest abundance along the inner edge where it borders the deciduous stage, and along the outer portion where it grades into the deciduous mesophytic forest of the moraines. This disposition of the species is largely attributable to the fact that they carry on a large part of their physiological work before the deciduous trees mature their spring foliage. Pinus appears but sparingly in the hemlock stage, unless it be upon slightly elevated ground. It, like the hemlock, has a tendency to develop pure stands, and is found in better estab- lished and drier situations. Both of these forms very conunonly advance upon the uplands, where they become members of the morainic forests. Such migrations are not very extensive, and these species rarely become dominant members under such circumstances unless special moisture conditions favor this development. Upland Ponds Numerous small ponds are formed upon the moraines. They commonly occur where clay lies at the bottom of depressions and is in turn overlain by coarser glacial drift. The seepage of water from the latter may be sufficient to supply the amount lost by evaporation etc., or, as frequently happens, they may dry up more or less completely during the latter part of summer. The vegetation associated with these has a different aspect from that occuring in the great lowland swamps. There is a notable absence of the sedge-bulrush stages, and a strong de- velopment of the shrubby associations. Such ponds are com- monly from ten to seventy-five yards in width, and since they are usually surrounded by the morainic mesophytic forest, the humus is built up quite rapidly by the decomposition of leaves and fallen trees, which are added in excess to the humus formed from the decay of plants within the area itself. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 109 As previously stated, the most conspicuous feature is the shrub stage and the strong hummock development associated with it. The aquatic stages may be almost entirely absent; Lemna minor, Spirodela polyrhiza, and certain algae, being the species present when there is any representation. The reason for the tendency to eliminate the aquatics is perhaps to be found in the acidity of the water. The decomposition of the leaves sets free the chemical materials formed and deposited there as byproducts during their activity in summer. These compounds are largely acid, and are detrimental to the development of aquatic species; or if present in sufficient quantities may entirely inhibit such development. Upon the hummocks the chief shrubby representatives are Cephalanthus occidentalis , Ilex verticillata, Pyrus arbutifolia, Cornus stolonifera, Viburnum cassinoides, and Vaccinium corym- bosum. In addition to these they may be occupied by Osmunda cinnamo7nea, Osmunda- regalis, Woodwardia virgi?iica, Onoclea sensibilis, Aspidium spinulosum, Cypripedium acaule, and a few others. Woodwardia areolata is a rare component in the flora here, although never reported from western Pennsylvania. The following tree species appear upon the margins of such ponds and succeed the shrubs, Nyssa sylvaiica, Quercus palus- iris, and Quercus bicolor. During the replacement of the shrubs, pure stands of either Quercus bicolor or Quercus palustris may occur. Pure stands of this kind are of very frequent occurrence. Later Acer ruhrum and Fraxinus nigra may make an appearance. From this condition there is a direct passage to the mesophytic forest types. THE LAKE-FOREST SERIES While the swamp series most commonly occurs in the natural reclamation of western Pennsylvania lakes there is another sequence giving rise to associations of a different nature, which terminates more rapidly in the mesophytic forest of the region. This order is found where there is more uniform and complete drainage than in the cases of swamp successions. This elimin- ates to a large extent the annual flooding of the region, due to 110 J. E. CRIBBS spring rains and the melting of winter snows. Hence it makes possible the more rapid succession. The hmnus becomes com- pact at an earlier stage than in the preceeding series; evidently due to the more uniform water table, and the more complete disintegration of organic matter. The Aquatics The aquatic stages in this sequence bear a close resemblance to those of the swamp series, and it will suffice in discussing them here to merely allude to some of the differences which may occur. Among the submersed aquatics there are a number which develop in greater abundance in the lake successions than in the swamp series. This is especially true of those which are in- hibited by the presence of acid in the water. Of these Nitella is perhaps the most conspicuous. In the aero-aquatic and marsh zones there are found some differences. In addition to the species already enumerated as characteristic of this position in the former series, there occur a few additional ones which are more strictly limited to fresh water ponds and lakes. Among these are Pontederia cordata, Sagittaria latifolia, Iris versicolor, Sparganium eurycarpum, Eleocharis olivacea, Cicuta maculata, and Castalia odorata. The Fen One of the essential differences in the swamp and lake-forest series occurs in the appearance of a fen instead of an open-swamp stage. The land lies low but is quite firm and is not, as in the latter instance, characterized by the formation of hummocks. The transition from the marsh to the fen is usually gradual and is a change from a rush to a sedge stage. The flora is typically low and herbaceous, and consists es- sentially of Lycopus americanus, Lycopus virginicus, Ly thrum alatum, Scirpus americanus, Bcehmeria cylindrica, Radicula palustris, Carex cristata, Carex scirpoides, Carex stricta, Carex crinita, Carex flava, Carex aurea, Verbena hastata, Eupatorium PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 111 perfoliatum, Gentiana Andrewsii, Gentiana crinita (rare), Asclepias incarnata, Hypericum virginicum, Lobelia syphilitica, Campanula aparinoides, Typha latifolia, Acorus calamus, Gerardia paupercula, and Ranuncidus ahortivus. The outer portion of the fen is infringed upon by a belt of shrubs which is usually narrow. It is composed of Salix glau- cophylla, Salix longifolia, Cornus stolonifera, Cephalanthus occi- dentalis, etc. The zone of shrubs may be very extensive when the area is low, but commonly forms a mere fringing belt about the edge of the forest which succeeds it, if the slope from the fenland is appreciable. The latter is commonly the case, so that the forest is comparatively well drained and is distinctively of the mesophytic type. This is, in most respects, similar to the floodplain forest which will be discussed later. The Forest The forest margin may contain such outposts as Crataegus, Prunus virginiana, Pyrus coronaria, Populus tremuloides, and Populus grandidentata. Its inner structure in brief is as fol- lows. The most important tree members are Ulmus americana, Acer ruhrum Tilia americana, Juglans cinerea, Carpinus caro- liniana Quercus alba, Quercus rubra, Carya ovata. Magnolia acuminata, Ostrya virginiana, etc. The herbaceous representation is dependent upon the density of the forest, but the number of species is commonly large. The vernal flora developed here is very rich and includes among it's members Erythronium americanum, Phlox divaricata, Viola cucullata, Viola pallens, Viola pubescens, Cypripedium parvi- florum. Geranium maculatum. Podophyllum peltatum, Claytonia virginiana, Anemone quinquefolia, Anemone pennsylvanica, Tril- lium grandifiorum , Trillium erectum, Streptopus amplexif alius, Thalictrum dioicum, Smilacina racemosa, Hepatica acutiloba, etc. THE RAVIXE-VALLEY SERIES Most ravines are formed upon slopes with a comparatively steep gradient, where the cutting of a channel is facilitated both because of the inclination, and the great amount of sediment 112 J. E. CRIBBS carried. Since the vertical cutting is more rapid than the lateral, small streams of this sort soon become flanked on either side by steep slopes; the steepness being dependent upon the nature of the soil and the position of the rock bed beneath. When ravines are formed in the rock which underlies a shal- low soil, they are characterized by steep or almost vertical slopes; but when formed in the glacial clays, the slopes, steep at first, are much more rapidly eroded as the stream increases in length, and volume of current. Thus, during the later stages of any stream's history there is a series of topographical features al- ways present, each one of which, because of the different physical conditions accompanying it, displays a floral composition of it's own. The clay and rocky ravines will be found on the outer and higher margins of the basin, and are continuous below first with the broad ravine, then with the narrow valley, and finally with the broad open valley where the slopes are of low gradient and the stream has built an alluvial floodplain of the material carried down from the higher levels. There is a close correlation of the plant associations to the physical factors involved in these habitats; and the variation of certain of these factors, as for instance the position of the water table, or the exposure to direct sunlight, etc., is responsible for accompanying changes in the vegetation. The Rocky Ravine Rocky ravines develop where there is an outcropping of under- lying rock, or where it approaches close to the surface. They are commonly found on side slopes of broad valleys where the action of erosion by the main stream has exposed the rock strata, and small tributaries entering, have cut their way through. Such ravines at first are but a few feet in width, and because of the highly resistant character of the rock, the walls are usually quite vertical. By the process of erosion they are slowly broken down and the material resulting from the weather- ing collects at their bases forming small talus slopes upon which most of the vegetation develops. The narrowness of such de- PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 113 files, the common presence of water in the stream bed, and the seepage of water from the walls, afford an abundance of avail- able moisture not common to the adjoining regions. Additional features conducive to mesophytism are found in the protection afforded from the wind by the nature of the depression itself, and the prevention of rapid evaporation by the development of a shade along the margins. During the early stages of such a ravine three plant zones are usually distinguishable. Lowermost is one which is character- ized by the presence of the liverworts, Marchantia polymorpha, Conocephalus conicus, and Pellia epiphylla. At this point there is commonly found a deep shade, and plenty of moisture. Immediately above the liverwort zone may occur one in which the dominant forms are mosses. The difTerentiation of this region sometimes does not occur, so that the mosses appear more or less scattered throughout the lower zone and form a transition directly to the crevice pioneers above. The crevice plants form an assemblage represented by species which develop upon the steep faces of the rock walls, sending their roots into the joint planes and crevices where they depend upon the small amount of humus and the moisture it retains, for their sustenance. When the rock faces are strongly exposed to the desiccating influences of wind and sun, such pioneers are of necessity quite xerophytic in structure, and restricted in their development. In such situations occur Aquilegia canadensis, Poa compressa, Verbascum Thapsus, Aster oblongifolius, Aster anomalus, Hedeoma pulegioides, Melilotus alba, etc. However when this same position is protected by shade there is a distinct mesophytic aspect pre- sented, even by the crevice plants, and one finds Cystopteris bulbifera, Arabis canadensis, Arabis laevigata, Solidago latifolia, Aspidium marginatum, Aspidium spinulosum, Polypodium vid- gare, Asplenium Trichomanes, and associated with them various lichens including Endocarpon, Psychia, etc. Under the best of conditions the rock walls offer but uncertain anchorage; so that small species are dominant. When, however, the talus formed at the base of the rock walls has accumulated in sufficient quantity, there is initiated, a condition more favor- THE PLANT WORLD, VOL. 20, NO. 4 114 J. E. CRIBBS able for plant development. The talus is present on one side only during the earliest stages of the ravine, the other being occupied by the stream which shifts its position, removing the weathered rock now from one side and now from the other. As the ravine approaches a width of twenty yards, a talus forms on each side and increases in amount as the weathering process continues Upon the moist talus slope develop numerous mesophytic species such as Pilea pumila, Cystopteris bulbifera, Smilacina racemosa, Acer spicatum, Aralia nudicaulis, Acer ruhrum, Tilia americana, Solidago caesia, Impatiens biflora, etc. Broad Rocky Ravine As a small stream of this sort cuts back it's source, there gradually occurs a widening of the ravine. This comes about through the agency of the underground water, which dissolves out the more soluble portions and causes the rock to break up. This occurs most commonly by their splitting along joint planes. The appearance of shale or less firm rocks beneath may facilitate the process, so that the talus is built up of fine weathered mate- rial, intermingled with which are always found great quantities of large and small rocks. When a ravine of this character has attained a width of from one to two hundred yards, the talus is usually still richly supplied with moisture, and there may appear one of two types of flora, — (1) One dominated by evergreens (2) One dominated by deciduous species. Evergreen Type. Of these the evergreen apparently develops when there is an abundance of cold water seeping through the talus from the upper slope. When this stage appears it gener- ally persists until the ravine has developed into an open valley with a width of a quarter of a mile or more. The chief members of the broad rocky ravine during the ever- gi'een stage are Tsuga canadensis, Aspidium spinulosum, Lyco- podium lucidulum, Aspidium marginale, Porella, Taxus cana- densis, Lycopodinm obscurum, Tiarella cordifolia, Polystichum acrostichoides, Pinus Strobus, Clintonia borealis, Clintonia umbella- tula, Habenaria orbiculata, Cypripedium parviflorum, Viburnum alnifolium. Viburnum acerifolium, Acer spicatum, Trillium un- PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 115 dulatum, Moneses uniflora, Cypripedium acaule, Mitchella re- pens, Arisama triphyllum, Tnentalis americana, Sambucus racemosa, etc. Tsuga frequently develops in so close a formation that it inhibits practically all herbaceous undergrowth, but more com- monly the stand is of the above composition in which the dom- Fig. 3. Narrow mesophytic ravine. The chief representatives here are Tilia americana, Quercus rubra, Acer rubrum, and Castanea deniata. inant forms, both tree and herbaceous, are evergreen. It fre- quently happens that one encounters a few forms of Tilia, Acer rubrum, Fraxinus americana, and Castanea dentata associated with the evergreen assemblage. Deciduous Type. The development of the deciduous type of 116 J. E. CRIBBS flora in the rocky ravine is commonly associated with a lower water content of the soil than is found in those bearing the evergreens. A large number of species and a large number of individuals of each, is a striking feature of the deciduous type as compared to the relatively few species found in the evergreen stages. Then too, there are generally but six or eight species which are very abundant in the latter type, the others being of less frequent occurrence; while a large number are strongly represented in the former. The most important members of this stage include Sassafras variifolia, Tilia americana, Fraxinus americana, Acer ruhrum, Ruhus odorata, Quercus rubra, Primus serotina, Betula lutea, Betula lenta, Ulmus americana, Hamamelis virginiana, Acer spicatum, Viburnum acerifolium, Samhucus racemosa, Magnolia acuminata, etc. Of the herbaceous representatives there is a large number, but since a considerable part of these are also associated with the mesophytic woods of the uplands and the floodplains, it will suffice to note at this point some of those which are most typical. These would include Aspidium spinulosum, Aspidium marginale, Polystichum acrostichoides , Aspidium Goldieanum (rare), Asplenium angustifolium {rare), Asplenium Filix-foemina, Asplenium acrostichoides, Dicksonia punctilohula, Chimaphila umbellata, Cypripedium acaule, Cypripedium parviflorum, Ari- saema triphyllum, Pilea pumila, Camptosorus rhizophyllus (rare), Osmunda cinnamomea, Osmunda Claytoniana, Polypodium vul- gare, Psedera quinquefolia, Vitis cordifolia, and Impatiens hiflora. The fern members represented here are seen to be numerous — a feature characteristic of the broad ravine with a deciduous flora. The Clay Ravine One of the most striking differences between the rocky and clay ravines occurs during the initial stages. The relative instability of the latter does not admit of the formation of ver- tical slopes. During the thawing in spring, and the period of heavy rains which follows, there may be extremely rapid erosion PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 117 of the slopes, accompanied by slumping. This is especially true in exposed situations, and the slopes there are practically void of vegetation. The early stages of the clay ravine are seen to be xerophytic in character. This is true of those which are exposed; but if Fig. 4. Undergrowth in the deciduous stage of the broad ravine, showing the prolific development of ferns which is a characteristic feature. Osmunda claytonia, and Polypodium vulgare are the forms most conspicuous above. such development takes place in protected areas, as for example in a mesophytic forest, it may present an entirely different aspect. The erosion here is much slower and is seldom suffi- ciently rapid to completely remove the humus from the slopes; although there is usually a distinct creep, resulting in a greater '*^f 118 J. E. CRIBBS inclination of the trees growing there. In the latter instance the ravine may be distinctly mesophytic throughout its his- tory, and in the former instance eventually becomes so. In sheltered situations the flora is essentially the same in composition from the early stages to one at which it has at- tained a width of some forty or fifty yards. As compared to the rocky ravine, the soil moisture is generally less and the humus is not so well developed. The latter fact is due to the creep, which is more pronounced here because of the greater regularity of the slope. The development of an evergreen flora is less common than in the former situation, but may occur where there is a distinct seepage of water. When compared with the rocky ravine at a similar stage, it is found that the tree representation is much greater, especially as to individuals. When in sheltered places, the species are usually the most mesophytic of the climax forest, and include Tilia americana, Fagus grandifolia, Castanea dentata, Acer ruhrum, Prunus serotina, Magnolia acuninata, Sambucus race- mosa, Quercus rubra, etc. The herbaceous species are in large part similar to those of the rocky ravine also, and show a rich fern assemblage. Additional species which are more typical of the clay ravine are Aspleniu7n platyneuron, Epipactus re- pens, Vaccinium canadense, Pyrola secunda, Aralia nudicaulis, Caulophyllum thalictroides, etc. The Valley The development of the valley from the broad ravine stage, infers a gradual transition; just as does the development of the broad ravine by the slow process of lateral erosion of the slopes of the narrower stage. The chief change in the factors which constitute the habitat here as compared to those of the broad ravine are: (1) A greater access of winds, (2) Greater exposure to direct sunlight, (3) Lowering of the water table, especially on the upper slopes of the valley. (4) A higher average tem- perature with a lower relative humidity. This combination of factors all tend toward the same re- PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 119 suit; namely, the JDroduction of a flora less mesophytic in com- position than that found in the environments afforded by the activities of the earlier stages of the stream. As suggested before, the evergreen stage may persist until the development of the valley. This is not so commonly true of the glaciated area as of the unglaciated region farther east, and seems to be associated with more favorable moisture conditions. For in- stance, it is frequently retained upon the lower portions of the slope, but gives way upon the higher portions to a deciduous forest as the process of widening continues. The evergreens here retain a structure closely comparable to that described for the ravine stage, but during the transition to the upper zone it becomes more open in formation and the undergrowth as well as the trees indicate a lower mesophytism. Since the point at which the water table is lowest is near the crest of the valley slopes, the specific forms encountered there have a more pronounced xerophytism. This upper region may be represented by Quercus alba, Quercus coccinea, Hamamelis virginiana, Prunus virginiana, Castanea dentata, Epigea repens, Pyriis coronaria, Polytrichum commune, Fragaria virginica, Prenanihes alba, Pteris aquilina, Hieraciiim venosum, Potentilla canadensis. Aster umbellatus. Aster cordifolius, Solidago ccesia, Smilax hispida, Smilax herbacea, Vaccinium vacillans, Corylus americana, Rubus allegheniensis, Verbascum Thapsus, Rubus villosus, Gaultheria procumbens, Epipactus repens, Aspidium noveboracense, Phegopteris hexagonoptera, etc. The upper zone is more xerophytic when the lower one is deciduous. The dominant species is regularly Quercus alba; and with it may appear Quercus coccinea, Castanea, Prunus serotina, and Quercus rubra, or they may be absent. The lower slopes when deciduous are represented by such forms as Tilia, Fagus, Castanea, Acer, Quercus rubra, Betula lenta, Prunus serotina, and an undergrowth of Carpinus, Hamamelis, Ostrya, and numerous herbaceous forms, the composition varying with the factors of the habitat. Even the smaller of the valleys have developed flood plains upon which occur a few species parti- 120 J. E. CRIBBS cularly referable to this habitat, such as Quercus imbricaria Quercus bicolor, Ulmus americana, and Platanus occidentalis. The discussion of the flood plain will be referred to the river series which follows, for it shows its best development along the larger streams. {To be continued) CRITICAL FLOWERING AND FRUITING TEMPER- ATURES FOR PHYTOLACCA DECANDRA FRANCIS E. LLOYD McGill University, Montreal, Canada The behaviors of the poke-weed {Phytolacca decandra) in two diverse climates, widely different from its own, those namely of Tucson, Arizona, and Carmel, California, have been observed for several years by Dr. D. T. MacDougal and the writer. Of these behaviors perhaps the most interesting is the failure to reproduce by seed at Carmel, in contrast with Tucson where fruits and seeds are formed in abundance. At first blush it would seem that this contrast is due to temperature relations, and this turns out to be the case. Indeed, as it has happened, the temperature relations are so clearly indicated in the be- havior of the plant at Carmel, that it is possible to determine, within a very small error, the critical flowering and fruiting temperatures. Since the plant grows well enough though not quite normally! in this locality, attaining a stature of a meter more or less, and making a consistent, but under the circum- stances unsuccessful attempt at flowering, it appears that the failure in this constitutes the factor limiting its ability to per- sist unaided. Under exceptional circumstances, however, seed may be produced, and it is these circumstances which afford the data herein offered. Before presenting data, the cogency of which rests upon an understanding of the climate during the growing season at Car- mel, a brief summary of this will be given. In the accompany- ing table, the temperature ranges for ten weeks are spread, to- gether with the numbers of days having temperature ranges included within limits of five degrees as indicated. On days having temperatures not higher than 70° there is usually no 1 Ann. Rep. Dept. Bot. Res. Carnegie Inst. Wash, for 1914, p. 71. 121 122 FRANCIS E. LLOYD sunshine, although on exceptional days there may be an occasional short period scarcely longer than a half-hour, generally less. Such days may be described as fog days. These may be "low- fog" days, or "high-fog" days (to use local terms), Carmel lying directly on the coast and usually overshadowed by the ocean fog-bank, the edge of which reaches a short distance inland. These days, on which one sees the sunlit hills one to three miles distant, constitute about 70% of the whole time, and furnish the dominant climatic conditions. Of direct sunlight, there were during the ten weeks about seventy-five hours, about 9% of the total possible sunshine hours, calling these 12 per day. The distribution of the sunshine hours is also indicated in the table. Of the seventy days, only five (with six hours or more of sunshine) or at most eight (including those with five hours of sunshine) could be called sunshiny. The humidity is usually rather high. On two fog-days, the wet and dry bulb readings were 57° and 63°, and 59° and 66°, or indicating relative humidities of 69% and 66% ; on two days of continuous sunshine 62° and 70°, and 63.5° and 74°, indicating relative humidities of 64% and 56%, at the minimal points. At night the temperatures are uniformly low and the dew point is usually reached. There is no rain, though the condensation of moisture on the pine trees during the night is often sufficient to wet the whole surface of the ground beneath. An occasional "weeping fog," enough merely to wet the soil surface, might by the unaccustomed visitor be regarded as rain. The climate is ideal for many plants, as the luxuriant growth of geraniums, fuchsias, foxgloves and the like shows. It is such cool and humid conditions w^hich make possible along the California coastal belt the growing of beans and many other vegetables to remarkable perfection. But introduced species show a various behavior toward such conditions, as the work at the Coastal Laboratory of the Carnegie Institution of Wash- ington is showing. Of these species, Phytolacca decandra, in its above mentioned idiosyncracy, is a striking example. During five years of observation in the experimental garden no instance of seed development has been found to occur under CRITICAL TEMPERATURES FOR PHYTOLACCA 123 ordinary conditions. Usually the first inflorescence remains with its flowers unopened but alive for weeks, attaining only small size. Flowers have however been seen to open, and the inflorescence to develop into fair length, on stems which had been accidentally prostrated, evidently as a result of the higher tem- peratures near the soil surface. Only during the past summer did flowers in this situation succeed in setting seed. It seems evident that the prevailing fog-day temperatures, acting as a limiting factor, are responsible, since when they are slightly TABLE 1 Temperatures for ten weeks (July 3 to September 10 inclusive), 1916 TEMPERATURE FAHR. NUMBER OF DAYS HAVIXG TEMPERATURE BETWEEN Day Night 60-65 (Low) (Fog) 6G-70 (High) (Fog) 71-75 (Part) (Sun) 76-80 (Full) (Sun) HOURS SDN PER DAY Maxi- mum Mini- mum Mini- mum 1 2 3 4 5 6 7 8 9 10 72 76 78 75 71 72 80 69 78 82 62 65 64 60 59 62 68 62 63 67 42 47 44 45 42 45 46 50 45 44 1 3 2 4 4 1 2 0 5 5 2 3 3 1 5 6 1 2 1 1 1 2 2 1 3 1 1 0 2 3 2 4-0 2-5 5-4 1-2 1-1 2-7 4-6-6-4 5-3-6-6-1 Tota Is 17 33 11 9 75 raised fruit is developed more or less normally, in spite of the low" night temperatures and cold soil. The following exceptions in the general behavior of the plant support this view. Plants grown within a small glass shelter produced an abun- dance of fruit quite normal in every detail. The seed was used for propagation, and gave practically perfect germination. About 200 large plants were grown therefrom during 1915-16, none of which set seed, excepting only two plants, to be pres- ently discussed, though inflorescences (but not open flowers) were produced in abundance. The temperature within the glass 124 FRANCIS E. LLOYD shelter ranged, on fog-days, about 10° higher at the maximum than without. It is safe to infer that, were the prevaiUng day temperatures 10° higher at the maximum, Phytolacca decandra would grow and reproduce normally.^ and it may be remarked too that the appearance and structure of the vegetative parts would also be normal. It appears however that a full ten de- grees is not necessary. In 1915 a plant growing outside but quite near to the glass shelter produced on a branch quite close to the wall a single spray of fruit. The inflorescence was so placed as to be sheltered from the down-draft of cool air which is nearly constantly mov- ing down the gulch in which the garden is situated, while it received moreover reflected light and heat from the glass side of the shelter. In 1916, another inflorescence was produced, but was later blasted, after reaching full size and beginning to set seed. It is naturally difficult to get at a precise expression of the temperature differences to which this plant and those nearby, and which did not produce fruits, were subjected. However, by taking wet and dry bulb readings on typical days during the warmest hours, the readings were obtained which are given in table 2. Repeated readings at various times did not reveal any de- partures from the above. It appears to be very near the truth to say that, were the prevailing temperatures five degrees higher, fruits and seed would be developed in at least sufficient abun- dance to insure a population. This is further supported by the evidence obtained by de- termining the differences of temperature shown by other ad- jacent positions in which seed were and were not produced. Of the 200 well-developed plants of 1916 above mentioned, one only had red foliage. These plants, as is usual at Carmel, were checked in their growth with the oncoming of the summer fog after the latter part of May, and in consequence the more ter- minal leaves formed rather close rosettes, generally with young inflorescences more or less inclosed. In the red foliaged plant only did these flowers open, and evidently started well toward the 2 Phytolacca dioica fruits abundantly at Berkeley. CRITICAL TEMPERATURES FOR PHYTOLACCA 125 development of seed, though at length after attaining a length of about 1.5 cm., they failed and remained stunted. In the plants lacking the red pigment the flowers remained unopened. In the former case the red pigment was responsible for ameliorat- ing the temperature conditions. On a high fog day the tempera- tures indicated by a black and a clear bulb thermometer were 61° and 64° respectively at the height of the flowers, and this difference may be taken to be as wide at any rate as that which would be shown by the rosettes of a green and a red foliaged plant. There can scarcely be a doubt that a prevailing tem- perature a few degrees, not more than five, higher than 64° would TABLE 2 AIR TEMPERATURES Wet bulb Dry bulb Low-fog day : In draft of air down gulch In protection of glass shelter 54.5 57.5 Black bulb. 61.0 61.0 62.5 64.0 69.0 64.0 56.0 59.5 High -fog day: • • In air current Clear bulb. 59.0 In position of developing flowers* Thin fog (faint shadow) : Near developing flowersf In air current 58.0 58.5 62.0 ^— 66.0 — 61.5 - * Seeded in 1915, blasted in 1916. t Later blasted. have insured the setting and development of seed in the red foliaged plant. Of the green foliaged plants one had been accidentally pros- trated, so that the main stalk up to the first branching lay within 10 cm. of the ground. Thereupon the axillary buds developed a few small leaves and inflorescences. Those lying within 10 cm. of the bare soil surface produced a few seeded fruits, scattered among a majority of blasted ones. It seemed in this case that occasional days, probably grouped in periods of two or three, afforded favorable temperatures within 10 cm. of the soil surface, due of course to the influence of the heat radiated 120 FRANCIS E. LLOYD from the soil. The temperature gradient from the soil upwards on a typical high-fog day is indicated in table 3. Without assuming that the temperatures found on this day were the absolute favorable ones, it may be argued that the temperature differences as between positions 5 cm. and, at most, 20 cm. are sufficient to cause the seeding and non-seeding of the plant, and this difference lies within five degrees at the most. In 1915 a plant was prostrated, and lay on a grassy and there- fore cooler surface, and another w^as purposely so placed. Flowers were formed, but no fruit. It is therefore concluded that if the prevailing day tempera- TABLE 3 TEMPERATURES Wet bulb Dry bulb Soil (1 cm. deep) 63.0 57.5 56.5 82 0 The bulb lying on the surface UnshacTed 71 0 Shaded 70 0 5 cm. above the surface 66 0 10 cm. above the surface 20 cm. above the surface 62.5 59 0 tures at Carmel, California, which are low enough to prevent reproduction by seed, were five degrees higher, during the warm- est hours, reproduction by seed would take place at least in sufficient measure to enable the species to persist.^ The tem- peratures which permit vegetative activities are not identical with, but are lower than those more intimately connected with reproduction. The more delicate physiological responses shown in anthesis and dependent processes are probably responsible for the frequently observed peculiarities of flowering in many of the higher plants, e.g., the cacti.'* In the instance before us an illustration is afforded of the possible effect of slightly in- adequate temperatures on distribution by inhibiting reproduction. ^ Seeds germinate and seedlings develop well in the situation in which flower- ing and seed-development do not take place. '' F. E. Lloyd: Observations on the Flowerine Periods of certain Cacti. Plant World 10: 31-39. 1907. BOOKS AND CURRENT LITERATURE The Wilcox Flora of the Lower Eocene. — The flora of the Wil- cox formations, recently monographed by Berry/ is one of unusual interest to botanists as well as to geologists. This is due to the care- ful manner in which the flora has been studied and described by Berry, and to the fact that it is one of the largest floras that has been recorded from a single horizon in a comparatively restricted area. It com- prises 128 genera in 59 families and 33 orders, more than 94% of which are Angiosperms. Floristically, the Wilcox flora resembles that of parts of tropical and subtropical America, particularh' the strand veg- etation of the Caribbean coast from Central America to northern Brazil. In addition, the Wilcox flora contains a number of genera, such as Artocarpus, Nipa, Cinnamomuni, Banksia, etc., which have- at present an oriental distribution. As is well known, there has been in the past considerable contro- versy in regard to the value of foliar characters as diagnostic criteria. The instability of the gross or superficial characters of leaves has been emphasized by many taxonomists, and by a number of morphologis"ts who have desired to bring into the limelight the conservatism of in- ternal structures. For example, Bentham,- after making a very com- prehensive study of the Proteaceae, stated in regard to detached leaves, "I do not know of a single one which, in outline or venation, is exclusively characteristic of the order, or of any one of its genera.' Seward,^ the well known English paleobotanist, considers that, "Vena- tion characters must be used with care even in determining classes or groups, and with still greater reserve if relied on as family or generic tests." In view of supposed difficulties in identifying plants by the impres- sions of their leaves, the following conclusions of Berry are of consider- able interest: "Many botanists love to dwell on the temerity of the paleobotanists in determining species from impressions of leaves. I 1 Berr3% E. W., The Lower Eocene Floras of Southeastern North America. Professional Paper 91, U. S. Geol. Survey, pp. 481, pis. 116, Washington, 1916. 2 Bentham, G., Presidential Address. Linn. Soc, p. 17, London, 1870. 3 Seward, A. C, Fossil Plants, 1: 99, Cambridge, 1898. ' 127 128 BOOKS AND CUERENT LITERATURE admit at the outset that some identifications based on fragmentary materials are altogether too uncertain. There is more or less conver- gence in foliar characters in unrelated or remotely related families and there may also be considerable variation in the leaves of a single species, but foliar characters in general are more fixed than those of almost any other organs of plants. They are subjected to less com- plex environmental factors and always have been. It should be re- membered that characters which are less essential to the vital activi- ties of plants, such as the form of the leaf, when once acquired may continue practically unchanged for thousands of years and afford a surer clue to relationships than characters more immediately within the field of action of natural selection." Approximately 100, or somewhat less than one-third of the species listed by Berry, are forms which had previously been described by Heer, Hilgard, Unger, Hollick, Knowlton, Newberry, Veatch and Les- quereaux. The investigations of Berry have led him to refer approx- imately 50% of these forms to different genera from those to which they were assigned by previous investigators. Even more significant is the fact that 40% of the forms have been transferred to different orders. Such striking discrepancies in the identification of leaf impressions by paleobotanists might easily be considered to indicate that foliar characters are not to be relied upon in determining the relationships of fossils. However, the reviewer is inclined to believe that these discrepancies are largely due to the fact that many of the earlier deter- minations were based upon more or less fragmentary material and a less comprehensive study of the foliar characters of living plants. A considerable portion of Professor Berry's monograph is devoted to the description of various orders, families and genera of the Angio- sperms, particularly their present distribution and occurrence in vari- ous geological formations. This portion of the volume, which has been printed separately,* should prove very useful for general reference. It is to be hoped that Professor Berry will publish the results of his detailed study of the form and venation of leaves, since an accurate key to the plants of the tropics based upon vegetative characters would be of much economic and scientific value. — I. W. Bailey. ^ Berry, E. W.; The Affinities and Distribution of the Lower Eocene Floras of Southeastern North America. Am. Phil. Soc, 53: No. 214, pp. 129-250, June- July, 1914. BOOKS AND CURRENT LITERATURE 129 Geography of the Peruvian Andes. — The Yale Peruvian Expedi- tion of 1911, carried out under the direction of Prof. Hiram Bingham, was devoted to .surveying and geographical reconnaissance along the 73d meridian, which here cuts obliquely across the entire South Amer- ican Cordillera. Some of the results of this expechtion have just been pulilished bv Dr. Isaiah Bowman in a form and style which render them of interest to- a wide audience.^ In addition to presenting the results of topographic surveys Dr. Bowman has given an extended ac- count of the development of the physiographic features of the Peruvian Andes, with special attention to the results of glaciation and the erosion produced by snow. The greatest interest of the book, however, lies in its description of the varied topography and chmatic conditions of southern Peru, and in its vivid portrayal of the manner in which the distribution of races of men is controlled by these conditions and by the character of the domesticated plants and animals which it is pos- sible to maintain under each of these sets of conditions. The plains at the eastern base of the Andes are covered by heavy tropical forest of the monsoon type, which extends up to elevations of 3000 to 4000 feet. The direction of the trade winds is such as to bring heavy precipitation and extremely moist conditions to the eastern slopes of the mountains, carrying the forests up to elevations of 10,000 feet and more. The alpine grasslands and shrubbery extend to altitudes as great as 17,000 feet, where Indian shepherds maintain the loftiest permanent dwellings that are known in any part of the world. The Pacific slopes of the Cordillera are extremely varied, being lightly forested at middle elevations, particularly on shaded slopes, and occu- pied by an extremely hght scrub at lower elevations. The deep and narrow valleys are the seats of the principal populations and of the most intensive agriculture. Some of them are situated in moist climates, while others are advantageously located for irrigation. The coastal strip presents extremely desert conditions. In Peru the vertical limits of the cultivation of familiar economic plants between latitudes of 13° and 16° S. are much higher than in the mountainous regions with which we are more famihar. The banana and the orange are both grown up to about 6000 feet, and sugar cane up to 8000 feet in the valley of the Salcantay. Corn is grown in the Cuzco basin at 11,000 feet, wheat is grown at 12,000 feet, and barley at 13,000 feet, while the cultivation of the native strains of potato is 1 Bowman, Isaiah, The Andes of Southern Peru. Pp. 336, figs. 204, maps 7. New York, Henry Holt and Company, 1916. THE PLANT WORLD, VOL. 20, XO. 4 130 BOOKS AND CURRENT LITERATURE carried above 14,500 feet into the region of nightly occurrence of frost. Arborescent cacti are abundant up to elevations of 11,500 feet, and isolated patches of quenigo woodland are found in the cloud belt at 14,000 feet. It is impossible to give in this place the extended notice which is due the physiographic work accomplished by Bowman. In addition to this material, however, his book is replete with observations of in- terest to every student of the relation of organisms to environment. — Forrest Shreve. Tolerance of Fresh Water by Marine ■ Plants. — In a recent paper^ Osterhout points out that tolerance of fresh water by marine plants is not strictly due to gradual adaptation, as has been supposed. In the case of eel grass (Zostera marina), with which the author experi- mented at Mount Desert Island, Maine, the same differences oc- curred in the leaves and roots of plants growing in the mouths of streams and plants growing in salt water remote from the mouths of streams, in their abihty to withstand fresh water. Eel grass growing in the ocean near the mouths of streams has the leaves immersed in a layer of water that is alternately fresh and salt, and its roots embedded in mud which is almost constantly uniformly saline, while the same species growing away from estuaries has both leaves and roots immersed in a salt medium. Leaf cells in both cases withstand exposure to fresh water for several hom^s, but root cells are quickly killed. That the longer life of the leaf cells is not due to any difference in cell wall struc- ture is shown by the fact that both leaves and roots were plasmolyzed with equal rapidity when immersed in hypertonic sea water, and then recovered at the same rate when again placed in ordinary sea water. Neither does difference in permeability to water explain difference in behavior, for death is not primarily due to increased water absorption. Following Loeb's point of view, the author suggests that the differ- ence in tolerance of fresh water exhibited by marine plants is due to the difference in outward diffusion from the protoplasm of substances, especially inorganic salts, which are necessary to the normal activity of. their protoplasm. Thus the more tolerant plants lose salts less rapidly than those less tolerant of fresh water. He also suggests as the explanation of this effect, that in the protoplasm of less tolerant plants larger amounts of globulins or other colloids may be present . 1 Osterhout, W. J. V., Tolerance of Fresh Water by Marine Plants and its Relation to Adaptation. Bot. Gaz. 63: 146-149, 1917. BOOKS AND CURRENT LITERATURE 131 which undergo a change of state when the concentration of salts is lowered to a certain point. — Lawrence Whitehead. Structure of Coal. — Among the notable achievements of recent botanical effort are Jeffrey's studies on coal. For this work a special technique had to be devised, since the methods of the petrologist had not proved suitable for such friable and highly compressed material. The new method^ consists essentially in a preliminary swelling by melted phenol or by caustic soda dissolved in alcohol, followed by treatment with hydrofluoric acid and potassium chlorate (or nitric acid) for the purpose of desilicifying and bleaching, after which the material is im- bedded in celloidin and the sections cut bj' means of a microtome. One of the first fruits^ of the new method was the proof that cannel and boghead coals consist not of algae, as had previously been claimed, but of spores of vascular plants. It has been found possible to dis- tinguish b}" the microscope coals of different sorts and locaUties.^ But more important is the light thrown on the mode of formation of coal,* a matter which has been much discussed. — M. A. Chrysler. 1 Jeffrey, E. C, Methods of Studying Coal. Science Conspectus, 6: 71-76, 1916. 2 Jeffrey, E. C, The Nature of Some Supposed Algal Coals. Proc. Amer. Acad. Sci.'46: 273-290, pis. 1-5, 1910. ^ Jeffrey, E. C, On the Composition and Qualities of Coal. Econ. Geology 9: 730-742, pis. 19-22, 1914. ^ Jeffrey, E. C, The Mode of Origin of Coal. Jour. Geol. 25: 218-230, 1915. NOTES AND COMMENT The prize which was offered by The Plant World in November, 1915, for the best paper in soil physics has been awarded to Dr. Howard E. Pulling, of the Department of Plant Physiology of The Johns Hopkins University, for a contribution entitled The Rate of Water Movement in Aerated Soils. The giving of the prize was made possible by the generosity of a friend of this journal who requested that his name should not be used in connection with it. The judges were Mr. R. O. E. Davis, of the Bureau of Soils, Prof. A. G. McCall, of the Maryland Agricultural Experiment Station, and Prof. Charles F. Shaw, of the College of Agriculture of the University of California. The first number of the Memoirs of the Gray Herbarium of Har- vard University is devoted to A Monograph of the Genus BrickeUio, by Prof. B. L. Robinson. Brickellia is a wholly American genus of compositae with 91 species, 35 of which are found in the western United States. This difficult group is treated in a most thoroughgoing manner, with a discussion of the diagnostic value of the various features of habit and structure which is calculated to inspire confidence in the deduc- tions of the author. He remarks "No other feature offers in Brickellia so many plausible grounds for distinctions as does the pubescence, particularly the presence or absence of double pubescence, partly glandular and partly non-glandular. Yet these characters, on further examination and especially after the study of much material, nearly always break down hopelessly and are seen to be subject to complete intergradation ; and what is more significant appear in many cases to be so readily changed .... as to render highly artificial any distinctions based upon them." There is a strong suspicion lurking in the vicinity of much of the taxonomic work of the present day that a similar statement could be made for a great many genera in which differences of pubescence have sufficed to establish specific distinctions. Prof. Herbert E. Gregory has pul^lished the results of his work on the geography and water resources of the Navajo Country, in north- eastern Arizona (Water Service Paper No. 380). This region, bounded 132 NOTES AND COMMENT 133 by the Little Colorado, Colorado, and San Juan rivers, and extending well into New Mexico, is nearly as large as South Carohna, and is one of the least visited and least known areas in the United States. To historians and anthropologists this countr}^ has long been of great interest because of its unique Indian villages, which have persisted in a few favored locaHties for many centuries. Until very recently the natural history of the central and northwestern part of the Navajo country was almost unknown. Professor Gregory's paper comprises a brief description of the types of vegetation and a map showing the distribution of pine, piiion and juniper forests. The Thirtieth Annual Report of the Bureau of American Ethnology contains a paper which is of interest in connection with a region adja- cent to the Navajo Country. This is Mrs. Matilda Coxe Stevenson's Ethnobotany of the Zuni Indians, a paper which will take a very high place among studies of this kind. Mrs. Stevenson began to work among the Zunis as early as 1879, when their ceremonials and medical practise had not been modified by the interference of the white man. A remarkable advance had been made by the medicine men in utilizing the plants available to them in treating specific symptoms. Thej^ were accustomed to narcotizing their patients before an operation, and were possessed of effectual disinfectants for wounds, as well as cathartics, emetics, remedies for the bites of snakes and ants, and other important specifics. The use of the various food plants is also de- scribed, showing that the introduction of corn several centuries ago replaced a diet of the raw or cooked seeds of Atriplex poiveUii, Cheiio- podium leptophyllum, Artemisia wrightii, and the grass Eriocoma cuspi- data. The Zuiiis state that "when we depended entirely on the small seeds of plants for our foods, our flesh was not firm and good as it is now." Descriptions are also given of the use of various plants as sources of material for spinning thread, weaving baskets, dyeing pot- tery, and elaborating the toilets of persons engaged in ceremonial observances. Among recently issued lists of local floras may be mentioned A Catalogue of the Flora of Isle Royale, Lake Superior, by William S. Cooper; The Flowering Plants, Ferns and Fern Allies growing without cultivation in Lambton County, Ontario, by C. K. Dodge; and A Cata- logue of the Plants of Jasper County, Missouri, by Ernest J. Palmer. The first two were published in the Sixteenth Report of the Michigan 134 NOTES AND COMMENT Academy of Science, the last in the Annals of the Missouri Botanical Garden. John Wiley and Sons have recently piibhshed a German-English Dictionary for Chemists, by Dr. Austin M. Patterson. It is a handy book of 316 pages, containing not only strictly chemical words but many that are used in plant physiology, agricultural chemistry and mineralogy, as well as the common words which have acquired a tech- nical meaning in these sciences. Mr. Samuel E. Cassino, of Salem, Mass., is collecting material for a new edition of his well known Naturalist Directory, which he expects to bring out late in the present year. This work comprises both ama- teur and professional naturalists, and is useful to those who wish to buy, sell, or exchange specimens of any sort. THE PHYSICAL CONTROL OF VEGETATION IN RAIN-FOREST AND DESERT MOUNTAINS FORREST SHREVE The Desert Laboratory, Tucson, Arizona It is possible to compare the physical conditions of two widely separated localities with respect to the influence which these conditions exert upon their respective vegetations without at the same time entailing any comparison of the vegetations them- selves. It is the aim of this paper to bring out some of the contrasts between the manner in which vegetation is controlled by the conditions in the humid mountains of a tropical island and in the arid mountains of a temperate continental region. The details upon which these generalizations are based are to be found in the author's publications on the montane rain- forests of Jamaica' and on the Santa Catalina Mountains of Arizona. 2 The point of view of this paper may be indicated by calling attention to the fact that two mountain ranges may differ ut- terly in flora, and may differ very greatly in vegetation at the same time that the controlling environmental factors are iden- tical in the two. For example, there is a sharp dissimilarity between the San Bernardino Mountains of southern California, and the Santa Catalina Mountains. The latter have only 2% of the species found in the former. The latter have desert and evergreen oak scrub (encinal) where the former have chaparral and nut pine scrub. In spite of these floristic and vegetational differences, however, there is a very close agreement between the relative importance of the various physical factors in these ^ Shreve, Forrest, A Montane Rain-Forest: A Contribution to the Physiologi- cal Plant Geography of Jamaica. Carnegie Inst. Wash. Publ. 199, 1914. 2 Shreve, Forrest, The Vegetation of a Desert Mountain Range as Conditioned by Climatic Factors. Carnegie Inst. Wash. Publ. 217, 1915. 135 THE PLANT WORLD, VOL. 20, NO. 5 MAT, 1917 136 ■ FORREST SHREVE two mountains, and a still closer agreement in the manner in which these factors control the vertical and local distribution of vegetation. Between two regions as widely separated as Jamaica and Arizona we would expect to find the very great dissimilarity of flora and vegetation that is known to exist. Between the physical controls of the two regions there are also great differ- ences, sometimes even direct antitheses. In the dripping fog- filled forests of Jamaica one would expect to find the local dis- tribution of the vegetation dependent upon a very different set of environmental conditions from those that control the sclero- phyllous and semisucculent plants of the arid slopes of the Arizona mountains. The difference of latitude from 19° N. to 32° N., and the insular position of the Blue Mountains contrasted with the continental position of the Santa Catalinas, lie at the bottom of all else that may be said regarding their dissimilarities. The tropical mountain gradient of temperature renders the summit of the Blue Mountains cool, but very rarely and only locally subject to frost, whereas the whole vertical extent of the Santa Catalinas is exposed to frost and their upper altitudes to rela- tively severe and prolonged low temperatures. The trade winds of the Caribbean Sea carry a constant and enormous mass of moisture-laden air to the slopes of the Blue Mountains, making their windward side reek with fog and frequent rain, and giving their leeward side a drier, but by no means dry cli- mate. The winds which ascend the Santa Catalina Mountains are both hot and extremely dry, usually exerting a very desiccat- ing effect upon the vegetation of the lower half of thp mountain and only occasionally, in the mid-summer or mid-winter rainy seasons, gathering sufficient moisture to cause precipitation. The climatic conditions of the Blue Mountains are extremely constant when contrasted with those of the Arizona Mountains. The daily temperature curve of the former swings through six to ten degrees, the curve of the latter through forty to fifty- five degrees; and the annual amplitudes are quite as unlike. The frequence and regularity of rain or fog, or at least of heavy KAIN-FOREST AND DESERT MOUNTAINS 137 cloudiness, cause a period of four or five clear rainless days to be an episode of note to the inhabitants of the Blue Mountains. In the Santa Catalinas a period of four or five days of cloudiness and rain is an even greater rarity, and the rainless periods of the lower slopes often last for eight to twelve weeks. In other words the vegetation of the Jamaican mountains is living under a very uniform set of conditions; it enjoys a climate which is practically seasonless, and is able to prosecute its activities throughout the year. To the plants of the Arizona mountains there come the checks of the winter season and the equally sig- nificant checks of the arid seasons; resulting in short periods of great activity and intervening periods of dormancy or of actual injury by drought or cold. An ascent of either the windward or the leeward slope of the Blue Mountains will bring to notice a gradual change of flora and of dominant species. On the former slopes there will be a relatively slight change in the general physiognomy of the vege- tation on passing from the warm lowland rain-forests to the cool rain-forest of the mountains, with its lower stature and greater wealth of pteridophytes, brj^ophytes and other pronouncedly hygrophilous plants. On the leeward slopes there is a sharp contrast between the savannas and thorn forest of the coastal plain and the evergreen broad-leaved forest of the lowest hills, but there is only a negligible change in the collective ecological character of the forest from an elevation of 1000 feet to some of the localities as high as 6000 feet. The lack of sharp altitudinal changes of vegetation on the two sides of the island serves to emphasize the unlikeness of these sides when compared with each other at any altitude whatever. The contrast is between a pronounced rain-forest, reeking with moisture, and a relatively open and dry evergreen broad-leaved forest. In short, the un- like moisture conditions of the windward and leeward sides of Jamaica cause a sharper differentiation of vegetation than do the altitudinal temperature differences. In this respect the Santa Catahna Mountains are wholly dissimilar from the Blue Mountains, as they have no major climatic influence causing a difference between any portions of them that lie at the same 138 FORREST SHREVE elevation, and they have important groups of both moisture and temperature factors which cause a pronounced vertical differentiation of the vegetation. Mountains which lie outside the equatorial regions of the earth almost invariably exhibit differences of vegetation on their north-facing and south-facing slopes. These differences, due superficially to slope exposure, are underlaid by complex as- semblages of factors which are by no means the same in all of the diverse climatic provinces in which such difTerences may be observed. The constant direction of the trade wind at Jamaica causes the marked dissimilarity of the north and south slopes which has been mentioned, and thereby masks any effect of slope exposure that would be possible at the low latitude of that island. In the Santa Catalinas, on the other hand, there is a well-marked difTerence of vegetation on opposed slopes at all elevations. The difference is very conspicuous at certain alti- tudes, and is commonly about as great as the difference between situations of the same slope exposure which are 1000 vertical feet apart. One of the most familiar features of the tropical rain-forest is the ''stratification" of its various plant types, by virtue of which the dominant trees shelter smaller trees, these form a canopy for tree-ferns or shrubs, these in turn shade large herba- ceous plants, ferns or small shrubs, while on the ground itself are the smallest and most hygrophilous of herbaceous plants. In the somewhat stunted forest of the Blue Mountains there is not such a pronounced stratification of the vegetation as may be seen in the richer forests of the lowlands, but it is neverthe- less a very noticeable feature of the ravines and more gentle slopes, particularly of the windward side of the range. In the Santa Catalina mountains the lowest, or Desert slopes, and the lightly forested Encinal region are naturally without any strati- fication of the vegetation, and the pine forests of the higher ele- vations are as nearly devoid of it as are the pine forests of the southeastern United States. In the heavier fir forests of the highest summits of the Santa Catalinas there is the usual scat- tering accompaniment of lax and slender deciduous trees and a ground cover of small shrubs and herbaceous plants. RAIN-FOREST AND DESERT MOUNTAINS 139 In the Blue Mountains there is a difference of physical condi- tions between the floor of the forest and its canopy which is sufficiently great to be designated '^ith all propriety as a differ- ence of climate. Instrumental measurement of the daily curves of temperature and humidity on the floor of the rain-forest and in its canopy has been made in connection with a study of the factors controlling the distribution of the filmy ferns. ^ The difference between the highly uniform conditions of temperature and the steadily high humidity of the lowest portion of the rain-forest, and the greater amplitude of both these factors in the tree tops, is undoubtedly exceeded in a striking degree in the loftiest lowland rain-forests. Such difference is paralleled by some of the structural features of the tallest forest trees, of the plants of the middle stratum, and of those residing on the ground or on the lowest portions of tree trunks. It is particularly in leaf structure that such difference is manifested; the trees pos- sess relatively small, heavily cutinized leaves with deep palisade tissue, frequently several layers in thickness, while the under- trees and shrubs have leaves similar to those of temperate deciduous trees, and the herbaceous plants have large thin leaves with a single layer of chlorophyllous tissue and an extensive development of intercellular spaces. These structural differ- ences are chiefly correlated with the unlike water relation of the foliage in the canopy and that on the ground, and with the dis- similar light conditions. The rain-forest, in brief, makes its own climate in so far as the plants of the lower strata are con- cerned, and the steadying effect which the forest cover has upon the moisture conditions within the forest and in the soil itself is also of vital importance to the dominant trees. Even in the heaviest bodies of forest which clothe the desert mountain ranges of Arizona there is no difference between the physical conditions of floor and canopy except it be of very infrequent and transitory occurrence. The long rainless periods of the desert are common to the mountain tops as well, although their desiccating effect is lessened by a shorter growing season, ^ Shreve, Forrest, Studies on Jamaican Hymenophyllaceae. Bot. Gaz. 51: 184-209, 1911. Li LIBRARY ; 140 FORREST SHREVE by lower temperatures, and by a higher soil moisture at the out- set of the dry seasons. The low humidities of the desert are to be found with only slight ameUoration at the highest mountain altitudes, and the differences of total wind movements and of the character and intensity of insolation are nearly identical. There are many respects, therefore, in which the controlling physical conditions of the desert are carried with little change to the mountain tops. The forest of the desert mountain does extremely little to make its own climate except in so far as it affords a shade for the herbaceous plants of the closed stands of fir and spruce. In the pine forest of the Santa Catalinas, and to some extent in the fir forest, the herbaceous plants are of a notably xerophilous stamp and with the exception of a very few annuals they are characterized by deep-seated root systems. The lowest stratum of the pine forest is subjected to all of the adverse conditions of water supply and water loss that from time to time affect the trees themselves. The stabilization of climate that is effected by a heavy rain-forest in a moist climate is totally lacking in a desert mountain forest. An attempt to segregate the various plant communities that make up the collective vegetation of the two mountains under consideration will reveal the fact that in each of them the topo- graphic relief is the first-hand basis upon which such segregation can be most naturally made. In the Santa Catalinas and in the Blue Mountains it is the valley-bottoms, the slopes and the ridges which present the most striking vegetational differences. The vegetational differences correlated with topography are much more striking in the Santa Catalinas than in the Blue Mountains, but this is largely due to the altitudinal interdigita- tion of the desert, encinal and forest on the Santa Catalinas, as contrasted with a mere difference of composition and stature in a forest of uniform general type in the Blue Mountains. The great irregularity of the precipitation in Arizona registers its most important effect upon the vegetation in causing great annual fluctuations in the evaporative power of the air and in the moisture of the soil. In Jamaica the soil moisture is uni- formly and almost constantly high, so that it fails to operate RAIN-FOREST AND DESERT MOUNTAINS 141 as a differential factor in the distribution of the vegetation. In spite of the great seasonal fluctuations of atmospheric humidity in Arizona there is a relatively small difference in the values of this factor for any series of locations or habitats at any given time. The great differences in the evaporative power of the air which are found in different locations and at different altitudes are chiefly attributable to wind and temperature. Atmospheric humidity is not, therefore, a differential factor in the desert mountains of Arizona, although it is the strongest single factor involved in determining the habital distribution of plants in the Blue Mountains of Jamaica. The actual factors which un- derlie the topographic control of the vegetation in the two mountains are therefore diametrically opposed. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA WITH SPECIAL REFERENCE TO PHYSIO- GRAPHIC RELATIONSHIP. II J. E. CRIBBS Grove City College, Grove City, Pennsylvania THE RIVER SERIES The vegetation associated with physiographical features developed by rivers is in some respects similar to that just described for the valley. There is the young topography of the river, when the eroding or sandy shores are succeeded almost immediately by steep cliffs; and at the other extreme there is the old topography which is characterized by a broad floodplain and low sweeping valley slopes. The stages between these are transitional and are closely comparable to the smaller valley type. Bluffs River bluffs may be best studied along the Allegheny River, for throughout much of its course it is included by abrupt slopes which rise from either side to a height of 200 to 500 feet. At most points on the river there is considerable talus formed at the base of the slopes, and the rocks which outcrop here are thus covered in part by loose rocky soil which affords an excellent place for plant development. However, when the outcropping rocks form vertical cliffs, there is presented a situation, which, because of the extreme exposure to desiccating influences, limits the vegetation to a few crevice plants. Aquilegia canadensis, Verhascmn, Clematis virginiana, Ruellia ciliosa, Rhus toxico- dendron, Poa compressa, etc., may appear in this position. In striking contrast to the xerophytism of the rock bluffs is the talus below them. This is formed by the accumulation of weathered materials from the cliffs above and hence is practically 142 PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 143 the same in chemical composition. Except in the more exposed situations, it bears an assemblage of forms which displays a high degree of mesophytism. When such talus deposits come upon exposed points, the water table is lowered, and they bear a flora adapted to dry situations, including with other forms Rhododendron maximum, Kalmia latifolia, Melilotus alba, Eqiiise- tum arvense, Aster Shortii, Aster Drummondii, Aster oblongifolius, Vaccinium pennsylvanicum, Qiiercus velutina, Quercus alba, Clematis virginiana, Pteris aquilina, etc. When the talus occurs in protected positions, it is usually well supplied with moisture which enters from the layers of stone and shale above. This environment is well adapted to sustain a dense stand, and under such favorable conditions the vegetation is luxuriant. Rhododendron and Kalmia develop profusely here, occupying especially the rocky portions of the talus near the river banks. Other conspicuous members include Tilia, Mag- nolia, Acer rubrum, Acer saccharinu7n, Betula lenta, Betula liitea, Quercus alba, Quercus rubra, Fraxinus americana, Tsuga cana- densis, Juglans nigra, Prunus serotina, Sambucus racemosa, Ribes Cynosbati, Aralia racemosa, Aspidium margiyiale, Aspidium spinulosum, Asplenium Filix-foemina, Tiarella cordifoUa, Aris- cema triphyllurn, Habenaria orbiculata, Habenaria Hookeri, Osmorhiza longistylis, Gaultheria procumbens, Cypripedium acaide, Trillium undulatum, Vitis vulpina, Psedera quinquefolia, Rhus toxicodendron, Smilax hispida, Liriodendron tulipifera, Poly- stichum acrostichoides, etc. One noticeable feature associated with the talus, is the pro- lific development of the lianas. They reach their strongest development on the talus and frequently, when exposed cliffs appear above, clamber up the surface, or more commonly de- scend from above and by developing a shade upon the cliffs aid greatly in retaining moisture, so that the crevice species are better enabled to retain their position. A second feature char- acteristic of the rocky river slopes is the abundance of Rhodo- dendron and Kalmia. Not uncommonly the river bluff is of a different nature from that already described. Steep slopes may occur where sand- 144 J. E. CRIBBS stones of fine stratification, and shales outcrop. Here, unequal erosion gives rise to small shelves which collect the weathered material, and thus forms a slope of which a considerable part has a shallow soil and humus that are relatively unstable. This is rendered more so by the seepage of water from the rock. Very frequently in the spring landslides occur, caused by the saturated soils higher up on the slope loosing their stability and sliding to Fig. 5. Undergrowth in the evergreen stage of the broad ravine. This type is characterized by a low number of species most of which are evergreen. The forms represented here are Taxus Canadensis, and Aspidium Marginale. the bottom under the force of gravity. Such slides are de- structive to the vegetation as they not only completely uproot all plants in their path, but remove the humus and soil, so that the rock is left bare where they have passed. A single cliff of this kind may show evidences of a dozen or more of such slides. It is at once evident that an environment of this kind is not well adapted to the development of a dense forest. The mois- ture is sufficient, and the desiccating influences frequently not PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 145 too great, but the instability of the soil together with its shallow- ness forbid such a type; and instead there occurs a vegetation rather low, more or less open, and in some respects not unUke that occurring in the deciduous forest stage of the swamp series. The composition here is usually as follows: The chief tree representatives: Betula lenta, Acer ruhrum, Tsuga, and Primus mrginiana. The following members when represented occur upon the upper portions of such slopes: Quercus alba, Quercus velutina, Amalanchier canadensis, Primus pennsylvanica, Popu- lus tremuloides, Populus grandidentata, Rhus typhina and Quercus coccinea. The herbaceous and shrubby species most typical of these steep, moist slopes include Aspidium spinulosum, Osmunda cinnamomea, Silene virginiana, Lonicera americana, Lonicera Sullivantii, Lonicera dioica, Smilacina racemosa, Con- ocephalus conicus, Pellia epiphylla, Aster junceus, Solidago Drummondii, Ruhus idceus, Agrimonia gryposepala, Cornus stolonifera, Gaylussacia, and Vaccinium. Flood Plains Flood plains are most extensively developed by rivers during their late history when they flow through broad winding valleys. The gradient of the stream is then low and the valley slopes long, low, and sweeping. They appear much earlier in the history of the river, but it is in the broad river valleys that the most characteristic plains appear. Their topography is practically level and the soil chiefly alluvial in nature. When the river has too low a gradient, and does not cut a channel of considerable depth, the plain is submerged during periods of high water. Under these conditions the water table is high, and the area is broken up by the presence of loops and old channels, which re- tain water and give the whole region a low swampy aspect. Very commonlj^, however, there is a channel eroded through the plain to sufficient depth to retain the water during ordinary stages; so that it is only at rare intervals of flood that the upper portion of the plain is submerged. The deepening of the river's bed insures better drainage of the plain, and together with the 146 J. E. CRIBBS relative freedom from submergence, permits of a development of vegetation far in advance of that occurring upon the lower flood plains. Three general regions are distinguishable. Each bears a definite relation to the stages of the river, and is characterized by a typical flora. The three regions are: (1) the Littoral Zone; (2) the Transition Zone, (3) the Upper Floodplain. The Littoral Zone. By the littoral zone is meant that part of the plain immediately next the river, where there is a direct effect upon the vegetation by the waters of the stream at its ordinary levels. Locally this zone might well be subdivided into three or four parts which bear the same relationship to each other as do those of the lake successions. It is only in slow streams or along protected banks that there is a considerable development of submersed aquatics. When represented, the chief components are Elodea, Nitella, Myriophyllum, Cerato- phyllum, and Polygonum amphibium. The aero-aquatics and floating aquatics are commonly more evident and include Nymphea advena, Potomageton natans, Potomageton americanus, Potomageton obtusifolius, Sagittaria latifolia, Scirpus validus, Typha latifolia, Sparganium eurycarpum, etc. They occupy the same relative position as in the lake series. Upon the banks of the stream appear a few forms characteristic of this position, such as Salix nigra, Acer saccharinum, Cornus stolonifera, and Platanus occidentalis. Associated with these is commonly found Mentha spicata, Lycopus americanus, Laportea canadensis, Poly- gonum virginianum, etc. The Transitional Zone. The transitional zone may be well defined or not but comprises the area submerged by the river during periods of high water. It usually has a vertical eleva- tion of from 4 to 10 feet above the normal level of the river. To many forms the frequent inundation is detrimental, hence they are excluded from this region. The species are largely herbaceous and include Polygonatum mrginianum. Ambrosia trifida, Lysimachia Nummularia, etc. Of the few shrub species represented Salix and Cornus stolonifera, are most common in occurrence. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 147 The Floodplain Forest. The floodplain proper lies outside of and above the transition zone. Its soil is alluvial and usually bears a mesophytic forest. One would naturally expect this; first, because of richness of soils of this type, and in the second Fig. 6. A pure stand of Tsuga Canadensis occurring as the first stage on the slopes of the Allegheny Plateau. place because of the water supply which is generally favorable for such a growth. The floodplain is subject to occasional submergence, but it is only during exceptionally high stages that the upper portion of this area is inundated. This occurs mostly at the time of heavy 148 J. E. CRIBBS spring rains before the appearance of the vernal flora; and, excepting the .mechanical effect of the impact of floating ice upon the trees near the channel, seldom has much direct effect upon the vegetation. The period of submergence is usually too brief, and the amount of sediment deposited at the time of the recession of the waters to the original channel is generally in- sufficient, to injure the development of vernal species. In composition the forest of the floodplain is typically meso- phytic. Among its members are a few species which are es- pecially characteristic of this situation, and a large number which are typical of the mesophytic forest in general. Of those especially referable to this habitat may be mentioned Ulmus americana, Platanus occidentalis, Acer saccharinum, Juglans cinerea, Quercus bicolor, Iris versicolor, Acer saccharum, Carya ovata, Carya laciniosa, Salix nigra, Mertensia virginiana, Echi- nocystis lobata, Polygonatwn commiitatum, Acorus calamus, Lobelia siphilitica, etc. Of these Carya, and Acer saccharum, are generally dominant species and not uncommonly form almost pure stands. The remaining members of the forest are largely representatives of the mesophytic deciduous forest of the uplands also; and, as an account of the composition there will be given under the discussion of that subject, it will suffice here to note some of the general features only. Perhaps one of the most noticeable features of the floodplain forest s the unusual assemblage of vernal species. The rich humus and alluvial soil afford an excellent environment for the development of this type. One encounters the following species here, and frequently in great abundance: Phlox divaricata, Viola cucullata, Viola pubescens, Viola pallens, Erythronium americanum, Geranium maculatum. Podophyllum peltatum, Clay- tonia virginiana, Anemone quinquefolia. Anemone pennsylvanica, Trillium grandifiorum, Trillium erectum, Streptopus amplexi- folius, Thalictrum dioicum, Smilacina racemosa, Hepatica aculi- loba, Mertensia virginiana, Senecio aureus, Dicentra Cucullaria, Cypripedium parviflorum, Botrychium virginianum, Panax tri- folium. Iris versicolor, Anemone thalactr aides, etc. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 149 It is at once seen that although the floodplain forest includes the larger number of the upland mesophytic species, the domi- nant members are different. That is, Acer saccharum, Gary a ovata, Uhnus americana, Juglans cinerea, Platanus occidentalis, Quercus bicolor, and Acer saccharinum, are dominant and char- acteristic members in the former, while those most representa- tive of the latter are Fagus grandijolia, Acer ruhrum, Magnolia acuminata, Castanea dentata, Quercus alba, Liriodendron tulipi- fera and Quercus rubra. THE UPLAND FORESTS The upland forests of western Pennsylvania may be divided into two types with reference to the topography and soils upon which they occur: (a) The morainic forests, or the type occur- ing as a climax upon the glaciated area of the western most part ; and (b) The forests upon the unglaciated clays. Upon Morainic Soils If the chemical composition of the soil is the chief factor in determining the type of vegetation it shall bear, one might reason that the morainic clays would be characterized by a flora of closely smilar composition over wide areas; for these soils are relatively uniform in composition, and at the same time are usually well represented by all the essential elements. This is due to the fact that they are composed of a mixture of soils brought together by the glacier from widely separated points. There is no such uniformity, however, but various topographical features with the same soils, regularly show a change in com- position. For instance, that occurring upon exposed upland slopes has a very different makeup from that characteristic of wooded depressions, and that of level uplands has many features uncommon* to either. It is the forest occupying gently rolling areas which shows the climax development of the region ; for those occurring in other situations are advanced to this type eventually, as the topog- raphy changes. The climax forest is deciduous and contains 150 J. E. CRIBBS four conspicuous members, namely, Acer ruhrum, Quercus alba, Fagus grandijolia, and Castanea dentata. There are additional species always present; some of which are more mesophytic than these; and in such instances they are usually forms typical of the moister depressions such as Tsuga, Tilia, Fraxinus, Mag- nolia, Liriodendron, and Pinus. Other components of the forest with a lower degree of mesophytism include Carya ovata, Carya alba, Carya glabra, Quercus imbricaria, Quercus rubra, Cornus florida, Osirya virginiana, Prunus serotina, Carpinus caroliniana, etc. Fig. 7. The white-pine — hemlock stage, which follows the Tsuga formation. A pure stand of conifers which will ultimately be replaced by Acer ruhrum, Mag- nolia acuminata, and Fagus grandifolia as indicated by the undergrowth. Of the four dominant tree members, Fagus, Quercus, Casta- nea, and Acer, the last two are found as components in the flora in almost all situations developed on morainic topography. The beech is more mesophytic, and has a tendency to avoid the dry exposed slopes; assuming rather a position with more favor- able moisture relations such as is afforded upon the rolling upland or upon the moist slopes of valleys. The white oak is least mesophytic of these and develops in purest stands upon the higher slopes where the water conditions are less favorable for PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 151 the beech. The chestnut and maple have the abiUty to adapt themselves to the rich mesophytic forest, or to the more exposed slopes of the uplands. The shrubby and herbaceous flora necessarily varies in com- position as the tree membership varies; but is always conspicu- ous for its large number of species. The following forms include the more important members: Hamamelis virginiana, Ribes gracile, Ribes oxycanthoides, Ribes floridum, Rubus idceus, Rubus allegheniensis, Smilax hispida, Smilax herbacea, Lycopodium obscurum, , Lycopodium lucidulum, Lycopodium complanatum, Lycopodium clavatum, Lonicera americana, Mitchella repens^ Psedera quinquefolia, Pteris aquilina, Botrychium virginianum, Fragaria virginiana, Osmorhiza longistylis, Aralia nudicaulis, Podophyllum, Anemonella thalictroides, Oakesia sessilifolia, Aris- cema triphyllum, Geranium maculatum, Cypripedium acaule, Boehmeria cylindrica, Uvularia grandiflora, Uvularia perfoliata, Onoclea sensibilis, Aspidium spinulosum, Aspidium noveboracense^ Phegopteris hexagonoptera, Polygonatum biflorum, Polystichum. acrostichoides, Smilacina racemosa, Osmunda Claytoniana, Os- munda cinnamomea, Medeola virginiana, Trillium graridiflorum^ Trillium sessile, Viola pubescens, Viola pallens, Carex pennsyl- vanica, Maianthemum canadense, Monotropa uniflora, Epifagus virginiana, Aster umbellatus. Aster cordif alius, Solidago coesia, Prenanthes alba, Prenanthes altissima, Habenaria Hookeri, Epi- pactus repens, Sambucus racemosa, Asplenium Filix-fcemina, Asplenium platyneuron, Trientalis americana, Gaultheria pro- cumbens, Polytrichum commune, Corallorrhiza maculata, Galium circoBzans, Carex platyphylla, Carex pennsylvanica, Euonymus obovatus, Vitis labrusca, Rhus toxicodendron, Tiarella cordifolia, Mitella diphylla, Circcea lutetiana, Streptopus amplexifolius, etc. Upon Unglaciated Clays To the east of the glacial drift the topography is strikingly irregular, being cut up into a great series of hills and valleys by the erosive activity of numerous small streams. Clay soils predominate throughout most of this region. The structural THE PLANT WORLD, VOL. 20, NO. 5 152 J. E. CRIBBS arrangement of the underlying rocks is such as to give rise to numerous springs and a strong seepage of water from many of the slopes. The elevation of this area ranges from about 750 feet at Pittsburgh to 1850 feet in southern Warren County. Because of the complete dissection of this region into hills and valleys, it has a topography very unlike the glacial worked soils, and the disposition of the flora is likewise striking and characteristic. Three vertically disposed stages occur here, namely (a) An evergreen forest stage, (b) A mixed (or transi- tion) forest, (c) A deciduous forest. The Evergreen Forest The evergreen forest occupies the lowest position on the slopes; and extends from their bases to a height of some 150 feet, or in some cases even to the height of 350 feet. The soil is decidedly rocky ; and with an abundance of cool water supplied by seepage, produces an environment which is closely similar to that existing in the rocky ravine of the glacial zone. The white pine-hemlock forests appearing here are the most valuable of any in Pennsylvania. The large stands of primaeval pines in Forest and Warren Counties are perhaps the finest large tracts of this timber available; and from an ecological as well as econo- mic standpoint are of the greatest interest. They are the deepest shaded forests in western Pennsylvania and necessarily demand of the undergrowth a high abihty for development under poor light conditions. These forests are striking in that the number of species rep- resented is very low, and, because on the whole, the floral composition is less variable than that of any other situation. The lower portion of the evergreen zone is dominated by Tsuga, which develops forming a very close stand, or even one which is quite pure. Betula lenta, and Betula lutea, are the only decidu- ous trees represented here, and occur along the borders of the streams and in the small ravines upon the slopes. The lower strata of the forest like the upper, are prevailingly evergreen; the dominant species being but four in number, namely, Lyco- PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 153 podium lucidulum, Aspidium spinulosum, Viburnum alnifolium, and Oxalis acetosella. Accompanying these may be found in greater or lesser amount, Habenaria orbiculata, Tiarella cordi- folia, Mitella diphylla, Maianthevium canadense, and Clintonia borealis. The seedlings present in the undergrowth of this stage are predominantly of Betula and Tsuga. Occasionaly those of Fagus, Acer rubrum, or Magnolia occur; but these are unable to develop to maturity except when an opening is afforded, as in a windbreak. The birch and hemlock alone are well adapted to this situation and they successfully retain it against the invasion of outside forms. The seedlings of both of these species have the peculiar habit of germinating on old stumps or fallen logs, thus avoiding the necessity of contending with rival species for a position during their early development. When the old stump decays, the new member has already taken the position of the old one; or when the log upon which such seedlings are develop- ing falls upon the humus, the root system quite readily extends itself into the soil and makes possible the further development of the seedlings concerned. While the lowest portion of the slope is almost exclusively represented by Tsuga, at the height of approximately 80 feet, Pinus Strobus becomes sufficiently abundant to be conspicuous. From this point of entrance it occurs associated with the hem- lock to the top of the ridge, or may be replaced at a higher level by a deciduous stage. The Mixed, Forest It is in the pine-hemlock zone just before the entrance of the pioneer deciduous forms that the finest timber occurs; the pines frequently attaining a height of 175 feet and a diameter of 5 to 6 feet, while the hemlock may attain an equal diameter and a height of 150 feet. The mixed forest consists largely of evergreens, especially in the lower portion of the zone. The conifers gradually de- crease, however, with the increase of altitude; and there occurs a 154 J. '^- CRIBBS proportionate increase in the representation of deciduous species until they entirely replace the former. This mixed type of forest commonly extends from a point about 100 feet above the bottom of the slope to a height of 250 feet or even as much as 450 feet. The lower border is determined by the entrance of Acer ruhrum and Fagus, both trees of distinctly mesophytic char- acter. Magnolia gains an entrance slightly higher on the slopes and is soon followed by Quercus rubra. Betula lenta commonly extends throughout the mixed forest stage, occurring most abundantly in wet depressions and the numerous small ravines. An essential fact that should not be overlooked is, that the decidu- ous members of this stage are our most mesophytic trees, and species which occur as regular components in the climax decidu- ous forest of the moraines. The disposition of the undergrowth when considered from the lower to the upper portions of this stage, also shows transitional features. In the deep shade of the pine-hemlock-beech-maple stage it is closely similar to that accompanying the evergreen formation on the lower slopes, being low and dominantly ever- green; but as the deciduous members become more prominent the lower stratum likewise undergoes a change. Lycopodium, Clintonia, and Viburnum, are gradually replaced by different species; the latter two by other species of the same genus, namely, Clintonia umbellatula, and Viburnum acerifolium. Numerous new species are added to the flora and include Actcea alba, Geranium maculatum, Lycopodium obscurum, Polygola pauci- flora, Sambucus racemosa, Streptopus aureus, Lonicera americana, Trillium undidatum, Viola pubescens, etc. Tree seedlings constitute most of the woody undergrowth, so that in addition to the shrubby species already cited, Kalmia latifolia, Smilax hispida, and Rhododendron maximum are the only forms of frequent occurrence. Seedlings of Fagus, Acer, Magnolia, Tsuga, and Betula, are conspicuous throughout this zone, but those of Pinus Strobus are relatively scarce. PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 155 The Deciduous Forest As previously stated, the conifers are generally replaced on the higher slopes by a stage which is typically deciduous. It should be noted, however, that Tsuga and Pinus persist through the mesophytic stages; so that the upper deciduous forests are quite xerophytic in comparison with those of the preceding zones. The humus is not so well estabUshed, nor is the available supply of soil water comparable to that of the areas just described. The dominating species here are usually Quercus alba and Castanea dentata. Associated species occurring in greater or lesser abundance are Quercus velutina, Quercus rubra, Magnolia acuminata, Fagus grandifolia, Prunus serotina, Amalanchier canadensis, Fraxinus americana. Sassafras variifolia, Cornus florida, Carpinus caroliniana, Ostrya mrginiana, etc. The seedling representation suggests a relative permanency of this stage, since it is quite the same as that of the adult assemblage. The undergrowth of shrubs and herbs includes among other species, the following: Clintonia umbellulata, Aralia nudicaulis, Aspidium marginale, Aspidium spinulosum, Cornus canadensis, Fragaria virginiana, Gaidtheria procumbens, Hieracium venosum, Lonicera americana, Maianthemum canadense, Medeola virginiana, Mitchella repens, Polygonatum biflorum, Polystichum acrosti- choides, Prenanthes alba, Pteris aquilina, Ribes Cynosbati, Rubus allegheniensis, Smilacina racemosa, Solidago ccesia, Uvidaria sessilifolia, and Vaccinium vascillans. SUMMARY The plant associations of western Pennsylvania bear a close relationship to the topographical features of the region; so that a particular type of vegetation may be expected in similar environments, although widely separated. The fact that distinct types of vegetation and flora are thus associated with any given contour feature is referable to its close relationship to the factors which bear directly upon plant activities. For instance, the environment to which growing plants are subjected in the ravine is closely similar, whether the 156 J. E. CRIBBS ravine occurs upon the glacial drift at an altitude of 600 feet, or upon unglaciated clays at an altitude of 1500 feet. The differ- ence in the factor or temperature is but slight; the subjection to desiccating influences is very similar whether it be a question of access of wind or sun. The relative humidity, in so far as there is any appreciable difference, resolves itself into a question of soil moisture. So far as soil composition is concerned, the variations are in no instance striking. The greatest factor determining the composition of the associations is soil moisture, and the greatest differences in the disposition of the vegetation may be assigned either directly or indirectly to this factor. In the case of ponds and swamps there occurs an interesting relation. The aquatic condition, or the high saturation of the soil, inhibits the process of oxidation; so that the acids and other by-products of the plant's activities accumulate more rapidly than they can be removed by chemical reduction. These sub- stances perhaps have a direct influence upon the vegetation developing there. It is at least apparent that the consumption of what oxygen is available by the process of decay, lowers the amount in the water so that it becomes more difficult for the plants to secure a sufficient amount. It is primarily because of the undrained condition of such areas, however, that these detrimental materials are retained in an objectionable form, for they are soon leached out of soils when they are properly drained. The determination of an evergreen forest or a deciduous one as found in ravines and valleys, appears also to be closely associ- ated with soil moisture. There seems to be a modifying factor here, — presumably not so much the temperatiu-e of the atmos- phere as the relative coldness of the waters which seep from the ravine slopes. Similar topographies usually mean similar combinations of physical factors; and like combinations of physical conditions mean the recurrence of a given type of vegetation. Although always of the same type, there usually occur slight differences in composition ; a fact attributable to unequal or local distribution. The vertical disposition of the three types of forest on the PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 157 unglaciated foothills is interesting, in that they are quite com- parable to associations on the morainic soils. For instance, the lower zone bears a close relation to the evergreen association in the broad rocky ravine; the mixed forest is closely comparable in many ways to the climax mesophytic forest, containing as it does the most mesophytic of the deciduous trees of this region; and the upper deciduous forest has a composition similar to that of the drier slopes upon the moraines. The major factors in determining the association in each of the instances are the same, namely, the available soil moisture, and exposure to desic- cating influences, especially the wind. The climax formation of western Pennsylvania is a mesophytic deciduous forest of which Acer, Fagus, Castanea, and Quercus are the dominant members, but always occur associated with additional species. The composition of the climax formation is not directly refer- able to physiographical conditions but to climatic ones; and in accordance with the annual rainfall (41.7 in.), its relatively equal distribution during the months of greatest vegetative activity, and the average temperature for the period of growth (61°F.), this type is to be expected. LITERATURE Christy, C. W. : Preliminary check list of the flora of Crawford County, Penn- sylvania. Illick, J. S.: Pennsylvania Trees. Pa. Dept. Forestry, Bull. 11, 1916. Jennings, O. E. : Botanical survey of Presque Isle, Erie Co., Pa. Ann. Carnegie Mus., 5: 289-421. Jennings, O. E.: A note on the ecological formations of Pittsburg and vicinity. Sci. 27: 828-830, 1908. Jennings, O. E.: Notes on the distribution of certain plants in western Penn- sylvania. Fern Bull. 18: 99-101, 1910. Shaper, J. A. : Plants of Allegheny County, Pennsylvania. Ann. Carnegie Mus. 1. BOOKS AND CURRENT LITERATURE Climatic Conditions as Related to Plant Growth. — The re- cently published work of McLean^ marks a new departure in the pre- cise experimental study of a subject which has heretofore been treated ma nly by general statistical methods. Nine stations were selected in different parts of Maryland, each possessing a ong series of climato- logical observations. Four plants were grown at each of these stations and subjected to accurate growth measurement. The soil conditions were made uniform for all of the cultures by transporting Norfolk sand for use at each station. The soil moisture was maintained at a continuous optimum in the pots by use of the auto-irrigator. The regular meteorological observations were supplemented by readings of evaporation from the porous cup atmometer. Each culture was allowed to grow for four weeks, being measured as to size and leaf area at the end of the first fortnight, and similarly measured at the close of the second fortnight, together with a determination of the dry weight. The- data which have been published relate only to the growth of soy-bean at two of the stations — Easton, located at an elevation of 32 feet on the Delaware-Chesapeake peninsula, and Oakland, at an elevation of 2500 feet on the Allegheny plateau. The length of the growing season employed at Easton was 171 days and that at Oakland 103 days. For the first fortnight of growth the Easton climate pro- duced a mean leaf area which was 33.3 % greater than that secured at Oakland. When the length of the growing seasons is taken into ac- count the efficiency of the Easton climate is 2.21 times that of the Oakland climate. The published data make it possible to correlate each of the five growth criteria with each of the climatological elements a,nd with such derived climatic features as the ratio of rainfall to evap- oration, sums of effective temperature, etc. All of the growth cri- teria exhibit a seasonal march from low values to mid-summer maxima, falling again in the latter part of the growing season. The last fort- nightly period at Oakland exhibited higher temperature and greater ^McLean, Forman T., A Preliminary Study of Climatic Conditions in Mary- land, as Related to Plant Growth. Physiol. Res. 2: 129-208 (No. 4), 1917. 158 BOOKS AND CURRENT LITERATURE 159 growth than the last week at Easton. The maxima of temperature and growth occurred about a month earher at Oakland than at Easton These are both facts of great importance in the application of pheno- logical data to agricultural problems. The evidence for soy-bean showed the growth of the first fortnight to be controlled by temperature and that of the second fortnight by the rainfall-evaporation ratio. The securing of facts of this character will make invaluable additions to our meagre knowledge of what* may be designated as the physiological life histories of plants. McLean's work emphasises the fact that we must reckon not only with the com- plexities of the en\dronmental conditions but also with the changes in the requirements of the plant itself from germination to maturity. The publication of liis results mth Windsor bean, corn, and wheat will be awaited with interest, for in them we mil doubtless have to face a third set of complexities^those by which various species of plants differ in their environmental requirements and in their onto- genetic changes of requirement. — Forrest Shreve. Laboratory Manual of Soil Biology. — The last five or six years have witnessed the appearance in this country of many laboratory manuals or guides for the student of soil microbiology. Prior to the pubhcation of the Soil Bacteriology Laboratory Guide by Lipman and Brown in 1911, there were no publications of the sort in English. Since then, however, there have appeared in quick succession the number above given. Some of these manuals, to be sure, comprised exercises in several branches of agricultural bacteriology, including soil bacteriology, but at least three have been devoted solely to the last named subdivision of bacteriologJ^ The subject of the present re\dew is the most recent addition to the group of little volumes referred to.^ It consists primarily of the usual exercises given to the advanced student of soils in our labora- tories on ammonification, nitrite formation, nitrate formation, deni- trifieation, symbiotic and non-symbiotic nitrogen fixation, cellulose decomposition, sulfofication, desulfofication, iron oxidation, and car- bon dioxide production. Added to these as new features, are exercises, on the study of soil protozoa, soil fungi, enzyme activity of soil mi- croorganisms and more elaborate directions for chemical and bacterio- logical methods, and for the preparation of media, than are given in 1 Whiting, A. L., Laboratory Manual of Soil Biology. Pp. ix + 143. John Wiley and Sons, New York and London, 1917 ($1.25). 160 BOOKS AND CURRENT LITERATURE the other three manuals on soil bacteriology. The problems and questions given at the end of every exercise are also more elaborate and thorough than those of the other manuals. The references given with every exercise, however, are by no means complete enough and offer no improvement over those, for example, given in Burgess' Man- ual of Soil Bacteriology. On the whole, Mr. Whiting's little book is well arranged, well print- ed, and well bound and calculated to serve the student at the present time. The writer of this brief review questions, however, the need for another work of this kind now, even allowing for the slight improve- ments which the book possesses over its predecessors. Soil biology is admittedly a science in its formative stages, and if it was attempted to prepare a new manual for every novel exercise or two as these ap- peared every year, we should be swamped with such works in a short time. The making of laboratory manuals can in my opinion easily be overdone. Moreover, many of the subjects now included in such manuals as the one under review are soon to be, if they are not already obsolete and of little significance. — Charles B. Lipman. NOTES AND COMMENT Exercises were held at the Brooklyn Botanic Garden on April 19 to 21 in dedication of the new laboratory building and plant houses. The laboratory building will accommodate the library and herbarium, laboratory rooms for morphology, physiology, and genetics, rooms for instruction and exhibition, as w^ell as a children's room and a public lecture hall. The exercises epitomized the work of the Garden, em- bracing addresses on topics that have to do with the popularisation and dissemination of botanical knowledge, and also a series of three sessions for the reading of scientific papers. Some thirty-nine titles were read, embracing subjects in nearly all departments of botanical activity. Almost 200,000 cords of wood are consumed every year by the wood distillation industry in New York State, according to a report just published by The New York State College of Forestry. The woods principally used are maple, birch and beech, the first giving the largest amount of acid from which the final products are refined. Waste from sawmills in the hardwood regions is sometimes used, but pitchy and soft woods such as pine and spruce are undesirable because of their low yield of products. The crude acid which is one of the first prod- ucts of distillation is combined with slaked lime to form acetate of hme, which in turn is sold to the manufacturers of acetic acid. The acid is used in the manufacture of white lead and acetone, and has a wide variety of uses in the textile and leather industries and the man- ufacture of smokeless powder and other explosives. Wood alcohol is another of the valuable materials obtained from the distillation of wood, being used in the manufacture of paints and varnishes, dyes, formaldehyde and photographic films, and in the stiffening of hats. Wood tar and wood gas are two of the minor products which are prin- cipally used as fuel at the distillation plants. The possibility of such a close utihzation of all parts of the tree in this industry makes it pos- sible to manage timber lands on a basis of great economy. 161 162 NOTES AND COMMENT The rapidly growing list of books in the Rural Science Series, which is being edited by Prof. L. H. Bailey and published by the Macmillan Company, has been recently augmented by the appearance of a hand- book entitled Strawberry-Growing, by Prof- S, W. Fletcher, of Penn- sylvania State College. All of the practical aspects of strawberry culture are given thorough treatment. The books on horticulture which c'id such good service a generation ago — as, for example, Peter Henderson's Market Gardening for Profit — gave one set of recommen- dations and cautions for all users of the book. Professor Fletcher's book is hke others in the same series in giving specific attention to the distinct requirements of strawberry culture in the different parts of the United States and Canada. A bulletin of the Agricultural Experunent Station at Amherst, Mass., prepared by Prof. George E. Stone, treats the selection, plant- ing, diseases, and care of shade trees in an exceptionally thorough man- ner. The methods of tree surgery are fully explained and some in- teresting facts are brought out regarding the direct and indirect injur- ies caused to trees by electric currents and arc lamps. It is to be hoped that the newer states will learn to emulate the painstaking care that has long been given shade trees in New England. Dr. N. M. Fenneman has recently published a map of the physio- graphic divisions of the United States (Annals of the Association of American Geographers, Vol. 6). The map shows divisions of three orders and is accompanied by a full discussion of the features that have been used as a basis for the demarcation of these areas. The map and text constitute the report of a committee of five men ap- pointed by the Association of American Geographers to carry out this work, which possesses importance in many branches of biological investigation. A Dictionary of Plant Names has been prepared by H. L. Gerth van Wijk and published b}^ Martinus Nijhoff, of the Hague. The two volumes give cross references involving the Latin names and the names in Dutch, Enghsh, French, and German. AN ENUMERATION OF THE PTERIDOPHYTES AND SPERMATOPHYTES OF THE SAN BERNARDINO MOUNTAINS, CALIFORNIA S. B. PARISH San Bernardino, California The name San Bernardino Mountains is applied to that part of the southern Sierra Nevada between the Cajon and the San Gorgonio Passes, a distance of some 50 miles in a nearly east and west direction. Their general ridge line is 4000-6000 feet above sea level, but at their eastern extremity they culmin- ate in the twin peaks of San Bernardino and San Gorgonio (or Grayback), respectively 10650 and 11725 feet high. The distance north and south across the mountains is about 20 miles. The curving southern and western ridge rises from a base 1200- 1500 feet in altitude and overlooks the San Bernardino Valley; from a like base the eastern acclivities of the terminal peaks face the Colorado Desert ; on the north they have a higher base, 3500- 4000 feet in altitude, and look out upon the Mojave Desert. On all sides the ascent is abrupt, and there is no proper foothill region. Except for hmited outcrops of limestones, sandstones and con- glomerates at a few places along the southern base, the rocks are of the granite series, often exposed in naked masses. The resultant soils are stony, coarse and porous for the most part, but in the valley bottoms they are finer and contain more or less humus. All the streams have eroded deep channels, the larger profound and steep canons. The general aspect of the mountains is extremely rugged. The streams have their sources in numerous mountain valleys, most of them of small size. Bear Valley is the largest of them, and has a length of 10 miles and a width of 1 or 2. The upper end of it is occupied by a "dry lake" of the same type as those 163 THE PLANT WORLD, VOL. 20, NO. 6 JUNE, 1917 164 S. B. PARISH of the Mojave Desert, which its rim looks out upon; but the climatic conditions cause this lake to be filled more frequently and deeply and to retain its water for longer periods, sometimes for several years. The flora of this end of the valley is much affected by the proximity of the desert. The lower part of the valley was formerly a green subalpine meadow, a sedgy pool in the center; now all is submerged beneath the deep waters of a great reservoir. This appears to have effected the extinction of some of the plants which formerly grew here. The flora of the Fig. 1. Winter view of the San Bernardino and San Gorgonio Peaks from the San Bernardino Valley mountains is being further modified by the inroads of the thou- sands who now resort to them for their summer vacations. It is to be regretted that records relating to the meteorology of these mountains are few, and for altitudes above 6500 feet entirely wanting. Table 1 presents the mean precipitation at two stations in the mountains, and for comparison that at San Bernardino, at their southern foot, and at Barstow, the nearest available station on the Mojave Desert, not far from their northern base. From this table it is seen that the precipitation at Bear Val- ley is nine times as great as* that at Barstow, more than twice PLANTS OF THE SAN BERNARDINO MOUNTAINS 165 that at San Bernardino, and one and three-tenths greater than that at the station on Mill Creek near the base of the mountains. The altitudinal distance between the last station and Bear Valley is 3550 feet, and the increased rainfall at the higher of them is 8.24 inches. The smnmit of San Gorgonio is 5224 feet above Bear Valley, and with the same proportionate increase of rainfall it would receive 11.85 inches more than the Valley, or a total of 44.57 inches, which is probably less than the actual amount. At all altitudes above 3500-4000 feet nearly four-fifths of the precipitation is in the form of snow, which melts promptly at the lower limits, but on the high peaks lingers into early summer, and often later on northern exposures. Most of the precipita- TABLE 1 Mean monthly and annual precipitation in inches Barstow Bear Valley Dam Mill Creek San Bernardino Q H a < 2,150 6,500 2,950 1,054 19 20 10 42 0.14 0.22 0.13 0.03 0.16 0.68 0.09 0.17 0.23 0.57 0.79 0.17 0.44 1.37 1.07 0.60 IS n n S ?! m S > o H ^ « 0.27 2.39 1.29 1.37 0.61 3.61 2 53 2.59 0.580.460.570.100.05 7.184.568.87 4.583.706.82 3. 33.2. 8612. 921. 1910. 580 1.541 2.121.22 580 3.61 17:32.74 0.1624.50 0815.89 tion on the highest mountains finds its way into the Santa Ana River, which seeks, but seldom reaches, the Pacific C '^an; the rest of it is carried by the Whitewater and is absorbed by the sands of the Colorado Desert. The valleys which drain to the north are the headwaters of the Mojave River and their out- flow would be carried by it to the great depression of Death Valley, but under present climatic conditions ages have elapsed since that destination was attained. Records of temperature are still more imperfect than those of precipitation. At Little Bear Valley (5500 feet altitude) the recorded extremes are 93° to —2° F. At Bear Valley (6500 feet altitude) there is no high record, but for low —14° F. These records cover a period of six years only, and give but an approxi- 166 S. B. PARISH mation to the value of the temperature coefficient. There are no records of the atmospheric humidity, but this must of neces- sity be low in a limited area surrounded by extensive regions of great aridity. It will be readily understood that this narrow ridge, however lofty its summits, facing on every side deserts and arid hills and plains, can have no other than a xerophytic flora; and such, with but few exceptions, is its character. The great majority of the plants — trees, shrubs and herbs — exhibit in various degrees the famihar modifications characteristic of xerophylly. For the same topographical reasons the zonation of this flora is far less well defined than that of mountains more favorably situated and of greater extent. Yet nowhere else in America save on the adjacent San Jacinto Mountain, is there displayed in such close conjunction so wide a range of phytogeographic regions. The two deserts at the north and east are occupied by a Lower Sonoran flora, and members of it and cognate species abound on the sides of the mountains which face them; the flora of the opposite base is Upper Sonoran and greatly, but not as greatly, modifies that of the southern ascent. The less tilted area between is covered by a Transition coniferous forest; above this, on the flanks of the culminating peaks, the Canadian and Hudsonian regions are represented; and at the very summit of San Gorgonio, above the tree fine, are to be found a few Arctic- Alpine plants. From various local conditions this zonation, especially above the Transition, is interpenetrating and often confused, but it has a real and distinguishable existence. In the following catalogue an attempt is made to define the zonal distribution of the different plants, so far -as the writer's knowledge of it permits. Further investigations will doubtless correct the assigned distribution in some instances, but it is believed to be fairly accurate. The southern slope of the mountains is covered with a close growth of shrubs, the trees and herbs being mostly confined to the bottoms and sides of the numerous canons, most of which carry permanent brooks. This is called the Chaparral Zone; the Lower Chaparral extends from 1500 to nearly 3000 PLANTS OF THE SAN BERNARDINO MOUNTAINS 167 feet altitude, and the Upper Chaparral thence to the ridge Une. The former subzone is characterized by such shrubs as Adenostoma fasciculatum, along its lower limits, and above by Juglans californica, Ceanothus crassifoUus, and C. divaricatus; the Upper by Pseudotsuga macrocarpa, U mbellularia californica and Ceanothus integerrivius. The opposite, or desert slope is also overgrown with shrubs, but of species entirely different from those found on the southern side. It is designated the Piiion Zone, and its altitudinal Umits Fig. 2. Forest of yellow pine in the Lower Transition Zone are between 3500 or 4000 to 6000 or 7000 feet in various parts. Among its notable plants are Pinus. vionophylla, Fremontia californica and Ceanothus Greggii. The subzones are not well distinguished, but such plants as Salvia pilosa, Purshia glandulosa and Pentstemon Eatoni are found only in the Lower, and Brick- ellia oblongifolia linifvlia, Malvastrum Davidsonii and Caidanthus crassifoUus glaber only in the Upper. The canons of this slope, that of the Mojave River excepted, are without permanent streams, save occasionally for short distances, and even springs are in- frequent; but their flora is more abundant and more varied than 168 S. B. PARISH that of the dry ridges and hills. Though arid the canon soils are relatively moister than those of the hills and the shelter of their cliffs and steep sides affords a varied environment con- ducive to a diversified plant life. Fig. 3. Alpine slopes of San Gorgpnio Peak, with open forest of limber pine The limits of the Transition Zone are approximately between 5000 and 7000 feet altitude. They are occupied by a forest of PLANTS OF THE SAN BERNARDINO MOUNTAINS 169 mixed conifers, the dominant tree being Pinus ponderosa; in the Lower subzone are found Cornus Nuttallii, C. californica and Quercus Kelloggii and in the Upper Juniperus occidentalis, Cercocarpus ledifolius and Ceanothus cordulatus. At about 7000 feet begins the Canadian Zone, with Pinus murrayana as its index, and at about 9000 to 10000 feet this merges into the Hudsonian, which extends nearly to the suminit of San Gorgonio, and is indicated by the presence of Pinus fiexilis. These two zones are much confused, and their hmits poorly understood. Finally at the very summit of San Gorgonio is a feeble repre- sentation of the Arctic-Alpine flora. In the following catalogue the term "zone" is used for con- venience to denote areas of unequal phytogeographical value. But few common names are given, for the reason that but few are in popular use, and the function of the botanist is not to pro\dde such names, but to record those actually in general use. CATALOGUE OPHIOGLOSSACEAE Botnjckium simplex E. Hitchc. Am. Journ. Sci. 6: 103. In a canon of South Mountain, Mill Creek, G. R. Robertson, and Big Mead- ows, Hall, both in the Canadian Zone; but few plants in either place. POLYtODIACEAE Polypodium vulgare Linn. var. hesperium Nels. & Macbr. Bot. Gaz. 61: 30. In rock crevices in the Hudsonian Zone. Polypodium californicum Kaulf. Enum. Fil. 102. Abundant in shaded rock crevices in the Lower Chaparral Zone. Gymnogramma triangularis Kaulf. Enum. Fil. 75. Gold Fern Abundant in shaded gravelly or stony soil in the Lower Chaparral Zone. Only the yellow-powdered form is found. Notholaena tenera Gillies, Bot. Mag. t. 305. A few plants only, in rock crevices in Cushenberry Canon and Water Canon, both in the Lower Pinon Zone. Adiantum capillus-veneris Linn. Sp. PL 1096. Maidenhair Fern Occasional on the face of shaded dripping cliffs in the Lower Chaparral Zone. Adiantum pedatum Linn. Sp. PI. 1095. Snow Canon, an Hudsonian island of Mill Creek Canon. 170 . S. B. PARISH Pteris aquilina Linn. var. lanuginosa Hook. Fl. Bor. Am. 2: 196. Bracken A low form prevails as a ground cover in the open pine forest of the Lower Transition Zone, and a more luxuriant form is frequent about springy- places and on stream banks in the Lower Chaparral Zone. Cheilanthes Fendleri Hook. Sp. Fil. 2: 103, t. 107 B. Frequent in crevices of rocks in the Upper Chaparral and Transition Zones, and occasional in the Pinon Zone. Pellaea andromedaefolia Fee, Gen. Fil. 129. Frequent on shady and stony hillsides in the Lower Chaparral Zone. Pellaea ornithopus Hook. Sp. Fil. 2: 145 A. Abundant, usually in the shelter of shrubs or stones and in clay soil, in the Lower Chaparral Zone. Pellaea wrightiana Hook. var. californica Lemmon Ferns Pac. Coast 10. Occasional in exposed rock crevices, or in rocky soil, in the Canadian Zone. Cryptogramma aciirostichoides R. Br. App. Frankl. Journ. 767. Infrequent in the Canadian and Hudsonian Zones. Big Meadows; Dollar Lake. Woodwardia radicans Smith, Mem. Acad. Turin, 6: 412. Frequent about springs and on shaded stream banks in the Lower Chaparral Zone. Asplenium filix-foemina Bernh. ; Schrad. Neues Journ. Bot. 1: 26. Lady Fern Occasional about springs and streams and in bogs in the Transition Zone. Dryopteris filix-mas Schott. Gen. Fil. Among rocks, Upper Holcomb Valley, a single collection, and the only one reported from the state. • Polystichum muniium Presl. Tent. Pterid. 83. Common on shaded stony canon sides in the Chaparral Zone. Polystichum scopulinum Maxon, Fern Bull. 8: 29. Locally abundant in rock crevices at the Hudsonian island in Snow Canon. Aspidium rigidum Swartz var. argiUum Eaton, Wheeler's Surv. 6: 333. Common on shaded and stony canon slopes in the Chaparral Zone. Cystopte.ris fragilis Bernh.; Schrad. Neues Journ. Bot. 1: 26. Frequent in damp crevices and on stony stream banks in the Transition Zone. Woodsia oregana Eaton, Canad. Natur. 1:91. Rare on rocky cliffs in the Canadian Zone. EQUISETACEAE Equiselum arvense Linn. Sp. PL 1061. Occasional, and sometimes locally abundant, in wet soils, in the Chaparral, Transition and Canadian Zones. Equisetum Funstoni A. A. Eaton, Fern Bull. 11: 10. Rare in sandy soil in canons of the Lower Chaparral Zone. Equiselum robusium R. Br.; Engelm. Am. Journ. Sci. 46: 88. Infrequent in mucky soil in the Lower Chaparral Zone. PLANTS OF THE SAN BERNARDINO MOUNTAINS 171 SELAGINELLACEAE Selaginella Bigelovii Underw. Bull. Torr. Club 25: 130. Abundant in the shelter of stones and shrubs, and in rock crevices, in the Lower Chaparral Zone. Selaginella Watsoni Underw. Bull. Torr. Club 25: 127. Frequent in crevices of rocks in the Hudsonian and Alpine Zones, and in the Hudsonian island in Snow Canon. ISOETACEAE Isoetes Bolanderi Engelm. in Parry, Am. Natur. 8: 214. Formerly in the shallow stream which drained Bear Valley, which is now deeply submerged by the reservoir. Probably extinct ; not otherwise known in southern California. PINACEAE Pinus CouUeri Don, Linn. Trans. 17: 440. Big-cone Pine Irregularly distributed, in large or small groups, throughout the Transi- tion Zone. A tree 40-60 feet high. Pinus flexilis James, Long's Exped. 2: 35. Limber Pine Near the summit of San Gorgonio Mountain between 10000-12000 feet altitude, and characterizing the Hudsonian Zone; also in the Hudsonian island of Snow Canon, at 6500-7000 feet altitude. A tree 15-30 feet high; often prostrate at its upper limits. Pinus lambertiana Dougl. Trans. Linn, Soc. 15: 500. Sugar Pine Scattered, mostly singly, throughout the Transition Zone, preferring the moister and richer soils of flats and ravines. The largest tree in these moun- tains is a Sugar Pine of more than 7 feet diameter growing near Strawberry Flat. This species attains a height of 100-200 feet. Pinus monophylla Torr. & Frem. Frem. 2d Rept. 319, t. 4. Pinon Common in arid soil in the Pinon Zone, of which it is the characteristic tree. A short-trunked tree 1.5-35 feet high. Pinus murrayana Balf. Rept. Oreg. Exped. 2, t. 3. Tamarac Pine Common in the Canadian Zone, of which it is the characteristic tree. A spreading tree 50-75 feet high. Pinus ponderosa Dougl. in Lawson, Man. 355. Yellow Pine The dominant tree in the open coniferous forest of the Transition Zone, and passing into the Canadian. A massive tree, 100-150 feet high. Pinus ponderosa Dougl. var. Jeffreyi Vasey, Rept. U. S. Comm. Agric. 1875, 179. Black Pine Throughout the Transition forest, much less abundant than the species and usually found in flats or near the borders of meadows. A smaller tree, 50-75 feet high. Pinus tuberculata Gordon, Journ. Hort. Soc. 4: 218, t. Dwarf Pine Forming a belt nearly half a mile wide, on the arid southern face of the mountains between City and East Twin Creeks, at 3500 feet altitude, in the Upper Chaparral Zone. The southern limit of the species, and its only known occurrence in southern California. Arborescent in habit, but only 5-15 feet high. 172 S. B. PARISH Pseudotsuga macrocarpa Mayr, Wald. Nordam. 278. Hemlock Abundant on the sides of canons in the Upper Chaparral Zone. There are also a few trees on the north side of the mountains near Gold Mountain. A large tree, 75-90 feet high. Abies concolor Lindl. & Gord. Journ. Hort. Soc. 5: 210. White Fir Scattered throughout the coniferous forest, preferring moister soils, and attaining its best development in the Upper Transition and the lower part of the Canadian Zone. A noble tree, 100-150 feet high. CUPRESSACEAE Libocedrus decurrens Torr. PL Frem. 7, t. 3. Mountain Cedar Scattered throughout the coniferous forest of the Transition Zone, mostly in the moister soils of flats and ravines. A thick-based tree, 75-100 feet high. Juniperus californicus Carr. Rev. Hort. IV. 3: 166. Desert Juniper Occasional in dry soil in the Lower Chaparral and Lower Pinon Zones. A large shrub, but arborescent on the Mojave Desert. Juniperus occidentalis Hook. Fl. Bor. Am. 2: 166. Mountain Juniper Abundant on the lower slopes and dry flats of Bear and Holcomb Valleys. An irregular tree, 20-50 feet high. GNETACEAE Ephedra viridis Coville, Contr. Nat. Herb. 4: 220. A species of the Mojave Desert, ascending the Pinon Zone to Doble and Rose Mine. SPARGANIACEAE Sparganium an gusti folium Michx. Fl. Bor. Am. 2: 189. In pools, Bluff Lake, in the Canadian Zone. NAJADACEAE Potamogeton nutans Linn. Sp. PI. 126. Abundant, floating in ponds, and now in the reservoir. Bear Valley, in the Upper Transition Zone. Potamogeton pectinatus Linn. Sp. PI. 127. Frequent in shallow pools. Bear Valley. JTJNCAGINACEAE Triglochin maritima Linn. Sp. PI. 338. Frequent in marshes. Bear Valley. ALISMACEAE Sagittaria arifolia Nutt.; J. G. Smith, Rept. Mo. Bot. Card. 6: 32, t. 1. Emergent in pools, Bluff Lake. I PLANTS OF THE SAN BERNARDINO MOUNTAINS 173 GRAMINEAE Andropogon macrourns IMichx. Fl. Bor. Am. 1: 56. In wet muck, Arrowhead Hot Springs, lower border of the Lower Chaparral Zone. Panicum huachucae Ashe; Journ. Elisha Mitchell Soc. 15: 51. San Bernardino Mountains, Ahrams 2737, ace. Hitchc. in Jeps. Fl. Cal. Panicum pacificwn Hitchc. & Chase, Contr. Nat. Herb. 15: 229, t. 241. Frequent in damp soil in the Lower Chaparral Zone. Aristida fendleriana Steud. Syn. PI. Glum. 1: 420. Infrequent in the Piiion Zone. Cactus Flat ; Rose Mine. Stipa coronaia Thurb. in Wats. Bot. Cal. 2: 287. Frequent on dry hillsides in the Lower Chaparral Zone. Stipa Elmeri Piper & Brodie, U. S. Dept. Agr. Div. Agrost. Bull. 11: 46. On dry flats at Mill Creek Falls, Upper Transition Zone. Stipa eminens Cav. Ic. PI. 5: 42, t. 467, f. 1. Frequent on dry hillsides in the Lower Chaparral Zone. Stipa Lettermani Vasey, Bull. Torr. Club 13: 53. On dry hillsides and flats, Bear Valley. Stipa Paris hii Vasey, Bot. Gaz. 7: 53. Occasional on dry hillsides in the L^pper Transition and Upper Piiion Zones. Mill Creek Falls is the type station. Stipa speciosa Trin. & Rupr. Mem. Acad. Petersb. VI. Sci. Nat. 5^: 45. Occasional on dry hillsides on the borders of the Lower Piuon Zone. Oryzopsis hymenoides Ricker; Piper, Contr. Nat. Herb. 11: 109. Sand Grass. Rare on dry hills at the upper end of Bear Valley, ascending from the desert where it is abundant. Muhlenbergia californica Vasey, Bull. Torr. Club. 13: 53. Locally abundant on the stony borders of Cold Creek in the Lower Chaparral Zone. Muhlenbergia filiformis Rydb. Bull. Torr. Club 32: 600. Infrequent in dry soil from Talmadge's Meadow in the Lower Transition Zone to the summit of San Gorgonio Mountain. Muhlenbergia microsperma Trin. Gram. Unifl. 193. On a dry sand bank at Waterman's Hot Springs, Lower Chaparral Zone. Alopecurus aristulatus Mich. Fl. Bor. Am. 1: 43. Frequent in wet meadows. Bear Valley. Sporobolus asperifolius Nees & Meyen, Acta Acad. Leop. Circ. 19: 141. Bear Valley, ace. Abrams' Flora Los Angeles. Agrostis exarata Trin. Gram. Unifl. 207. Occasional on dry hills, Bear Valley. Agrostis idahoensis Nash, Bull. Torr. Club 24: 42. Infrequent in the L'pper Transition Zone. Bear Valley; Mill Creek Canon. Agrostis schiedeana Trin. Mem. Acad. Petersb. VI. Sci. Nat. 4^: 327. In wet meadows, Bear Valley. Agrostis stolonifera Linn. Sp. PI. 62. Occasional in wet sand in the Lower Chaparral Zone. European. 174 S. B. PARISH Deschampsis danthonioides Munro; Benth. PI. Hartw. 342. Abundant in open forest in the Transition Zone. Deschampsia caespitosa Beauv. Ess. Agrost. 91, t. 18, f. 3. In wet meadows. Bear Valley. Trisetum spicatum Richter, PI. Europ. 1: 49. Occasional in-dry soil in the Lower Transition Zone. Koeleria crisiata Pers. Syn. PI. 1: 97. Frequent on dry canon sides in the Upper Chaparral Zone. Avenafatua Linn. Sp. PI. 80. Occasional in the Lower Chaparral Zone. European. Danthonia americana Scrib. U. S. Dept. Agr. Div. Agrost. Circ. 30: 5. Infrequent in Bear Valley. Bouteloua gracilis Lag.; Steud. Nom. Bot. ed. 2, 1: 219. Infrequent in the Upper Transition Zone. Santa Ana Canon, Hall; Bear Valley.. Melica imperfecta Trin. Mem. Acad. Petersb. VI. Sci. Nat. 2': 59. Abundant on canon sides in the Chaparral Zone. Melica imperfecta Trin. var. minor Scrib. Proc. Acad. Philad. 1885, 42. On bushy hillsides at the head of Edgar Canon (type). Upper Chaparral Zone. Melica imperfecta Trin. var. refracta Thurb. in Wats. Bot. Cal. 2: 303. Summit of Waterman Canon, in the Upper Chaparral Zone. Melica stricta Bolander, Proc. Cal. Acad. 3: 4. Occasional on dry ridges in the Upper Transition Zone. Bear Valley. LamarHa awrea Moench, Meth. PI. 201. Occasional in the Lower Chaparral Zone. European. Poa atropurpurea Scribn. U. S. Dept. Agr. Div. Agrost.. Bull. 11: 53, t. 10. Locally abundant on dry hillsides, Bear Valley, the type station. PoafendlerianaYasey, U. S. Dept. Agr. Div. Agrost. Bull. 13^: t. 74. Rose Mine, Upper Pinon Zone. Poa lo7igiligua Scribn. & Williams, U. S. Dept. Agr. Div. Agrost. Circ. 9: 3. Hillsides at Mill Creek Falls, Upper Transition Zone. Poa nevaden.sis Vasey; Scribn. Bull. Torr. Club. 10: 66. Hillsides at Bear Valley. Poa pratensis Linn. Sp. PI. 67. Bluegrass In meadows, Bear Valley; evidently native. Poa scabrella Benth. ; Vasey, Grasses U. S. 42. Occasional on canon sides in the Lower Chaparral Zone. Glyceria elata Hitchc. in Jeps. Fl. Cal. 162. Infrequent on the wet margins of streams in the Lower Transition Zone. Puccinellia nuttalliana Hitchc. in Jeps. Fl. Cal. 162. In subalkaline soil, Bear Valley. Festuca eriolepis Desv. in Gay, Fl. Chil. 6: 428. On dry slopes in the Chaparral Zone. Festuca megaleura Nutt. Journ. Acad. Philad. II, 1: 188. Frequent on dry slopes in the Lower Chaparral Zone. Festuca microstachys Nutt. Journ. Acad. Philad. II, 1: 187. Frequent on dry slopes in the Chaparral and Transition Zones. PLANTS OF THE SAN BERNARDINO MOUNTAINS 175 Festuce Myurus Linn. Sp. PI. 74. Frequent in drj- soil in the Lower Chaparral Zone. Festtica octoflor a Walt. Fl. Carol. 81. Frequent in dry soil in the Lower Chaparral Zone. Festuca pacifica Piper, Contr. Nat. Herb. 10: 12. Occasional on dry slopes in the Lower Chaparral Zone. Festuca Parishii Hitchc. in Jeps. Fl. Cal. 169. Occasional on bushy slopes in the Upper Chaparral Zone. Mill Creek is the type station. Festuca supina Schur. Enum. PI. Transs. 784. San Gorgonio Mountain, Reed, Hall, ace. Hitchc. in Jeps. Fl. Cal. Bromus arenarius Labill Nov. Holl. PI. 1: 2.3. Abundantly naturalized about Pine Flat, Waterman Canon. Upper Chaparral Zone. Australian. Bromus carinatus H. & A. var. CaliJornicv,s Shear, U. S. Dept. Agr. Div. Agrost. Bull. 23, 60. Occasional in the Lower Chaparral Zone. Canon Diablo. Bromus grandis Hitchc. in Jeps. Fl. Cal. 175. Locally abundant on rocky hillsides at the mouth of Snow Canon. Bromus hordaceus Linn. Sp. PL 77. Occasional in the Lower Chaparral Zone. European. Bromus marginatus Nees; Steud. Syn. PI. Glum. 1: 322. On hillsides near the mouth of Snow Canon in the Upper Transition Zone. Bromus orcuttianus Vasey var. Hallii Hitchc. in Jeps. Fl. Cal. 175. San Bernardino Mountains, Mrs. Wilder ace. Hitchc. I.e. Bromus rubens Linn. Cent. PI. 1: 5. < Often abundant on dry slopes in the Lower Chaparral Zone. European. Bromus subvelutinus Shear, U. S. Dept. Agr. Div. Agrost. Bull. 23: 52. San Bernardino Mountains, Hall, ace. Hitchc. in Jeps. Fl. Cal. Bromus villosus Forsk. var. Gussonei Aschers. & Graebn. Syn. Mitteleur. Fl. 2: 595. Broncho Grass Often abundant in the Lower Chaparral Zone. European. Bromus vulgaris Shear, U. S. Dept. Agr. Div. Agrost. Bull. 23: 43. San Bernardino Mountains, Abrams, ace. Hitchc. in Jeps. Fl. Cal. Agropyron Parishii Scribn. & Smith, U. S. Dept. Agr. Div. Agrost. Bull. 4: 28. Locally abundant on stony hillsides, Waterman Canon, at 3000 ft. alt. The type station. Hordeum jubatum Linn. Sp. PI. 85. , Occasional in dry soil in the Transition Zone. Hordeum murinum Linn. Sp. PI. 85. Occasional in the Lower Chaparral Zone. European. Hordeum nodosum Linn. Sp. PI. ed. 2, 1: 126. Abundantly naturalized in the Chaparral and Transition Zones. European Elymus glaucu^ Buckl. Proc. Acad. Philad. 1862:99. Frequent in the Chaparral and Transition Zones. Elymus glaucus Buckl. var. Jepsoni Davy in Jeps. Fl. W. Mid. Cal. 79. Deep creek, in the Lower Transition Zone, Abrams, ace. Hitchc. in Jeps. Fl. Cal. 176 S. B. PARISH Sitanion jubatum J. G. Smith, U. S. Dept. Agr. Div. Agrost. Bull. 18: 10. Occasional in dry soil, Bear Valley. Sitanion calijornicum J. G. Smith, U. S. Dept. Agr. Div. Agrost. Bull. 18: 13. Infrequent in the Upper Transition Zone. Mill Creek; Bear Valley. Sitanion minus J. G. Smith, U. S. Dept. Agr. Div. Agrost. Bull. 18: 12. Summit of San Gorgonio Mountain, Mrs. Wilder. CYPERACEAE Cyperus aristatus Rottb. Descr. Nov. PI. 22. In wet sand. Waterman Hot Springs, in the Lower Chaparral Zone. Cyperus Parishii Britton in Parish, Bull. S. Cal. Acad. 3: 52. In a wet meadow, Head of Edgar Canon, in the Upper Chaparral Zone. Schoenus nigricans Linn. Sp. PI. 1: 43. On wet banks. Arrowhead Hot Springs. Eleocharis montana R. & S. Syst. 2: 154. On wet banks, Arrowhead Hot Springs. Fimhristylis thermalis Wats. King's Expl. 5: 350. In soil moistened by warm water. Arrowhead and Waterman Hot Springs. Scirpus microcarpus Presl. Rel. Haenk. 1: 195. Common along streams in the Lower Chaparral Zone. Scirpus pauciflorus Lightf . Fl. Scot. 1078. Rare; dry meadow. Bear Valley, in the Upper Transition Zone. Carex (Primocarex) exserta Mack. ined. Rare ; on a dry, stony hillside, Bear Valley. Carex (Primocarex) tmdticaulis Bailey, Bot. Gaz. 9: 117. Frequent on dry hillsides, in pine forest, throughout the Lower Transition Zone. Carex (Vignea) Abramsii Mack. Bull. Torr. Club 36: 482. In a marsh between Bear Valley and Bluff Lake (type), and on Deep Creek, Abrams, in the Transition Zone, and on High Creek, Grant, in the Canadian Zone. Carex (Vignea) abrupta Mack. ined. High Creek, Grant, and Bluff Lake, Mrs. H. E. Benton, in the Canadian Zone. Carex (Vignea) albomarginata Mack. ined. Summit of San Gorgonio Mountain, Mrs. C. M. Wilder, in the Alpine Zone. Also on the summit of San Jacinto Mountain, and distributed from both stations as C. Preslii Steud. Carex (Vignea) alma Bailey, Mem. Torr. Club 1: 50. Frequent on stony stream banks in the Chaparral and Lower Transition Zones and rare in the Pinon. Carex (Vignea) athrostachya Gray, Proc. Am. Acad. 7: 393. Frequent in meadows. Bear Valley. Carex (Vignea) Bolanderi Olney; Gray, Proc. Am. Acad. 7: 393. In marshes, Mill Creek Falls and Head of Waterman Canon. Carex (Vignea) festiva Dewey, Am. Journ. Sci. 29: 246. In wet meadows. Bear Valley. PLANTS OF THE SAN BERNARDINO MOUNTAINS 177 Carex (Vignea) feta Bailey, Bull. Torr. Club. 20: 417. In a cienega, Waterman Canon, in the Lower Chaparral Zone. Carex {Vignea) Jonesii Bailey, Mem. Torr. Bot. Club. 1: 16. In a meadow, Bluff Lake, in the Canadian Zone. Carex {Vignea) multicostata Mack. ined. In a meadow. Bear Valley Dam, Parish 1306, type. Carex {Vignea) specifica Bailey, Mem. Torr. Club 1: 21. Frequent in dry soil in the Transition Zone. Carex {Vignea) stellulata Good. var. ormantha Fernald, Rhod. 3: 222. Locally abundant in a wet meadow. Bluff Lake. Carex {Vignea) subfusca W. Boott in Wats. Bot. Cal. 2: 234. In a wet meadow, Bear Valley. Carex {Eucarex) aurea Nutt. var. celsa Bailey, Mem. Torr. Club'l: 75. C. Hassei Bailey, Bot. Gaz. 21: 5. In a meadow at Seven Oaks, in the Transition Zone. More abundant in the Cismontane Valleys. Carex {Eucaryx) laciniata Boott in Benth. PI. Hartw. 3: 341. Locally abundant along a dry stream bed. Waterman Canon, in the Lower Chaparral Zone. Carex {Eucaryx) lanuginosa Michx. Fl. Bor. Am. 2: 175. In a marsh, Edgar Canon, in the Lower Chaparral Zone. More abundant at lower altitudes. Carex {Eucarex) nebraskensis Dewey, Am. Journ. Sci. 2: 107. Occasional on stream banks in the Transition Zone. Carex {Eucarex) Parishii Mack. ined. Bear Valley, in the Upper Transition Zone and Waterman Canon in the Lower Chaparral Zone. Carex {Eucarex) quadrifida var. caeca Bailey, Bot. Gaz. 21: S. In meadows in the Upper Transition, Canadian and Hudsonian Zones. Carex {Eucarex) Schottii Dewey, Bot. Mex. Bound. 231. In swamps. Bear Valley. More abundant in San Bernardino Valley. Carex {Eucarex) senta Boott, III. 4: 174. Frequent in meadows in the Upper Transition Zone. Carex {Eucarex) triquetra Boott, Trans. Linn. Soc. 20: 126. Frequent on dry bushy hillsides in the Lower Chaparral Zone. Carex {Eucarex) utriculata Boott in Hook. Fl. Bor. Am. 2: 221. Frequent in very wet meadows. Bear Valley. Carex {Eucaryx) utriculata var. yninor Boott in Hook. Fl. Bor. Am. 2: 221. With the species. LEMNACEAE Lemna minima Phil. Linnaea 33: 239. Bear Valley, ace. Abrams Fl. Los Ang. Lemna trisulca Linn. Sp. PI. 971. Bear Valley, ace. Abrams, Fl. Los Ang. 178 i S. B. PARISH JUNCACEAE Luzula comosa E. Mey. Synop. Luzul. 21. Frequent in damp soil in the Transition Zone. Luzula comosa E. Mey. var. macraniha Wats. Bot. Cal. 2: 203. Growing with the species, but less abundant. Juncus balticus Willd. Berlin. Mag. 3: 298. Big. Meadows, Holl. Bear Valley. Mill Creek. Juncus hufonius Linn. Sp. PI. 328. In wet sand. Bear Valley and Bluff Lake. Juncus canaliculatus Engelm. Bot. Gaz. 7: 6. In moderately damp soil in the Chaparral, Transition and Piiion Zones. The type was from Mill Creek Canon. Juncus effusus Linn. var. pacificus Fern. & Weig. Rhodora 12: 89. In damp soil in the Lower Transition Zone. Juncus interior Weigand, Bull. Torr. Club, 27: 516. In meadows in the Lower Transition Zone. Juncus latifolius Buchen. Monog. June. 425. Caespitose in wet meadows and on stream banks in the Upper Transition Zone. Juncus mertensianus Bong. Mem. Acad. St. Petersb. VI. Sci. Nat. 2: 167. ■ In a marsh at 6000 ft. alt.. Mill Creek Canon. Juncus nevadensis Wats. Proc. Am. Acad. 14: 303. Common in meadows in the Transition Zone. Juncus obtusatus Engelm. Trans. St. Louis Acad. 2: 495. In meadows in the Lower Transition Zone. Juncus oxymeris Engelm. Trans. St. Louis Acad. 2: 483. Occasional in the Transition Zone. Juncus Parryi Engelm. Trans. St. Louis Acad. 2: 447. Summit of San Gorgonio Mountain, Mrs. Wilder. Juncus phaeocephalus var. paniculatus Engelm. Trans. St. Louis Acad. 2: 484. Occasional by streams in the Chaparral and Transition and Canadian Zones up to 8200 ft. alt. Juncus textilis Buchen. Abh. Nat. Ver. Brem. 17: 336. Waterman Canon, in the Lower Chaparral Zone. Juncus triformis var. unijlorus Engelm. Trans. St. Louis Acad. 2: 493. On wet sandbars. Bear Valley. Juncus xiphioides E. Mey. Synop. June. 50. Borders of streams and marshes in the Transition and Pinon Zones. {To he continued) REDWOODS, RAINFALL AND FOG WILLIAM S. COOPER University of Minnesota, Minneapolis, Minnesota The distribution of tlie redwood of California (Sequoia semper- virens Endl.) has been commonly related to the summer fogs so characteristic of the coast of that state. It is certain that other influences have a share, notably rainfall; but no investigations using other than merely observational methods have been made bearing ujjon the relative importance of these and other factors. The following study, though somewhat crude in method, yielded fairly exact results as to the rainfall factor, and seems to offer useful evidence bearing upon the problem. The work was done during the rainy seasons of 1913-1914 and 1914-1915, in the Santa Cruz Mountains, Stanford University being used as a base of operations. My thanks are due to each member of the staff of the Department of Botany of Stanford University for assistance in many ways. The Santa Cruz Mountains trend northwest and southeast, approximately parallel to the coast. East of them lie the southern extension of San Francisco Bay and the Santa Clara Valley, and west of them is the Pacific Ocean. Southward they are a complex mass 30 km. in maximum breadth, deeply cut by abrupt valleys and caiions. Northward they gradually narrow, and opposite Palo Alto and Redwood City they have more of the character of a single ridge with projecting spurs, the longer ones pointing westward. Still farther north they are again complex, but lower, and they finally die out in the hills south of San Francisco. The east face of the mountain mass, bsing a fault scarp, is nearly everywhere abrupt, and the highest points of the range, such as Black Mountain (847 m.). Castle Rock Ridge (912 m.), and Loma Prieta INIountain (912 m. +) are near the eastern margin. 179 THE PLANT WORLD, VOL. 20. NO. 6 180 WILLIAM S. COOPER In the main body of the range redwood forest is the prevaihng vegetation type. This great forest mass extends from near Santa Cruz northward, covering the ridges and valleys of the central part of the range with fair solidity as far as Butano Ridge. North of this its extent is more limited and its continuity some- what broken, the south facing slopes and ridge tops being clothed instead with chaparral or grassland vegetation. At a point on the main ridge directly west of Palo Alto the redwood forest ends, chaparral, oak forest, and meadow sharing the region northward. Obviously the main factor in the distribution of the redwood is water in some form or other. In the Santa Clara Valley the supply is hopelessly inadequate except along the banks of the permanent streams. The same is true in a less extreme degree of the two foothill regions and the coast. Turning to the moun- tain region proper, a puzzling fact appears. Certain areas, apparently not differing in topography and soil from nearby ones which support luxuriant redwood forest, are practically without these trees. The mass comprising Black Mountain and Monte Bello Ridge is a conspicuous example. Even in the deep caiions such as that of Stevens Creek, which surround and penetrate the mass, redwoods are almost absent. The same is true of the mountains and canons of the northeast face of the range, southeastward from Black Mountain. These slopes and valleys are farthest from the Pacific, and therefore a very natural hypothesis to explain the absence of redwoods here is that it is due to insufficient rainfall — quite certainly an adequate cause in the case of the Santa Clara Valley and in the foothills. The localities were conveniently situated, and therefore I attempted to solve the problem by comparing the precipitation in nearby areas, similar in topography and soil, some bearing luxuriant redwood forest, some with none at all. Observations were not confined to the mountain region itself. Rain gauges of a type shortly to be described were set out in a group of stations, beginning at Palo Alto in the Santa Clara ViLlley, and extending westward and southwestward across the Santa Cruz Mountains to the ocean shore. I have arranged the REDWOODS, RAINFALL AND FOG 181 table of results under five regional heads, from east to west; Santa Clara Valley, Eastern Foothills, Santa Cruz Mountains, Western Foothills, Coast. The stations are numbered in table 1, and the map indicates their locations. Fig. 1 The mountainsj,themselves have been already described. The other divisions are as follows: The northwestern end of the Santa Clara Valley (Sta. 1-4) is at present largelylunder cultivation, but was formerly covered 182 WILLIAM S. COOPER by grassland, chaparral, and open oak forest (Quercus agrifolia Nee and Q. lohata Nee). The altitudes are negUgible. The eastern foothill region (Sta. 5-7), several kilometers wide west of Palo Alto, narrows almost to extinction southeastward, the mountains fronting abruptly upon the valley. The altitudes of stations occupied range from 120 m. to 250 m. The vegeta- tion consists dominantly of chaparral of several types, with oak forest {Quercus agrifolia most important) in ravines and on steep north slopes. Close to the main mountain front a few redwoods occur beside streams. The western foothills are indefinite in extent, merging gradually with the higher mountains to the east. The stations occupied, both of which are in valleys, were 97 m. and 106 m. in altitude. The hills are mainly grassy, with little chaparral and few oaks. Tongues of redwood extend down the cafions toward the ocean. The coast in part is bordered by a flat strip 2 km. wide or less; in other places the hills come to the ocean, and steep slopes and sea cliffs occur. The coast station at Tunitas was at the top of one of these cliffs, 70 m. above tide. The vegetation of the seaward facing slopes is the characteristic coastal scrub, including Baccharis pilularis DC, Rhamnus calif ornica Esch., Rhus diver siloba T. & G., and Lupinus orhoreus Sims. While interested in the problem of the redwood, my attention was called by Dr. Forrest Shreve to a simple means for measuring total precipitation for long periods, which is in use among the ranchers in the vicinity of Tucson, Arizona, and which was used by Dr. Shreve in his studies in the Santa Catalina Mountains. This device seems to have sufficient possibilities for usefulness to merit a full description. I wish also to suggest some modi- fications which seem to me to be improvements. The instru- ment consists essentially of a container of convenient size fitted with a tin funnel to receive the rain. A little kerosene, put into the container, floats upon the surface of the water and prevents loss by evaporation. The precipitation is determined by pour- ing the contents into a graduate. The amount of the kerosene is deducted and the volume of water is divided by the receiving area of the funnel. REDWOODS, RAINFALL AND FOG 183 After some experimentation I developed the following as the most convenient form for the apparatus. For the container I used a 2 gallon galvanized iron kerosene can, with a screw top 3 or 4 cm. in diameter and a spout with a screw cap. This con- tainer, fitted with the funnel as described, was found sufficient to accommodate safely 225 cm. of precipitation. The can was painted black to reduce its visibihty; notwithstanding which, the inevitable small boy found and appropriated several. The funnel was of the ordinary tin kitchen variety, the receiving end being about 6 cm. in diameter. To minimize splashing I added a vertical tin collar 2.5 cm. high, and a circle of coarse ware netting was placed within to prevent clogging by debris. The funnel was fitted to a hole in a cork stopper which in turn fitted the opening in the top of the container. All joints were made waterproof, and the top of the funnel was accurately levelled after the apparatus was put in place. That these pre- cautions are necessary is shown by the following table: Standardization of four instruments I II III IV Before waterproofing and levelling After waterproofing and levelling 1.00 1.00 0.67 0.92 0.83 0.92 0.88 0.94 Three further tests confirmed the approach to uniformity indicated above. As a precaution, a small bent glass tube with down pointing outer end was run through the cork beside the funnel as an outlet for au\ It was thought that an exceptionally heavy rain might so fill the tube of the funnel that no air could escape through it, thus causing temporary overflow. I have no means of knowing whether this is a necessary safeguard. The funnels were numbered and the receiving area of each was com- puted from the average of three diameters. Figure one shows one of the instruments in position. Twelve instruments were set out October 18, 1913, and taken' in May 13, 1914. Complete records were obtained from, seven, and approximate records from four others which had disappeared 184 WILLIAM S. COOPER between the midwinter reading in January and the final one. These were computed by adding to the partial record an amount proportional to the average amount received during the second half of the season by those from which complete records were obtained. On October 27 and 31, 1914, gauges were set out at practically the same series of stations as the year before, and at a number of additional ones, including the summit of Black Fig. 2. Rain gauge in place at top of coastal bluff Mountain and the hamlet of Bellvale. These were taken in June 28 and July 28, 1915. Several others, placed at various strategic points, disappeared during the winter. In the table I have added figures from the United States Weather Bureau reports, obtained during the same two seasons at nine stations which are useful in supplementing the results personally secured. From table 1, in which the results of the rainfall observations are summarized, the following conclusions have been drawn. < < c o ^g T3 O O ■a o O S « < -a o o ■a >:: < > < < sojdv» ;; ira .^ -^ M M ZnjQ BlUBg, o 1^ 00 O St!;iUTlX 05 9lBAI[9a r- o en CO 00 ui fepooMpau ^s-^IiJ to o 00 CO CO CO 00 SpBOJSSOJQ ■BIHA -< d CO JO ^siia jiuiiung ui 16£ CO A 173.25 CO «o •jioiuing -jn lo^ia o »iO gpEOJSSOJQ j|il\[ aS'Bj; pui3 9tnd(y puouicj uag. (M •i[9si::i japinog. •* 171.12 171.37 - tjpuojj ■G'J CO CO CO o o Jiaajo SB^runx JO pBatj jb aSpiH 3 o o ^irauing •;i\[ s^gaijj CO to CO csi CO Cl CO pT3oy^ ((J^ S^SUIJJ sojBQ soq. 8^P!H -tadsBf apispoow asof UBg, CO IiaqdiuBO, CO CO o o Ol ■BJBJO B^aug, in en 00 00 CO o^iyoiM. o m 3 •ftci Oh a4. Oh 03 o > « 2: a I O CO n 1-H C I 3 03 m OS o "a 2 o ^ a 03 < Q I • < 185 186 WILLIAM S. COOPER First of all, we have striking instances of the great difference in precipitation which frequently occurs in California in stations only a few kilometers apart. The greatest distance between any two places listed here is 54 km. The series from Palo Alto to Tunitas is especially interesting. In 1914-1915 the figures for five stations along this line, one in each physiographic pro- vince, were as given in table 1. It should be mentioned that the two winters studied were seasons of more than average rain- fall. The mean annual precipitation for Palo Alto is about 40 cm. It is also indicated that altitude is the main factor influencing the ^amount of precipitation. The immediate vicinity of the coast is relatively deficient as well as the interior valley. TABLE 2 STATIOX REGION EISTANCE FROM PALO ALTO ALTITUDE RAINFALL Palo Alto Woodsidfi Valley E. foothills km. 9.6 14.4 17.6 24.0 m 17 122 623 106 70 cm. 66.48 81 39 King's Mt Tunitas Creek TunitavS Mountains 139.32 W. foothills Coast 83.36 75.29 Further, returning to the hypothesis suggested on a previous page, that difference in rainfall is responsible for the presence of redwood forest in certain areas in the mountains and its absence in others, we gather from the table the following evi- dence. In both groups of rainfall stations — those with and those without redwood forest — precipitation is abundant. In fact, the stations without redwood forest are consistently a little more rainy than those possessing it. Our hypothesis therefore is unsupported ; rainfall difference is not here the deciding factor ; and high precipitation alone is not sufficient to make possible the development of redwood forest covering mountain slopes away from streams. The explanation for the last statement is found in the long dry season characteristic of the California climate. During this critical period the soil everywhere away from permanent REDWOODS, RAINFALL AND FOG 187 streams becomes very dry, in relatively mesophytie as well as in xerophytic habitats. I have demonstrated this in unpublished work dealing with the ecology of the chaparral. Soil moisture determinations made in the eastern foothill region on opposite north and south facing slopes dominated respectively by chapar- ral (xerophytic) and oak forest (mesophytie) show that the water contents of the two habitats, differing greatly during the rainy season, become almost equally deficient by the end of the dry, 1.4% being the minimum for the chaparral and 3% for the oak forest (average of three depths). The redwood soil in the mountains would doubtless show the same severe depletion, though probably to a somewhat less degree. The evaporation rate too is very high at the critical period. In the week ending September 19, 1913, at the same foothill station, it reached the maximum for the year of 51 cc. loss per day from the porous cup atmometer. The redwood is unusually sensitive to the danger of rapid water loss, even when the soil water supply is ample. -This is shown by the following instance. Early in May, 1915, a terrific north wind swept over central California, so desiccating in its effects that roses were turned to paper and gardens showed the effects for weeks afterward. A few days later I crossed the Santa Cruz Mountains and found on the north facing slopes every redwood brown as if scorched by fire. Trees growing in ravines but projecting abo^^e the ridge top were green below and brown above. Frequently trees of redwood and douglas fir were seen side by side, equally exposed. Invariably the redwood was brown and the douglas fir unharmed. In this connection it is of interest to note that in the mountain areas where redwood is practically absent, douglas fir is abundant. It is thus sho^ATi conclusively that even in certain mountain areas which have ample winter precipitation, redwood is ex- cluded from all places except the immediate vicinity of streams because of desiccation of the soil during the rainless season accompanied by high evaporation rate. This state of affairs might be improved by the lowering of the evaporation rate, resulting in conservation of the hmited supply of available ^ * 188 WILLIAM S. COOPER water; and the ocean fogs, which cover parts of the mountains on a large majority of summer days, do this effectively, as has been pointed out by several writers. Fogs also add a certain amount to the soil water supply, as Cannon has noted. ^ The ground under a redwood tree during a fog is often decidedly wet, but whether this water is abundant enough or penetrates deeply enough to be of much consequence is doubtful. At any rate the decrease of evaporation is of very great importance. Light might be thrown upon the problem if data could be obtained concerning the extent of the region which is ordinarily covered by the fog blanket. I can give here some general observations which are helpful. From Palo Alto the east face of the Santa Cruz Mountains, extending from a point about west of Redwood City southeastward to the mass of Black Moun- tain, is in full view. The northwestern half is clothed with red- woods; the Black Mountain mass has none. On a majority of days during the summer a fog blanket may be seen covering the northwestern end of the range, sometimes of greater, sometimes of less extent, but centering in the region of King's Mountain, where the redwood forest is heaviest. Frequently it pours over the edge and descends the eastern slope. Redwoods are fre- quent upon this slope and are not entirely confined to the immedi- ate vicinity of streams. Less frequently the fog is seen to spread southward along the summit ridge, but very rarely indeed does it reach Black Mountain. The explanation probably is that in the region of King's Mountain the range is relatively narrow and the fog attains the eastern slopes; west of Black Mountain the mountain region is much broader, and the fog blanket, if of the same dimensions as farther north, stops short of the eastern edge of the mountains, possibly near Butano Ridge. The fog-frequented area around King's Mountain includes the four stations which I established in the redwood forest region; the fogless drea of Black Mountain and its environs includes all of my four stations located in country devoid of redwood - forest; and the latter region has slightly the higher rainfall of the two. It is therefore apparent that the first condition neces- 1 Cannon, W. A. On the relation of redwoods and fog to the general precipita- tion in the redwood belt of California. Torreya 1 : 137-139. 1901. REDWOODS, RAINFALL AND FOG 189 sary for redwood forest is an ample supply of soil water ; but that this alone is not sufficient. The second, a summer fog blanket, cutting dowTi the rate of evaporation, is just as essential. The results may be expressed in tabular form (table 2). TABLE 3 VALLEY E. FOOTHILLS MOUNTAINS w. FOOTHILLS COAST Rainfall Deficient Deficient Ample Ample Deficient Deficient Ocean fog None Occasion- al Abundant Occasion- al Abundant Abundant Redwoods None ex- Occasion- Luxuriant Occasion- Along None cept oc- al along forest al along streams casional streams streams along streams SUMMARY The redwood requires a high ratio of water supply to water loss, and is unusually sensitive to the danger of rapid transpira- tion, even when the supply is ample. Soil moisture studies in the Palo Alto region indicate that during the rainless season the soil becomes dangerously dry, even in the more mesophytic habitats. The redwood may exist in regions where the rainfall is deficient, but only close to permanent streams. For full development of redwood forest, covering mountain slopes which may become relatively dry as well as the inmiediate environs of permanent streams, heavy wdnter precipitation is necessary, but alone is not sufficient. Abundant summer fog is also essential, its effects being to decrease the water loss, and in some degree to add to the soil water supply. \ATiere summer fogs do not occur, or where they occur infrequently, no true forest of redwood is possible, even though the rainfall be as high or higher than in fog-frequented areas. In areas of the former kind the infrequent redwoods are confined to the banks of streams, as in regions of deficient precipitation. For the rainfall studies involved in the above work a simple type of rain gauge, making possible sunmiation of precipitation for long periods, was used, and is described in the body of the paper. BOOKS AND CURRENT LITERATURE Recent Work on the Life Histories of the Kelps. — Since Drew's announcement^ that the motile cells of Laminaria are actually gametes, and not zoospores, as they were previously considered, there has been a good deal of skepticism as to the accuracy of his observations. Recent papers by Sauvageau" and Kylin^ have cleared the matter up in a most interesting way. To Sauvageau belongs the credit of priority. Kylin's results, however, confirm and add somewhat to the earlier observations. The facts as given by Kylin may be summarized as follows. On germination, the zoospores give rise in three to five weeks to gameto- phytes. The male gametophytes are short, monosiphonous, and irregularly branching. They produce antheridia singly as small terminal or lateral cells. The antherozoids have not been observed. The female gametophytes may be similar to the male but with fewer and larger cells, or may consist of a single large cell produced from the swelling gerin tube of the germinating zoospore. Li either case all cells of the female gametophytes are oogonia, each producing a single egg, which is extruded from a narrowed terminal neck. Fertilization was not observed. The (fertilized) egg develops directly into an unbranched sporophyte (the Laminaria plant), which is at first mono- siphonous and later becomes a flattened plate. By the end of the first summer the young sporophyte is 2 to 3 dcm. long. Cytological details are entirely lacking. It is to be expected that these will soon be forthcoming. ^ Drew, G. H. The -Reproduction and Early Development of Laminaria digitata and Laminaria saccharina. Ann. Bot. 24. 1910. - Sauvageau, C. Sur la sexualite heterogamique d'une Laminaire {Saccorhiza bulbosa). Sur les debuts du dcveloppement d'une Laminaire {Saccorhiza bulbosa.) Compt. rend, de I'acad. sci. Paris 161. 1915. Sur les gametophytes de deux Laminaires (L. flexicaulis et L. Sac- charina). Ibid. 162. 191G. Sur la sexualite heterogamique d'une Laminaire (Alaria esculenta). Ibid. 162. 1916. ^ Kylin, H. Ueber den Gencrationswechsel bei Laminaria digitata. Svensk. bot. Tidskr. 10, 551-561. 1916. 190 BOOKS AND CURRENT LITERATURE 191 The establishment of alternation of generations of the type described fills to a certain extent the tremendous gap between the Fucaceae and the Phaeosporales, and clears up the hitherto doubtful homologies of the former. Improbable as it seemed on the face of it, the Fucus plant is really a sporophyte homologous with Laminaria, while the game- tophyte of Laminaria corresponds to the cell-generations within the oogonium and antheridium of Fucus. The gametophyte of Laminaria, though much reduced, is an independent plant, while that of Fucus reaches a stage even nearer total suppression than is shown in the typical Angiosperm. It is as remarkable as it is unexpected that the brown algae should show a series parallel to that of the archegoniates, the more so since the evidence at hand indicates an antithetic origin of the sporophyte in the higher plants, while in the brown algae there is good reason to believe that the sporophyte is of homologous origin. If closer study confirms this interpretation of the facts, the Lami- nariaceae must be classed with Fucus among the Cyclosporales, stand- ing between the Cutleriaceae and the Fucaceae. — I. F. Lewis. Dicotyledonous Woods. — The interrelationships of the dicotyle- dons are confessedly a tangle. Since 50% of the families are entirely made up of wood}' plants, the comparative structure of the wood ought to furnish facts of great value. But it has been found difficult to say what diagnostic features are of phylogenetic value, and only recently a beginning has been made in this direction. All that can be said at present is to "report progress," as is evidenced by papers of Adkinson,^ Hoar,^ Jeffrey and Cole,^ in addition to earlier papers from the same laboratory. Plowman has contributed an illuminating com- parison of the box elder with true maples,** in which he concludes on anatomical and other grounds that "Negundo aceroides" became segregated from Acer during the Glacial Period. — M. A. Chryslek. ^ Adkinson, J. Some Features of the Anatomy of the Vitaceae. Ann. Bot. 27: 133-139. 1913. 2 Hoar, C. S. A Comparison of the Stem Anatomy of the Cohort Umbeli- florae. Ann. Bot. 29: 55-63, pis. 4, 5. 1915. Ibid. The Anatomy and Phylogenetic Position of the Betulaceae. Amer. Jour. Bot. 3: 415-435. 1916. ' Jeffrey, E. C. and Cole, R. D. Experimental Investigations on the genus Drimys. Ann. Bot. 30: 359-368, pi. 7. 1916. ■* Plowman, A. B. Is the Box Elder a Maple? Bot. Gaz. 60: 169-192, pis. 5-10. 1915. NOTES AND COMMENT The report of the Office of Forest Investigations of the United States Forest Service for the fiscal year 1916 describes the recent results of the investigative work which has been under way for several years. There has been a slight decrease in reforestation experiments and a greater attention to fire protection and excessive erosion. A study is being made of chmatic conditions and the moisture of the forest fitter in connection with the danger of fires; and of the influence of vegetation, topography, wind and other factors on the spread of fires. Added to the injury which erosion inflicts upon the forest itself is the further harm that comes from the silting up of reservoirs and irrigation canals, which are usually fed from National Forests. Both remedial and pre- ventive measm'es are being taken to reduce erosion, particularly by the proper control of grazing. Some very definite results have now been secured for the guidance of work in planting and reforestation. For most trees, and in the majority of localities, planting has been found more successful than direct seeding. It has also been found that seeds produced in a given locality are better for use in that place than seeds imported from elsewhere. All phases of nursery practice, including selection, planting and germination of seeds, treatment of seedlings, and transplanting have now been placed on a thoroughly scientific basis, and it is possible to plant certain well studied trees with assurance of high percentages of &urvival. The study of the climatic conditions in various forests types is now being pursued at all of the Forest Experi- ment Stations, receiving the most attention at 12 localities in the central Rocky Mountain region in the vicinity of the Fremont Experiment Station. Atmospheric and soil temperature, soil moisture and pre- cipitation are being observed at aU of the stations, and evaporation, wind velocity, and sunshine at some of them. Great interest will attach to the results of this work, from which it will be possible to learn the chmatic requirements of some of the leading types of natural vegeta- tion in the western states. The investigations mentioned, and numer- ous minor ones which are reported, show that the Investigative Office of the Forest Service is engaged in work which combines the greatest practicality and national importance with a high degree of scientific 192 NOTES AND COMMENT 193 value. Through no other agency will be able to learn so much about the ecology of forest trees and the nature of the conditions in our di- versified forest areas. Mr. C. R. Tillotson has recently prepared a pamphlet on Nursery Practice on the National Forests (Department of Agricultme, Bull. No. 479), which contains a very full account of the methods by which seedling trees are produced, cared for, and transplanted in the nurseries of Nebraska, Idaho, Washington, and California. The Agricultm-al Experiment Station of Colorado has i.ssued a bul- letin on the Native Vegetation and Climate of Colorado in their Rela- tion to Agi-iculture, prepared by Prof. Wilfred W. Robbins. The avail- able temperatine and precipitation data have been assembled, digested and discussed in their relation to vegetation and crop possibilities. Maps are given showing the distribution of mean summer temperatures, aver- age length of frostless season, average date of last spring frost, and mean annual precipitation. After describing the climatic conditions for the state as a whole the author treats each of the vegetational regions in greater detail. The ten stations in the yellow pine forest region vary in mean annual precipitation from 14.79 inches at the dryest to 24.36 inches at the wettest. The growing season is shown to receive approximately half of this amount. The eleven stations in the sagebrush shrub-steppe vary in precipitation from 7.94 inches to 18.69 inches. Similar illumi- nating comparisons are made between the temperatm*e conditions of these and other areas. In the discussion of climatic details and their relation to agricultural plants the author shows great familiarity with his state and with the problem? under investigation. The large number of workers who will be interested in Professor Robbins' very compact bulletin will have a suspicion that he could have written one five times as thick without exhausting his data or the diversities of his state and its problems. An important contribution to West Indian taxonomy has been made by Dr. Otto E. Jennings, who has published a list of the plants collected by himself and others in the Isle of Pines, and now contained in the herbarium of the Carnegie Museum. A very brief description of the vegetation of the island shows two of its important formations to be pine barren and open forest of slash pine, bearing considerable resemblance to the adjacent barrens of the province of Pinar del Rio in Cuba. 194 NOTES AND COMMENT Prof. W. F. Ganong has contributed to the Smith Ahimnae Quarterly an article describing the botanical equipment and curriculum of Smith College. The well known high standards which are maintained by Professor Ganong and his associates in the botanical department of this college give to all teaching botanists an interest in the equipment and methods which are there in use. THE REVEGETATION OF TAAL VOLCANO, PHILIP-/^''^ '^•^ PINE ISLANDS FRANK C. GATES Carthage College, Carthage, Illinois On January 30, 1911, culminated the last severely destructive eruption of Taal Volcano, of which Dean C. Worcester's de- scription may be found in the April, 1912, number of the Na- tional Geographic Magazine. This eruption entirely destroyed all the \dllages on the island as well as some of those on the mainland, with the loss of about 1400 lives. Ashes, pumice, small stones, and acid vapors were spread over the island and thrown across the lake to the mainland, devastating the coun- try to the west and southwest of the volcano. Ashes were in addition thrown over large areas of surrounding country, re- sulting in the defoliation of the vegetation not otherwise affected. The volcano was left bare of plants. It did not long remain plantless, however, as the following account of the pertinent facts of its revegetation up to March, 1915, will indicate.^ The volcano is a low mountain (304 meters) situated in a lake, known as Taal Lake or Lake Bombon, in Batangas Province, about 63 km. south of Manila, Luzon Island, P. I. The surface of the island is very rugged, due to the very active erosion brought about by the heavy tropical rains, 1750 to 2000 mm., which run off the steep slopes of the volcano with great rapidity. The active crater is in the center of the island. It is about 2,3 km. long and 1.7 km. wide at the top. More than half of the bottom is occupied by a lake, whose elevation is about 2.5 meters above sea level — the same as that of the surrounding Lake Bombon. 1 For a more detailed account, including an annotated list of the plants found on the volcano up to April, 1914, see Gates, F. C. "The Pioneer Vegetation of Taal Volcano." Philippine Jour, of Science, 9, Sect. 0:391-434, 1914, with plates III to X. 195 THE PLANT WORLD, VOL. 20, NO. 7 JULY, 1917 196 FRANK C. GATES The water of the crater lake is clear, although dark-colored, and salty. Its. temperature decreased from about 37°C. in October, 1913, to about 32° in April, 191^, after which it began to in- crease. By March, 1915, it had reached 39° and a noticeable amount of steam was rising from the lake for the first time in my experience. Swimming in the crater lake, although much like salt water bathing, was, of course, much more exciting. In April, 1914, a little steam had been noted coming from vents in the north crater wall and from a few places along the shore of the lake. By March, 1915, a number of bubbling centers had developed, particularly in the southern half of the lake, more steam was issuing from the vents previously noted, and several additional vents had come into existence. From the first, sulfurous vapors were noticed from certain points in the crater rim, but none were detected in the bottom of the crater until March, 1915. Steep precipitous walls form the boundary of the crater on all sides. The crater rim is highest on the south and north sides, with altitudes of 304 and 230 meters, respec- tively, and lowest to the west, where it is but 95 meters high. Previous to the eruption of 1911, the region outside of the crater was vegetated from the strand to the rim of the crater. The vegetation could be briefly summed up as trees, parang (thickets), grassland and culture in various combinations. Some trees over 75 cm. in diameter were present even on the crater slope. Within the crater a tree of Ficus indica was present, A number of barrios (\dllages) were located along the shore of Lake Bombon, particularly in the northern part of the island and in their vicinity a few cultivated plants have since been found. While parts of a very few plants in certain well protected situations on the far sides of Mounts Bignay, Ragatan, Binin- tiang Malaki, and Balantoc did survive the rain of acid ash and mud and the mechanical violence of the eruption, vegetation over the rest of the island was entirely destroyed. No vegeta- tion appeared until rains leached the acid out of the soil. Except for sparing and very local regeneration in the areas mentioned above, no vegetation appeared in the first rainy ^j> ^ 0 t> P 5 33 0 "^ ■^ 03 a) ^ m j3 7-H tc ,^ 1— t c3 o" o u 1 O o (M -t^ 0" 0 3 < o" JS 0 CO 1-H 05 s ;h 0 "o -2 15 0 tH 0 0 S 0 to o -*-- c5 'd a S 2 _o ■^ "p 0 "3 to ^2 > .2 Si > 0 0 -^ S § ^ c V '"C '■*J ^ o s > 0 c :3 0 -*-i S ^ c -i-j ^ 3 0 0 bC p to > ^ § s bC 0 t3 S P _a3 O 03 0 g 0 1^ cc •- ^ c3 0 bC 0 C a: o CO bC « a a c3 0 --- o C o b£ % 0 bC C 0 0 w' OJ "m c3 0 -t^ C 0^ l-f -^^ ^ 3 bc c 0 e 3 03 03 0 0 03 is o Id s o 02 0) ■ 0 0 -t-j a 0 u a a ^3 '-5 '6 t3 CO O 1} 0 c3 -2 C C 2 [m • 1-4 rt > -1^ o 03 1 a 0 c3 a 0 0 S3 a -^ ^ o CO a: O _3!2 03 o 03 H a "B 0 > aj ;-. , c 0 c3 2 p 0 W ■3 C C p '2 a; 3 -1^ to ^^^ k. ' 0 r^ S bC C3 p 3 > 2 0 'bb p p 0 0 0 0 10 < > si « -C 3 -C3 0 a 0 -, 03 u > O bC iH CO « _ tc "= . :S ^ ^ bC C3 .-H c3 q=l a O o m 03 > 03 u bC hC C 03 u ■*^ cc 3 bC > a> bC (>1 ■>• a; o cc rt -H 03 o3 WO ■ (-. 03 a; u > 03 j^^ s ^ o c W rH =3 j2 5 't; < 3 .2 ^ O O ^^ ^^ bC u CI o 05 ^ a o3 3 >, O o3 5 W - ■ 5i e £2 o <» Si .s -^ £r 3 3 CO o3 bC ^ 3 -^ ZJ rr, ^ &*, ' — * r\ ,— 03 o3 "3w is a^ '^ fe 03 . « Ph -* w ^ « ^ . — 1 3 O O « 03 6 -^e s bc e ts 03 f^ '^ 3 Ss s~ I o O "2 -. 'a 03 e «*; 03 03 ^^§ bC o3 3 o; "13 o O .3 c3 -3 ,3 03 (M O : ^ bC S P3 03 o cc 00-=. O , , fc< T3 3 c3 cc CO 03 bC d Q W S fe 3 o3 bC C ~* o ^ S e ^ '13 -, regulated by the faucet E. 5 is a smaller glass jar resting on a support C and containing soil in which the experimental plants may be grown at approximately constant soil temperature. F, Control culture jar at room temperature. adopted the simple method illustrated in figure 1, using a single culture jar sunken in a larger receptacle through which cool tap water trickled just rapidly enough to maintam the desired tem- perature. Wishing to secure simultaneously a series of con- stant temperatures we have since expanded this idea, under the supervision of R. E. Hartman, who is investigating the relation of soil temperatures to the development of tobacco and its infection with the root parasite Thielavia hasicola. The essen- tial method is illustrated in figure 2. In this way, Hartman has maintained fairly constant temperatures at points between SOIL TEMPERATURES IN PHYTOPATHOLOGY 235 Fig. 2. Graduated temperature tank. This is installed on a greenhouse bench. It has 12 compartments {1-12), each of which can be held at a different constant temperature. Cold water flows into compartment 1 at A through a constant pressure valve. About one-fourth of the intake water is allowed to pass into compartment 2 through the hole B which is 2 inches below the top of the partition and another hole 8 inches below B (not shown in diagram). About I overflows through the waste pipe C. The water passes similarly from com- partment 2 to 3, and from 3 io Jf. with gradually elevated temperatures until in compartment 5 the temperature approximates that of the greenhouse. Com- partments 6-12 are for graduated temperatures above that of the greenhouse. In these the water is static, the higher temperatures being regulated by four devices: first, an asbestos cover D; second, electric heating bulbs E; third, live steam pipes F; fourth, the regular steam heating system of the greenhouse of which the pipes at G lie as close as possible under compartment 12 and slope to a distance of 9 inches from the bottom of compartment 1 at G' . In addition a sheet of asbestos H is laid on the pipes at this lower end to check the radiation. Each compartment has a drain cock J . At lower left corner is sectional view to show detail of wall construction: K, 1 inch board; L, 1^ inch hair-felt; M, galvanized iron lining. By proper regulation and manipulation during the past winter it has been possible to hold each compartment within a fluctuation of about 1° at tem- peratures as follows: compartment 1, o°C.; 2, 9°; 3, 13°; i, 16°; 5, 19°; 6, 21°; 7, 23°; 8, 26°; 9, 29°; 10, 32°; 11, 36°; 12, 40°. In each compartment were sunk 4 battery jars (/) filled with soil for the culture of the experimental plants essen- tially as illustrated in figure 1. 236 L. R. JONES 5° and 40°C. He will publish the final outcome later, but the results to date show that this method will yield data ol much interest to the physiologist as well as the pathologist. The satisfactory interpretation and practical application of such results is, however, dependent upon securing reliable and comparable field data over a wide range of territory, north, south, east and west. We, as phytopathologists, should therefore be ready to cooperate in any way practicable in the soil temperature survey which is being organized under the leadership of the Ecological Society of America. It should be a further stimulus in this endeavor that Russian plant pathologists have already inaugurated plans for a similar survey in their territory (21) and possibly international cooperation may follow any success in such national undertakings. LITERATURE CITED (1) Smith, E. F. Bacteria in relation to plant diseases 2: 36, et seq. 1911. (2) Jones, L. R. and Oilman, J. C. The control of cabbage yellows through disease resistance. Wis. Agr. Exp. Sta. Res. Bui. 38. 1915. (3) Livingston, B. E. Physiological temperature indices for the study of plant growth in relation to climatic conditions. Physiol. Researches 1:399. 1916. (4) Oilman, J. C. Cabbage yellows and the relation of temperature to its occurrence. Ann. Mo. Bot. Gard. 3: 1916. (5) TisDALE, W. H. Relation of soil temperature to infection of flax by Fu- sarium lini. Phytopathology 6: 412. 1916. (6) Orton, W. a. Environmental influences in the pathology of Solanum tuberosum. Jour. Wash. Acad. Sci. 3: 180. 1913. (7) Orton, W. A. Potato wilt, leaf roll and related diseases. U. S. Dept. Agr. Bui. 64. 1914. (8) Link, O. K. K. A physiological study of two strains of Fusarium in their causal relation to tuber rot and wilt of potato. Bot. Oaz. 52: 169. 1916. (9) Humphrey, H. B. Studies on the relation of certain species of Fusarium to the tomato blight of the Pacific Northwest. Wash. Agr. Exp. Sta. Bui. 115. 1914. (10) Jones, L. R. The damping off of coniferous seedlings. Vt. Agr. Exp. Sta. Rept. 20: 342. 1908. (11) GiFFORD, C. M. The damping off of coniferous seedlings. Vt. Agr. Exp. Sta. Bui. 157. 1911. (12) WoLLENWEBER, H. W. Pilzparasitc Wilkekrankheiten der Kulturpflanzen. Ber. d. deut. bot. Gesell. 31: 17. 1913. SOIL TEMPERATURES IN PHYTOPATHOLOGY 237 (13) Hecke, L. Der Einfluss von Sorte und Temperatur auf dem Steinbrandbe- fall. Zeitschr. f. Landw. Versuchsw. Oesterr. 12: 46. 1909. (14) MuNEBATi, O. Sulla recettivita del frumento per la carie in rapperto al lempo di semina. Atti r. Accad. Lincei Rendic. 21: 875. 1912. (15) Heald, F. D. and Woolman, H. M. Bunt or stinking smut of wheat. Wash. Agr. Exp. Sta. Bui. 126. 1915. (16) Jones, L. R. Some observations regarding oat smut. Vt. Agr. Exp. Sta. Rpt.9:106. 1895. (17) Brefeld, O. Untersuchungen a. d. Gesamtgebiete der Mykologie. 11: 1895. (18) TuBEUF, C. F. VON. Studien u. d. Brandkrankheiten d. Getreides u. ihre Bekampfung. Arb. Biol. Abt. f. Land. u. Forst. k. Gsndhtsamt. 2: 179.' 1901. (19) Balls, W. L. Temperature and growth. Ann. Bot. 22: 557. 1908. (20) Jones, L. R. Disease resistance of potato. U. S. Dept. Agr. Bur. PI. Ind. Bui. 87: 14. 1905. (21) DoROGiN, G. I. Materiale po mikologhi i fitopatologhii Rossii. 1: 3. 1915. (See abst. in Internat. Rev. Sci. and Pract. Agric. 7: 608. 1916.) THE BEGINNINGS AND PHYSICAL BASIS OF PARASITISM D. T. MACDOUGAL Desert Laboratory of the Carnegie Institution, Tucson, Arizona A series of experiments for the purpose of determining the major conditions under which one seed-plant, ordinarily auto- phytic, might become parasitic upon another were begun at the Desert Laboratory in 1908. The method of making the prepara- tions, the behavior of the xeno-parasites, and the absorbent relations of the enforced host and experimental parasite have been described by the author in various papers. ^ In addition to the experimental tests several cases have been encountered in the field work from the Desert Laboratory in which Opuntias were seen established on Parkinsonia, Acacia and Carnegiea -wdth the roots in nutritive contact with the tissues of the supporting plant and under such conditions that the sole supply of solution must have been received from the newly-found host. An instance of this kind was encountered on March 15, 1913 when a field party found a sahuaro 57 miles southwest of the Desert Laboratory bearing near its summit an Opuntia, which was in all certainty Opuntia Blakeana, (probably equivalent to 0. phaeacantha) . During the course of cutting down the tree cactus for an examination of the relations of the two plants, a Papago Indian came up and showed the author the same species in the soil nearby, and he gave the native name as "e'epa." It is identical with the Opuntia which has been found on Carnegiea m another instance. The tree cactus was about 20 feet in height and bore two large lateral branches, while a third had been broken off near 1 See MacDougal, D. T., Induced and Occasional Parasitism. Bull. Torr. Bot. Club. 38:471. 1911. An Attempted Analysis of Parasitism. Bot. Gaz. 52, 249, 1911. 238 THE PHYSICAL BASIS OF PARASITISM 239 the summit of the tmnk. A cavity had been formed in the trunk in the sinus formed by a branch, and this was heavily Uned with callus and had a capacity of about a liter. The tangled mass of roots of the prickly pear completely filled the cavity holding together a compact mass of organic matter de- rived partly from the original tissue now decayed. Near one side of the root-mass, however, an active, strongly-growing whitish root a few millimeters in diameter had pushed through the callus walls and dowTi into a crevice of the live cells of the Carnegiea. Its branches were spread out and were apphed to the pale tissues of the host although no mechanical adhesion of any consequence was detected. It was clear however that some degree of absorption would be possible, and the appear- ance of rapid growth on the part of the Opuntia was one which could result only from a supply of material. The case was one of undoubted parasitivsm, and moreover the dependent in this case had been in this position for an extended period since the clump of roots was heavy and seven main stems of the cylindrical form characteristic of the basal part of the plant were found, each of which had at times produced flattened joints. Some were now in a shrivelled condition and doubtless many had been formed in the previous years for which an adequate supply of solution was not available and they had been cast off. Dr. W. B. MacCallum has recently discovered a similar case of parasitism of an Opuntia on a sahuaro on the lands of the company engaged in guayule culture at Continental, 30 miles south of Tucson. An Opuntia with many joints was established in the angle formed by a branch and the main stem. As the parasite was not more than 2 meters from the ground it could be readily photographed and examined. It was not disturbed, how- ever. All of the tree cacti here had been bored by the "car- pinteros" or woodpeckers, and it is probable that the seed from which this plant originated had been deposited in a cavity made by these birds (see fig. 1). The sahuaro, which had an age of nearly two centuries, stood in the rectangular mass of stones supposedly marking a prehistoric human grave. 240 D. T. MACDOUGAL These occurrences raise interest in the relative conditions which must prevail in two plants so that one becomes parasitic on the other. The earlier experimental studies of the author led him Fig. 1. Sahuaro {Carnegiea giganlea) growing on prehistoric human grave near Continental, Arizona. Opuntia growing as a parasite in axis of lowermost branch. to conclude that a necessary condition of parasitism wa.s a higher osmotic concentration of the species which could become parasitic. THE PHYSICAL BASIS OF PARASITISM 241 Harris and Lawrence have carried out an extensive investi- gation of the problem on Loranthaceous parasites in the Jamai- can rain forests, and in a paper now in press have shown that in case of plants growing under these conditions the parasite is generally but not invariably characterized by a higher osmotic concentration of its fluids. They also show that on theoretical grounds- higher osmotic pressure of the tissue fluids is not a necessary prerequisite of successful parasitism in the case of a species living under natural conditions. - That the absorbing organs of a plant might withdraw liquids from tissues of another plant, the sap of which had a higher con- centration, is also to be concluded from the results of recent work on imbibitional phenomena at the Desert Laboratory. Extended series of measurements established the fact that a mixture consisting of 90% or more of agar and 10% or less of protein, albumen, gelatine, tyi'osin or cystin, takes up water in a manner remarkably parallel to that of pieces of tissue of living plants. This similarity is regarded as more than a coincidence. The plant protoplast consists largely of carbohy- drates of the pentosan group, with which are mixed varying proportions of nitrogenous material w^hich may be in the form of protein, amino-acids, etc. Such a mixture would have identi- cal relations to w^ater either as sw^elling plates in the labora- tory, or as water-absorbing sheets or strands of colloid in the cell. A number of agencies or conditions are found to affect the total amount of water which may be taken up by this "plant- colloid " mixture. Thus, for example, nearly all of such mix- tures absorb slightly more water in acidified solutions than in alkaline, and many times as much from neutral as from either acid or alkaline solutions. Some salts in the solution increase imbibition and some lessen it. These generalizations rest upon measurements made by the following method : Small sections of dried plates of a mixture of "plant-colloids " were placed in trios in glass dishes into which 2 Report Dept. Bot. Res. Carnegie Inst, of Washington for 1916, pp. 79 and 80. 242 D. T. MACDOUGAL various solutions might be poured. Triangular pieces of thin glass were laid on these pieces. The swinging vertical arm of an auxograph rested in a socket in the middle of this plate. When the entire preparation was in readiness and the pen at the other end of the compound lever was marking properly on the ruled paper of a revolvmg cylinder, the solution was poured into the dish. The rate, course and amount of expansion was recorded by an inked line. (See Mem. N. Y. Botan. Garden, 6, pp. 5-26, 1916, for a description of instrument.) A mixture of agar 90 parts and glycocoll 10 parts gave the following swelling coefficients: DISTILLED WATER HUNDREDTH NORM.\L HYDROCHLORIC ACID HUNDREDTH NORMAL SODIUM HYDRATE per cent 2800 per cent 1000 per cent 500 A cell which reacted as did these plates of "plant-colloid" would be notably affected by acidity or alkalinity, especially in the imbibition of water from protoplasts with which it might be in contact. Acidity and alkalinity are conditions encountered very nearly all the time in the cell, but these are not the only factors affect- ing imbibition. Salts, especially of potassium and calcium, are practically always in solution in cell sap. It is customary to say that some salts increase the swelling power of gels, but most of such assertions rest upon the results of experiments with gelatine. Mixtures of agar and any protein substance swell less in any salt solution than in distilled water. The swelling of a mix- ture of 90 parts agar and 10 parts glycocoll in salts is illustrated by the figures in table 1. "V^Tien plant-colloids are affected in this differential manner by acids, alkalies and salts, it is ob\dous without further citation of experimental results that these and other features may play a part in the possibilities of parasitism. Combinations are THE PHYSICAL BASIS OF PARASITISM 243 TABLE 1 ■ Swelling of mixtures of protein and agar WATER HUNDREDTH MOLECULAR FIFTIETH MOLECULAR TENTH MOLECULAR Potassium nitrate per cent 3266 per cent 1800 per cent 1733 per cent 1333 Calcixim nitrate 1333 1200 800 possible which may cause water absorption in great volume independently of osmosis and in fact in opposition to it.^ The penetration of a host by the haustorimn of a parasite is not to be regarded as conditioned by the simple osmotic balance between two tracts of cells of equivalent physical condition. The invaded tracts of the host are usually composed of expanded vacuolated cells in which osmosis resulting from the solutions in the vacuoles is the dominant hydrostatic agent, although the colloids suspended in these vacuoles, and the denser colloids of the cytoplasm have their own imbibitional capacities. The younger cells of the haustorium which push into such masses are probably not yet vacuolated. Absorption by them is almost wholly by imbibition and this would be carried on against any probable osmotic action of a vacuolated cell. Thus a thin plate of "plant colloid " mixture absorbed water from a solution of potassiimi nitrate which had an osmotic coefficient of 60 atmospheres, and swelled about 400% in volume in fifteen hours. A second feature, the force of expansion of the invading proto- plasts, would be no less important. The pressure set up, like that of a swelling seed, would be great enough to cause me- 3 See MacDougal, D. T. Imbibitional Swelling of Plants and Colloidal Mix- tures. Science, N. S., 44: 502-505, October 6, 1916. Also, MacDougal, D. T. and Spoehr, H. A. The Behavior of Certain Gels Useful in the Interpretation of the Action of Plants. Science, N. S. 45: 484^S8, 1916. 244 D. T. MACDOUGAL chanical penetration of the host, as it would be far greater than any force attributable to osmotic action. After the haustorial development has carried that organ to a mature stage the nutritive contact with the host is one in which osmosis doubtless plays an important part. The proportion of nitrogenous substance in the parasite, the acidity, and the con- centration of salts might be the determining factors m both the making and maintenance of a nutritive couple of host and parasite. AN ENUMERATION OF THE PTERIDOPHYTES AND SFERMATOPHYTES OF THE SAN BERNARDINO MOU:s TAINS, CALIFORNIA S. B. PARISH San Bernardino, California CACTACEAE Cereus (Echinocereus) mohavensis E. & B. Pac. R. Rep. 4: 33 t. 4, f. 8. In dense caespitose masses on rocky or stone steeps in canons of the Pinon Zone. Cushenberry Canon. Green Lead. In smaller clusters on ridges in Bear Valley. Opuntia Covillei Britton & Rose, Smiths. Misc. Coll. 50, pt. 4: 332. (?) On the rocky shores of Baldwin Lake, Bear Valley. Mill Creek Canon near Forest Home. Seven Oaks. AH these stations are in the Upper Transi- tion Zone, but the species is of the arid mesas of San Bernardino Valley, and the reference is unsatisfactory. ONAGRACEAE Zauschneria calif ornica Presl. Rel. Haenk. 2: 28, fc. 52. Frequent on dry or stony banks in the Upper Chaparral and Lower Transi- tion Zones. Chamaenerion angusti folium Scop. Fl. Car. ed. 2, 1: 27L Occasional along streams in the Upper Transition and Canadian Zones. Epilobium adenocaulon Hausskn. Oesterr. Bot. Zeit. 29: 119. In meadows in the Transition Zone. Epilobium anagallidifolium Lam. Diet. 2: 376. In a meadow, Bluff Lake. Epilobium glaberrimiim Barbey, in Brew. & Wats. Bot. Cal. 1: 220. Frequent in moderately dry soil in the Transition Zone. Epilobium paniculattim Nutt.; T. & G. Fl. 1: 490. Frequent in the Transition Zone. Epilobium ursinum Parish; Trel. Rept. IVIo. Bot. Gard. 2: 100. Frequent in wet meadows in the Transition Zone. Gayophytum pumilum Wats. Proc. Am. Acad. 18: 193. Occasional in dry meadows in the Lower Transition Zone. Gayophytum. ramosissimum T. & G. Fl. 1: 513. Frequent on flats in the Lower Transition Zone. Oenothera (Sphaerostigma) bistorta Nutt.; T. & G. Fl. 1: 508. Frequent in canons in the Chaparral Zone. 245 THE PLANT WORLD, VOL. 20, NO. 8 246 S. B. PARISH Oenothera bistorta Nutt. var. Reedii Parish, comb. mov. Sphaerostigma bistorta Walp. var. Reedii Parish, Muhl. 3: 107. Occasional on dry hills in the Chaparral Zone. Oenothera (Pachylophusa) caespitosa Nutt.; Fras. Cat. Rare, Cushenberry Canon in the Piiion Zone. Oenothera (Anogra) californica Wats, in Brew. & Wats. Bot Cal. 1: 228. Occasional on hillsides in Bear Valley. Oenothera (Onagra) Hookeri T. & G. Fl. 1: 493. Occasional in meadows and by streams in the Transition Zone. Oenothera (Eulobus) leptocarpa Greene, Pitt. 1: 302. Frequent in dry soil in the Lower Chaparral Zone. Oenothera (Sphaerostigma) strigulosa T. & G. Fl. 1: 512. Frequent in dry soil in the Lower Chaparral Zone. Godetia Bottae Spach, Monog. Onagr. 73. Abundant in canons in the Lower Chaparral Zone. Godetia quadrivulnera Spach, Monog. Onagr. 69. Frequent in canons in the Lower Chaparral Zone. Clarkia rhomboidea Dougl.; Hook. Fl. Bor. Am. 1: 214. Frequent in moist soil in the Upper Chaparral and Lower Transition Zones. Clarkia xantiana Gray, Proc. Bost. Soc. Nat. Hist. 7: 145. Rare. Bluff Lake, Miss Hnchinson. Boisduvalia Douglasii Spach, Monog. Onagr. 80, t. 31, f. 2. Occasional in meadows in the Lower Transition Zone. Heterogaura californica Rothr. Proc. Am. Acad. 6: 354. Frequent on shady banks in the Lower Transition Zone. Circaea pacifica Aschers. & Mag. Bot. Zeit. 29: 392. Occasional in damp thickets in the Lower Transition Zone. ■ HALOKRHAGIDACEAE Hippurus vulgaris Linn. Sp. PI. 4. In shallow water, Bear Valley. Myriophyllum spicatiim Linn. Sp. PL 992. Abundant in Bear Valley Reservoir. ARALIACEAE Aralia californica Wats. Proc. Am. Acad. 11: 114. On the borders of streams in shady places in the Upper Transition Zone. TTMBELLIFERAE Hydrocotyle umbellata Linn. Sp. PI. 1: 234. Seven Oaks, Grant. A common species in San Bernardino Valley. Sanicula nevadensis Wats. Proc. Am. Acad. 11: 139. Occasional on open pine ridges in the Lower Transition Zone. Sanicula Menziesii H. & A. Bot. Beechey 142. Frequent on shady banks in the canons of the Lower Chaparral Zone. PLANTS OF THE SAN BERNARDINO MOUNTAINS 247 Osmorhiza brachypoda Torr. Jour. Philad. Acad. n. ser. 3: 89. Frequent on shady banks of the canons of the Lower Chaparral Zone. Osmorrhiza nuda Torr. Pac. R. Rept. 4, 93. Occasional on shady banks in canons of the Lower Chaparral Zone. Deweya arguta T. & G. Fl. 1: 641. Frequent on rocky hillsides in the Chaparral Zone. Drudeophytum Parishii C. & R. Contr. Nat. Herb. 7: 82. Frequent on rocky hillsides in Cush^nberry Canon, in the Pinon Zone, and occasional in the Lower Transition Zone. Drudeophytum vestitum C. & R. Contr. Nat. Herb. 7: 83. Infrequent on stony hills. Bear Valley . To be expected at higher altitudes. Eulophus Parishii C. & R. Rev. Umbell. 112. Abundant on pine flats and in dry meadows in Bear Valley, and occasional elsewhere in the Upper Transition Zone. Sphaenosciadium eryngii folium C. & R. Contr. Nat. Herb. 7: 128. Occasional by stream banks in the Upper Transition Zone. Angelica tomentosa Wats. Proc. Am. Acad. 11: 141. Frequent on stream banks in the Upper Chaparral and Transition Zones. Leptotenia multifida Nutt.; T. & G. Fl. 1: 630. Infrequent on dry hills in the Chaparral Zone. Cogswellia Parishii C. & R. Contr. Nat. Herb. 12: 450. Frequent on stony hillsides in Bear Valley. Euryptera lucida Nutt.; T. & G. Fl. 1: 629. Rather rare in dry soil in the Lower Chaparral Zone. Heracleum lanatum Linn. Sp. PI. 249. Frequent on stream banks in the Upper Chaparral and Transition Zones. CORNACEAE Cornus californica C. A. Mey. Bull. Phys.-Math. Acad. Petersb. 3: 372. Frequent along stream banks in the Lower Transition Zone. Cornus NuUallii Audubon; T. & G. Fl. 1: 625. Dogwood. Frequent near streams in the Lower Transition Zone. Garrya pallida Eastw. Bot. Gaz. 36: 460. Mill Creek canon, in the Upper Transition Zone. Garrya Veatchii Kellogg, var. Palmeri Eastw. Bot. Gaz. 36: 458. Occasional on dry hills and in washes in the Lower Chaparral and Lower Pinon Zones. MONOTROPACEAE Pterospora andromedea Nutt. Gen. 1: 269. Frequent in pine forest in the Transition and Canadian Zones. Sarcodes sanguinea Torr. PI. Frem. 17, t. 10. Snow Plant. Frequent in open pine forest in the Transition and Canadian Zones. PYROLACEAE Chimaphila Menziesii Spreng. Syst. 2: 317. Rare in the Upper Transition Zone. Mill Creek Falls and Snow Canon. 248 S. B. PAPISH Pyrola aphylla Smith; Hook. Fl. Bor. Am. 2: 48, t. 137. Occasional in pine forest in the Transition Zone. Pyrola picta Smith var. pallida Parish, comb. nov. P. pallida Greene, Pitt. 4: 39. Whitewater Basin, Upper Transition Zone, Mrs. Wilder. ERICACEAE Bryanthus Breweri Gray, Proc. Am. Acad. 7: 367. San Gorgonio Mountain, in the Canadian Zone, Wright. Arctostaphylos glauca Lindl. Bot. Reg. 21, t. 179. Frequent on dry hillsides in the Upper Chaparral and Lower Transition Zones. Arctostaphylos patida Greene, Pitt. 2: 171. Frequent on hillsides in the Upper Transition Zone. Arctostaphylos Pringlei var. drupacea Parry, Bull. Cal. Acad. 2: 494. Occasional in canons of the Transition Zone. Arctostaphylos pungens HBK. Nov. Gen. & Sp. 3: 278, t. 259. Occasional on hillsides in the Upper Transition Zone. Arctostaphylos tomentosa Dougl. Bot. Reg. 21, t. 7911. Occasional on hillsides in the Upper Chaparral and Lower Transition Zones. PRIMULACEAE Dodecatheon alpinutn Greene, Eryth. 3: 39. Frequent on stream banks at Bluff Lake. Androsace septentrionalis Linn. var. subidifera Gray, Synop. Fl. 2, pt. 1: 69. San Gorgonio Mountains, Hall 764^, in hb. Univ. Cal. STYRACACEAE Styrax californica Torr. Smith. Contr. 6: 4. Abundant on caiion sides in the Chaparral Zone. OLEACEAB Fraxinus dipetala H. & A. Bot. Beech. 362, t. 87. Mill Creek Caiion, in the Lower Chaparral Zone. Fraxinus coriacea Wats. Am. Natur. 7: 30. Cleghorn Canon, ace. Abrams in Bull. N. Y. Bot. Gard. 6: 436. GENTIANACEAE Gentiana acuta Michx. Fl. 1: 177. Occasional on damp banks in the Upper Transition and Canadian Zones. Gentiana detonsa Rottb. Act. Hafn. 10: 254, t. 1. Locally abundant in wet meadows near Knight's Camp, Bear Valley. Gentiana humilis Stev. Act. Mosq. 3: 258. G. viridula Parish, Bot. Gaz. 38: 461. On the borders of a stream. South Fork of Santa Ana River, in the Canadian Zone, Mrs. Wilder. PLANTS OF THE SAN BERNARDINO MOUNTAINS 249 Gentiana simplex Gray, Proc. Am. Acad. 6: 87, t. 16. Occasional in meadows in the Transition and Canadian Zones. Frasera neglecta Hall, Bot. Gaz. 31: 388. Frequent on open forested flats and hillsides in Upper Holcomb Valley. APOCYNACEAE Amsonia brevifolia Gray, Proc. Am. Acad. 12: 64. In dry soil at Cactus Flat in the Pifion Zone. Amsonia tomentosa Torr. Frem. 2d Rept. 316. Growing with the foregoing species. Apocynum androsaemifolium Linn. Sp. PI. 213. Frequent in rocky places in the Transition Zone. ASCLEPIADACEAE Asclepias eriocarpa Benth. PI. Hartw. 323. Occasional in dry soil in the Lower Transition Zone. Asclepias mexicana Cav. Ic. 1: 42, t. 58. Infrequent in damp soil in the Lower Chaparral Zone. CONVOLVULACEAE Convolvxdus occidentalis Gray, Proc. Am. Acad. 11: 89. Occasional among bushes in the Lower Chaparral Zone. Convolvulus luteolus var. Julcratus Gray, Proc. Am. Acad. 11: 90. Occasional on dry open slopes in the Lower Transition Zone. Cuscuta californica Choisy, Cusc. 183. Very abundant, infesting shrubs, on dry hills in the Lower Chaparral Zone. POLEMONIACEAE Polemonium coeruleum Linn. Sp. PI. 162. Bear Valley, Hall and L^pper Meadows on the South Fork of Santa Ana River, Mrs. Wilder, in each instance only a single plant. Collomia grandifiora Dougl.; Lindl. Bot. Reg. 14, t. 1166. Frequent in open pine forest in the Transition Zone. Collomia heterophylla Hook. Bot. Mag. 56, t. 2895. Frequent on dry slopes in the Lower Chaparral Zone. Collomia linearis Nutt. Gen. 1: 126. In meadows. Bear Valley. Phlox austromontana Coville, Contr. Nat. Herb. 4: 151. In dense mats, in dry soil, at the upper end of Bear Valley. Phlox dolichantha Gray, Proc. Am. Acad. 22: 310. Common in open pine forest in Bear Valley. Gilia achilleifolia Benth. Bot. Reg. 19: t. 1622. Common on sheltered banks in canons of the Lower Chaparral Zone. Gilia californica Benth.; DC. Prodr. 9: 316. Abundant on dry banks in the Lower Chaparral Zone. 250 S. B. PAKISH Gilia ciliaia Benth. PI. Hartw. 325. Common on dry banks in the Lowe'* -Chaparral Zone. Gilia dichotoma Benth. DC. Prodr. 9: 314. A desert species found scantily in the canon of City Creek in the Lower Chaparral Zone. Gilia latiflora Gray, Synop. FI. 2, pt. 1: 147. Rare, Mill Creek, in the Lower Chaparral Zone. Gilia leptantha Parish, Zoe 5: 74. Seven Oaks, Transition Zone (type), Grout. Gilia liniflora Benth. var. pharnacioides Gray, Proc. Am. Acad. 8: 363. Frequent in dry soil in the Lower Chaparral Zone. Gilia montayia Parish, comb. nov. Linanthus montanus Greene, Eryth. 3: 120. Frequent on dry slopes in the Transition Zone. Gilia Nuttallii Gray, Proc. Am. Acad. 8: 267. In rocky soil on the mountain side above Seven Oaks. Gilia pungens Benth. var. Hookeri Gray, Proc. Am. Acad. 8: 268. Occasional in rocky places in the LTpper Transition and Canadian Zones. Gilia pungens Benth. var. tenuiloba Millik. LTniv. Cal. Publ. Bot. 2: 41. Occasional in rocky places in the Upper Transition and Canadian Zones. Gilia suhalpina Brand, Pflanzenr. IV, 250: 98. Green Valley, in the Lower Transition Zone, ace. Brand, I. c. Gilia tenui flora Benth. var. altissima Parish, Eryth. 6: 90. Abundant on dry ridges in the Lower Transition Zone, the type region. Navarretia Breweri Greene, Pitt. 1: 137. On dry slopes in Bear Valley; the southern limit of the species. Navarretia densifolia Brand, Pflanzenr. IV, 250: 165. Frequent in coarse dry soil in the Upper Transition Zone. Navarretia virgata Brand, Pflanzer. IV, 250: 167. Abundant in dry soil in the Lower Chaparral Zone. HYDROPHYLLACEAE Ellisia chrysanthemifolia Benth. Trans. Linn. Soc. 17: 274. Occasional in damp shady places in the Lower Chaparral Zone. Meniophila Menziesii H. & A. var. integrifolia Parish, Eryth. 6: 91. Frequent, mostly in shady places, in the Chaparral and Lower Transition Zones. The type was from the head of Waterman Canon. Nemophila sepulta Parish, Eryth. 7: 93. Abundant on rich banks and in meadows in Bear Valley (the type station) and occasional elsewhere in the L^pper Transition Zone. Phacelia brachyloba Gray, Proc. Am. Acad. 10: 324. Occasional, often abundant in burned places, in the canons of the Lower Chaparral Zone. Phacelia curvipes Torr. & Wats. var. pratensis Brand, Univ. Cal. Publ. Bot. 4: 222. Abundant in open pine forest in Bear Valley, and occasional elsewhere in the Transition Zone. Phacelia curvipes Torr. & Wats. var. grandiflora Brand, Pflanzenr. IV, 251: 116. Occasional in dry soil in the Upper Chaparral and Lower Transition Zones. PLANTS OF THE SAN BERNARDINO MOUNTAINS 251 Phacelia distans Benth. Bot. Sulph. 36. Frequent on open hillsides in the Lower Chaparral Zone. Phacelia hispida Gray, Syn. Fl. 2, pt. 1: 161. Frequent on shady hillsides in the Lower Chaparral Zone. Phacelia magellanica Coville f. alpina Brand, Univ. Cal. Publ. Bot. 4: 217. Frequent on dry gravelly hillsides in the Upper Transition Zone. Phacelia magellanica Coville f. egina Brand, Pflanzenr. IV, 251: 218. Green Valley, in the Lower Transition Zone, Hall 1317. Phacelia magellanica Coville f. virgata Brand, LMv. Cal. Publ. 4: 219. Frequent in drj^ soil in canons of the Upper Chaparral Zone. Phacelia mohavensis var. exilis Gray, Synop. Fl. 2, pt. 1 : 165. Frequent in open pine forest in the Transition Zone. Bear Valley is the type station. Phacelia ramosissima Dougl. var. suffrutescens Parry; Gray, Synop. Fl. 2, pt. 1: 416. Frequent on bushy banks in the canons of the Lower Chaparral Zone. Phacelia Whitlavia Gray, Proc. Am. Acad. 10: 322. Occasional on open banks in the Lower Chaparral Zone. Emmenanthe penduliflora Benth. Trans. Linn. Soc. 17: 281. Occasional on banks in the Lower Chaparral Zone. Nama Parryi Gray in Brew. & Wats. Bot. Cal. 1: 621. ' Occasional in dry soil in the Chaparral, Lower Transition and Pinon Zones. Nama Rothrockii Gray in Brew. & Wats. Bot. Cal. 1: 621. Locally abundant on a dry ridge between Holcomb Valley and Green Lead. Hesperochiron californicum Wats. King's Expl. 5: 280, t. 30. Abundant in some damp meadows in Bear Valley, as at the mouth of Grout Creek. Eriodictyon trichocalyx Heller, Muhl. 1: 108. Seven Oaks, Grant, type. BORAGINACEAE Lappula florihunda Greene, Pitt. 2: 182. Frequent in open pine forest and dry meadows in the L'pper Pihon, Upper Transition and Canadian Zones. Allocarya hispidula Greene, Pitt. 1: 17. In meadows at Bear Valley. Oreocarya confertiflora Greene, Pitt. 3: 112. Occasional on dry hillsides in the Pinon Zone. Cushenberry Canon and Rose Mine. Oreocarya suffruticosa Greene var. abortiva Macbr. Proc. Am. Acad. 51: 547. Frequent in dry meadows in Bear Valley, the type station. Eremocarya micrantha Greene var. lepida Macbr. Proc. Am. Acad. 51: 345. ^ Frequent in dry sandy soil in the Transition Zone. *,•■«, Plagiobothrys asper Greene, Pitt. 3: 262. Little Bear Valley in the Lower Transition Zone. * -^ * L I H R A I Plagiobothrys ursimis Gray, Proc. Am. Acad. 20: 285. > '-^V '^Hb^ Frequent in dry meadows in Bear Valley, the type station. V' '.^ 252 S. B. PARISH Cryplanthe horridula Greene, Pitt. 5: 55. "Summit of the dividing ridge between San Bernardino Valley and the Mojave Desert," ace. Greene, I. c. Cryptanthe microstachys Greene, Pitt. 1: 116. Frequent in dry soil in the canons of the Lower Chaparral Zone. VERBENACEAE Verbena prostrata R. Br. Hort. Kew. ed. 2, 4: 41. Occasional in damp soil in the Chaparral Zone. LABIATAE Trichostema micranthutn Gray, Synop. Fl. 2, pt. 1 : 348. Frequent in dry soil in the Transition Zone, the type region. Trichostema Parishii Vasey, Bot. Gaz. 5: 173. Occasional on dry hills in the Lower Chaparral Zone. Mentha arvensis Linn. var. glabrata Fernald in Gray's Man. ed. 7, 711. Frequent in meadows and near streams in the Transition Zone. Mentha rotundifolia Huds. Fl. Angl. 221. Locally established along Waterman Creek, near Vail's. Pycnanthemum californicum Torr. Journ. Acad. Philad. n. s. 2: 99. Occasional in damp soil in canons of the Chaparral Zone. Scutellaria angustifolia Pursh, Fl. 2: 412. Frequent in stony soil and rock crevices in the Transition Zone. Mo7iardella australis Abrams, Muhl, 8: 34. Frequent in dry soil throughout the Transition Zone. Monardella lanceolata Gray, Proc. Am. Acad. 11: 102. Frequent in dry soil in the Chaparral Zone. Monardella linoides Gray. var. striata Parish, Eryth. 7: 96. Frequent on dry hillsides in the LTpper Transition and Canadian Zones. Monardella macrantha Gray var. Hallii Abrams, Muhl. 8: 29. Locally abundant in Mill Creek canon near the quarry, in the Lower Chaparral Zone. Salvia apiana Jeps. Muhl. 3: 144. White Sage. Abundant on dry hillsides and benches in the Lower Chaparral Zone. Salvia mellifera Greene, Bull. Cal. Acad. 1: 236. Black Sage. Abundant on dry hillsides and benches in the Lower Chaparral Zone. Salvia pachystachya Parish, Eryth. 6: 191. Occasional on dry slopes in the Upper Transition Zone. Bear Valley is the type station. Salvia pilosa Merriam, N. A. Fauna 7: 322. Frequent on dry hillsides in the Lower Pinon Zone, the type region. Agastache urticifolia Kuntze, Rev. PI. 511. Locally abundant along streams at Oak Glen and Potato Canon in the Lower Chaparral Zone. Prunella vulgaris Linn. var. lanceolata Fernald, Rhod. 15: 183. Occasional in wet meadows in the Transition Zone. PLANTS OF THE SAN BERNARDINO MOUNTAINS 253 Stachys adjugoides Benth. Linnaea 6: 80. Occasional in wet soil in the Transition Zone. Stachys albens Gray, Proc. Am. Acad. 7: 387. Frequent in damp soil in Bear Valley. SOLANACEAE Nicotiana attenuata Torr. ;Wats. King's Expl. 5: 276. Occasional on dry slopes in the Transition Zone. Solanum Xanti Gray, Proc. Am. Acad. 11: 90. Occasional in open ground in the Chaparral and Transition Zones. Solanum Xanti Gray var. intermedium Parish, Proc. Cal. Acad. ser. 3, 2: 168. Frequent on dry bushy or rocky banks in the Lower Chaparral Zone. SCROPHULARIACEAE Scrophularia caUfornica Cham. Linnaea 2: 585. Occasional in canons in the Lower Chaparral Zone. Collinsia bartsiaefolia Benth. in DC. Prodr. 10: 318. Frequent in canons in the Upper Chaparral Zone. Collinsia Ckildii Parry; Gray in Brew. & Wats. Bot. Cal. 1: 237. Frequent on damp banks in the Transition Zone; the type region. Collinsia grandiflora Dougl. var. pusilla Gray, Syn. Fl. 2, pt. 1 : 256. Abundant in wet sand in Bear Valley. Collinsia Parryi Gray, Syn. Fl. 2, pt. 1: 257. Frequent on damp banks in canons of the Lower Chaparral Zone; the type region. Pentstemon Bridgesii Gray, Proc. Am. Acad. 7: 379. Occasional on hillsides in the Upper Transition Zone. Pentstemon caesius Gray, Proc. Am. Acad. 19: 92. Frequent among rocks above Bear Valley, the type station. Pentstemon cordifolius Benth. in DC. Prodr. 10: 329. Frequent among shrubs in caiions of the Chaparral Zone. Pentstemon Eatoni Gray, Proc. Am. Acad. 8: 395. Occasional in canons in the Lower Pifion Zone. Pentstemon heterophyllus Lindl. Bot. Reg. t. 1899. Occasional on hillsides in the Lower Chaparral Zone. Mill Creek. Pentstemon labrosus Hook. f. Bot. Mag. t. 6738. Abundant in open pine forest in the Lower Transition Zone. Pentstemon Palmeri Gray, Proc. Am. Acad. 7: 378. Common on dry open ridges in the Transition Zone. Pentstemon ternatus Torr. Bot. Mex. Bound. 115. Frequent among shrubs in the canons of the Lower Chaparral Zone. Mimulus cardinalis Dougl.; Lindl. Hort. Trans. 2: 70, t. 3. Frequent on stony stream banks in the Lower Chaparral Zone. Mimulus florihundus Dougl.; Lindl. Bot. Reg. t. 1125. Occasional in damp shady places in the Lower Chaparral Zone. Mimulus (Diplacus) glutinosus Wendl. var. brachypns Gray in Brew. & Wats. Bot. Cal. 1:563. Abundant on canon sides in the Chaparral Zone. 254 S. B. PARISH Mimulus Langsdorfii Don; Sims Bot. Mag. t. 51. Abundant along streams and in wet places in the Chaparral and Transition Zones. Mimulus Langsdorfii Don var. nasulus Jeps. Fl. W. Mid. Cal. 407. Occasional in damp shady places, especially among rocks, in the Chaparral Zone. Mimulus Langsdorfii Don var. Tilingii Greene, Lond. Journ. Bot. 33: 8. Borders of cold springs and streams in the Upper Transition and Canadian Zones. Mimulus moschatus Dougl. var. sessilifolius Gray, Syn. Fl. 2, pt. 1: 447. Frequent on wet banks in the Transition Zone. Mimulus Palmeri Gray, Proc. Am. Acad. 12: 82. Abundant on flats in the Transition Zone. Mimulus exiguus Gray, Proc. Am. Acad. 20: 307. On damp sandy flats. Bear Valley. Bluff Lake. Mimulus priniuloides Benth. Scroph. Ind. 28. Abundant in wet meadows. Bear Valley. Bluff Lake. Mimulus rubellus Gray; Torr. Bot. Mex. Bound. 116. Rare in moist soil in the Transition Zone. Limosella aquatica Linn. Sp. PI. 631. Rare on the muddy banks of shallow ponds. Bear Valley. Bluff Lake. Veronica americana Schwein.; Benth. in DC. Prodr. 10: 468. Abundant in shallow water and along stream banks in Bear Valley. Veronica serpyllifolia Linn. Sp. PI. 12. In swampy places at Bear Valley and Bluff Lake. Casiilleja cinerea Gray, Proc. Am. Acad. 19: 95. Abundant on stony hillsides at the upper end of Bear Valley, the type station. Castilleja foliolosa H. & A. Bot. Beechey 154. Frequent on dry bushy hillsides in the Lower Chaparral Zone. Castilleja linearifolia Benth. in DC. Prodr. 10: 468. Frequent on hillsides in Bear Valley. Castilleja Martini Abrams, Bull. S. Cal. Acad. 1: 69. Frequent on hillsides in the Upper Chaparral and Lower Transition Zones, and occasional in the Pinon Zone. Casiilleja stenantha Gray, Syn. Fl. 2, pt. 1: 295. Occasional in wet meadows in the Chaparral and Transition Zones. Orthocarpus lasiorhynchus Gray, Proc. Am. Acad. 12: 82. Abundant on damp flats in the Transition Zone. Cordylanthus Nevinii Gray, Proc. Am. Acad. 17: 229. Frequent in open pine forest in the Transition Zone, the type region. Ftdicularis semibarbata Gray, Proc. Am. Acad. 7: 385. Abundant in open pine forest in the Transition Zone. OROBANCHACEAE Aphyllon comosum Gray in Brew. & Wats. Bot. Cal. 1: 584. Rare. Bear Valley. PLANTS OF THE SAN BERNARDINO MOUNTAINS 255 Boschniakia strobilacea Gray, Pac. R. Rept. 4: 118. Very rare. San Gorgonio Mountain, in the Hudsonian Zone, Wright. LENTIBULARIACEAE Utricularia vulgaris Linn'. Sp. PI. 18. Abundant, floating in ponds, and now in the reservoir, in Bear Valley. RUBIACEAE Kelloggia galioides Torr. Wilkes Exped. 17: 332, t. 6. Very common in dry rocky places in the Transition Zone. Galium Andrewsii Gray, Proc. Am. Acad. 6: 288. Occasional in dry shady places in the Upper Chaparral Zone. Galium aparine Linn. Sp. PL 108. Occasional in damp shady places in the Lower Chaparral Zone. Galium bifolium Wats. King's Expl. 5: 134, t. 14. Rare. Bear Valley, Davidson. Galium Brandegii Gray, Proc. Am. Acad. 12: 58. Occasional in meadows, Bear Valley and Bluff Lake. Galium midtiflorum Kellogg, Proc. Cal. Acad. 2: 97, t. 26. Frequent on dry stony hills about Bear Valley. Galium, multiflorum Kellogg var. parvifolium Parish, Zoe 5: .54. Frequent on dry stony hills in the Upper Transition and Canadian Zones. Galium trifidum Linn. var. subhiflorum Wiegand, Bull. Torr. Club 24: 399. In wet meadows. Bear Valley; type station. Galium triflorum Michx. Fl. Bor. Am. 1: 80. Frequent along shady stream banks in the Lower Chaparral Zone. CAPRIFOLIACEAE Saynbucus velutinus Dur. & Hilg. Pac. R. Rept. 5: 8. Bear Valley, Hall 1347, in hb. Univ. Cal. Symphoricarpus Parishii Rydb. Bull. Torr. Club 26: 545. Abundant on dry hills in the LTpper Transition and Canadian Zones, type region. Symphoricarpus mollis Nutt.; T. & G. Fl. 2: 13. Frequent in canons of the Chaparral Zone. Lonicera interrupta Benth. PI. Hartw. 313. Rare. Waterman Caiion in the Upper Chaparral Zone. Lonicera subspicata H. & A. Bot. Beech. 349. Frequent among shrubs in the Chaparral Zone. CAMPANULACEAE Specularia biflora Gray, Proc. Am. Acad. 11: 82. Rare in the Transition Zone. Fawnskin Park. Heterocodon rariflorum Nutt. Trans. Am. Phil. Soc. n. ser. 8: 255. Rare in the Transition Zone. Lapraix Mill. 256 S. B. PARISH LOBELIACEAE Lobelia splendens Willd. Hort. Berol. t. 86. Occasional in wet meadows in the Transition Zone. COMPOSITAE Microseris linearifolia Schultz Bip. Pollichia 12-24: 308. Occasional on damp banks in the Lower Chaparral Zone. Stephanotneria cichoriacea Gray, Proc. Am. Acad. 7: 552. Abundant on rocky banks in the Upper Chaparral Zone. Stephanomeria virgata Benth. Bot. Sulph. 32. Frequent on dry banks in the Lower Chaparral Zone. Rafinesquia californica Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 429. Occasional among bushes in the Lower Transition Zone. Malacothrix saxatilis T. & G. Fl. 2: 486. Rare on rocky banks, Mill Creek, in the Lower Chaparral Zone. Taraxicum officinale Weber var. lividum Koch, Fl. Germ. 428. Abundant in wet meadows in the Transition and Canadian Zones. Troximon heterophylliim Greene f. normaJe Hall, Univ. Cal. Publ. Bot. 3: 277. Frequent in dry meadows in the Transition Zone. Troximon retrorsum Gray, Proc. Am. Acad. 9: 216. Frequent in open pine forest in the Transition, and occasional in canons in the Upper Chaparral Zone. Troximon plebeium Greene, Pitt. 2: 79. Occasional in the Lower Transition Zone. Crepis acuminata Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 437. Frequent on dry slopes in the Upper Transition Zone. Crepis occidentalis Nutt. Jour. Acad. Philad. 7: 29. Frequent on dry slopes in the Upper Transition Zone. Crepis occidentalis Nutt. var. subacaidis Kellogg, Proc. Cal. Acad. 5: 50. Bear Valley, ace. Coville, Contr. Nat. Herb. 3: 562. Hieracium albiflorum Hook. Fl. Bor. Am. 1: 298. Frequent in crevices of rocks in the LTpper Transition Zone. Hieracium Grinnellii Eastw. Bull. Torr. Club 32: 217. Fish Creek, in the Upper Transition Zone, ace. Hall, Univ. Cal. Publ. Bot. 3: 285. Hieracium horridum Fries, Epic. Hier. 154. Frequent in rocky places in the Upper Transition and Canadian Zones. Hieracium Parishii Gray, Proc. Am. Acad. 19: 67. Along a rocky ledge above Vail's in Waterman canon, in the Lower Transi- tion Zone; type station. Brickellia arguta Robins. Mem. Gray HI). 1: 102, t. 79. Occasional in rocky places in the Lower Pinon Zone. Brickellia oblongif olio Nutt. var. Km/oZm Robins. Mem. Gray Herb. 1: 104. Locally abundant on dry stony flats above Cactus Flat and at Rose Mine, both in the Upper Pinon Zone. Gutierrezia californica T. & G. Fl. 2: 195. Bear Valley, in the Upper Transition Zone. PLANTS OF THE SAN BERNARDINO MOUNTAINS 257 Chrysopsis Wrightii Gray, Synop. Fl. 1. pt. 2: 446. NeaT the summit of San Gorgonio Mountain, W. G. Wright, July, 1882, ace. Gray, I. c, but not since met with. Solidago calif ornica Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 328. Frequent on dry slopes in the Upper Chaparral and Transition Zones. Solidago confinis Gray var. luxurians Hall, Univ. Cal. Publ. Bot. 3: 46. Locally abundant in wet mucky soil at Arrowhead Hot Springs in the Lower Chaparral Zone. Aplopappus gossypinus Hall, Univ. Cal. Publ. Bot. 3: 49. Frequent in meadows in Bear Valley (type) and Holcomb Valley. Ericameria cuneata McClatchie var. spaihulata Hall, Univ. Cal. Publ. Bot. 3: 52. Frequent in rock crevices in the Lower Pinon Zone. Ericameria Parishii Hall, Univ. Cal. Publ. Bot. 3: 55. Occasional on dry hillsides in the Lower Chaparral Zone. Waterman Canon is the type station. Chrysothamnus nauseosus Britton, in Britt. & Brown HI. Fl. 3: 326. Occasional in dry soil in the Lower Transition Zone. Chrysothamnus nauseosus Britton var. occidentalis Piper, Contr. Nat. Herb. 11: 59. Frequent in dry soil in the Lower Transition Zone. Chrysothamnus viscidiflorus Nutt. var. stenophylliis Hall. Univ. Cal. Publ. Bot. 3:58. Occasional on dry ridges in Bear and Holcomb Valleys. Hazardia squarrosa Greene, Eryth. 2: 112. Frequent on dry banks in the Lower Chaparral Zone. Corethrogyne filaginifolia Nutt. var. bernardina Hall. Univ. Cal. Publ. Bot. 3: 71. Frequent in dry soil in the Lower Chaparral Zone. Corethrogyne filaginifolia Nutt. var. glomerata Hall. Univ. Cal. Publ. Bot. 3: 72. Oak Glen, in the Lower Transition Zone, Geo. Robertson, type. Corethrogyne filaginifolia Nutt. var. rigida Gray, S\n. Fl. 1 pt. 2: 170. Frequent on stoiiy hillsides in canons in the L^pper Chaparral Zone. Aster canescens Pursh, Fl. 2: 547. Infrequent in the Upper Transition Zone. Aster delectabilis Hall, Univ. Cal. Publ. Bot. 3: 82. Frequent in wet meadows in the L'pper Transition and Canadian Zones. The type was collected by R. J. Smith on a tributary of Mill Creek. Aster Fremonti var. Parishii Gray, Sjmop. Fl. 1, pt. 2: 192. Frequent on stream banks, Bear Valley (type) and Bluff Lake. Erigeron concinnus T. & G. var. aphanactis Gray, Proc. Am. Acad. 6: 540. Abundant on dry slopes at Doble, Bear Valley. Erigeron compositus Pursh var. discoideus Gray. Am. Journ. Sci. ser. 2, 33: 540. Summit of San Gorgonio Mountain, Mrs. Wilder. Erigeron foliosus Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 309. Occasional in dry soil in the Chaparral and Lower Transition Zones. Erigeron striatus Greene, Bull. S. Cal. Acad. 1: .39. Houston Flat, in the Lower Transition Zone, Shaw (type) ace. Greene, I.e. Psilocarphus globiferus Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 340. On dry flats, Bear Valley. ■ A / I^V" J! ?* >. « ^ '\^ 258 S. B. PARISH Filago californica Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 405. Infrequent in the Transition Zone. Antennaria densa Greene, Leafl. 2: 151. Summit of San Gorgonio Mountain, Abrams & McGregor, type. Antennaria dimorpha Nutt.; T. & G. Fl. 2: 431. Abundant, forming depressed mats, Bear Valley. Antennaria marginata Greene, Pitt. 3; 290. South Fork of Santa Ana River, Mrs. Wilder. Not otherwise known in California. Antennaria media Greene, Pitt. 3: 289. Summit of San Gorgonio Mountain, Mrs. Wilder; Wright. Antennaria speciosa E. Nelson, Proc. Nat. Mus. 23: 705. Occasional on hillsides in the Upper Transition Zone. The type was collected in Bear Valley. Gnaphaliuni californicwm DC. Prodr. 6: 224. Frequent on dry banks in the Lower Chaparral Zone. Gnaphalium microcephalum Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 404. Frequent in canons in the Lower Transition Zone. Gnaphalium palustre Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 403. Occasional on wet sandy banks in the Transition Zone. Helianthus gracilentus Gray, Proc. Am. Acad. 11: 77. Frequent on dry banks in the Lower Chaparral Zone. Ve7-besina dissita Gray, Proc. Am. Acad. 20: 299. Dobbs' Camp, Mill Creek Canon, Upper Transition Zone, Robertson. Madia dissitiflora T. & G . Fl . 2 : 405. Occasional in canons in the Lower Chaparral Zone. Madia elegans Don in Lind. Bot. Reg. t. 1458. Frequent in canons in the Chaparral Zone. Hemizonella minima var. parvula Hall, Univ. Cal. Publ. Bot. 3: 148. Frequent on dry ridges in the Lower Transition Zone. Hemizonia Wheeleri Gray in Brew. & Wats. Bot. Cal. 1: 617. Abundant in open pine forests in the Upper Transition Zone. Eriophijllum brachylepis Rydb. N. A. Fl. 34: 88. On dry slopes in open pine forest. Bear Valley, type station. Eriophyllum confertifloruni var. irifidum Gray, Proc. Am. Acad. 19: 25. Frequent on dry slopes in the Lower Chaparral Zone. Eriophyllum lanatum var. obov'atum Hall, Univ. Cal. Publ. Bot. 3: 186. Frequent on dry slopes in open pine forest in the Transition Zone. Hymenopappus lugens Greene, Pitt. 4: 43. Occasional in open pine forest in the Upper Transition Zone. Bear Valley is the type station. Chaenactis carphoclinea Gray, Bot. Mex. Bound, 94. A desert species ascending Cushenberry Caiion to the upper end of Bear Valley; infrequent. Chaenactis santolinoides Greene, Bull. Torr. Club 9: 117. Frequent, mostly in stony places, in the Transition Zone. The type was collected in Little Bear Valley. Hulsea heterochroma Gray, Proc. Am. Acad. 7: 359. San Gorgonio Mountain in the Canadian Zone; very seldom collected. PLANTS OF THE SAN BERNARDINO MOUNTAINS 259 Hulsea vestita Gray, Proc. Am. Acad. 6: 547. Frequent in rocky and gravelly soil in the Upper Transition Zone, and in a depauperate form (var. pygmaea Gray) reaching the summit of San Gorgonio Mountain. Helenium Bigelovii Gray, Pac. R. Rept. 4: 107. Occasional in meadows and along streams in the Upper Transition and Canadian Zones. Achillea millefoliuvi Linn. var. lanulosa Piper, Mazama 2: 97. Yarrow. Frequent in meadows in the Transition Zone. Artemisia albula Wooten, cont. Nat. Herb. 16: 193. Common on dry, open flats about Doble, at the upper end of Bear Valley. Artemisia californica Less. Linnaea 6: 523. On dry hills in the Lower Transition Zone. Artemisia dracunciiXoides Pursh, Fl. 2: 742. Occasional on hillsides in the Chaparral Zone and in dry meadows in the Transition Zone. Artemisia Rothrockii Gray in Brew. & Wats. Bot. Cal. 1: 618. In the Upper Transition Zone, Vernon Bailey, ace. Hall, Univ. Cal. Publ. Bot. 3: 297. Artemisia tridentata Nutt. Trans. Am. Philos. Soc. ser. 2, 7: 398. Abundant on dry open fiats at the upper end of Bear Valley. Raillardella argentea Gray in Brew. & Wats. Bot. Cal. 1: 417. In gravelly soil at the summit of San Gorgonio Mountain. Arnica bernardina Greene, Pitt. 4: 170. Frequent in meadows in the Upper Transition and Canadian Zones. The type was from Bear Valley. Tetradymia glabrala Gray, Pac. R. Rept. 2, pt. 2: 122, t. 5. Occasional in dry soil at the upper end of Bear Valley. Senecio ionophyllus Greene, Pitt. 2: 220. Occasional in dry soil in the Upper Transition Zone. Senecio ionophyllus Greene var. bernardinus Hall, Univ. Cal. Publ. Bot. 3: 232. Frequent in open pine forest in the Upper Transition Zone. Bear Valley is this type station. Senecio ionophyllus Greene var. sparsilobatus Hall, Univ. Cal. Publ. Bot. 3: 232. Occasional in coniferous forest in the Canadian Zone. Barton Flats is the type station. Senecio serra Hook. var. sanctus Hall, Univ. Cal. Publ. Bot. 3: 230. Occasional on moist north slopes in the Canadian Zone. Senecio triangularis Hook. Fl. Bor. Am. 1: 332, t. 115. Occasional by stream banks and in wet places in the Canadian and Hudson- ian Zones. Carduus californicus Greene var. bernardinus Parish Hall, Univ. Cal. Publ. Bot. 3:241. Frequent on dry hillsides in the Chaparral, and occasional in the Lower Transition Zone. Little Bear Valley is the type station. Carduus Drummondii var. acaidescens Coville, Contr. Nat. Herb. 4: 142. Common and often abundant in dry meadows and flats in the Transition Zone. BOOKS AND CURRENT LITERATURE Soil Aeration and Plant Growth. — The importance of an ade- quate air supplj^ to the roots of plants as a factor in their well-being constitutes the keynote to much of the very extensive field experi- mentation and observation on the behavior of cultivated plants which Howard and his colleagues have carried on for over a decade at Pusa, in the valley of the Ganges, and at Quetta in Indian Baluchistan.^ The results of the work have been presented in^several papers, which, although primarily of agricultural interest, are nevertheless of wide application in the general study of the relation of the growth and activities of roots to the soil environment and to the establishment of the species. The work of Howard was carried on in the subtropical climate of northern India, but under widely different conditions as regards rain- fall. At Pusa the rainfall is about 50 inches annually, with 85% oc- curring in June-September, during the monsoon. At Quetta, on the other hand, arid conditions prevail. The annual precipitation is about 10 inches only, most of which is in the cold season. The soil of the Gangetic plain is a fine alluvium which puddles easily. The soil at Quetta resembles that at Pusa but it is loess, sometimes mixed with alluvium, and it also easily runs together on wetting. From these general facts we are not surprised to learn that at Pusa the soil of the valley of the Ganges is saturated with water during the monsoon, and as a matter of fact after every severe storm. A similar but less marked condition occurs at Quetta, where unwise and ill-timed irrigation often causes the same results. It consequently happens that problems associ- ated with the aeration of roots in both regions are of the first importance. In general Howard's method may be said to consist in observations on the behavior of crops, including trees already established, during the periods of rains, or under conditions attending irrigation. This is supplemented by field experiments which deal largely with the effects of bettered aeration of the soil. Some of the observations and conclu- 1 Among the more important papers are the following : Howard, A. and Gabrielle L. C. Howard. Soil Ventilation. Bull. No. 52, Agric. Research Institute, Pusa. 1915. Howard, A. Soil Aeration in Agriculture. Id. Bull. No. 61. 1916. 260 BOOKS .'U^D CURRENT LITERATURE 261 sions can be briefly given although a study of the papers will be neces- sary if a background for the results is desired. At Pusa the following are some of the effects of poor soil aeration noted on the monsoon crops. The summer crops are heaviest when the monsoon rains are below the average and well distributed. The surface skin which forms on the soil as a result of these storms checks growth; breaking the crust benefits crops immediately. Howard concludes that in the Pusa region the want of sufficient air in the soil does infinitely more harm to the monsoon crops than the want of water. So far as the crops of winter are concerned, analogous results are to be seen. Although relatively small in amount, the rains of winter also cause the formation of a crust on the soil, which interferes with shoot growth, and when this crust is broken the activities of the shoot are restored to their normally healthy condition. Possibly, however, the most striking result of poor soil aeration on the growth of shoots was observed in connection with established trees. A resting period occurs during winter when leaf-fall is common. With the rise in temperature that takes place in February, new leaves are formed, and flowering and shoot growth occur. Rapid growth goes on until the hot weather supervenes. At the commencement of the monsoon phase another period of growth takes place, but with the saturation of the soil growth slows down or nearly ceases. It is not renewed until the end of the monsoon, when with the drying out of the soil better aeration results. Growth is then renewed for the second time and goes on until the advent of cold weather. Although the soil temperature is favorable in summer and there is an abundance of moisture, the vegetative activities are greatly diminished owing to the want of oxygen or the presence of a harmful amount of carbon di-oxide. The immediate effect of inade- quate aeration of the soil is wilting, which has sometimes been treated as a disease. Numerous cultural experiments show that the effects exerted on shoots by poor soil aeration affect the roots primarily. Thus, any method by which good aeration is produced restores the healthy con- dition of the crops, or prevents the injurious effects attendant on an inadequate air supply. The fact that variation in soil aeration directly influences root growth is shown also in another manner by the behavior of gram under different soil conditions. When grown in three sorts of soil within 100 yards of each other and all well moistened, characteristic differences in the development of the root-systems of the plants were observed. THE PLANT WORLD, VOL. 20, NO. 8 262 BOOKS AND CURRENT LITERATURE In heavy soil the roots were confined to the upper soil layers. In light soil the roots penetrated deeply and extended widely. In soil of an intermediate character the root development was also intermediate. The results were confirmed bj^ the growth of gram with fragments of broken pottery added to the soil. In all cases soil which was provided with good aeration induced the type of root development that had already been observed in well aerated soil. Howard makes the inter- esting generalization that the distribution of gram, as a crop follows the occurrence of well aerated soils. The effects of inadequate aeration of the soil on crops of various kinds at Quetta are similar to the effects seen at Pusa, pointing to the undoubted general application of these conclusions in agriculture and in plant ecology. This has been pointed out recently^ and additional research only serves to emphasize its importance. — W. A. Cannon. The Book of Forestry. — The Book of Forestry^ is not for the technical forester nor the ecologist, but for the lay reader who wants information about forestry and conservation. The author's aim is to "awaken the love of the forest in the heart of young America, and a realization that forestry is necessary for the comfort, health, and prosperity of future generations." The book is divided into two parts. In the first part the author crowds into 177 pages a mass of facts, figures and information covering forest influences, conservation of natural resources, forest growth, uses and properties of woods, silvi- culture, forest protection, timber estimating, lumbering, timber pres- ervation and city forestry, with a chapter on the life of a forester thrown in. Under each heading enough is presented to give a reason- able idea of the subject. The second part contains brief descriptions and drawings of some of the more important American trees, and a key for identifying woods. In the appendix is given a table of uses of the principal American species, together with the range and maximum size of the tree, a sample volume table and log scale, a very short list of reference books in forestry, and a glossary of terms. A popular book does not require precision of statement, provided a correct im- pression is left with the reader, and, because of the difficulties inherent in this form of writing, we should overlook unimportant slips. But 1 Cannon, W. A. and E. E. Free. The Ecological Significance of Soil Aeration. Science, 44: 178. 1917. 2 Moon, P. F. The Book of Forestry, Pp. 315, figs. 64. New York, D. Appleton and Company, 1916. ($1.75). BOOKS AND CURRENT LITERATURE 263 at the top of page 48, after saying that the lower branches soon die from lack of light, he adds, "and the next high wind or ice storm breaks them off, leaving the lower part of the trunk bare of branches." If this were the case, it would be comparatively simple to grow trees which would yield clear lumber in a reasonable length of time. But dead limbs persist so long after death that only in very old trees do we find clear lumber. However, the book appears to be unusually free from mistakes of this character. Whoever has enjoyed Bruncken's admirable statement of the general principles of forestry^ will be glad to have Professor Moon's book as a source of facts hitherto so scattered through government publications and periodic literature as to be inaccessible to the general public. The narrative form and amusing anecdotes will increase the size of the audience and the usefulness of the book. — Barrington Moore. Megasporophylls of Conifers. — A much needed comparative study of the vascular supply of cone-scales in all groups of conifers has been made by Miss Aase,'^ who finds that two processes have been at work in the evolution of the ovulate strobilus: (1) reduction in number of sporophylls in the strobilus, and (2) fusion of bract and ovuliferous scale, with or without a corresponding fusion of their vascular supplies. The diagrams accompanying this paper must be taken into account in any future discussion of the morphology of the cone. — M. A. Chrysler. 1 Bruncken, Ernest. North American Forests and Forestry. Pp. 262. New York, G. P. Putnam's Sons, 1908. 2 Aase, H. C. Vascular Anatomy of the Megasporophylls of Conifers. Bot. Gaz. 60: 277-313. 1915. NOTES AND COMMENT In 1911 The Plant World asked a number of representative botanists at home and abroad to name one or two contributions which they regarded as the most important that had been made to botanical science in the preceding year or two (see vol. 15, p. 166). It will be remembered that the work of Winkler on graft hybrids was regarded as the most important, while a total of some 18 papers were named in the replies. As considerable interest was expressed in the results of this ballot it has just been repeated. Fifty American botanists were asked to name one or two contributions that had appeared in the last two or three years. Thirty-one replies were received to this difficult and perplexing question. Some of those who were interrogated found it impossible to frame a reply to wliich they would be willing to sul)- scribe. One reply states: "I do not see that any one or two contri- butions so far outrank all the others that they should be singled out for special mention. There have been many contributions, and our science is progressing rapidly, but it seems to me that in these days we are marching by platoons rather than singly." Six letters were received which gave expression to a similar feeling, wliile a number of others spoke only for the advances in the particular fields known to the writers. One correspondent has stated a very definite set of rulings by which he arrived at his vote, while others have given their choice in a more off-hand manner, or have covered their doubts by mention- ing five or six pieces of work. All of the replies have been treated alike, and all of the papers voted for have been listed below, regardless of the number mentioned and regardless of their date. The figures in parentheses following the first five titles indicate the number of votes received by these papers, all others receiving one each. Erwin F. Smith. Work on Crown Gall and its relation to cancer (several papers). (5). Frederick E. Clements. Plant Succession (Publications of Carnegie In- stitution). (3). N. Svedelius, in collaboration with H. Kylin. Work on the alternation of generations in red algae (various papers). (2). L. J. Briggs and H. L. Shantz. Work on the water relations of plants (several papers) . (2) . 264 NOTES AND COMMENT 265 Forrest Shreve. The vegetation of a desert mountain as determined by climatic conditions (Publications of Carnegie Institution). (2). L. H. Bailey and Collaborators. Cyclopedia of Horticulture. H. H. Bartlett. Genetical work on Oenothera (several papers). H. H. Dixon. Transpiration and the ascent of sap. R. A. Emerson and H. B. Frost. Work in Genetics. Lawrence J. Henderson. The Fitness of the Environment. T. A. Kiesselbach. Work on the transpiration of corn (Research Bulletin, University of Nebraska). P. A. Lehenbauer. Growth of maize in relation to temperature (Physiologi- cal Researches). F. LoHNis and N. R. Smith. Life cycles of bacteria (Journal of Agricultural Research). T. B. OsBORN and L. B. Mendel. Work on the chemistry of nutrition (numer- ous papers). W. .T. V. Osterhout. Work on theories of antagonism (numerous papers). AI. Cheveley Rayner. Work on obligate symbiosis in Call una (Annals of Botany). O. Renner. Work on the cohesion theory and water movement (several papers). B. L. Robinson. Monograph of Brickellia (ISIemoirs of the Gray Herbarium, Harvard LTniversity). C. Sauvageau. Work on alternation of generations in the Laminariaceae (several papers in Comptes Rendus). J. W. Shive. Physiological balance in nutrient media (Physiological Re- searches) . Forrest Shreve. Ecological work on montane rain forests (Publications of Carnegie Institution). W. P. Thompson. Work on the morphology of the Gnetales (Papers in Annals of Botany and American Journal of Botany). THE INDICATOR SIGNIFICANCE OF NATIVE VEGETATION IN THE DETERMINATION OF FOREST SITES CLARENCE F. KORSTIAN United States Forest Service, Ogden, Utah Phytogeographers have long recognized certain variations in the native vegetation of given regions, while phytoecologists have only recently made notable advances in the correlation of the vegetation with the climatic and edaphic factors of the habitat. Within the last decade the physiological ecologist has been doing some excellent work on the correlation of the native vegetation with the crop-producing potentiahties of the land, the results of which have a very practical appUcation in present- day agriculture. As a result of detailed studies in the Great Plains region of eastern Colorado, Shantz'^ concludes that the character of the native plant cover can be used as a rehable indicator of the con- ditions favorable or unfavorable for crop production, provided the relation between the vegetation and the en\dronment is correctly interpreted. The correlations which exist in the Great Plains between the different types of vegetation and the physical characteristics of the corresponding types of land are described in detail. Shantz discusses at length the ways in which the native vegetation may be used in that region to deter- mine the adaptability of the land for dry farming. The crop production on wire-grass land during favorable years is almost as good as on short-grass land and during normal and dry years much better crops are produced on wire-grass than on short- grass land. Using the native vegetation as an indicator of the 1 Shantz, H. L. Native Vegetation as an Indicator of the Capabilities of Land for Croj) Production in the Great flains Area, U. S. Dept. of Agri., Bur. of Plant Ind. Bui. 201, 100 pp. 1911. 267 THE PL.\NT -WORLD, VOL. 20, NO. 9 SEPTEMBER, 1917 268 CLARENCE F. KORSTIAN capabilities of crop production, the type of land that is charac- terized by the wire-grass association is classed as the most valu- able agricultural land in eastern Colorado. That type of short- grass land which bears a considerable growth of wire-grass or Psoralea is classed with or very close to the wire-grass associa- tion land, since the presence of these plants indicate conditions intermediate between those of the typical wire-grass association and those indicated by the typical grama — buffalo-grass asso- ciation. On new land where crops have not yet been produced, the character, growth, and condition of the native vegetation are the best possible indicators of crop production, either positive or negative, since plant growth is the ultimate criterion of the suitability of the physical environment. Kearney and others' have gone still farther in the scientific study of native vegetation from the indicator point of view in suggesting the possibility of correlating the distribution of the vegetation with the physical and chemical properties of the soil and the utilization of such a correlation in the classification of the agricultural potentialities of the land. The investigations in the Great Basin of central Utah were directed toward the solution of the problems of what types of vegetation indicate conditions of soil moisture favorable or unfavorable to dry farming and what types indicate the presence or absence of alkaline salts in sufficient quantities to injure cultivated crops. The results of the studies in Tooele Valley show that the dif- ferent types of native vegetation indicate the conditions of soil moisture and alkalinity of the land on which they are found and consequently provide a basis for estimating its potentiali- ties for crop production. A good stand and growth of sagebrush (Artemisia tridentata) indicates land .that is well adapted to both dry and irrigation farming. Where the stand of sage- brush is open and the growth poor the good soil is usually too shallow for profitable crop production, at least without irrigation. Dry farming is precarious on land covered by the Kochia (Kochia ^ Kearney, T. H., Briggs, L. J., Shantz, H. L., McLane, J. W. and Piemeisel, R. L. Indicator Significance of Vegetation in Tooele Valley, Utah. Journal of Agricultural Research 1 : 365-417. 1914. INDICATOR SIGNIFICANCE OF NATIVE* VEGETATION 269 vestita) and shadscale {Atriplex confertifolia) associations, due to the shallowness of the alkali-free soil. Land occupied by the greasewood — shad-scale {Sarcohatus vermiculatus and Atriplex * confertifolia) association is unsuitable for dry farming, but will produce good crops under irrigation. The work on the correlation of the native vegetation with the crop-producing capabihties of the land has frequently sug- gested to the writer the possibility of utilizing the native vegeta- tion in the determination of forest sites. In forestry, site is defined as an area considered as to its physical factors with reference to forest producing power; the combination of the climatic and edaphic conditions of an area or the forest habitat. For purposes of comparison the various sites are commonly segregated into site classes. Site class is a designation of the relative productive capacity or quality of different sites with reference to the species employed; the volume or the height produced at a given age being commonly used as the standard for classification. In the United States frequently only three classes are differentiated, designated by Roman numerals, quality I representing the most productive site class. In a perusal of forestry Hterature one is impressed with the apparent fact that until only recently has much attention been given to the native vegetation, aside from the forest trees them- selves, in the classification and segregation of forest sites. The majority of the references to the variation in the native her- baceous vegetation on different forest sites have been made incident to the describing of different sites or in characterizing their ground cover instead of from the indicator point of view. The rather radical work of Cajander^ must be cited as an exception to this statement. As a result of investigations of herbaceous and forest associations conducted in Finland, Ger- many, Austria-Hungary, Switzerland, Northern Russia and Siberia, Cajander concludes that, since no forester is in a posi- tion to determine definitely the limits of a dry or a moist soil, the difference in forest types must be based upon the character 2 Cajander, A. K. tjber Waldtypen, Helsingfors, 1909, Fennia 28, No. 2, 175 pp. Reviewed by Raphael Zon in Proc. Soc. Amer. Foresters 9: 119-125. 1914. 270 'clarence f, korstian of the living ground cover as the clearest indicator of the site. Although Cajander admits that in virgin forests the composi- tion of the forest itself correlated with the living ground cover is the best criterion of the physical conditions of growth, he further maintains that in forests which are under the influence of man the living ground cover alone may serve as a criterion and indicator of the physical conditions of the site. The latter statement is at variance with American ideas because of the failure to correlate the living ground cover with the different physical conditions of growth and the failure to appreciate the effect of the varying density of the forest cover on the living ground cover. In pointing out the value of the native vegetation as a cri- terion of the potential productivity of land and its application to modern land classification, Pearson^ maintains that a forest may be regarded as the aggregate effect or the summation of the physical conditions obtaining on the site on which it grows and that the consideration of the potentiality of the land need not be confined to the trees. Shrubs, herbs and even the lower forms of plant life may be correlated effectively with the physi- cal factors of the site and also with the tree growth. Pearson concludes that the simpler and more reliable basis for the deter- mination of the adaptability of the site for different crops con- sists in the use of characteristic forms of the native vegetation as indicators of the physical conditions of the site. Mason^ reports the abundance of huckleberry {Vaccinium scoparium) on the poorer lodgepole pine (Pinus contorta) sites of the Rocky Mountains. Alder {Alnus tenuifolia) and willow frequently occur as underbrush in moist situations of the same forest type. Clements" in discussing the vegetative succession on burned- over areas in the lodgepole pine forest of the central Rocky ^ Pearson, G. A. What is the Proper Basis for the Classification of Forest Land into Types? Proc. Soc. Amer. Foresters 8: 79-84. 1913. * Mason, D. T. The Life History of Lodgepole Pine in the Rocky Mountains. rj. S. Dept. of Agri. Bui. 154, pp. 11-12. 1915. ^ Clements, F. E. The Life History of Lodgepole Burn Forests, U. S. Dept. of Agri., Forest Service Bui. 79, 56 pp. 1910. INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 271 Mountains, points out differences in the density and composi- tion of the hving ground cover varying with the favorableness or unfavorableness of the different lodgepole pine sites. The vegetative vsuccession occurring on the burns during the course of the reestabhshment of the original forest cover shows, in an interesting way, the superseding of the xerophytically-inchned vegetation by vegetation possessing more mesophytic tendencies, until, as the site becomes more and more mesophytic, the orig- inal forest cover is eventually established. The relative meso- phytism of the site at each of the more or less distinct stages of the succession is indicated by the native vegetation occurring on the site at that particular time. It is true, however, that the vegetation of any of the unstable stages of the succession cannot be regarded as being indicative of the latent potentiality of the site. The ultimate climax stage of the succession must have been reached before much importance can be attached to the indicator significance of the native vegetation in the deter- mination of site, especially from the standpoint of the forester. Zon^ in describing the forest types in which balsam fir {Abies halsamea) occurs, states that sphagnum and other mosses are the principal species which comprise the living ground cover of the swamp type. Fern moss replaces sphagmmi as the pre- dominating ground cover of the flat type. Ferns and certain flowering plants become the conspicuous herbaceous plants of the hardwood slope type in which balsam fir is reported as attaining its best individual development although the best stand development occurs in the flat type. The descriptions of the forest tj'pes are supported by lists which show the relative proportion of the different species and the character of the vegetation comprising the living ground cover of the swamp, flat, and hardwood slope types. Hole and Singh ^ in studjdng the soil types and native vege- tation of the sal forests in the vicinity of the Forest Research 7 Zon, Raphael. Balsam Fir. U. S. Dept. of Agri. Bui. 55, pp. 4-7. 1914. ^ Hole, R. S. and Singh, Puran. Oecology of Sal (Shorea robusta) ; Part I, Soil composition, soil-moisture, soil-aeration. Indian Forest Records, Vol. V, Part IV, pp. 13-14. 1914. 272 CLARENCE F. KORSTIAN Institute, Dehra Dun, India, consider three principal soil types, each of which is characterized by distinct types of vegetation. The poorer soils, containing a large percentage of sand and a relatively small amount of silt, are frequently shallow, with gravel and boulders below. These soils are essentially dry and bear a dry forest with Acacia catechol and Dalbergia sissoo promi- nent, or grassland with Saccharum munja dominant. The well- aerated deep loams are covered with a sal forest or grassland with Saccharum narenga (often mixed with Anthistiria gigantea subsp. arundinacea) dominant. The poorly-aerated deep loams, differing from the w^ll-aerated soils in containing more clay and silt, in actually being heavier, or in having the water-table nearer the surface, are characterized by a moist forest with Betula frondosa, Stereospermum suaveolens, Terminalia, Cedrela toona and others, or grassland with Erianthus ravennae (often mixed Avith Anthistiria gigantea subsp. villosa) dominant. More recent work by the same investigators^ indicates that the dominant grasses on an area are excellent indicators of the soil conditions. In northern India, where Saccharuin narenga and A7ithistiria gigantea subsp. arundinacea tend to be dominant, the soil moisture and aeration are suitable for the best develop- ment of sal and the moist type of sal forest prevails, in the shaded parts of which the reproduction suffers from poor soil aeration. Such grasses as Saccharum munja, Saccharum spon- taneum, Eragrostis cynosuroides, Imperata arundinacea, Vetiveria zizanioides,. Andropogon contortus and Ischaemum angustifolium usually indicate a soil too dry, or too heavy, for the best develop- ment of sal and such forests as occur are of the dry sal type. Pearson^", in discussing the effect of a cover of aspen {Populus tremuloides) upon the estabUshment of Douglas fir {Pseudotsuga taxifolia), has made a very interesting comparison of two dif- ferent sites which occur at the transition between the Douglas ® Hole, R. S. and Singh, Puran. Oecology of Sal {Shorea rohusta) ; Part II, Seedling Reproduction in Natural Forests and its Improvement. Indian Forest Records, Vol. V, Part IV, pp. 83-84. 1916. 1" Pearson, G. A. The Role of Aspen in the Reforestation of Mountain Burns in Arizona and New Mexico. The Plant World 17: 249-260. 1914. INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 273 fir and western yellow pine {Pinus ponder osa) types at an elevation of 8700 feet on the San Francisco Mountains in north- ern Arizona. Both sites had the same exposure but one was aspen-covered and the other was in the open. After making detailed studies of the physical factors of the two adjacent sites, the survival and development of Douglas fir planted on both sites and the correlation of the native vegetation occmTing on the sites the conclusion was drawn that the open sites, due to their greater severity, should doubtless be reforested with west- ern yellow pine {Pinus ponderosa) while the aspen-covered areas should be planted with Douglas fir. The aspen thickets supported a luxuriant growth of broad-leaved mesophytic herba- ceous plants, such as Frasera scabra, Pteridium aquilinum and Verbasciim thapsus, while grasses {Muhlenbergia gracilis, Festuca arizonica, Festuca pseudovina, and Bromus polyanthus) pre- dominated in the openings. The growth of all herbaceous plants was invariably more luxuriant under the aspen than in the open. Shreve^^ reports a rather marked variation in the distribution of the vegetation occurring in a forest of Pinus arizonica on the Santa CataHna Mountains in southern Arizona. Throughout the pine forest are to be found a large number of herbaceous perennials, the greater majority of which accompany the closed stands of pine. The occurrence of another large group of plants is confined to the near proximity of streams and stream-courses. In the dense shade of the evergreen-oak woodland Pteris aquilina is reported as being common, and it again becomes common in the pine forest above 7500 feet, but is infrequent in the lower portion of the forest region. Alnus acuminata, Acer interius, and Quercus submollis become frequent along streams at about 6800 feet. Herbaceous plants are reported as being found in increasing numbers at or near the banks of streams between 6000 and 7400 feet, among which may be mentioned J uncus arizonicus, Aquilegia chrysantha, Thalictrum fendleri var. wrightii, Scrophidaria sp., Trifolium pinetorum, Fragaria ovalis, Poten- 11 Shreve, Forrest. The Vegetation of a Desert Mountain Range as Condi- tioned by Climatic Factors, Pub. 217, Carnegie Inst. Wash. 112 pp. 1915. ;^ILIBRARY W^^S^v^ 274 CLARENCE F. KORSTIAN tilla thurheri, Hypericum formosum, Lobelia griiina, Agrimonia hrittoniana var. occidentalism Gaura suffulta, and Tagetes lemmoni. Weaver'^'^ has recorded the variation in the vegetative under- growth with a change of the site in the cedar {Thuja plicata) forest on the Thatuna Hills in southeastern Washington. Near the streams the forest floor is covered with Athyrium cyclosorum which gives way farther back to a rather dense growth of Ruhus parviflorus, Vagnera amplexicaulis, Tiarella unijoliata, Trillium ovatum, Clintonia unifiora, Disporum ma jus, Pyrola sp., Actaea spicata arguta, and Coptis occidentalis, Viola sp., Streptopus amplexif alius, and Phegopteris dryopteris. These together with the cedar seedlings comprise the characteristic undergrowth, while farther up the slope there is almost no living ground cover. Fuller^^ notes the relation between the mesophytism of a site and the undergrowth in some comparatively undisturbed beech- maple forests about 45 miles southeast of Chicago, when he states that the lower evaporation in the ravine may be a suffi- cient explanation for the presence upon its slopes of a much greater abundance of such delicate forms as Dicentra canadensis, D. cucullaria, Impatiens biflora, and Asplenium angustifolium. Peters, i"* as a result of observations made in Northampton County, Pennsylvania as early as 1806, calls attention to the fact that the timber alone is not always an invariable indicator of the capabilities of the land. Hemlock {Tsuga canadensis), white pine {Pinus strobus), and pitch pine {Piiius rigida) were reported as occurring on deep, fertile loams as well as on the thinnest, sterile, sandy soils. It is readily seen that the vege- tation must be properly correlated with its habitat and the 1^ Weaver, John E. Evaporation and Plant Succession in Southeastern Wash- ington and Adjacent Idaho. The Plant World 17: 273-294. 1914. " Fuller, George D. Evaporation and the Stratification of Vegetation. Bot. Gaz. 54: 424-426. 1912. " Peters, Richard. The Departure of Southern Pine Timber and Proof of the Tendency in Nature to a Change in Products on the Same Soil. Memoirs of the Philadelphia Society for Promoting Agriculture, containing communica- tions on various subjects in husbandry, and rural affairs, Vol. J, page 30, Phila- delphia. 1815. From notes on plant succession abstracted and furnished by Dr. H. L. Shantz. INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 275 relation between vegetation and environment must be correctly interpreted. It should be clearly recognized that the use of native vegeta- tion as an indicator of forest sites is not without certain limita- tions. The use of native shrubby, and particularly herbaceous, vegetation as forest site indicators is not exactly comparable to using native open-land vegetation as an indicator of the crop productivity of an open-land site. In the case of the forest site the presence or-absence of an over-wood must be recognized as an influential factor. The use of shrubby and herbaceous vegetation as indicators of forest sites encounters more obstacles in the dense Douglas fir, lodgepole pine, and Engelmann spruce {Picea engelmanni) forests than in the comparatively open west- ern yellow pine forests. In the dense forests herbaceous plants are rather scarce except in partial openings or where the stand is below its normal density. The vegetation of the denser forests also varies in its composition from place to place, not only according to the favorableness of the site, but also with the density of the crown cover and consequently the amount of shade in the forest. The floor of the fir, spruce and lodgepole pine forests is more hea\41y and continuously shaded than that of the densest stands of western yellow pine. The factor of shade is of great importance in conditioning the character of the shrubby and herbaceous vegetation of dense forests. While engaged in the remeasurement of a set of permanent sample plots aggregating 26.4 acres on the San Mateo Division of the Datil National Forest in west central New Mexico in the summer of 1915 the writer was impressed with the variation in the vegetation occurring on the different w^estern yellow pine sites. The San Mateo Mountain range extends in a gen- eral north and south direction and rises to a height of 9500 to 10,500 feet above sea level. The north and west por- tions of the mountains slope quite gradually to the adjacent rolling plains. The east and south portions of the range break off quite abruptly to the plains. The majority of the steeper east and south aspects bear such species as Jimi- perus monosperma, J. pachyphloea, Pinus edulis, Quercus chry- 276 CLARENCE F. KORSTIAN solepis, Q. undulata, and Cercocarpus breviflorus, while western yel- low pine predominates on the more gradual slopes which are more retentive of soil moisture. In the more protected and more moist situations, such as canon bottoms and north slopes at the higher elevations, Pseudotsuga taxifolia, Abies concolor, Pinus fiexilis, Picea engelmanni, P. parryana, and Populus tremuloides are found. Western yellow pine occupies the more gradual slopes and situations at the intermediate elevations. A rather erratic altitudinal distribution of the species is evident in the San Mateo Mountains. At the elevation of the plots, which is approximately 8000 feet above sea level the cafion bottoms, north slopes and lower south slopes are occupied by an almost pure stand of western yellow pine which is typical of the San Mateo Moun- tains, while a belt of the more xerophytic species is frequently found on the more exposed upper south slopes above the western yellow pine. The plots were established in 1910 with the principal object of determining the rate of growth and decadence of western yellow pine in this locality. They are located in the cafion bot- toms and on the slopes, the gradients of which vary from 3 to 50%. Prior to the establishment of the plots the area had been cut-over, removing many of the mature and over-mature trees and a large proportion of the merchantable material. A modi- fied selection system of cutting to a variable diameter limit was followed when the timber was marked. Occasionally large merchantable trees were reserved as seed or fire insurance trees or to maintain the general continuity of the forest cover. When the plots were established in 1910, the diameters and total heights of all trees 3.6 inches or more in diameter at 4.5 feet above the ground were measured. Each tree was described, especially with reference to its vigor, health or decadence, its crown class and all diseases, defects or abnormalities were noted. The plots were remeasured and examined in 1915, thus giving their history for the intervening five-year period. Two well-recognized forms of Pinus ponderosa are distin- guished, "black jack" and "yellow pine," based on age, rate of growth, and the resulting color of the bark. The term "black INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 277 jack" applies to the young, vigorous trees under 125 to 150 years old which are characterized bj'' a dark, almost black, or dark brown, narrow-furrowed bark. The "j^ellow pine" form comprises the older trees which are characterized by a yellowish or reddish brown, widely fmTowed bark. A marked difference occurs between the form and volume of "black jacks" and ''yellow pines." The average ''black jack" has a greater taper, a more rapid rate of growth and approximately 10% smaller cubic volume than the average "yellow pine" of the same diam- eter and height, which are the main reasons for the segregation of "black jack" and "yellow pine" by technical foresters. Two distinct western yellow pine sites were very readily recognized through apparent differences in the composition, density, rate of growth, and vigor of the forest and the cor- responding differences in the shrubby and herbaceous vegeta- tion. The soil of Site I, which occupies the canon bottoms and the protected north slopes, is a deep gravelly clay loam contain- ing considerable amounts of organic matter and is consequently comparatively retentive of soil moisture. Site II, which i as a shallow well-drained gravelly soil containing little organic mat- ter, is found on the ridge-tops and exposed south slopes. At the time of the 1915 examination the two sites were segregated and each was mapped separately. Approximately 16.0 acres were classed as Site I, while 10.4 acres fell into Site II. The growth data were segregated in separate compilations for each site and for the two forms of western yellow pine.^^ The total volume growth or increment of all trees measured was computed for the five-year period. The total volumes were computed by applying a volume table based on diameter and total height to the dimensions of each tree at each time of measurement. The difference between the total volumes at each time of measurement represents the periodic increment and the average volume growth per year during the period con- sidered is the periodic annual increment. Table 1 shows the 15 The writer is indebted to Forest Examiners H. B. Wales and J. W. Stokes for assistance rendered in the collection and compilation of the growth data presented in this paper. 278 CLARENCE F. KORSTIAN increment of both forms of western yellow pine for Sites I and II. The data are significant in that they indicate the relative pro- ductivity of the two sites and the variability of the increment depending on the kind and amount of growing stock. The data given in table 1 represent the net increment since the volumes of all trees which died during the quinquennium were considered as negative increment and the volumes of all trees TABLE 1 Increment data for 26. Jj. acres of tTjpical ivestern yellow pine in the San Mateo Mountains of west central New Mexico, based on five years' growth TOTAL MERCHANT.\BLE VOLUME* MERCHANTABLE INCREMENT, 1910-1915 TOTAL CUBIC VOLUMEf CUBIC INCREMENT, 1910-1915 1910 1915 u 'I 1^ ^ o c3 eS 3 u < feet B.M. 75 55 130 1910 1915 a .2'S |i fees — T u a o a P- < Site I "Blackjack".... "Yellow Pine".. feet B. M. 16,720 22,250 feet B.M. 22,700 26,690 feet B.M. 5,980 4,440 feet B. M. 1,196 888 CU. ft. 9,723.4 4,872.5 cu. ft. 10,872.3 5,730.7 CU. ft. 1,148.9 858.2 cu. ft. 229.8 171.6 cu. ft. 14.4 10.7 Total for species. . . 38,970 49,390 10,420 2,084 14,595.9 16,603.0 2,007.1 401.4 25.1 Site II "Blackjack".... "Yellow Pine"... 3,110 8,040 3,720 10,450 610 2,410 122 482 12 46 58 2,955.5 2,642.6 3,147.1 3,244.7 191.6 602.1 38.3 120.4 3.7 11.6 Total for species. . . 11,150 14,170 3,020 604 5,598.1 6,391.8 793.7 158.7 15.3 * Includes the volumes in feet, board measure, of all western yellow pine trees 12 inches and over in diameter breast high. t Includes the volumes in cubic feet of all western yellow pine trees 3.6 inches and over in diameter breast high. gromng into the 4-inch class as positive increment. The fact that the plots were cut-over in 1910 under Forest Service regu- lations accounts for the relatively small amount of merchantable growing stock. The abundance of poles from 4 to 10 inches in diameter breast high which were left on the area accounts for the proportionately greater cubic volume of the growing stock. Since a number of trees grew into the merchantable class during INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 279 the quinquennium and are included for the first time in the 1915 board-measure computations, the annual increment per acre as shown in board feet is perhaps somewhat greater than the mean annual increment would be for a longer period. The annual increment per acre in cubic feet is therefore considered as a better criterion of the relative productivity of each site. It is noteworthy that Site I produced 25.1 cubic leet per acre per year as against 15.3 cubic feet for Site II or, in other words Site I produced a cubic volume of 64% more than Site II during the same five-year period. It is also interesting to compare the average breast high diameter growth of both forms of western yellow pine on the two sites. ''Black jack" averaged 0.85 inch on Site I while the diameter growth of this form on Site II was only 0.71 inch. The breast high diameter growth of ''yellow pine" on Site I averaged 0.75 inch, while on Site II it averaged only 0.54 inch. The mean diameter growth for the species as a w^hole amounted to 0.83 inch on Site I and 0.68 inch on Site II. During the course of the compilation of the pertinent data presented above an opportunity was offered to compare the average increment per tree of the different crown classes. All of the trees on the permanent sample plots were classified ac- cording to their dominance or relative position in the crown cover, into the following crown classes: X = Isolated: Trees growing in the open which do not form a con'tiguous part of the regular forest canopy. D = Dominant: Trees with crowns extending above the general level of the forest canopy and receiving full light from above and partly from the side; larger than the average trees in the stand, and with crowns well-developed but possibly somewhat crowded. C = . Codominant: Trees with crowns forming the general level of the forest canopy and recei\nng full light from above but comparatively little from the sides; usually with me- dium-sized crowns more or less crowded on the sides. I = Intermediate: Trees with crowns below, but still extending into the general level of the forest canopy, receiving a little 280 CLARENCE F. KORSTIAN direct light from above but none from the sides, usually with small crowns considerably crowded on the sides. S = Suppressed: Trees with crowns below the general level of the forest canopy and receiving no direct light either from above or from the sides; usually with small, poorly developed crowns. Table 2 shows the average increment per tree for the different crown classes on Sites I and II, only those trees being included which were living and were measured in 1910 and 1915. The greater apparent increment of the dominant crown class might be explained by the fact that in the X class a greater amount of TABLE 2 Periodic cubic increment of ivestern yellow -pine segregated by crown classes for Sites I and II .< SITE I SITE II COMPARATIVE o INCREMENT O K Basis Total periodic in- crement Periodic increment per tree Basis Total periodic in- crement Periodic increment per tree OF SITE II WITH SITE I no. of trees cu.fl. cu. ft. no. of trees cu. ft. CXI. ft. per cent X 230 622.3 2.70 204 314.1 1.54 57 D 168 617.8 3.68 87 184.4 2.12 57 C 411 721.4 1.75 247 268.9 1.08 61 I 119 69.9 .58 74 29.5 .39 67 s 14 4.4 .31 5 1.2 .24 77 limb-wood is produced, while in the dominant class, due to their relative position in the forest, there is a stimulation in the production of body-wood which is the portion of the tree meas- ured to determine the increment. When the individual trees, the component parts of an aggregate stand, are given separate consideration it is evident that not only the effects of the physi- cal site are revealed in the increment but also the effects of the individual's associates, especially their influence on the amount of light the individual receives or the amount of growing space available for its use. Although the average increment per tree varies directly with the favorableness of the conditions of the site, the writer does not wish to leave the impression that crown form may be regarded as an expression of site quality. INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 281 It is true that crown form reflects the growing conditions as determined by competition but competition cannot be regarded as a site factor. The differences in the native vegetation on the two different sites were so apparent that the writer immediately conceived the idea that it could be correlated with increment and used as an additional criterion in the determination of the productivity of a given forest site. The vegetation on a number of 5 by 10-loot quadrats was listed in addition to that on the regular permanent reproduc- tion plots of the same size, which were instituted with the pri- mary object of studying the establishment of natural reproduc- tion on the cut-over areas. Although the plots had been cut- over in 1910, the logging operation which was conducted under Forest Ser\T.ce regulations did not destroy the continuity of the forest canopy sufficiently to noticeably interfere with the sta- bilized climax vegetation since the virgin western yellow pine forest was originally comparatively open and park-like. The vegetation which was found on these Ust quadrats is systemati- cally summarized in table 3, showing for the cafion bottoms, the north slopes, south scopes and ridge tops the percentage of the quadrats on which each species was found. The arrangement of the families is essentially an adaptation of Engler and Prantl's "Die Natiirlichen Pflanzenfamilien" as used in the United States National Herbarium, which aims to indicate something of the natural developmental relationships of the families by proceeding from the simpler to the more complex. The writer desires to .express his indebtedness to Prof, J. J. Thornber of the University of Ai'izona and Grazing Examiner R. R. Hill of the United States Forest Service for determining numerous plants and for verifying the list. A perusal of the list shows marked differences in the individuality of the vegetation of the two sites. Site I is shown to produce such typical mesophytes as Mnium sp., Agrostis hiemalis, Bromus polyanthus, Muhlenbergia wrightii, Populus tremuloides, Arenaria confusa, Cerastium longipeduncu- latmn, Silene laciniata, Aquilegia chrysantha, Thalictrum wrightii, Draba helleriana, Potentilla atrorubens, P. crinita, Rosa fendleri, 282 CLARENCE F. KORSTIAN TABLE 3 Systematic summary of vegetation on fifty-three list quadrats tahen at random on the San Mateo Division of the Datil National Forest, New Mexico Bryaceae Mnium sp POACEAE Agropyron tenerum Vasey Agrostis hiemalis (Walt.) B. S. P Blepharoneuron tricholepis (Torr.) Nash Bromus polyaiithus Shear Bromus porteri (Coult.) Nash Festuca arizonica Vasey Koeleria cristata (L.) Pers Muhlenbergia gracilis (H. B. K.) Trin Muhlenbergia wrightii Vasey Poa rupicola Nash Sitanion hrevifolium J. G. Smith Sporobolus ramulosus (H. B. K.) Kunth Cyperaceae Cyperus fendlerianus Boeckel Commelinaceae Commelina dianthifolia Delile Li LI ace AE Yucca sp Orchidaceae Achroanthes montana (Rothr.) Greene Salicaceae Populus tremuloides Michx Fagaceae Quercus gamhelii Nutt Quercus grisea Liebm Polygonaceae Eriogonum alatum Torr Eriogonum jamesii Benth Polygonum douglasii Greene Chenopodiaceae Chenopodiumob longifolium (S. Wats.) Rydb PER CENT OP QUADRATS ON WHICH SPECIES OCCUR Canon bottom (12 quad- rats) 25 17 8 50 17 42 33 8 0 17 17 0 0 0 8 0 0 0 0 0 North slope (13 quad- rats) 15 0 0 0 0 69 15 69 54 0 0 31 15 23 0 0 46 0 8 8 0 Total site I (25 quad- rats) 12 4 12 4 60 16 56 44 4 0 24 16 20 0 0 0 8 24 0 4 4 0 South slope (23 quad- rats) 0 0 56 0 30 0 74 65 0 39 17 13 61 0 4 0 0 9 9 22 0 4 Ridge top (5 quad- rats) 0 0 20 0 0 20 100 40 0 0 80 0 20 20 0 20 0 20 40 40 20 0 Total site II (28 quad- rats) 0 0 50 0 25 4 64 61 0 32 29 11 54 4 4 11 14 25 4 4 INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 283 TABLE 3— Continued Nyctaginaceae Allionia divaricata Rydb ■ . . . . PORTULACACEAE Portulaca oleracea L SiLENACEAE. Arenaria confusa Rydb Cerastium lojigipedunculatuni Muhl. . Silene laciniata Cav Silene pringlei S. Wats Ranunculaceae Aquilegia chrysantha A. Gray Thulictrum imghtii A. Gray Brassicaceae Draba heUeriana Greene Erysimum, elatum. Nutt Heterolhrix lungifolia (Benth.) Rydb Rosaceae Cercocarpus hreviflorus A. Gray Fragaria bracteata Heller Potentilla ati'orubens Rydb Potentilla crinita A. Gray Rosa fendleri Crep Fabaceae Anisolotus wi-ightii (A. Gray) Rydb., A ragallus lambertii Greene Astragalus accvmbens Sheld Lathyrus graminifolius (S. Wats.) White Phaseolus angustissirmis A. Graj' . . . . Vicia americana Muhl Oxalidaceae Oxalis stricta L Geraniaceae Geranium fremontii Torr Geranium richardsonii Fi^ch. & Trautv Linaceae Linum 7ieomexicanum Greene Euphorbiaceae Euphorbia fendleri Torr. & Graj^ PER CENT OF QUADRATS ON WHICH SPECIES OCCUR Canon bottom (12 quad- rats) 17 8 0 0 8 0 0 8 0 0 8 33 8 8 17 0 17 0 25 0 0 0 North slope (13 quad- rats) 0 0 31 0 23 0 31 8 0 0 0 31 0 0 38 8 23 38 62 8 38 8 8 8 Total site I (25 quad- rats) 0 24 4 12 4 4 16 4 4 0 0 20 4 4 36 8 16 24 40 4 28 4 16 4 4 4 South slope (23 quad- rats) 13 0 0 0 9 0 0 0 4 17 9 4 0 0 0 26 0 30 35 0 26 0 4 0 0 0 Ridge top (5 quad- rats) 0 0 0 0 0 20 0 0 0 0 0 0 0 0 0 0 60 20. 80 CO 0 0 0 0 0 0 0 Total site II (28 quad- rats) 11 0 0 0 11 0 0 0 4 14 7 4 0 0 0 32 4 39 39 0 21 0 4 0 0 0 THE PLANT WORLD, VOL. 20, XO. 9 TABLE 3— Continued Rhamnaceae Ceanothus fendleri A. Gray Viola ncomexicana Greene Apiaceae Pseudocymopterus tenuifolius (A. Gray") Rydb Gentianaceae Amarella scopulorum Greene Gentiana higelovii A. Gray Polemonicaceae Gilia greeneana Woot. & Standi BORAGINACEAE Lithospermum multiflorum Torr Menthaceae Prunella vulgaris L SCROPHULARIACEAE Castilleja trinervis Rydb Mimulus langsdorfii Don Pentstevion gracilis Nutt Pentstemon virgatus A. Gray Campanulaceae Campanula peiiolata A. DC ASTERACEAE Achillea lanulosa Nutt Ariemesia fonvoodii S. Wats Artemesia mexicana Willd Artemesia sp Chryso'psis villosa (Pursh) Hook Coleosanthus peliolaris (A. Gray) Greene Conyza coulteri A. Gray Dugaldea hoopesii (A. Gray) Rydb Erigeron divergens Torr. & Gray Gymnolomia multi flora (Nutt.) Benth & Hook Hymenopappus mexicamis A. Gray. . . . Hymenopappus radiatus Rose Machaer anther a aquifolia Greene Oreochrysum parryi (A. Gray) Rydb?. Senecio quaerens Greene? Solidago ncomexicana (A. Gray) Woot. & Stand Stevia serrata Cav Villanova dissecla (A. Gray) Rydb... . PER CENT OF QUADR.\TS ON WHICH SPECIES OCCUR Canon bottom (12 quad- rats) 17 0 0 8 0 8 16 8 0 8 33 8 17 0 8 0 0 25 17 0 0 42 0 0 0 17 25 North slope (13 quad- rats) 0 23 38 15 8 23 0 54 0 15 8 69 0 46 8 15 0 0 15 0 0 8 0 77 0 0 38 0 n Total site I (25 quad- rats) 8 16 20 8 8 0 16 36 4 8 8 52 4 32 4 12 0 0 20 4 8 4 0 60 0 0 20 8 12 South slope (23 quad- rats) 9 0 48 0 0 22 4 0 0 0 26 0 0 4 30 0 4 44 4 4 56 0 4 17 13 35 17 13 0 0 Ridge top (5 quad- rats) 40 0 60 0 0 0 20 0 20 0 40 0 0 0 0 0 40 20 0 0 100 0 20 20 0 20 20 20 0 0 0 Total site II (28 quad- rats) 14 0 50 0 0 18 7 0 4 0 29 0 0 4 25 0 11 43 4 4 64 0 7 18 11 32 18 14 0 0 284 INDICATOR SIGNIFICANCE OF NATIVE VEGETATION 285 Geranium richardsonii, Viola neomexicana, Amarella scopulorum, Gentiana higelowii, Prunella vulgaris, Mimulus langsdorfii, Penstemon virgatus, Campanula petiolata, and Solidago neo- mexicana. Site II bears such transitory species and xerophytes aa Poa rupicola, Commelina dianthifolia, Yucca sp., Quercus grisea, Portulaca oleracea, Heterothrix longifolia, Cercocarpus hreviflorus, and Hymenopappus radiatus. The moss {Mnium sp.) was only found in cool, moist and shaded situations, thereby indicating unusually favorable site conditions. The monkey flower {Mimulus la7igsdorjii) was the only plant which was confined to the proximity of water, indicating excessive soil moisture conditions. Practically all of the species listed as occurring entirely on Site II, which do not overlap on other sites, were found in hot, dry and unshaded situations and might be regarded tentatively as indicators of poor western yellow pine sites in the San Mateo Mountains. The mesophytes listed as possible Site I indicators were not found on poorer sites in this locahty. However, it may be true that further detailed studies in the San Mateo Mountains might require a different listing of the vegetation than that here given. A number of the species Hsted as occurring on only one site are, to the writer's personal knowledge, kno^\^l to occur on different sites in other parts of the Southwest. The vegetation on Site II was comparatively sparse and more open than on Site I where it was also more luxuriant and vigorous. Those species which were found to overlap on both sites normally made their optimum development on Site I. Approximately twice as many species were found on Site I as on Site II. It is there- fore with some reluctance that certain opinions are advanced regarding the indicator significance of the natural vegetation. The writer is not attempting, however, to state that certain species are positive site indicators or that others are negative indicators. The rather superficial nature of the field observa- tions will only permit of a few more or less general statements concerning the latent possibihties in the use of the native vege- tation in the classification of forest sites and in the determina- tion of their productivity. 286 CLARENCE F. KORSTIAN In studying the indicator significance of the native vegetation it is necessary to go directly to the individual species instead of attempting to stop at the association, society, or community, since the vegetation as an integral is composed of individual sj>ecies and in intergrating the vegetation it must be remembered that the behavior of the vegetation is a resultant function of the behavior of the component species. It is impossible in arid and semi-arid regions having many diverse biological growth forms, to select a group of plants which may be regarded as associates without finding that the association may have been disorganized elsewhere and that some of the individuals enter into other associations as component parts. It is freely admitted that the best ultimate criterion of site quality is the increment of the aborescent species concerned, as judged by the measurement of an approximately fully stocked stand. In cases where the increment data are rather meager or are entirely lacking the native vegetation present should serve as a valuable criterion of site for those species addicted to growing in rather open, park-like stands, such as western yellow pine. In this connection it should be remembered that a plant rarely requires more than a few years at most to reach the adult form, w^hile the forest often requires a century or even two in which to reach maturity. The \\Titer believes that the native vegetation found on deforested areas may be considered as a criterion of the latent potentialities of the site for forest produc- tion provided the vegetation has not been too severely and too recently disturbed and that the more important phases of the successional series are properly understood. Studies are under way at the Utah Forest Experiment Station in central Utah, the object of which is to determine the feasi- bility of using native plants as indicators of suitable forest plant- ing sites. By making detailed studies of the root systems and subterranean moisture-absorbing surfaces of the typical her- baceous, shrubby and arborescent species of each important association, the value of the native vegetation as indicators of those climatic and edaphic conditions under which the important coniferous species may be planted successfully should be deter- INDTCATOR SIGNIFICANCE OF NATIVE VEGETATION 287 mined. The studies of the depth and character of the root systems will lead to the determination of the different successional stages of the native vegetation on burned-over or cut-over land. It is very probable that the sudden removal of the vegetative cover renders the site less favorable for the successful establishment and optimum development of the climax species and the more favorable for the invasion of species normally occurring on poorer sites at lower elevations. The fundamental study of forest planting .sites logically re- solves itself into three categories: (1) the empirical establish- ment of plantations and the observation and study of their survival and subsequent development, (2) the measurement and study of the most important phj^sical factors of the site, such as the available soil moisture or growth water and evaporation, and (3) the indicator significance of the native vegetation occur- ring on the sites impljdng a very careful correlation of all three phases, especially the correlation of the species with the physical conditions which produce them, and a study of the relative transpiration of the natural and planted vegetation. It is readily conceivable that site studies of this character will be of the utmost value in explaining the presence or absence of tree growth on certain areas, in the judicious selection of the proper species and sites in the reforestation of much of the denuded forest land of the United States, and in establishing a working basis for the classification of the potential productivity of forest lands. Only after considering the relative agricultural and forest productivity of the land on a combined scientific and economic basis, can a positive conclusion be reached that its greatest utility lies in its use for forestry or for agricultural purposes. THE ADAPTATION OF TRUOG'S METHOD FOR THE DETERMINATION OF CARBON DIOXIDE TO PLANT RESPIRATION STUDIES^ A. M. GURJAR Minnesota Agricultural Experiment, Station , St. Paul, Minn. In plant studies invohdng the phenomena known as respira- tion, there is often occasion to determine the quantity of carbon dioxide respired. This is regarded as an accurate, and at the same time the most readily determinable, index of respiratory activity available in laboratories not provided with an elaborate respiration calorimeter. Satisfactory methods for the deter- mination of carbon dioxide are accordingly ot interest to plant physiologists and biochemists who are concerned with this phase of phytochemistry. In the preliminary work on the study of the respiration of stored grain which the writer is conducting, it became evident that there were two requisites which the method for the deter- mination of carbon dioxide must satisfy in order to be applicable to this purpose. First, since the plant tissues are constantly respiring, in determining the rate of respiration it is necessary that the accumulated carbon dioxide be rapidly removed from the respiration chamber. Second, the method must accom- modate the wide variations in the quantity of carbon dioxide to be determined, wdthout materially sacrificing accuracy. The customary, and most convenient method of determining the quantity of carbon dioxide in the atmosphere of the res- piration chamber, is to sweep COo-free air through it, and absorb the respired CO2 in some form of absorption train. The con- ventional absorption train, in which small potash bulbs are employed, is of limited value because of the slow rate at which 1 Published with the approval of the Director as Paper No. 58 of the Journal Series of the Minnesota Agricultural Experiment Station. 288 1 DETERMINATION OF CARBON DIOXIDE 289 the gases must be passed through it. It cannot be employed where the time element is significant. The method of Truog^ in which the carbon dioxide is absorbed in a measured quantity of I Ba(0H)2 solution contained in a special absorption tower, and the residual barium hydroxide titrated against a standard HCl solution, seemed best adapted to this purpose. The ad- vantages of this method, together with a discussion of titrimetric methods, are presented by Truog. In assembling the apparatus certain difficulties were encountered, however, and an attempt was made to overcome them. Thus the original form of absorp- tion tower did not provide an adequate means for transferring the standard Ba(0H)2 solution, and C02-free water from the stock bottles to the absorption tower without exposing them to the atmosphere. An automatic pipette was accordingly con- structed which was connected to both the stock bottle and the tower in such a manner that the Ba(0H)2 solution could be trans- ferred and measured through a closed system protected from the laboratory air by soda-lime tubes. A convenient arrangement for rendering the wash- water free from CO2 without disconnecting the reservoir w^as also assembled. These additions rendered the apparatus more efficient for plant respiration studies, and they are described in detail in this paper. DESCRIPTION OF THE APPARATUS The complete apparatus is illustrated in the accompanjdng figure. The absorption flask and tower tube are similar to those employed by Truog, except that the tube is provided mth an adapter, D, at the top. This adapter has a belled top, which not only affords a tight connection with the rubber stopper, E, but can be readily separated from the stopper in disconnecting the several parts of the apparatus. This adapter is connected to the tube, C, by means of a packing of pure gum tubing. The stopper, E, has two holes, one of which admits the tip of the automatic pipette, H, and the other the lower tube ol the U-tube, ^ Truog, E. Method for the determination of carbon dioxide and a new form of absorption tower adapted to the titrimetric method. Jour. Ind. and Engin. Chem. 7: 1045-1049. 1915. 290 A. M. GURJAR F. The automatic pipette is connected through a three-way cock to the stock bottle containing the Ba(0H)2 solution and is filled by raising the pressure in the bottle by means of the rubber bulb, L, opening the pinch-cock, 2, and turning the glass cock to the proper position. The pipette is drained by turning the stop-cock over, and a mouth piece, /, is provided with an inter- mediate soda-lime tube, S. One of the arms of the U-tube, F, is fused to a cylindrical separatory funnel, G, which serves as a container for the. water used in diluting the Ba(0H)2 solution and in washing out the tower when the aspiration is completed. This funnel is filled by raising the pressure in the large stock bottle of water with the rubber bulb, L, and opening the pinch-cock S. The other arm of the U-tube is connected to the intake of the meter, M, which in turn is connected to the aspirator. This arrangement makes unnecessary a third hole in the stopper, E. The U-tube and auto- matic pipette are supported by clamps attached to a standard. TECHNIQUE OF THE DETERMINATION Clean glass beads are placed in the tower, C, to a depth of from 16 to 20 inches, the depth depending upon the quantity of Ba(0H)2 solution to be used. The stopper, £',is placed tightly in the adapter, D, at the top of the tower, and carbon dioxide-free air is aspirated rapidly through the beads and tower to free them of CO2 Alter about five minutes of \dgorous aspiration the suction is released, and the automatic pipette is filled to the mark* with Ba(0H)2 solution. Should the solution overrun the mark on the pipette stem, on releasing the air pressure by opening pinch-cock, /, the solution will run back in the bottle by opening pinch-cock,^, and the proper level may be reached in the pipette. The three-way cock of the automatic pipette is then turned over, and the Ba(0H)2 solution allowed to flow into the tower. The last drop is removed by blowing twice through the mouth-piece, J . It was found that when blown uniformly, the pipette would dehver with a maximum variation of 0.01 cc. Since 1 cc. of | Ba(0H)2 is equivalent to about 6 mgm. of CO2, 25 cc, will absorb DETERMINATION OF CARBON DIOXIDE 291 about 125 mgm. of CO2 and leave a safe excess of Ba(0H)2. Should the quantity of CO2 to be absorbed exceed this amount, two charges from the pipette must be transferred to the tower; if less, one charge is employed, and about an equal volume of C02-free water. The tubulure of the suction flask is then con- Fig. 1 nected to the respiration chamber, a minimum of rubber tubing being exposed to the current of gases. In the bulk-grain respira- tion studies, an 18 in. calcium chloride tower, A, has been employed as a respiration chamber. The latter is connected at the top to a gas washing de\dce charged with 50% KOH solution for remov- 292 A. M. GURJAR ing the CO2 in the air employed for flushing out the air in the chamber. Pinch-cock, 6, being opened, aspiration is begun at a slow rate, the gases being drawn through the meter, M. The meter readings show the volume of air which has been drawn through the system. With bulk grain ten volumes of the capac- ity of the respiration chamber completely flushes out the CO2 in the latter. After about one volume of air has been drawn through the tower the rate of aspiration may be increased. It has required about 45 minutes to complete the aspiration in the studies mentioned. The tower is then disconnected at the stopper, E, and elevated from the suction flask sufficiently to permit the beads and Ba(0H)2 solution to flow down into the flask. About 50 cc. of COo-free water are run from the separatory funnel, G, down the sides of the tower, while the latter is being revolved in such a manner as to insure thorough washing of its inner wall. The suction flask is disconnected from the respiration chamber, the tower hfted out of the flask, and the residual Ba(0H)2 titrated against a standard HCl solution, using phenolphthalein as an indicator. Checks of the apparatus and method, using C. P. CaCOs have demonstrated their desirability and accuracy for this purpose. PREPARING THE CARBON DIOXIDE-FREE WATER The stock-bottle for the CO2 free water may be easily filled without removing the stopper by disconnecting the rubber tube to which pinch-cock, 3, is attached, and connecting it to the distilled-water container, opening pinch-cock, 4, and connecting the tube to which it is attached to the aspirator. When suction is applied by means of the latter, water is rapidly drawn into the bottle. The water may be tendered free from carbon dioxide by closing pinch-cock, 3, and opening pinch-cock, 5. Air may thus be passed vigorously through the water, about thirty min- utes of aspiration rendering it sufficiently pure for this purpose. To determine its freedom from CO2, 100 cc. are titrated against ■/o KOH, using phenolphthalein as an indicator. It should not require more than 0.2 cc. of the KOH solution to produce a permanent pink coloration. DETERMINATION OF CARBON DIOXIDE 293 The apparatus arranged and operated in the manner described seems to satisfy the requirements outhned in the second para- graph. It has been employed in this laboratory with very satisfactory results. ENVIRONMENT OF SEEDS AND CROP PRODUCTION BYRON D. HALSTED and EARLE J. OWEN New Jersey Agricultural Experiment Station, New Brunswick, New Jersey In this paper are given the results of a series of tests carried out for the purpose of determining the effect which might be exerted on germination and early growth by placing seeds in different positions, and also the relative viability and vigor of seeds from different positions in the pod. Seeds of the Scarlet Runner bean were employed in all of the tests because of their large size and favorable flat shape. Only three positions of the seeds were tested, namely (1) laid flat, (2) with the eye up, (3) with the eye down. The depth of planting was uniformly 2 inches below the surface, and special care was taken to have the center of gravity of each seed, however placed, level with the surface of the soil, after which the cover of fine earth was added and the top of the bed brought to a level by means of a straight- edge. There were six plantings in duplicate, making in all 4050 seeds. The varying conditions during the winter made some differences among the six sets of experiments, but all of the seed-positions were treated alike, and are strictly comparable. At the same time a test was made of the relative value for planting of seeds from pods with two, three and four seeds respectively and also of the bearing of the position of the seeds in the pod upon their viability and vigor. All the tests were made during the period extending from November 21, 1916 to March 12, 1917. No record of the soil temperature was made during the first series, but it was compar- able with that for the last one. It is noted that the Scarlet Run- ner seeds are sensitive to the soil heat, and the viability falls rapidly with the temperature, for example from 92.9% in early December to 76.0% in February (18.1°C.) and arose again to 94.2% in March (21.5°C.) 294 SEEDS AND CEOP PRODUCTION 295 The seedlings were harvested when they averaged near 300 mm. in length, the periods of growth ranging from twenty-four to thirty days and records for each seedling were made of its weight (that of the original seed being deducted) and of lengths of hy- pocotyl, first, second and third internodes and total length. The averages for the time required for the seedling to reach the surface of the soil (emergence) are: flat 12.54 days, eye up 13.02 days and eye down 12.80 days. This shows that seeds placed flat are a full half day quicker in breaking ground than when the eye is placed uppermost. Table 1 shows the greatest viability for the position with the eye down and least where the seeds are placed with the eye up. The greatest vigor is associated with the fiat seeds, but the TABLE 1 Averages for the three positions in the soil for the combined six series Viability Vigor (green weight) Hypocotyl First internode Second internode. . . . Third internode Total length 86.12% 8.98 gr. 12.54 mm. 137.17 mm. 97.43 mm. 46.80 mm. 310.11 mm. EYE UP oi .uu/o 8.78 gr. 11.63 mm. 137.6 mm. 93.20 mm. 35.80 mm. 292.11 mm. EYE DOWN 87.22% 8.74 gr. 12.96 mm. 136.88 mm. 96.71 mm. 49.56 mm. 317.83 mm. hypocotyl is longest where the seeds are planted with the eye down. It is noted that the loss of hypocotyl length when the seeds are with eye up, is balanced by the longer first internode, so that the length from root juncture to the second node is prac- tically the same for all three soil positions, but after that point is passed, the seedlings from seeds planted with the eye up fall behind the others. There is little choice between the flat and the eye down position and therefore in field planting the ordinary method seems satisfactory, namely to drop the seeds flat upon the ground. Weight. Table 2 shows that the seed-weights vary much with the numbers of seeds and with the position of the seeds. 296 BYEON D. HALSTED AND EARLE J. OWEN in the pod. The seeds averaged lowest in weight in the 2-seeded pods and there was but little difference in the 3-seeded and 4-seeded pods, the former being the heavier. For position in the pod, the basal seeds averaged lightest and the middle seeds are the hea\dest, those from the middle of 3-seeded pods being heaviest of all. TABLE 2 Relations of number of seeds and their position in the pod to weight, viability and vigor TYPE PLANTED 2-seeded, base 2-seeded, tip 3-seeded, base 3-seeded, middle 3-seeded, tip 4-seeded, base 4-seeded, first middle. . . 4-seeded, second middle. 4-seeded, tip WEIGHT (seed) grams 0.847 0.908 1.066 1.171 1.101 0.997 1.082 1.127 1.107 VIABILITY per cent 87.30 84.18 81.53 87.51 75.08 76.43 83.76 84.40 83.73 VIGOR (seed- ling weight) grams 7 8 7 7 7 7 741 388 329 960 593 153 8.038 8.193 7.764 Pod averages 2-seeded 0.928 1.115 1.078 85.74 81.37 82.08 9 065 3-seeded 7 627 4-seeded 7 408 Position averages Base 0.970 1.138 1.041 81.75 84.08 81.00 7.408 Middle ' 8.038 Tip 7.915 Viability. Germination power is greatest in the seeds from 2-seeded pods and there is but little difference between those of the 3-seeded and 4-seeded pods. The seeds borne in the middle have a higher viability than either the basal or tip ends. Vigor. The seeds from 2-seeded pods produce a greater average weight of seedling than those from 3- and 4-seeded pods. In pod averages with a single slight exception, there is a uniform negative correlation between seed-weight and both viability and vigor. SEEDS AND CROP PRODUCTION 297 When considered as to the position in the pod the heaviest seeds show the greatest \dabiUty and produce seedhngs of greatest vigor, while the hghtest seeds (again with a shght exception) show the least ^dability and \dgor. Observations. The above results indicate that the common practice of dropping the seeds flat upon the soil is satisfactory. The comparatively smaller seeds when borne two in a pod are superior in viability and vigor, and the middle seeds (from 3- and 4-seeded pods) outrank all others in weight. Both number of seeds and their position in the pod are environ- mental factors that influence the crop-producing value of the seeds. If the selection of seeds for planting is with pods only, the first choice is those bearing two seeds. If only position in the pod is considered the middle seeds are chosen, but if both pod and position are regarded the tip seeds in two-seeded pods are superior to all others and the second choice is the third seed from the base in 4-seeded pods, followed closely by seeds from the other two middle positions. The second seed from the base is always of high grade and may be exceeded by the one next above when the pod has four seeds. BOOKS AND CURRENT LITERATURE The Mosses of New York. — Doctor Grout's Moss Flora of New York City and Vicinity ^ is a valuable addition to the list of bryological works now available for moss students in the northeastern and middle Atlantic states: It is an attractive book of 119 pages, containing keys to the families, genera, and species, descriptions of families and genera, and interesting notes on the habitat and distribution of the various species. At the back of the book are 12 plates, containing 20 half-tone illustrations made from some of the excellent photographs for which the author is noted. The area embraced in the book, or annotated list as it might be called, includes all counties of New York and New Jersey lying adjacent to the city, with localities outside of this area for rare or unusual species. The author notes that he has for fifteen years "made a careful study in the field, of the mosses of eastern Long Island and of Staten Island" and he accordingly^ includes all available data for Long Island. The area includes the region around Closter, New Jersey, so exhaustively collected over by the late C. F. Austin, whose work is thus referred to by Dr. Grout: 'Tn New Jersey the mosses of the north and those of the south meet, and it seems to one who scans Austin's work with care that he found there almost all the mosses of eastern North America." Dr. Grout's list enumerates about 380 species and varieties, with notes on a few other species, so that its range of usefulness is greater than its title would indicate. A carefully prepared list such as this will always stimulate study in the locality to which it pertains and, in any of the more densely settled regions it will, to quote again from the author's preface, "put on scien- tific record facts of natural history that will soon have vanished beyond the possibility of record or recall." We hope to see other regions of our country represented by lists of this character. Noting the peculiar lack of tree-growing mosses around New York City the author is inclined to believe the cause to be gases produced m the city. The reviewer is inclined to believe that, around industrial cities at least, iron-ore dust, coal dust, etc., with associated products such as sulphurous and sulphuric acids, may be of importance in pre- 1 Grout, A. J. The Moss Flora of New York City and Vicinity. Pp. 119, pis. 12. Published by the Author, New Dorp, N. Y., October 1916. 298 BOOKS AND CURRENT LITERATURE 299 venting the appearance of small-spored plants such as mosses, Hchens, hverworts, and parasitic fungi on fences, tree trunks, leaves and other situations. — O. E. Jennings. Growth-Forms of Natal Plants. — Bews has added another paper to the valuable series in which he' has so materially increased our knowledge of the ecological aspects of Natal' This contribution discusses the growth-forms exhibited in the 3034 species which form the flora of Natal. The system of Raunkiar is used, with its most recent modifications, comprising the recognition of stem-succulents and epiphytes and the subdivision of the large erect and woody plants, or phanerophytes, into three classes on the basis of their height. The author is by no means blind to the artificial character of the Raunkiar system of growth-forms, and expresses his preference for the more natural system of Warming. The simplicity of the former, .however, and the difficulty of applying even the least exacting system to the plants of a region which is ecologically so little known, have led him to use this popular system of analyzing the ecological character of the flora. Natal is poor in large trees and in stem-succulents and epi- phytes. Large shrubs and small trees (microphanerophytes) and small shrubs (nanophanerophytes) each form 14% of the flora. Root- perennials and other low perennials (chamaephytes) form 19% of the flora, while the true root-perennials (hemicryptophytes) and the bulb- ous and tuberous plants (geophytes) each form 18%. When com- pared with the average conditions for the world (the normal "spectrum"), Natal is shown to be rich in chamaephytes and geophytes and relatively poor in hemicryptophytes and therophytes (annuals). Bews dis- cusses fully the role of the various growth-forms in the forests, bush, and veld of Natal. — Forrest Shreve. Working Plans for Forest Organization. — The original edition of Recknagel's Theory and Practice of Working Plans, which appeared in 1913 has recently been revised and corrected.^ As the title implies, the book concerns itself with the practice rather than the scientific side of forestry. It deals, with that branch of forest practice known as Forest Organization. Quoting from the introd action: "Forest organiza- tion, a subdivision of forest management, deals with the principles of 1 Bews, J. W. The Growth-Forms of Natal Plants. Trans. Royal Soc. So. Africa, 5: 605-636. June, 1916. - Recknagel, A. B. The Theory and Practice of Working Plans. NeM' York, John Wiley and Sons, 1917. i THE PLANT WORLD, VOL. 20. NO. 9 300 BOOKS AND CURRENT LITERATURE organizing a forest for business." The book is intended for professional foresters and students of forestry; it is too technical for the layman who merely desires a general view of the subject. As a text book it has already gained wide popularity in forest schools. As stated in the preface to the first edition, the author makes no claim for presenting original theories, but aims merely to present the best of European ideas adapted to the needs of American forestry. European text books, while serving as a foundation for American forestry, have often failed to meet the needs of the student and practi- tioner in this country, because European conditions are very different from those met here. The endeavor of the author has therefore been to present the most fundamental principles and to show how they may be applied under American conditions. Numerous references to American forest problems bring the ideas home to the American reader in a way which the. older European literature can not do. — G. A. Pearson. The Node of Angiosperms. — The first member of a series of papers by Sinnott and Bailey on the phylogeny of the angiosperms proposes a principle^ which may prove to be of broad application in classification. Study of a large number of angiosperms shows that while the petiole is too much influenced by ecological factors to furnish facts of phylo- genetic significance, the basal region of the leaf shows a simpler and more constant condition, and in it the number of leaf -traces is char- acteristic of the great groups. It is concluded that among angio- sperms the primitive number of traces is three (as in Amentiferae), and that evolution has taken place in two directions: (1) by increase in the number of leaf-traces, as in Umbelliflorae, (2) by reduction to one trace as a consequence of fusion of the original three (Cruciferae) , or of disappearance of the two lateral strands (Aquifoliaceae). In another paper of the series^ the theory is extended to account for the position and distribution of stipules. In the third paper of the series^ the origin of herbaceous angiosperms from woody forms is discussed at length, from the standpoints of paleobotany, anatomy, phylogeny and phytogeography. It will be seen that the good old story of transi- tion from herbaceous to woody stem structure has received some hard blows of late years. — M. A. Chrysler. 1 Sinnott, E. W. The Anatomy of the Node as an Aid in the Classification of Angiosperms. Amer Jour. Bot. 1: .303-322. 1914. 2 Sinnott, E. W. and Bailey, I. W., Nodal Anatomy and the Morphology of Stipules. Amer. Jour. Bot. 1: 411-453. 1914. 'Sinnott, E. W. and Bailey, I. W. The Origin and Dispersal of Herbaceous^ Angiosperms. Ann. Bot. 28: 547-600, pis. .39, 40. 1914. NOTES AND COMMENT The Plant World is now in its twentieth year. It began its career as a magazine for the amateur botanist and nature-lover. The number of amateurs interested in botany twenty years ago was not as great as the number of men and women who are today professional- ly engaged in botanical work or the application of scientific principles to problems of plant utilization or plant production. When The Plant World was founded the professional botanists of this country were outnumbered by hundreds of persons who derived pleasure and bene- fit from the collecting of plants or the use of the microscope. At the present time the men who are engaged in research or instruction in pure botany, and the men who are deriving enjoyment from botanical pursuits as a hobby, are even more heavily outnumbered by the thou- sands who are using their knowledge of plants in the service of man- kind. The changes that have been made in The Plant World during the twenty years of its existence have been a reflection of the changes in botany and its allied subjects, and have been a part of the growth of science. It occupies a unique place among botanical journals in hav- ing no financial support from any institution or society, deriving its income entirely from subscriptions and from sources of profit wliich are bestowed upon it by members of the Plant World Association. This makes its policies more independent and its field of service more capable of rapid adjustment to the changes of the tunes. We are now passing through a period of our national history in which it seems particularly fitting that we should consider the func- tions which are being performed by our scientific journals, and the role that they can play in the relation of science to the general progress of human affairs. The sums of money expended in the publication of scientific work are largely a direct tax upon science itself, being derived either from the emoluments of individual scientists, or' from funds which are just as available for promoting investigation as for publishing results. It is the earnest desire of the members of the Plant World Associa- tion that this journal use its resources in a very clear-cut sense of 301 302 NOTES AND COMMENT service to botany in particular and to science in general. Like the majority of botanical and zoological publications The Plant World is not in the custom of paying for its contributions, and is therefore in the position of offering to its readers that wliich its contributors have regarded as worthy of their time and efforts. Practically all of the papers published in The Plant World during the past five years have been contributed by readers of the journal. It is to this group, there- fore, that we must look for all efforts to increase the effectiveness of our pages at the present time. We are deeply desirous that this journal should serve not only as a record of investigations but as a means of articulating the botanical work of America with the progress of science in general and with the appreciation of the growing audience outside of strictly professional circles to whom the larger features of our advancement are of interest and value. The Plant World is anxious to have its readers make still further use of its pages as a medium of publication. Articles embodying original work are always of the highest order of importance, but it is desirable that such articles be succinct, even if they are not brief, both for the sake of the economy which is now (and always) a national duty, and for the sake of securing a larger audience among the hurried read- ers who also see many other periodicals. The time is rapidly approach- ing— if it is not already here — when the funds which are available for scientific work in America will be measured directly by the degree to which the intelligent people of our country understand the progress and problems of science. It is the manifest duty of the men who are engaged in scientific investigation to keep in view the utility of their work, which may be of an immediately practical character or may be of an indirectly practical but much more fundamental character. It is equally the duty of every worker in natural science to prepare from time to time short articles regarding his special field of work, written without undue use of technical terms and in a style which is readable without being superficially popular. The Plant World is not only willing to publish articles of this character but is anxious to secure them. The existence of a journal containing matter of this sort, covering botany and its allied fields, will be welcomed by the rapidly growing body of men and women who know something of the methods and aims of modern science but have no means of keeping in touch with its rapid and diversified progress. Without some medium by which the achievements and hopes of the investigator can be made known to the educated public of the country, our scientific work will NOTES AND COMMENT 303 find itself dissipated over a field of small and immediate practicalities, with its fundamental problems and important aims known only to a small group of highly trained investigators, who will find themselves isolated by the lack of being understood and hampered by the failure of securing financial support for their work. It is not an easy matter for the specialist to prepare articles of this character, but it is his duty to do so. There is no group of men in America who are better quaU- fied to perform such a service for botany than are the readers of this journal, and it is hoped that some of the splendid support which has filled its pages in past years v;ill be given it in future along the new lines indicated as well as along the familiar ones. After this journal was taken over by The Plant World Association in 1907 it depended for its financial support entirely on the income from subscriptions and advertising, and on the personal efforts of the members of the Association. During those years the journal was run with a small annual deficit, which was met by members of the Association, to whom interest-bearing notes were issued. During this period the size of the journal was maintained at a definite num- ber of pages and the most economical arrangements were made for printing. In order to provide an endowment for The Plant World, one of the members of the Association turned over to the journal the sale of ap- paratus wliich he had devised in the course of his scientific work, there- by making this apparatus generally available. Other members of the Association have since turned over special apparatus or publications to The Plant W^orld. The income derived from these sales has served to meet the deficit during the last two years, although it has been neces- sary to issue additional notes in order to secure a working capital for the maintenance of a stock of the items sold. The steadily increas- ing cost of printing and of illustrating has made very necessary the additional income secured. The absence of an annual deficit, how- ever, together with the loyal support which has been unfailingly given the Managing Editor by the members of the Association, has made it possible to issue a greater number of pages per annum and a larger amount of illustration than would have been possible otherwise. The generosity of our contributors has also been manifested on numerous occasions in connection with the regrettable but necessary ruling that articles more than 15 pages in length and illustrations in excess of four must be paid for at cost. The journal is now in the position of being 304 NOTES AND COMMENT assured of an income sufficient to publish its customary number of pages. The profits from the sale of apparatus have to be apphed to the replenislmient of stock, to the taking up of notes, and to the maintenance of a safe reserve, over and above wliich they are devoted solely to making the journal larger than it would otherwise be. THE INTERPRETATION AND APPLICATION OF CER- TAIN TERMS AND CONCEPTS IN THE ECOLOGI- CAL CLASSIFICATION OF PLANT COMMUNITIES^ GEORGE E. NICHOLS The Sheffield Scientific School of Yale University, New Haven, Connecticut During the past seven years much of the writer's study has been along the line of local physiographic plant ecology, and the need has constantly been felt of some logical and adequate, yet at the same time simple and to a certain extent elastic scheme which could be readily adapted to the ecological clas- sification of the vegetation of any region. The groundwork for such a classification is afforded by the principle of succes- sion, the fundamental bearing of which on the relationship and evolution of plant communities has been indisputably estab- lished by the work of Cowles (7, 8, 9, 11), Wliitford (24), Clem- ents (3, 4), Moss (16, 17) and others. The principal object of the present paper is to outline a plan of classification which it is thought will recommend itself because of its lack of com- plexity and because of the readiness with which it can be ap- plied, and in this connection to express the writer's views re- garding the interpretation and application of certain ecological terms and concepts. Incidentally, several new terms, or rather combinations of terms already in use, are introduced, which it is thought will prove serviceable by verj^ reason of their sim- plicity of interpretation and application. The scheme of clas- sification itself is by no means wholly new or original. It is the outgrowth, and perhaps not a very radical modification, of the classification originally devised by Cowles (S). THE UNIT OF VEGETATION WITH REFERENCE TO HABITAT The association. From the standpoint of physiographic ecol- ogy (synecology) the association, in the last analysis, repre- ' Contribution from the Osborn Botanical Laboratory. 305 THE PLANT WORLD, VOL. 20, NO. 10 OCTOBER, 1917 300 GEORGE E. NICHOLS sents the fundamental unit of vegetation. The association may be defined as: any group or community of plants, taken in its entirety, which occupies a common habitat (see Cowles 6, p. 939). In terms of dynamic plant geography it may be fur- ther defined as: any stage in a given successional series. Uniformity of habitat, then, affords the criterion of the as- sociation. The word habitat commonly has been applied some- what loosely, but from an ecological standpoint it is desirable that it should be dehmited as precisely as possible. As con- ceived by the writer, the habitat may be defined as: any unit area in which the combined influence of the various external factors which determine the ecological aspect of the vegetation is such as to produce an essentially uniform environmeiit. It is the environment which determines the ecological aspect of a plant community. The nature of the environment, in turn, is determined by a complex of physical and chemical factors which, in a general way, may be classified as (1) climatic, (2) edaphic, and (3) biotic. (1) The cli7natic factors comprise all those atmospheric conditions through whose widespread uni- formity the character of the regional climate is determined. These include: (a) atmospheric humidity, (b) precipitation, (c) temperature, and (d) light. (2) The edaphic factors in- clude all conditions which are attributable, directly or indirectly, to soil or topographic agencies. Their influences may be exerted either through the medium of the ground or through that of the atmosphere. The ground influences are attributable to: (a) soil factors (the physico-chemical nature of the soil, and the ground-water relations); (b) slope factors (the inclination of the ground's surface, i.e., the degree to which it departs from the level) ; and (c) dynamic physiographic agencies, where these are operative (as seen in the phenomena of erosion and deposi- tion). The edaphic atmospheric influences are seen in the local modification of the climate associated with differences in ex- posure, which in turn are attributable to variations in topog- raphy: thus, a north-facing slope commonly possesses a some- what different "local climate" from a south-facing slope; similarly, the "local climate" of a ravine differs from that of CLASSIFICATION OF PLANT COMMUNITIES 307 an exposed hillside; etc. While such local atmospheric dis- similarities represent merely modifications of the climate of the region, a distinction may well be drawn . between these local climatic factors, which in the main are attributable to edaphic influences, and the regional climatic factors. For the sake of convenience, any area in which the combined influence of the various edaphic factors is essentially uniform throughout may be termed an edaphic unit area. (3) The hiotic factors include all conditions which, directly or indirectly, are at- tributable to plant or animal agencies. Their influence is seen (a) in the ameliorating effect of humus on the water rela- tions, etc. of the soil, and (b) in the effect of shade, as it inhibits the development of intolerant plants, modifies the evaporating power of the air, etc. (in this connection, see Cowles, 11). In view of the foregoing remarks, the habitat may be further defined as any unit area in which the combined influence of climatic, edaphic, and biotic factors is essentially uniform throughout. Giving the term this precise interpretation, it becomes evident at once that many an area, such as a pond, a ra\dne, or a salt marsh, which only too frequently is char- acterized as a ''habitat," should be regarded rather as a series of habitats. The various factors which, as above indicated, are responsible for the local variations in the nature of the en- vironment and for the consequent' delimitation of distinct habitats, in other words, the edaphic and the biotic factors, taken collectively, may be termed the habitat factors, in contrast to the regional climatic factors, the influence of which is wide- spread and essentially uniform throughout the region. Although the nature of the habitat afl'ords the actual criterion, plant associations, as a rule are most readily distinguished in terms of their vegetation; thus, in the case of a pond: the Nymphaea association, the Scirpus-Typha association, etc. Floristic subdivisions of the association. In its ecological aspect an association is essentially homogeneous throughout. Floristically, however, it is commonly subject to more or less variation. Where the variation concerns the dominant species (fades) it is often possible to distinguish different consociations, 308 GEORGE E. NICHOLS i.e., subdivisions of the association ''characterized by a single dominant" (Clements 4, p. 129). Where the variation concerns species of secondary importance it is similarly possible to dis- tinguish different societies. Thus, a deciduous forest may be essentially uniform in its structure throughout, so far as the dominant species are concerned; or certain species may dominate locally, gi'V'ing rise to more or less distinct consociations. Simi- larly, the herbaceous or shrubby vegetation in such a forest may, and usually does, vary locally, giving rise to more or less distinct societies. In the case of both the consociation and the society, the floristic composition of the vegetation affords the sole criterion, although there may also be slight but rela- tively inconsequential variations in the habitat. The con- sociation and the society, then, represent floristic and not ecological units. The association-type. The nature of any given habitat is determined by a number of more or less definite, though not always tangible factors. Wherever, within a given chmatic region, a given set of habitat factors is duplicated, the same type of habitat is the result. To express it algebraically: if it is assumed that the nature of a given habitat. Hi, is determined by the combined influence of the factors, Ai, Bi, Ci, and Di, and if this fact be expressed by the equation Hi = f{Ai, Bi, Ci, Di), then wherever the combination of factors Ai, Bi, Ci, Di recurs, the value of H will be the same. Of course, the exact application in practice of this criterion of the habitat would necessitate a vastly more accurate knowledge of the factors which determine its nature than is actually available, so that as a matter of fact the parallels must be based to a large extent on superficial ob- servations. But, in a general way, numerous parallel series of habitats may be distinguished in every region. In comparing two neighboring ponds, for example, the habitat occupied by the Nymphaea association in the one may duplicate the habitat occu- pied by the Nymphaea association in the other; or the habitat of the Scirpus association in the one may duplicate the habitat of the Typha association in the other; etc. Similarly, the individ- ual habitats occupied in different Connecticut salt marshes by CLASSIFICATION OF PLANT COMMUNITIES 309 the Spartina glabra association are essentially similar through- out; and so on. Habitats which thus are equivalent to one another may be referred to a common habiiat-type. . In any given region, owing largely to the existence of these parallel series of habitats, there have been developed corre- spondingly numerous parallel series of associations. Different individual associations which are correlated with the same type of habitat and which as a result agree with one another in their ecological aspect, i.e., which are ecologically equivalent, even though the}^ may differ in their floristic composition, may be considered as belonging to a common association-type. Thus, the -Nymphaea association in one pond is obviously the ecologi- cal homologue of the Nymphaea association in a neighboring pond, while the Scirpus association in the one may similarly correspond to the Typha association in the other. In the same way, an oak forest association in one locality may represent the equivalent, from an ecological standpoint, of a hickory forest association in another locality; and so on. It will be seen that, unlike the association, the association-type is a more or less abstract conception. It may be simply defined as: a type of plant association which is correlated with a given type of habitat. The term association-type has already been used by Schroter (20) in a sense analogous to that here proposed. The exact delimitation of association-types of course presents many difficulties, but in a general way it is possible to group the innumerable individual associations of a region into a compara- tively'^ small number of association- types. To a limited degree it is possible to refer to these association-types in terms of the habitat (or of the edaphic unit area) thus : rock face association- type, — middle beach association-type. But such a method of nomenclature, while desirable in theory, has its limitations in practice, owing in part to the difficulty of finding expres- sions which even in a general way are descriptive of the habitats concerned (especially when biotic factors are taken into account) in part to the deficiency of our knowledge concerning the habi- tat factors. It is therefore usually necessary, just as in nam- ing the associations,. to resort to the vegetation for titles; thus: 310 GEORGE E. NICHOLS submersed aquatics association- type, water lily association-type, oak-hickory association-type, etc. It should perhaps be added that the conception of the habitat- type and of the association-type need not necessarily be con- fined to any given climatic region. This is exemplified particu- larly well by the association-types of salt marshes, which in temperate regions are essentially uniform in their ecological aspect under various climatic conditions. In general it can be stated, from the standpoint of dynamic plant geography, that in comparing the association-types in regions having different types of climate, the highest degree of parallelism is exhibited between the more primitive (i.e., the more xerophytic or more hydrophytic) association-types; and that, conversely, the least parallelism is exhibited between the more ultimate (i.e., the more mesophytic) association-types. In comparing association- types in regions having similar types of climate, on the other hand, the parallelism also extends to these more ultimate asso- ciation-types. THE SUCCESSIONAL RELATIONS OF PLANT ASSOCL\TIONS Geologic versus contemporaneous successio7is. Cowles (11) has defined three types of succession: regional successions, w^hich are attributable to widespread climatic changes; topographic successions, which are associated with changes in topography resulting from erosion and deposition; and biotic successions, which are due to plant and animal agencies. Regional succes- sions, on the one hand, extend over long periods of time; bi- otic successions, on the other, take place with comparative rapid- ity. According to Cowles, ''If, in their operation, regional agencies are matters of eons, and topographic agencies matters of centuries, biotic agencies may be expressed in terms of dec- ades. ... So rapid is the action of the biotic factors that not only the climate, but even the topography may be regarded as static over large areas for a considerable length of time" (11, p. 172). Now it is of course true that along actively erod- ing and depositing streams and coasts topographic agencies may operate with sufficient rapidity as to institute marked CLASSIFICATION OF PLANT COMMUNITIES 311 changes within a comparatively short period of time: along streams such rapid changes are commonly associated with the erosion of ravines in uncompacted rock and the building up and destruction of flood plains; along the coast they are associated with the erosion of bluffs in uncompacted rock, and the develop- ment or destruction of coastal swamps (e.g., salt marshes), beaches and sand dunes. In this connection, see especially Cowles (7, 8). But, in the large, rapid changes such as these are the exception rather than the rule. Over much the greater part of the earth's surface the changes due to topographic agencies are consummated so slowly that their influence on the vegetation, like that of climate, becomes apparent only when geologic periods of time are taken into account. It is indeed open to question whether in the main the successions due to topographic agencies do actually take place more rapidly than those due to changes in climate. In the glaciated regions of the eastern United States, for example, the land surface for the most part has undergone little alteration since the recession of the con- tinental ice sheet; yet during this period it is generally agreed that there have ensued profound climatic changes, which have been accompanied by correspondingly great transformations in the character of the vegetation (in this connection, see Nichols 18, pp. 237, 245, 249). If account is taken of the three types of succession defined by Cowles, then it is evident at once that vegetation can never attain a condition of equilibrium. As Cowles (8, p. 81) aptly phrases it, ''we have a variable approaching a variable rather than a constant." While conceding, however, the far-reaching importance of the climatic and topographic changes which have ensued and which will continue to ensue in geologic time, it seems to the writer that, in attempting to solve the relatively contem- poraneous problems of dynamic plant geography, much more is to be gained than lost by postulating the climatic conditions of the present, and by ignoring topographic changes, except in so far as these manifestly proceed with sufficient rapidity as to become effective within the present climatic era. 312 GEORGE E. NICHOLS Permanent and temporary associations. Postulating thus the continuance of a relatively uniform climate, from the standpoint of dynamic plant geography two secular classes of plant associa- tions are distinguishable: permanent and temporary, A per- manent association is one which has reached a condition of equilibrium with respect to climatic factors, on the one hand, and habitat factors, on the other. It has attained the highest degree of mesophytism which the nature of its environment will permit. It represents the culminating member of a specific successional series. A temporary association, on the other hand, is one which has not reached such a condition of equilibrium. Through the influence of various habitat factors it is destined to become superseded sooner or later by a (usually) more meso- phytic type of vegetation. It therefore represents merely a transient stage in a given successional series. The concept of a uniform regional climax association-typ3. Un- der favorable conditions, as a consequence of the progressive reaction of the habitat factors and the concomitant succession of plant associations, the vegetation of a given area may attain the big'. est degree of mesophytism which t^ e climate of t'le region permits. This type of association, which represents the climax for the region, may be designated the regional climax association-type.^ Now it is commonly stated or implied in ecological literature that in every region, as the logical consum- mation of progressive successional changes, the vegetation of all soils and all types of topography is destined eventually to acquire the same degree of mesophytism that characterizes the regional climax association-type; that, while in unfavorable situations the influence of certain habitat factors may diminish the rapidity of the succession, it -does not alter the final out- come; that ultimately, although the time may be indefinitely postponed, the regional climax is destined to be attained in all areas. If this idea is correct, then of course no associations can be regarded as permanent except those which belong to the regional climax association- type. This is the working-liypo- 2 Clements (4, p. 128) would restrict the use of the term association to these climax associations. CLASSIFICATION OF PLANT COMMUNITIES 313 thesis which the writer followed in his earlier field-studies; but observations continued over a number of years have made it seem increasingly evident that such an assumption is unten- able from the standpoint of contemporaneous dynamic plant geography. This hypothesis fails either to accord with theoreti- cal considerations or to harmonize with observed facts. Edaphic influences as limiting factors in succession. Now of course it is not disputed that the trend of succession is almost universally mesotropic; that in the vast majority of areas where the phenomenon of succession is taking place there is a constant tendency for the vegetation to approach in its ecological aspect that which characterizes the regional climax association-type. However, it is certainly true that the rate of succession is in- fluenced to a marked degree by the edaphic factors; and, in the opinion of the writer, the effect of these factors goes even fur- ther: not only do they influence the rate of succession; they also determine the extent to which the succession can proceed. In other words, they place a limit on the degree of mesophytism which is capable of attainment. The point which it is desired to emphasize is simply this: that while in edaphically favorable situations the regional climax association-type is capable of attainment, in edaphically unfavorable situations the succes- sion may become arrested at a point far short of this climax; and that in this way there may arise associations which, while they are less mesophytic than the regional climax association-type, nevertheless are permanent with reference to the coeval climatic conditions and must therefore be regarded as climax-types. This point is capable of logical demonstration, somewhat as follows. In the first place, it may be stated that the ecolog- ical aspect of any plant association is the combined function^ of those factors which determine the environment; in other words, the aspect of the vegetation is conditioned by the combined influence of the climatic and the habitat factors. Assuming, ' It would be perhaps more accurate to state that the ecological aspect of a plant association is a function of eich of the integral factors which in combina- tion determine the nature of the environment. It is thus a function of tempera- ture, a function of light, etc. rv yj 314 GEORGE E. NICHOLS then, the climate to be a regional constant, it follows that the ecological aspect of an association is the direct combined func- tion of the habitat factors. Carrying the process a step further, it seems obvious that, with certain exceptions like those noted in a preceding paragraph, all of the habitat factors are relatively constant except those which are due to plant and animal agen- cies. It would follow, therefore, that the ecological aspect of an association is the direct combined function of these biotic factors alone. Now, with these deductions in mind, it might perhaps be expected to follow that through the gradual amelio- ration of the habitat, brought about by the progressive reaction of the biotic factors, the culminating member of every succes- sional series throughout a given climatic region would be the same, the only difference between them being in point of the time when this ultimate condition is reached. But in this connection must be taken into account Liebig's Law of the Mini- mum, which states in effect that: if any reaction or process is the combined function of several factors' (or variables), the ex- tent to which the reaction or process may be carried is limited by the effect of that factor which possesses a minimum value, or which is present in relatively minimal amount. The appli- cation of this law to ecological problems has already been sug- gested by Adams (1) and Hooker (15); and herein lies the ex- planation of what the writer proposes to term the edaphic climax association. The edaphic climax association. Disregarding for the moment the influence of biotic factors, it may be stated, on the basis of Liebig's Law, that in every habitat the degree of mesophytism which it is possible for the vegetation to attain is conditioned by the limiting edaphic factor. Where all the necessary edaphic factors are sufficiently represented, the highest degree of meso- phytism permitted by the climate is capable of attainment. But the limiting influence of any one factor may prevent suc- cession from proceeding beyond a certain stage. The exact limiting factors of course vary with the habitat and are not easy of analysis, except in a very superficial way. A few illustrations, however, may be suggestive. In the case CLASSIFICATION OF PLANT COMMUNITIES 315 of a precipitous cliff, in a very general sense, tlie steepness of the slope may be regarded as the limiting factor. Along a bleak, exposed seacoast, wind, or perhaps better the absence of quiet air, may similarly represent the limiting factor. Most commonly, unavailability of sufficient water, to whatever causes this may be due, is the direct limiting factor. In a measure, of course, the favorable influence of certain habitat factors, may compensate (or integrate) the limiting effect exerted by others. On precipitous slopes in rock ravines, for example, the factor ''water runs off quickly" may be offset to such an extent by the factor "atmospheric humidity is great" that a mesophytic bryophyte flora is able to establish itself; but the factor ''no foothold for roots," which may be the chief obstacle to the development of a forest cover here, cannot be wholly compensated by any other factor. Most important of all habitat factors in their compensating influence are those due to plant and animal agencies, particularly humus accumu- lation and shade as they affect the water relations of the habitat (see Cowles, 11). The significance of these factors in relation to succession is universally recognized, and in some cases their compensating influence is sufficient to completely offset the effect of the limiting factor: in other words, through the cumula- tive effect of biotic factors the habitat may become so modified that it becomes possible for the climax association-type of the region to develop. But elsewhere, in varying degree, the in- fluence of the limiting factor is too pronounced to be completely overcome, and succession becomes permanently arrested at a stage less mesophytic than the regional climax. In the case of a swamp which has originated through the filling in of a lake by vegetable debris, for example, it is quite conceivable that, as a result of the gradual upbuilding of the substratum through the accumulation of humus, the habitat might event- ually come to approximate that of uplands. But here again a limiting factor, which might be designated "decomposition of humus when exposed to air," ordinarily prevents the upbuild- ing process from proceeding beyond a certain point. It should be added, although it is perhaps quite obvious, that the effect 316 GEORGE E. NICHOLS of certain edaphic limiting factors is in turn modified by cli- matic factors. In a Sphagnum bog, for example, the Sphagnum tends to grow upward above the original water level, and in cool humid regions like coastal New Brunswick and Nova Scotia (see Ganong, 12) raised bogs may thus be developed; but in less humid regions the evaporating power of the air represents a limiting factor which, in varying degree, inhibits this upward growth of the moss. The fact seems clear, then, as has already been suggested, that the climax of a successional series in any edaphic unit area is controlled largely by the influence of some limiting factor, and it therefore follows that the nature of the climax association may var> with the nature of the soil or of the topography. The term edaphic climax association may be defined as: the most mesophytic association which is capable of development in any given edaphic unit area through the progressive reaction of the various habitat factors. In a favorable situation, the habitat climax association coincides with the regional climax associa- tion-type. The term edaphic climax association may be used either (1) in point of time, with reference to a specific successional series, i.e., with reference to the series of associations which follow one another in a given edapliic unit area; or, (2) in point of spatial relations, with reference to the group of associations which comprise an association-complex (see the following section), where these are genetically related. Used in the latter sense, it suggests the successional relationship which exists between the various associations of the complex. One can refer to such edaphic climax associations as these in terms of the physiographic unit area concerned: thus, trap cliff climax, rock ravine climax, bog climax, salt marsh climax. One of the most forcible illustrations of the edaphic climax concept with which the writer is familiar is afforded by the New Jersey pine-barrens (see Taylor, 2,3; Harshberger, 14), This well-known phytogeographic area is situated in the midst of a region whose climate is capable of supporting a highly mesophytic forest. The portion of the coastal plain CLASSIFICATION OF PLANT COMMUNITIES 317 which it occupies has been uninterruptedly out of water and presumably covered with vegetation since upper Miocene times; yet in spite of this fact, today it is still occupied by a series of associations which, while they represent ''an old and climax concUtion, ancestrally infinitely more ancient than any- thing in the surrounding area" (23, p. 242), nevertheless, with reference to the climax association-type of the region, must be classed as primitive. It is significant that this particular series of edaphic climax associations has apparently maintained it- self in spite of changes in climate A stronger argument in favor of the potency of edaphic factors in limiting succession could hardly be conceived. A similar noteworthy example of a widespread edaphic climax is seen in the natural prairie of western Long Island (see Harper, 13). Although, like the pine-barrens, situated in a region of deciduous forests, this area, some 50 square miles in extent, at least during the present climatic era apparently has never be- come forested, and there is no reason to believe that under the present climatic conditions, even if left undisturbed, it would undergo any appreciable changes in the future. J'he association complex. Sometimes the nature of the habitat is essentially uniform throughout a given area, but more often, within an area which from a physiographic or some other stand- point it is desirable to treat as a unit, several different habitats are represented. Thus, for example, in the case of a pond, very largely as the result of differences in the depth of the water, there are numerous distinct types of habitat. Similarly, a salt marsh, a flood plain, a ravine, a rock hill, a sand plain, or a burned area may include a series of habitats which it is de- sirable to treat collectively. Any such series of habitats may be designated collectively as a habitat-complex. The term may be defined as: a group or series of habitats which occupy a unit area and are alike with reference to one or more habitat factors. The conception of the habitat-complex, like that of the habi- tat-type is capable of algebraic expression. In the case of a pond, for example, let it be roughly assumed that P = pond. 318 GEORGE E. NICHOLS an area which it is desired to treat as a unit. Let ^4 = the habitat factor "ground permanently covered by water;" and, for the sake of simplicity, let B = the habitat factor ''depth of water." Then, according as B varies, P = A(B)i + A{B)2 + A{B)3, etc. In other words, all the habitats of the area P are alike with reference to the habitat factor A, and the series of habitats thus embraced may therefore be regarded as constitut- ing a habitat-complex with reference to this factor. As another illustration, let it be assumed that B = an area which has been burned over; let F = the factor ''fire;" and let H = the factor "humus destruction." Then, according as H varies, B = F(H)i -\- F Hi + F(H)3, etc. The area B may thus be regarded as a habitat-complex with reference to the habitat factor F. Intimately associated with the habitat-complex is the associa- tion-complex. The relation between the two is analogous to that between the habitat-type and the association-type. In a pond, for example, correlated with the various individual habitats which comprise the habitat-complex, is a correspond- ing series of associations: the association of submersed aquatics, the Nymphaea association, the Scirpus-Typha association, etc. Similarly, in a salt marsh, there may be as many different as- sociations as there are habitats. And just as the habitats in such unit areas, taken collectively, may be referred to as a habitat-complex, so the group of associations which occupies the habitat-complex may be designated as an association-complex. An association-complex may therefore be defined as: a group or series of associations which occupies, and forms a unit with respect to, a habitat-complex. The various ways in which the term association-complex can be applied need hardly be sug- gested. The associations of any area, taken collectively, may be so designated. The concept finds its most significant ap- plication, however, in relation to the edaphic formation which will be discussed in the following section. The association-complex may be referred to in terms of the habitat-complex concerned; thus: pond association-complex (or simply pond complex), salt marsh association-complex, flood plain association-complex, burn association-complex, etc. CLASSIFICATION OF PLANT COMMUNITIES 319 The classification of associations. In classifying plant associa- tions, they should first of all be grouped with reference to the developmental relations of the habitats concerned; in other words, with reference to the successional relations of the associa- tions themselves The further classification of the association- complexes thus defined is discussed in subsequent paragraphs. {To he continued.) RELATION OF THE RATE OF ROOT GROWTH IN SEED- LINGS OF PROSOPIS VELUTINA TO THE TEMPERATURE OF THE SOIL W. A. CANNON The Desert Laboratory, Tucson, Arizona SUMMARY This paper is a summary of numerous observations, a portion only of which are presented, on the growth of the roots of mes- quite in soil, and is one of a series on the physiological-ecolog- ical relations of roots. The leading results can be given in brief as follows: The range of temperature of the soil at which root growth in seedlings of the mesquite will take place ranges from about 12°C., as the minimum, to about 42°C., as the maximum. The most rapid root growth observed in any experiment was of a root with an initial length of 16 mm. which in a period of 12 hours grew 51 mm. The temperature of the soil was 32.5° to 34°C., and the temperature of the air was 22.5° to 23.5°C. In roots about 50 mm. long, or less, at constant soil temper- atures, the rate of growth may gradually increase during a period of 48 hours, more or less. In roots about 50 mm. or more in length, the rate of growth either remains approximately constant with the passage of time up to 76 hours, more or less, or the rate gradually decreases. In roots about 50 mm. in length there may or may not be an acceleration of the growth rate during the first 3 to 6 hours of the experiment. In the longer roots this is usually wanting, but in the shorter roots it frequently occurs. Tha'ee types of growth rate variation are to be distinguished, namely, the gi-adual increase or decrease, as above noted, and which is associated with the length of the root, and major and minor variations. The latter are independent of the age of the 320 ROOT GROWTH AND TEMPERATURE 321 root, but are present in all growth curves which cover a sufficient length of time. The rate of growth in any individual growing in soil and under constant conditions of soil and air temperature and of illumination, may vary in one and the same experiment from 100% to about 300%. And the extreme range in rate variation between different individuals growing under the same condi- tions may be much gi-eater than this. The greatest variation in the rate of growth was observed in roots which were 50 mm., or less in length. Although the length of the root at the time of the ''grand period" of growth was not especially studied, the ''grand period" appeared to occur when the root was about 50 mm. in length. The behavior of the root as regards the growth rate, therefore, and as regards the variation of whatever kind in the rate, is probably to be associated with the relation of the time of observation to the root's development or more specifically to the "gi-and period" of growth. METHODS The sahent featiu-es of the method followed in the experi- ments, and in the procedure, may be briefly presented. Seed- lings only were used. Quick germination was secured by fil- ing a slot in the outer seed coats to admit water more readily. x\fter lying a few hours in water the seeds were transferred to glass tubes, 1.7 by 44 cm. in size, which contained sifted sand. The soil was kept continuously moist by frequent watering with tap water, or in some cases Knop's solution was substituted. However, it was learned that for the short time the experiments ran, the roots grew equally well in either the solution or the tap water, so that for the most part water only was used. The tubes were kept in a thermostat, arranged so that the shoots projected from it, and the soil did not usually vary more than 0.5°C. during the course of any experiment. In some instances the chamber in which the thermostats were situated was pro- vided with a means of controlling the temperature independ- ently of that of the thermostat. In others the shoots were ex- PHE PLANT WORLD, VOL. 20, NO. 10 322 W. A. CANNON posed to the diurnal temperature changes of the air about them. Since the soil temperature exercised a predominating influence in control of the rate of root growth, as appeared repeatedly, no especial attention was paid to the air temperature, except to record it. However, it may be said that most of the experi- ments were conducted in a chamber where the air temperature varied less than 2°C. during any experiment. Usually no at- tempt was made to control the illumination, although at the Coastal Laboratory constant illumination was secured by the use of a 100-watt nitrogen electric lamp placed approximately 2 meters from the thermostats. In the experiments all of the seedlings were used, and none were discarded because they were "abnormal." Therefore, the maximum range of variation in rate of growth was secured. One of the results obtained was a surprising effect on the vigor of the seedling caused by varying the depth of earth which was used to cover the seeds, suggesting in this fact a prolific cause for failure to survive in nature. To quite do away with this as a possible cause for variation in development seemed rather difficult, although uniformity in planting was attempted. As an instance of the effects of deep planting on the vigor of the seedlings a single experiment mil be cited. Five seeds were covered with 30 mm. of moist sand, and five seeds were barely covered with the sand. Cotton plugs were used to prevent excessive evaporation. Both cultures were treated in an other- wise similar manner. At the end of about two weeks it was found that the roots of the seedlings from the lightly covered seeds were from 83 to 153 mm. long, while the roots of those which developed from the seeds that had been covered deeply measured between 44 and 75 mm. in length, with one that was only 5 mm. long. Although there was thus a great difference in the development of the two groups of seedlings, there was nevertheless marked variation in the rate of growth in each group, and this variation occurred in such a manner as to lead to the conclusion that its cause lay in difference of whatever nature in the plants themselves. ROOT GROWTH AND TEMPERATURE 323 RATE OF GROWTH Preliminary experiments on the relation between the rate ol root growth in the mesquite and the temperature of the soil indicated that the roots of the species respond to a relatively large temperature range.- Root growth, although slow, does however occur at a soil temperature of about 12°C., and the rate of growth at a soil temperature of 15° to 16°C., as the fol- lowing summary will indicate, is fairly rapid. Experiments with seedlings, at a soil and air temperature of 15° to 16° C, were conducted for a period of 114 hours with root growth as follows: 8.5 mm., 15.5 mm., 8.3 mm., and 4.5 mm. What the upper limit of temperature for root growth may be was not learned although the following experiments at superoptimal soil temperatures indicate that growth goes on, although slowly, at a temperature of 41° to 42°C. Such experiments, that is, those above the ''optimal" soil temperatures, were conducted at the following temperatures: 36°C., 38° to 39°C., and 41° to 42°C. with results that can be briefly pressnted. At a temper- ature of 36°C., the roots of four seedlings, which had an initial length of 10 to 14.5 mm., increased 10.6, 13, 13.2, and 15.8 mm. in length in a period of 12 hours. In two of the plants the maxi- mum rate observed occurred 3 and 4 hours after the beginning of the experiment. Following this rapid growth the curve was a fairly level one. It was notable that the gradual increase in rate, covering a period of several hours, which, as will appear below, was observed at lower temperatures for young roots, did not take place. Four of the plants which had been used three days previously in the experiment above sketched were sub- jected to a soil temperature of 38° to 39°C. for 12 .hours. The roots of these plants grew 6.7 mm., 8.0 mm., 8.0 mm., and 7.2 mm. The root of another plant, not pre\'iously used, during the same time increased 13.5 mm. in length. The experiment was repeated with three, plants, which had been used in both the preceding experiments, and with a fresh one not previously used, at a temperature of 41° to 42°C., with the following re- sults. In 6 hours the roots of the used plants grew 0.1 mm., 324 W. A. CANNON 0.9 mm., 2.7 mm., and 2.8 mm., while that of the fresh plant increased 4.3 mm. in length. It is apparent, therefore, that 41° to 42°C. is not, for a period of 6 hours, the maximum tempera- ture for root growth in mesquite seofilings. The curve of growth, after the first 2 hours, was fairly level, although it is questionable whether this rate would have been maintained many hours. Root growth at soil temperatures between 28.5°C. and 3/i..Ji°C. Most of the experiments reported at this time were conducted TABLE 1 NUMBER OF EXPERI- MENT SOIL TEMPERATURE AIR TEMPERATURE DURATION OF EXPERI- MENT °C. "C. hours I 30-31.5 Room temperature 11 II .32-33.5 Room temperature 12 III 28.5 Room temperature 81 IV 28.5 Room temperature 93 V .30.5 20-24 66 . VI 34.2-34.4 Room temperature 45 VII 31 5 22-24.5 48 VIII 31.5 30.5-32 51 IX 32-32.7 31-32.5 36 X 31.5 29.8-30.2 45 XI 31.5 30-31 48 XII* 15.5-16 16 196 XIII 35-35.5 16 96 XIV 24 16 144 (*) In experiments XII, XIII and XIV readings were made twice daily. at temperatures clearly favorable for the growth of the roots of mesquite. Observations were made every 3 hours and the ex- periments extended over a period from 11 to 144 hours. The experiments are numbered for convenience from I to XIV. Table 1 gives the soil and air temperature, when known, to- gether with the duration of each experiment. Root growth at a soil temperature of '28. 5° C. Two series of experiments were conducted at a soil temperature of 28.5°C. in one of which the initial root length was 20 to 22 mm., and in the other the length of the roots at the beginning of the ROOT GROWTH AND TEMPERATURE 325 experiment was 3.8 to 5.8 mm. In the experiment with the shorter roots the rate of growth increased during the first 45 hours or more, and then declined or remained approximately constant. In the experiment with the longer roots the rate of growth increased up to 30 hours, more or less, when it de- creased or remained aboiit constant. Fig. 1. Root growth of mesquite seedling, experiment VII, plant no. 46. Temperature of soil,31.5°C. The initial root length was 16 mm. Readings every three hours. Growth X 15. Fig. 2. Root growth of mesquite seedling, experiment IV, plant no. 26, tem- perature of soil 28.5°C. Initial length of root was .38 mm. Readings at inter- vals of three hours. Growth X .30. A comparison of the character of curves made from the two groups of measurements indicates that the crest of the curve was reached sooner in the longer roots than in the shorter ones, and also that the growth rate varied more from reading to read- ing— at 3 hour intervals — in the shorter than in the longer roots. Root growth at a soil temperature of 30. 5° C. The initial length of the roots in the experiment at a soil temperature of 30.5°C., was between 41 and 62 mm. In each instance the rate 326 W. A. CANNON of growth inureased for 18 hours, more or less, and then de- creased. In the specimen with the longest roots, approximately the maximum rate was attained within 6 hours after the be- ginning of the experiment, after which the rate was fairly uni- form for about 30 hours and then declined. On the whole the curves of root growth in this experiment resemble the curves for growth of the longer roots in the previous experiment. Root growth at a soil tefnperature of 31. 5° C. Four series were run at a temperature of 31.5°C. In these experiments the roots of Nos. VII and XI had an initial length between 10 and 18 mm., those of No. VIII a length between 12 and 32 mm., and those of No. X an initial length of 85 to 105 mm. The results in experiments here numbered VII and X, which are to be con- sidered representative, are given in tables 2 and 3. In the experiments where the initial root length is 32 mm. or less, it was observed that usually there was a well marked in- crease in the growth rate with the passage of time, and that the minor fluctuations in the rate of growth were, as a rule, very pronounced. The generalizations can also be made in regard to root growth of such plants as had roots that were from 85 to 105 mm. in length at the beginning of the experiment, that the minor variations in growth were as a rule not considerable, and also that the curve of growth did not show the growth increase with the elapse of time, that was observed in shorter roots. On the contrary the growth rate remained approximate- ly constant or gradually became less. As a corollary to this it is of interest to note that the length of the roots in the former instance — that is where the initial length was shortest — was relatively great at the time of the most rapid growth. For example, in no. VII the root lengths were 38.3 to 63.2 mm. in length at this time; in the other experiments the root length at the time was variable, but usually they were relatively long. An examination of the notes accompanying the experiments shows that the variation is not to be associated with the pas- sage of time, the possible fluctuations in temperature of the soil or of the possible variation in the water relations, and prob- ably not with that of illumination. On the other hand it ap- ROOT GROWTH AND TEMPERATURE 327 TABLE 2 Experiment VII, root growth of mcsquite seedlings in millimeters SOIL TEMPER.^- TURE ,\IR TEM- PERATCRE HOUR FROM BEGIXNING EXPERI- MENT NO. 60 NO. 61 NO. 62 NO. 63 NO. 64 °c. °C. 31.5 30 3 3 3 2.7 • 3 1 2.8 5.9 31.5 30 6 3.1 2.6 4.7 2.8 7.4 31.5 30.3 9 3.4 2.9 3.2 2.4 7.2 31.5 31 12 4.6 3.3 3.1 1.1 5.3 31.5 30.5 15 3.1 3.3 4.2 15 7.5 31.5 30.5 18 3.9 3.9 3.8 2.2 9.4 31.5 30.5 21 3.1 4.6 2.2 1.9 7.6 31.5 30 24 3.3 4.5 2.8 1.7 7.5 31.5 30 27 3.3 4.2 3.4 0.3 8.2 31 5 30 30 3.5 4.7 4.1 1.6 9.2 31.5 30 33 3.5 4.5 2.4 0.6 8.3 31.5 30 36 3.2 3.8 1.8 0.6 7.1 31.5 30 39 3.8 4.0 1.4 0.5 10.0 31.5 30 42 3.1 3.5 1.4 0.8 8.4 31.5 30 45 3.0 3.3 3.1 0.8 8.3 31.5 30 48 2.6 4.2 2.8 0.2 8.0 TABLE 3 Experiment X, root growth of mesquite seedlings in millimeters SOIL TEMPER- ATURE AIR TEM- PERATURE HOUR FROM BEGINNING EXPERI- MENT NO. 55 NO. 56 NO. 57 NO. 58 NO. 59 "C. °C. 31.5 30.0 3 0.9 1.8 2.4 2.8 3.7 31.5 30.0 6 2.1 1.4 1.8 3.2 31.5 30.0 9 1.4 1.5 0.8 1.0 2.4 31.5 30.0 12 1.8 1.5 0.5 0.7 3.5 31.5 30.0 15 2.0 1.1 1.0 0.8 3.8 31.5 30.0 18 1.9 1.9 1.0 0.6 2.9 31.5 30.0 21 2.0 1.2 1.7 1.1 2.8 31.5 30.0 24 1.6 1.1 1.3 0.5 2.8 31.5 30.0 27 1.5 2.2 0.7 0.8 1.6 31.5 30.0 30 1.4 1.4 0.8 0.7 1.7 31.5 30.2 33 1.3 1.0 0.8 0.5 1.9 31.5 30.2 36 1.3 1.0 0.8 0.3 1.8 31.5 30.2 39 2.0 1.1 0.8 0.5 1.8 31.5 30.2 42 0.1 0.5 0.6 0.0 2.0 31.5 30.2 45 1.0 0.3 0.5 0.3 2.2 328 W. A. CANNON pears probable that the roots which are about 50 mm. in length under parallel conditions, have a more rapid growth rate than roots that are either much longer or much shorter than 50 mm. Fig. 3. Root growth of mesquite seedling, experiment X, plant no. 56. Soil temperature, 31.5°C. Readings every three hours. Initial length of root, 90 mm. Growth X 50. Root growth at a soil temperature of 34-2° C. One series was run at a temperature of 34.2°C., which is to be considered very near the optimum for root growth in the mesquite. The ex- periment lasted 45 hours. The initial root length was between 1 and 6 mm. The rate of growth was seen to be extremely variable from observation to observation, but there was an increase in the rate up to about the eighteenth hour, or later, when the roots were between 35 and about 50 mm. in length. In the case of plant 40, however, and plant 44 as w^ll, the maxi- mum rate observed occurred within 6 hours after the experi- TABLE 4 Root groioth of mesqiiite seedlings at a soil temperature of 15.5° to 16.5°C., in millimeters. Twelve-hour periods PERIOD NO. 65 NO. 66 NO. 67 NO. 68 NO. 69 NO. 70 First 0.4 0.2 0.2 0.8 0.5 0.8 Second 1.0 0.6 0.1 1.5 0.7 1.8 Third 1.2 0.8 1.5 0.8 1.8 Fourth 0.9 1.2 1.7 0 5 1.5 Fifth 1.0 0.9 0.5 1.2 1.3 1.2 • 2.2 1.4 1.3 0.6 1.3 0.9 1 8 Sixth 1.7 Seventh 1.2 Eighth 0.2 0.6 1.9 1.3 1.5 Ninth 0.5 1.6 , 1.3 1.2 Tenth.-,,.. -_...-..- 0.9 1.7 0.4 1.2 ROOT GROWTH AND TEMPERATURE 329 TABLE 5 Root growth of mesquite seedlings at a soil temperature of 35°C., in millimeters. Twelve-hour periods PEBIOD NO. 75 NO. 76 NO. 77 NO. 78 NO. 79 First* 11.0 13.5 12.5 19.6 14.5 Second 6.0 14.0 15.0 7.0 7.0 Third 6.0 17.5 12.5 14.5 10.0 Fourthf 5.0 16.0 18.0 11.0 5.5 Fifth 4.0 16.5 14.0 12.0 5.5 Sixth 2.5 11.0 11.0 6.5 4.5 Seventh 3 0 10.0 11.0 2.0 2.0 Eighth .*. 2.5 7.0 7.0 2.0 Ninth 2.0 2.5 4.0 Tenth 1.5 2.0 5.0 * First fifteen hours after setting up the experiment. t Fourteen hours interval. TABLE 6 Root growth of mesquite seedlings, soil temperature 24° io 25°C., in millimeters, for 12 hour periods PERIOD NO. 80 NO. 81 NO. 82 NO. 83 NO. 84 NO. 85 First 10.0 8.0 11.0 14.5 11.0 11.5 10.5 10.0 9.5 8.0 8.0 8.0 3.5 3.5 3.0 3.5 7.0 7.5 8.0 6.0 ^.b 9.5 5.0 5.0 7.5 5.0 3.0 3.0 3.0 1.0 1.0 1.5 1.5 3.0 2.5 2 5 3.5 3.0 1.7 1.7 5.5 5.5 6.0 8.0 9.5 13.5 12.5 8.5 5.0 7.0 5.0 5.0 8.0 Second 4.5 Third Fourth Fifth 5.5 8.0 9.5 Sixth Seventh ... 7.5 7.0 Eighth Ninth 3.5 3.0 Tenth Eleventh*. .: Twelfth* * Average of two readings. ment started. In plant 41 three high growth points appear on the curve, and they are of about the same value. In 45 hours the root of plant 41 increased 110 mm. in length. This, how- ever, is not the highest rate of root growth observed in the species. The root of one plant, not elsewhere reported on in this paper, grew 51 mm. in 12 hours, which is the most rapid 330 W. A. CANNON rate seen during the experiments. This occurred at a soil tem- perature of 32,5° to 34°C., or shghtly lower than the temperature of the experiment referred to in this paragraph. Root growth at an air temperature of 15.5° to 16. 5° C. Three experiments were planned in which the air temperature was the same, 15.5° to 16.5°C., but the temperature of the soil was un- like. In the first one (no. XII) the soil was of the same tem- perature as the air, in the second (no. XIII), it had a temperature of 24° to 25°C., and in the third (no. XIV), the temperature of the soil was 35°C. Readings were made every 12 hours. The cultures were kept in a dark chamber which was illuminated with one 100-watt nitrogen electric bulb placed about 2 meters from the plants. The leading results are summarized in tables 4, 5 and 6. The length of the roots at the beginning of the experiment was as follows: no. 65, ?; no. 66, 20 mm.; no. 67, ?; no. 68, 24 mm.; no. 69, 22 mm.; no. 70, 20 mm. The initial length of the roots in experiment XIII, table 5 was as follows: no. 75, 30 mm.; no. 76, 65 mm.; no. 77, 70 mm.; no. 78, 73 mm.; and, no. 79, 65 mm. In experiment no. XIV, table 6, the root length at the beginning of the observa- tions was as follows: no. 80, 12 mm.; no. 81, 5 mm.; no. 82, 10 mm.; no. 83, 8 mm.; no. 84, 8 mm.; and no. 85, 8 mm. An inspection of tables 5 and 6 will show that, with the ex- ception of no. 82, an acceleration of growth takes place until a well marked optimum, occurring a considerable time after the commencement of the experiment, is attained. This is followed by a gradual slowing in the rate. In the case of ex- periment XIII, table 5, the conditions both of temperature and of root length have operated to bring about a different result. Not only is the rate of root growth greater, but, also, the most rapid rate occurred at or near the beginning, and then gradually became less. It is suggested that the rapid growth rate as well as the decline in rate soon after the beginning of the ex- periment are not solely associated with the relatively high soil temperature to which the roots were subjected, but that the roots were not far from the period of most active growth, the ROOT GROWTH AND TEMPERATURE 331 ''grand period," and that this period may have been passed during the experiment. However, it is impossible to differen- tiate between the two, and other factors, peculiar to the method used, may have been in operation as well. VARIATION IN THE RATE OF GROWTH Three types of growth variation in the roots of the mesquite were observed. Of these two are associated with every root whose growth was studied, and one type appears to be depend- ent on the length of the root. The first two types may be called the major and minor fluctuations in rate. They are of few or many hours duration, and do not determine the distinguishing character of the growth curve, which is determined by the third type of variation. This can be characterized briefly. Generally speaking roots whose initial length at the commencement of observations are 50 mm., or less, in length, show a gradual accel- eration in the rate of growth for several hours, after which the rate decreases. In roots which are 50 mm. in length, or more, on the other hand, such acceleration appears not to be present, but on the other hand, the rate either remains fairly constant, or it decreases gradually. It should be noted that the length 50 mm. is only approximate and probably varies considerably. Another characteristic of the growth curve of the young mes- quite roots, as contrasted wdth that of the older roots, is the greater amplitude of the major and minor growth variations as above described. So far as the variation in rate of root growth in mesquite for the temperatures used is concerned, this can be summarized in a moment. In table 7 the average hourly maximum and mini- mum rate for the same individual is given. In all cases the maximum rate is the highest observed in the experiment, but, per contra, the minimum may, or may not be the least ob- served. The figures give, however, the actual range in the variation rate for the individual and at the temperature given. Although the leading conclusions as above given do not harmonize clearly with the results of recent workers in this field, whose results also are not in close accord, they, however, 332 W. A. CANNON TABLE 7 Average hourly maximum and minimum rate of root growth of the same individual, in millimeters SOIL TEMPERATURE NUMBER OF EXPERI- MENT MAXIMUM MINIMUM °C. 16.0 XII* 0.16 0.05 24.5 XIV* 1.12 0.4 35.0 XIII* 1.45 0.16 28.5 Hit 2.2 1.2 28.5 IV 3.2 1.06 30.5 V 2.6 0.76 31.5 X 1.2 0.53 31.5 XI 3.3 1.7 31.5 VIII 2.06 0.56 31.5 VII 2.5 0.83 * Average of 12 hours. t This and subsequent rates are average of 3 hours. suggest a rational basis for agreement. The writers referred to are Leitch^ and Lehenbauer' to whose work the reader is referred for literature covering the subject. Leitch used the roots of seedling Pisum and Lehenbauer the shoots of seedling maize. The third day after germination Leitch selected for study plants wdth roots about 15 mm. long and such as were the most uniform. This was at, or after the time of most active growth, and not before this time. Although Lehen]bauer did not manipulate his experiments with direct reference to. the "grand period," his procedure was uniform and it may have had a fairly constant reference to such period. The growth of shoots which were 10 to 12 mm. in length was studied. Ab- normal individuals were eliminated. The duration period of the experiments was 39 hours or less. These workers obtained, results differing somewhat in character. Leitch found among other things a fairly constant growth rate for any temperature, while, on the other hand, Lehenbauer found the rate to accel- 1 Some experiments on the influence of temperature on the rate of growth of Pisum sativum. Ann. Bot., 30: 25, 1916. - Growth of maize seedlings in relation tc temperature. Phys. Researches, 1: 247, 1914. ROOT GROWTH AND TEMPERATURE 333 erate at first and thus that the ''maximum" rate was not the rate at first noted. The results of the present study, in which young as well as relatively old roots were used and in which the experiments were continued over a relatively long period, sug- gest that possibly the differences in results obtained by the two writers may lie in the possible differences in the organs studied with respect to the period of most active growth, that is, to the "grand period." Experiments conducted prior to this period would exhibit an increase in the rate of gro^vth with the passage of time up to the attainment of the maximum rate at the crest of the "grand period." And, on the other hand, experiments conducted after the passing of the "grand period," would show a fairly level growth curve, or a descending one. BOOKS AND CURRENT LITERATURE Handbook on Algae. — In this/ the most important work of a general character on algae since the appearance of Oltmanns' Morphologic unci Biologic der Algen in 1904-1905, the author treats the Myxophyceae (48 pp.); the Peridinieae (33), the Bacillarieae (23), and the Chloro- phyceae (291). In addition 33 pages are devoted to the occurrence and distribution of freshwater algae. After each division of the work a good bibliography is given, though these extend for the m.ost part only to 1913, and in some instances to 1912. They indicate in a telling way the points of m.ost active algologi- cal research at the present tim.e. For example, under the Akontae 51 references are dated prior to 1900, while only 39 are more recent. On the other hand, the chapter on occurrence and distribution furnishes only 16 titles before 1900 and 62 of later date. It is a pity that in a book of this character the treatment is not brought more nearly up to date. This fault is, however, remedied to a slight extent by cursory mention in the Addenda (3 pp.) of a baker's dozen of titles from 1913 to 1916. A satisfactory index closes the volume. The size of the book properly precludes treatment of the Phaeophyceae and Rhodophyceae. How- ever, in the judgment of the reviewer it was a mistake not to attempt at least a summ.ary of modern work on the Flagellates, a group the im- portance of which is attested by a cloud of witnesses in recent years. Throughout the work the author's leaning toward taxonomy finds ex- pression, so that this side of the subject is emphasized at the expense of morphology and physiology. This is shown in the failure in m.any cases to present cji;ological results, though their importance is freely granted. As examples of such omissions, the work of Trondle on Spirogijra (1911) and of Tuttle on Oedogonium may be mentioned. The treatment of the Blue-Greens gives a satisfactory critical sum- mary of previous work. The author suspends judgment on most of the familiar controversial points in this group, although on occasion he speaks his mind freely, as for instance in dismissing the work of Kohl, 1 West, G. S., Algae. Cambridge Botanical Handbooks (edited by A. C. Seward and A. G. Tansley), Vol. I. Pp. 475, figs. 1284. Cambridge University Press, 1916 (25 shillings). 334 BOOKS AND CURRENT LITERATURE 335 Olive, and Phillips on mitosis as being the "result of unconscious seK- deception" (p. 9). In the discussion of Gaidukov's theory of "complementary chro- matic adaptation" no reference is made to the physiological work bearing directly on this question, that of Dory and of Schindler particularly. The classification of the Myxophyceae Is given in full very much as in the author's British Freshwater Algae (1904), though the detailed treatment extends only to the famihes, with remarks on the impor- tant genera. This is the method used throughout the book. The ab- sence of analjiiical keys and generic descriptions, which proved so use- ful in the earlier work, will be disappointing to users of the present book especially as the British Freshwater Algae is now out of print. The author clings to his notion that Glaucocystis should be included in the MjTcophyceae, though its color seems to the reviewer to be more than counterbalanced by other and more convincing characters. The author himseK is at pains to point out that color is too variable in the group to be relied on. Indeed, he naively uses this fact as an argu- ment against the name Cyanophyceae, not mentioning the well estab- lished priority of Mjoiophyceae as a reason for its retention. The section on Peridinieae will be hailed with a glad cry by many botanists. Here we find presented, in excellent and well digested form, the first general account of the group in English. Many points of gen- eral interest, such as Kofoid's work on mutation in Ceratium, are here made readily available. No phase of the subject is neglected. Equally good, though not filling such a crying want, is the section on Bacillarieae. Such accounts as this of the biology of the Diatoms are most welcome to the limnologist, and will be of great service when we get around to a scientific study of fish culture in fresh waters. The Chlorophyceae are given a general introduction of 28 pages, which includes an excellent summary of the principal systems of classi- fications thus far proposed. The more detailed treatment is reserved for the subdivisions of the group. These subdivisions reflect the changes in the point of view of the author since the publication of his earlier book in 1904. At that time he divided the Class Chlorophyceae 'into nine orders. The Heterokontae were ranked as a coordinate class. In the present work, however, the Chlorophyceae are grouped in four "Divisions," the Isokontae, with six orders (Protococcales, Siphonales, Siphonocladiales, Ulvales, Schizogoniales, Ulotrichales) ; the Akontae (order Conjugales); the Stephanokontae (order Oedogoniales) ; and the 336 BOOKS AND CURKENT LITERATURE , Heterokontae, with three orders (Heterococcales, Heterotrichales, Heterosiphonales). The order Microsporales of the older work is now made a famil}' of the Ulotrichales. It seems to the reviewer that the Heterokontae should have been retamed as a separate class from the Chlorophyceae, since the differences between the two are thoroughgoing and far-reaching, and since the points of origin in the Flagellatae are considered for good reason to be different in the two groups. However, the subdivision of the Hetero- kontae is m.uch more natural than in the older work, where only one order, the Confervales, was recognized. In this were lumped the most diverse famihes. The present satisfactory subdivision into three orders is modified from Pascher. In general the classification adopted by the author is along the lines suggested by Bohlin and by Blackman and Tansley, differing in impor- tant points from the schemes of Oltmanns, Chodat, and Wille. The material under the heading " Chlorophyceae" is so scattered in the different subdivisions that it is hardly possible to give a comprehen- sive review of it. Certain points may be commented upon. The statement (p. 138) that "no positive evidence of the reduction of chromo- somes" has been brought forward in the case of Spirogyra is, of coiuse, misleading, since Trondle's paper in the Zeitschrift fiir Botanik, 1911, settles this question. In the discussion of alternation of generations (p. 139) the chromo- some number is accepted as the only factor in delimiting sporoph>i,e and gametophyte. Thus the author says, granting the correctness of Allen's conclusions in Coleochaete, "It is scarcely possible to regard these post-natal phenomena [of the germination of the zygospore] as phyloge- netic fore-runners of the sporophyte of the Archegoniates." No golden calf of old was ever worshipped with the fervor that many botanists of today exhibit for the chromosome. As an example of the lengths to which it may go the recent paper of Cunningham on Spirogyra may be cited (Bot. Gaz. 63, p. 498), in which this remarkable conclusion may be found: "The filam.ent of Spirogyra, in this species and those with lateral conjugation, is homologous with the sporophyte of higher plants." Here not even the substance, but the mere shadow of the chromosome frightens common sense and the reasoned conclusions of comparative morphology off the page. So with our author's treatment of the subject. There follows a good discussion of polymorphism. Methods of cul- ture given in this connection will be found useful (pp. 143-144). The BOOKS AND CURRENT LITERATURE 337 culture medium of Chodat-Grintzesco might have been included with profit. The recommended addition of potassium chromate or potas- sium biGhrom.ate to the media has always been followed by disaster in the reviewer's cultures. Perhaps under very special circumstances such a procedure might be useful, but it certainly cannot be generally advised. Space forbids the detailed discussion of the many interesting questions of classification occurring to the reader. One such point may be men- tioned. The order Protococcales is broadly defined. The author seems quite justified in including here the Volvox series, though this disposition is not accepted by Collins, Oltm.anns, or Pascher. The line between major groups must be sharply drawn. Those species of Chlamydomonas in which the habit is like Palmella and in which motile cells are only rarely produced are plainly Protococcaceous. Chlamydomonas, therefore, fits snugly in the Protococcales, and the other Volvocines must follow. Our old friend Pleurococcus vulgaris has become Protococcus viridis Ag. Delimitation of the family of which this is the type is questionable. Trochiscia and Chlorella, other genera in the Protococcaceae, show im.- portant differences in reproduction from Protococcus. In fact, Proto- coccus may just as well be considered a reduced member of the Ulotri- chaceae, which its "protoderma state" nearly resembles. Trochiscia and Chlorella fit equally well in the Autosporaceae. The reviewer agrees with the author as to the phylogenetic history of the desmids. They are regarded as originally filamentous, then unicellular, and last in some cases secondarily filamentous. The chapter on Occurrence and Distribution of Freshwater Algae suffers from having much of the material proper to it distributed else- where in the book. The chapter forms a good introduction to the ecology of the group. The objection may be raised that the factors in- fluencing the occurrence and distribution of algae are not sufficient^ emphasized. The truth is we know next to nothing about these fac- tors, and m.aterial is lacking for their discussion. The work as a whole is carefully done, and misprints and minor pec- cadilloes are rare. Guillierm.ond will probably be annoyed by the consistently odd spelling of his name, the pedan't will feel a twinge on seeing "colonial unicells," the technician might object to the color reac- tion of cellulose with chlor-zinc-iodine being given as "blue" — all these in the first three pages — but the Ijotanist will welcome with pleasure and profit this well arranged and comprehensive account of most of the algal groups. True, much of it may be found in the British Fresh- THE PLANT WORLD, JVOL. 20, NO. 10 338 BOOKS AND CURRENT LITERATURE water Algae, but a good deal is relatively new, and hitherto available only in special papers. It is to be hoped that the series of handbooks, of which this is the first, will be carried forward with promptness and vigor. The usefulness of such reviews goes without question. The high price is unfortunate, as the number of readers will be lessened thereby. The book could be more cheaply produced without sacrificing its usefulness. However, the same might be said of Thuret's Etudes Phycologiques, now the delight of the botanical bibliophile. — I. F. Lewis. Medullary Rays. — ^The application of comparative anatomy to the criticism of other criteria of relationships is well exemplified in recent studies on the rays of coniferous woods. The sporadic occur- rence of marginal trachoids in the rays of cupressineous woods was earlier observed by several workers, among them Penhallow, who seems to have misinterpreted them. The observation of such cells in a wounded stem of Cunninghamia by Jeffrey^ set the matter in its true light, and this author interpreted the cells as a reversion to the ancestral condition seen for example in Pinus. Miss Gordon^ reported ray tracheids in Sequoia sempervirens, and Miss Holden^ showed that they occasionally occur in various genera of Taxodineae and Cupressineae. As to Abietineae, the earlier Pityoxyla lack marginal cells, while speci- mens from the Upper Cretaceous onward show them.^ They are accordingly of comparatively recent introduction, and while prominent in all pines of the present era, they are apparently in process of dis- appearance in Cedrus,^ and have practically disappeared from Abies, ^ and the Taxodineae and Cupressineae, though they may be recalled by wounding. Mention should be made in this connection of Thomp- son's theory of the origin of these cells.'' — M. A. Chrysler. ' Jeffrey, E. C. Traumatic Ray Tracheids in Cunninghamia sinensis. Ann. Bot. 22: 593-602, pi. 31. 1908. * Gordon, M. Ray Tracheids in Sequoia sem-pervirens. New Phyt. 11: 1-7. 1912. ' Holden, R. Ray Tracheids in the Coniferales. Bot. Gaz. 55: 56-65, pis. 1, 2. 1913. * Bailey, I. W. A Cretaceous Pityoxylon with Marginal Tracheides. Ann. Bot. 25: 315-325, pi. 26. 1911. 5 Chrysler, M. A. The Medullary Rays of Cedrus. Bot. Gaz. 59: 387-396. 1915. 6 Thompson, W. P. Ray Tracheids in Abies. Bot. Gaz. 53: 331-338, pis. 24, 25. 1912. ^ Thompson, W. P. The Origin of the Ray Tracheids in the Coniferae. Bot. Gaz. 50: 101-116. 1910. NOTES AND COMMENT An important gap in our knowledge of the developmental mor- phology of the Pteridophytes has been filled by Prof. A. Anstruther Lawson, of the University of Sydney, in his investigation of the pro- thallia of Psilotum and Tmesipteris (Trans. Royal Soc. Edinb., vols. 51, 52). This work gives us the first knowledge of the sexual genera- tion of these relict genera, if we except the work of Lang, based on material which Professor Lawson now regards as having pertained to some plant other than Psilotum. The members of both genera are commonly epiphytic on arborescent ferns, and the brown rhizome-like prothallia were found on the rough fern trunks in several localities. The development is very similar in the two genera, and the vegetative characters and development are alike in presenting important differ- ences from the prothallus of Lycopodium, as well as from that of Equi- setum. The relationship of these plants to Lycopodium is therefore not so close as has been presumed, and strength is thereby given to the view already advanced by several workers that they have their closest affinities with the extinct Sphenophyllales. The second part of Prof. W. F. Ganong's Textbook of Botany for Colleges has recently appeared (Macmillan, 1917). It is chiefly de- voted to a description of the morphology and relationships of the great groups of cryptogamic plants and the orders of phanerogamic plants. The treatment is brief and general, but is accurate and down to date, and the illustrations are both numerous and excellent. A final chapter on the ecological classification of plants is well done, but it demon- strates how difficult it is to marshal the generalizations of ecology into a well-ordered presentation such as that given the facts of morphology. The appealing style in which the book is written should give it a field of utility outside the classroom, among that small and rapidly vanish- ing body of adults who read to improve their minds. Around the Year in the Garden is a very practical and comprehen- sive book by which Mr. Frederick Frye Rockwell makes it possible for the man who is without a head gardener to carry out all of the opera- 339 340 NOTES AND COMMENT tions of garden and lawn. It differs from other manuals of gardening published by Macmillans in having the chapters arranged so as to describe, week by Week, the work of preparing hotbeds, sowing seeds, caring for growing plants, gathering the crop and storing it for home use. The book contains far too much information for its utility to be confined to the beginner. Prof. William Trelease, of the University of Illinois, has prepared a compact booklet of 200 pages on the native and cultivated woody plants of the eastern United States (published by the author, Urbana, lU.). There is a key to the genera embraced, and there are generic diagnoses, together with keys to the species. The book is designed primarily for the requirements of the gardener and the amateur, and will be valuable because of its concise but comprehensive character. A text-book for the half-year course in botany in high schools is being prepared by Dr. E. N. Transeau, of Ohio State Universit3^ It will be published by the World Book Company as one of a series of new high school texts which is appearing under the editorship of Prof. John W. Ritchie. The paper by Dr. Howard E. Pulling entitled The Rate of Water Movement in Aerated Soils, to which the first prize was given in the soil physics competition instituted by The Plant World, has been pub- lished in the September issue of Soil Science for the present year. .<^o®h THE INTERPRETATION AND APPLICATION OF CER^ TAIN TERMS AND CONCEPTS IN THE ECOLOGICAL CLASSIFICATION OF PLANT COMMUNITIES. II GEORGE E. NICHOLS The Sheffield Scientific School of Yale University, New Haven, Connecticut THE UNIT OF VEGETATION WITH REFERENCE TO PHYSIOGRAPHY The edaphic formation. As has been stated earlier, from an eco- logical point of view the fundamental unit of vegetation is the asso- ciation, the ecological aspect of which is determined by the habitat. Now in any given climatic region the habitats are not distributed indiscriminately. They are grouped, as has just been suggested, into more or less definite complexes, the boundaries of which are determined primarily by the physiographic features of the region. In brief, the various habitat complexes are associated with specific physiographic unit areas. From the standpoint of the physi- ography of the region as a whole, t^ese habitat-complexes deter- mined by physiography represent edaphic divisions of a higher order than the habitat; and likewise, from the standpoint of the physiographic ecology of the region concerned, the association- complexes which occupy these physiographic divisions represent vegetational divisions of a higher order than the association. Just as a ravine, a salt marsh, a rock hill, or a sand-plain may be regarded in its entirety as a physiographic entity, so its vege- tation, taken in its entirety, is to be regarded as an entity from the standpoint of physiographic ecology. In other words, just as the association can be regarded as a unit with reference to a specific physiographic unit area, so the association-complex, where it is determined by physiography, can be regarded as a unit with reference to the physiography of the region This physiographic unit of vegetation may be designated the edaphic formation. The edaphic formation may be defined as: an as- 341 THE PLANT WORLD, VOL. 20, NO. 11 NOVEMBER, 1917 342 GEORGE E. NICHOLS sociation-complex which is related to a specific physiographic unit area. The developmental concept of the edaphic formation. The so- called developmental concept of the formation was first suggested by Moss who, in his account of the geographical distribution of the vegetation of Somerset (16, p. 12; fide Clements, 4, p. 118), states that: "The series of plant associations which be- gins its history as an open or unstable association, passes through intermediate stages, and eventually becomes a closed or stable formation, is in this paper termed a plant formation. "^ In a later paper (17, p. 36) he defines the [edaphic] formation as comprising ''the progressive associations which culminate in one or more stable or chief associations [ = edaphic climax associations], and the retrogressive associations which result from the decay of the chief associations, so long as these changes occur on the same habitat." This concept of the formation has been adopted by the Committee for the Survey and Study of British Vegetation (see 21, p. IX), and the edaphic formation is so interpreted by the writer, except that he would substitute ''physiographic unit area" for "habitat" in the definition just quoted. By some ecologists the edaphic climax association alone is treated as a formation. In the opinion of the writer, however, not the edaphic climax association, but rather the entire as- sociation-complex should be regarded as constituting the physio- graphic unit of vegetation: the edaphic formation. The edaphic climax association represents merely the culminating phase of a specific successional series: the most mesophytic type of vegeta- tion capable of attainment in a specific physiographic unit area. It is the indicator, so to speak, of the degree of mesophytism which is attainable within the edaphic formation. As Moss ex- presses it (16, 17), it is the "chief" association of a successional series. It should be stated once more that the edaphic climax association of an edaphic formation may or may not coincide with the regional climax association-type. 1 The term formation is used by Moss in the sense that the term edaphic formation is used bv the writer. CLASSIFICATION OF PLANT COMMUNITIES 343 Primary and secondary edaphic formations. The term second- ary is here used with reference to edaphic formations in which the vegetation has been modified by factors other than those which are attributable to biotic (not including human) or phys- iographic agencies. Formations whose vegetation has not been so modified are regarded as primary. Secondary edaphic for- mations commonly arise through the partial or complete de- struction of the original vegetation by fire, lumbering opera- tions, or cultivation. The edaphic formation-type. In any climatic region, owing largely to the existence of numerous parallel series of physio- graphic unit areas, there have been developed correspondingly numerous parallel series of edaphic formations. Different in- dividual formations which are correlated with the same type of physiographic unit area may be referred to a common edaphic formation-type ; thus : ravine formation- type, rock hill formation, type, sand plain formation-type, etc. Like the association- type, the edaphic formation-type is an abstract conception. It may be defined as a type of edaphic formation correlated with a given type of physiograph3^ As in the case of the as- sociation-type, the conception of the edaphic formation-type may be extended beyond the boundaries of a given climatic region. Thus, the ra\ane, or the flood-plain, or the salt marsh formation-type of one region may resemble that of another; etc. Edaphic formation-types are referred to in terms of the physiographic unit area concerned, as has been done above. The classification of edaphic formations. Although worked out from a somewhat different point of view and therefore some- what differently formulated, the developmental concept of the edaphic formation was one of the fundamental features of Cowles' physiographic classification of plant associations (8, 9). Cowles was the first to fully appreciate the significance of physiography in relation to the local distribution of plant associations. ''The keynote," he writes (9, p. 8), "is that each particular topographic form has its own peculiar vegetation. This is due to the fact that the soil conditions upon which plants depend are deter- mined by the surface geology and the topography." He further 344 GEORGE E. NICHOLS states that, "From the standpoint of the vegetation the topo- graphic relations are more important than the geological. . . . all kinds of soils may have the same kind of vegetation when placed in similar topographic conditions, whereas the same soil may show many diverse types of vegetation." In classifying the edaphic formations within a given climatic region, topography, as related to the physiographic history of the region, is of fundamental importance. For, using this as a basis, it is possible to bring out the developmental relations of the physiographic unit areas involved, in much the same way that the classification of associations with reference to the phenomenon of succession brings out the developmental relations of the habitats concerned. It should be reiterated however, that while the contemporaneous features of the physiography of any region are the result of progressive development in the geologic past, from the standpoint of present-day physiographic ecology, with the exception of the relatively few areas in which changes man- ifestly are taking place rapidly, the physiography can be regarded as stable. That, on the whole, from the viewpoint of dynamic physiographic ecology, soil is of subvsidiary importance to topo- graphy in determining the character of the vegetation seems obvious. But that soil may also exert a far-reaching influence on the ecological character of the vegetation is emphasized by the survey of vegetation set forth in "Types of British Vegeta- tion" (21) where the formations are classified primarily with reference to soil. In general, then, the writer would classify the edaphic formations (1) with reference to topography, and (2) with reference to soil. The edaphic formation-complex. The edaphic formations of any area, taken collectively, may be regarded as an edaphic formation-complex. And juet as the association-complex of a physiographic unit area constitutes an edaphic formation, so the edaphic formation-complex of any climatic region consti- tutes a climatic formation. CLASSIFICATION OF PLANT COMMUNITIES 345 THE UNIT OF VEGETATION WITH REFERENCE TO CLIMATE Tfie climatic formation. Climatic factors determine the larger features of the plant covering of the earth. Owing to widespread differences in climate, there are correspondingly widespread differences in the general ecological aspect of vegetation. The vegetation of any region in which the essential climatic relations are similar or uniform throughout, taken in its entirety, is here regarded as constituting a climatic formation. The climatic formation, then, bears a similar relation to the climate of the earth that the edaphic formation bears to the physiography of a climatic region; a similar one to that w^hich exists betw^een the association and the habitat-complex of a physiographic unit area. In other words, if the association is the ecological unit of veg- etation from the standpoint of the habitat, and the edaphic formation is a unit from the standpoint of physiography, then the climatic formation is a unit from the standpoint of climate. Individual climatic formations are usually designated by com- bining the name of the geographic region concerned with that of the climax association-type of the formation; thus: the de- ciduous forest formation of eastern North America, the Great Plains short-gi'ass formation, the sage-brush desert formation of the Great Basin. The developmental concept of the climatic formation. Clements (4, pp. 3, 124-127) has adopted the developmental concept of the formation with reference to the climatic formation (in w^hich sense he uses the woi'd formation). He states that, "The unit of vegetation, the climax formation, is an organic entity. As an organism, the formation arises, growls, matures, and dies. Its response to the habitat is shown in processes or functions and in structures which are the record as w^ell as the result of these functions. Furthermore, each climax formation is able to reproduce itself, repeating with essential fidelity the stages of its development. The life-history of a formation is a complex, but definite process, comparable in its chief features with the life-history of an individual plant. The chmax formation is the adult organism, the fully developed community, of w^hich 346 GEORGE E. NICHOLS the initial and medial stages are but stages of development. . . . A formation, in short, is the final stage of vegetational development in a climatic unit. It is the climax community of a succession which terminates in the highest life-form pos- sible in the cHmate concerned. . . . It is delimited chiefly by development, but this can be traced and analysed only by means of physiognomy, floristic and habitat." It will be seen from the foregoing quotation that Clements regards as the climatic formation what from the writer's point of view would be termed the regional climax association-com- plex (or association-type). It is the opinion of the writer that the climax association-complex should not be so regarded, but that the entire edaphic formation-complex of the region, or, as before stated, the vegetation of the region in its entirety, should be considered as constituting a unit from the standpoint of regional physiographic ecology. It seems more logical to re- gard the chmax connnunities of the region, like other ecologically parallel series of communities, as belonging to a common as- sociation-type. As the most mesophytic type of vegetation attainable under the existing climatic conditions, the climax association-type may be looked upon as the climatic indicator, but not as the climatic formation. To sum up, the vegetation of any region having an essentially uniform climate throughout, taken in its entirety, constitutes a climatic formation, the gen- eral ecological aspect of which is determined by that of the climax association-type of the region. The advisability of using the terms: edaphic formation a7id cli- matic formation. In a review of Clements' ''Plant Successions," Tansley (22, p. 203) objects that if the concept of formation is restricted to a climax stage determined by climate, then ''it leaves out of account the establishment of permanent communi- ties of distinct life-form owing to edaphic conditions or to con- ditions determined by biotic reaction on the soil. It was to cover cases of this kind that Schimper introduced the term edaphic formation, and if its use be not allowed it is difficult to see how we are to classify such communities." Schimper (19, p. 161) says that "two ecological groups of formations should be CLASSIFICATION OF PLANT COMMUNITIES 347 distinguished — the climatic or district formations, the char- acter of whose vegetation is governed by atmospheric precipi- tations, and the edaphic or local formations, whose vegetation is chiefly determined by the nature of the soil." It is the opinion of the \\Titer that the only logical way to reconcile the divergent views of various authorities regarding the interpretation of the word formation is to retain the classification of Schimper, distinguishing between edaphic for- mations on the one hand and climatic formations on the other^ but modif>dng Schimper's concept to harmonize ^\ith the de- velopmental concept as set forth in preceding paragraphs of this paper. The climatic formation-type. On different portions of the earth's surface, o\^'ing to the existence of various parallel t>^es of climate, there have been developed correspondingly nmnerous parallel types of climatic formation. Thus, as dehixdted on Schimper's map (19, map 3), the sclerophyllous woodland formation of southern CaUfornia is paralleled by the sclero- phyllous woodland formation of the ^lediterranean region and that of South Africa. Similarly, the short-grass formation of North America finds its ecological counterparts in the grassland formations of Russia and China. Different indi\idual climatic formations which have thus developed in response to the same type of climate and which as a result agree with one another in their ecological aspect, even though they differ (as they usually do) in their floristic composition, are to be considered as belong- ing to the same climatic formation-type. Like the association- type and the edaphic formation-type, the climatic formation- type is an abstract conception. It may be defined as : a type of climatic formation correlated with a given tj^e of chmate. While, in practice, their exact dehmitation is of course a matter of considerable difficulty, in a general way it is possible to divide the vegetation which clothes much of the earth's surface into a relatively small number of formation-types. Brockmann-Jerosch and Riibel, in their universal classifica- tion of plant communities (2) have distinguished four vegeta- tion-types (lignosa, prata, deserta, and phytoplankton) and have 1 348 GEORGE E. NICHOLS further subdivided the plant formations of the earth into four- teen formation-classes and seventeen formation-groups. They do not, however, restrict the use of these terms to chmatic for- mations : under prata, for example, are included the salt marshes and fresh marshes of forested regions, as well as the climatically- conditioned grassland formations. The word formation-type, from the standpoint of regional physiographic ecology, is here used only with reference to climatic formations. Schimper (19) has used the term in this sense, distinguishing three chief types of climatic formations (woodland, grassland, and desert) as well as various types of subordinate rank. Climatic forma- tion-types, like climatic formations, are best designated in terms of the ecological aspect of the vegetation, as has been done in the illustrations cited above. The climatic formation-complex. In treating the vegetation of any large area, such as the continent of North America, where more than one type of climate and correspondingly numerous different climatic formations are represented, the term climatic formation-complex may be used to include collectively the cli- matic formations of the entire area. The climatic formations coiTiprising the complex may be genetically related in point of geologic time, as in the glaciated parts of eastern North America, but the term does not necessarily imply such a rela- tionship. The climatic formation-complex of the earth, taken in its entirety, might be regarded as forming a terrestrial formation. The application of the law of the minimum in regional physio- graphic ecology. In applying the Law of the Minimum to prob- lems in local physiographic ecology, climatic factors need not be taken into account since they are essentially constant throughout the region. The variable factors are edaphic; they are due, directly or indirectly, to variations in either soil or topography. In dealing with problems in regional physio- graphic ecology, however, where the chmatic factors also are variable, these of course are of paramount importance. Pre- cipitation, the evaporating power of the air, temperature, and light afford the chief hmiting factors, the factors which deter- mine the general aspect of the vegetation in a climatic formation. CLASSIFICATION OF PLANT COMMUNITIES 349 Even here, however, the edaphic Uniiting factors, at least in some cases, may be of great significance, and it need be only suggested that in an accurate analysis these, as well as the ch- matic limiting factors, must be considered. SUMMARY By way of summary, it may be stated that the fundamental unit of vegetation is the association. The associations of a unit physiographic area, taken collectively, constitute an edaphic formation. The edaphic formations of a unit climatic area, taken collectively, constitute a climatic formation. The climatic formations of the earth, taken collectively, may be said to constitute the terrestrial formation. The association is a unit determined by habitat, the edaphic formation a unit determined by physiography, the climatic formation a unit de- termined by climate, while the terrestrial formation might be said to be a unit determined by the atmosphere. ''The con- ception of a formation as an ecological genus and an association as an ecological species" (Cowles 10, p. 150) may be fui'ther amplified. If the association is regarded as an ecological species and the edaphic formation constitutes an ecological genus, then the climatic formation may be said to represent an ecological family, while the terrestrial formation might be regarded as a unit of a still higher order. In the preceding pages the various ecological units of veg- etation have been treated as an ascending series. Starting with the fundamental unit, the association, the units of a higher order have been treated in the order of their increasing com- plexity. Their relative rank and their relation to one another is brought out by the following synopsis. The terrestrial formation: = the climatic formation-complex of the earth The climatic formation : = the edaphic formation-complex of a cliniatic unit region The edaphic formation: = the association-complex of a physiographic unit area The association: = the plant-complex (community) of a unit habitat 350 GEORGE E. NICHOLS THE SCHEME OF CLASSIFICATION IN PRACTICE Outline classification of the vegetation of northern Cape Breton Island. The practical application of the classification of plant communities according to the concepts enunciated in the fore- going pages \\dll now be illustrated by a specific example. The vegetation of the area selected has been under investigation for four summers, and a full account of the writer's observations and conclusions here is in the course of preparation. Northern Cape Breton lies in the transition zone between the two great climatic formations of eastern North America: the deciduous forest chmatic formation and the northeastern evergreen conifer- ous forest climatic formation, and, owing largely to differences of elevation, both of these are well developed, the former on the lowlands and the latter on the highlands. The scheme adopted in classifying the various edaphic formations which comprise the deciduous forest climatic formation here, is outhned below. Such a scheme, it should be borne in mind, answers much the same purpose in the realm of physiographic ecology as an analyt- ical key in the realm of systematic botany. The classification has been carried as far as the ecological genus, i.e., as far as the group of associations which comprises an edaphic formation. The Vegetation of Northern Cape Breton The deciduous forest climatic formation I. The regional climax association-type II. The edaphic formation-complex of the region A. Primary formations of the xerarch successional series 1. The formation-types of ordinary uplands a. The association-complexes of exposed rock outcrops b. The association-complexes of talus c. The association-complexes of glacial drift 2. The formation-types of uplands along streams a. The association-complexes of rock ravines b. The association-complexes of open valleys c. The association-complexes of boulder plains d. The association-complexes of flood plains 3. The formation-types of uplands along the seacoast a. The association-complexes of sea-bluffs and headlands b. The association-complexes of shingle beaches c. The association-complexes of sandy beaches and dunes CLASSIFICATION OF PLANT COMMUNITIES 351 B. Secondary formations of the xerarch successional series a. Association-complexes due to cultivation b. Association-complexes due to fire 0. Association-complexes due to logging C. Primary formations of the hydrarch successional series 1. The formation-types of inland lakes and swamps a. The association-complexes of permanent lakes and ponds b. The association-complexes of periodic ponds c. The association-complexes of well-drained swamps d. The association-complexes of undrained swamps e. The association-complexes of poorly drained swamps 2. The formation-types of lakes and swamps along the seadoast a. The association-complexes of salt and brackish marshes b. The association-complexes of brackish ponds D. Secondary formations of the hydrarch successional series The northeastern evergreen coniferous forest climatic formation 1.. The regional climax association-type II. The edaphic formation-complex .... etc. Explanatory remarks. In attempting to make an ecological analysis of the climatic formation of a given region it seems logi- cal that the subject matter be first arranged under two heads: (I) The regional chmax association-type, and (II) The edaphic formation-complex of the region. This division has aheady been employed by Cooper (5), although he did not distinguish the edaphic formations as such. An understanding of the region- al chmax association-type, representing as it does the highest degree of mesoph}i:ism permitted by the climate, is prerequisite to the adequate interpretation of subordinate association-tj^^es and of successional relations. The term edaphic formation, given its developmental concept, of course includes the successions. The various edaphic formations which comprise the regional edaphic formation-complex are next assembled into two suc- cessional series which, adopting the terminology suggested by Cooper (5, p. 11), are termed respectively the xerarch and the hydrarch series. The term xerarch, to quote Cooper "is ap- phed to those successions which, ha\4ng their origin in xero- phytic habitats, such as rock shores, beaches, and cliffs, become more and more mesoph>i;ic in their successive stages; [the term hydrarch] to those which, originating in hydrophytic habitats, 352 GEORGE E. NICHOLS such as lakes and ponds, also progress toward mesophytism." The formations of these two series are further grouped as pri- mary and secondary. Considered next with reference to the larger topographic features- of the region, the edaphic formations of the xerarch series are divided into three groups: (1) The formation-types of ordinary uplands; (2) The formation-types of uplands along streams; (3) The formation-types of uplands along the seacoavSt. The edaphic formations of the hydrarch series are similarly grouped under two heads: (1) The formation-types of inland lakes and swamps; (2) The formation-types of lakes and swamps along the seacoast. They might equally well be divided into four groups: (1) The formation-types of glacial lakes and swamps; (2) The formation-types of sink-hole lakes and swamps; (3) The formation-types of river lakes and swamps; (4) The formation-types of coastal lakes and swamps; except that river lakes and swamps are scarcely represented in this region. Finally, the association-complexes which comprise the vari- ous edaphic formations are further grouped with reference to whatever specific physiographic unit areas it seems best to dis- tinguish. Under this head are considered the character and the successional relations of the individual associations and association-types. This latter part of the scheme in particular is so elastic and so capable of modification that it may be readily adapted to the speciial requirements of any region and to the individual views of any investigator. (1) Adams, C. C, An outline of the relations of animals to their inland en- vironments. Bull. 111. State Lab. Nat. Hist. 11: 1-32. 1915. (2) Brockmann-Jerosch, H. and RtJBEL, E., Die Einteilung der Pflanzen- gesellschaften nach okologisch-physiognomischen Gesichtspunkten, pp. 1-72. /. 1. Leipzig. 1912. (3) Clements, F. E., The development and structure of vegetation. Bot. Surv. Nebraska, Rep. 7, pp. 1-175. Lincoln. 1904. (4) Clements, F. E., Plant succession. Carnegie Inst. Wash., Publ. 242. pp. I-XIII + 1-511. PI. 1-61. 1916. 2 A similar physiographic classification on the basis of soil might be made, should this be considered of more importance than topography. CLASSIFICATION OF PLANT COMMUNITIES 353 Cooper, W. S., The climax forest of Isle Royale, Lake Superior, and its development. Bot. Gaz. 55:1-44, 115-235. f. 1-55 + map. 1913. Coulter, J. M., Barnes, C. R., and Cowles, H. C, A text book of botany, vol. 2. Ecology, pp. 490-964. /. 700-1234. New York. 1911. Cowles, H. C, The ecological relations of the vegetation on the sand dunes of Lake Michigan. Bot. Gaz. 27: 95-117, 167-202, 281-308, 361-391. /. 1-26. 1899. Cowles, H. C, The physiographic ecology of Chicago and vicinity. Bot. Gaz. 31: 73-108, 145-182. /. 1-35. 1901. Cowles, H. C, The plant societies of Chicago and vicinity. Geog. Soc. Chicago, Bull. 2, pp. 1-76. /. 1-39 + map. 1901. Cowles, H. C, Review of Warming's Ecology of Plants. Bot. Gaz. 48: 149-152. 1909. Cowles, H. C, The causes of vegetation cycles. Bot. Gaz. 51: 161-183. 1911. Ganong, W. F., Upon raised peat-bogs in the province of New Brunswick. Trans. Roy. Soc. Canada, Ser. II. 3^: 131-164. /. 1-9. 1897. Harper, R. M., The Hempstead Plains. Bull. Amer. Geog. Soc. 43: 351- 360. /. 1-5. 1911; also, The Hempstead Plains of Long Island, Tor- reya 12: 277-286. /. 1-7. 1912. Harshberger, J. W., The vegetation of the New Jersey pine-barrens, pp. 1-327. /. 1-284 -\- map. Philadelphia. 1916. Hooker, H. D., Jr., Liebig's Law of the Minimum in relation to general biological problems. Science N. S. 46: 197-204. 1917. Moss, C. E., Geographical distribution of vegetation in Somerset: Bath and Bridgewater district. Royal Geog. Soc. Publ., pp. 1-71. /. 1-24 + map. London. 1907. Moss, C. E., The fundamental units of vegetation. New Phytol. 9: 18- 53. 1910. Nichols, G. E., The vegetation of Connecticut, V — Plant societies along rivers and streams. Bull. Torrey Bot. Club 43: 235-264. /. 1-11. 1916. ScHiMPER, A. F. \V., Plant geography upon a physiological basis, English edition, pp. 1-839. /. 1-502 + maps 1-4- Oxford. 1903. ScHROTER, C, Die Vegetation des Bodensees. Zweiter Teil. 1902. Cita- tion from Clements (4, p. 119). Tansley, a. G., and others. Types of British vegetation, pp. 1-416. pi. 1-36 + f. 1-21. Cambridge. 1911. Tansley, A. G., Review of "Plant Succession" by F. E. Clements. Jour. Ecol. 4: 198-204. 1916. Taylor, N., On the origin and present distribution of the pine-barrens of New Jersey. Torreya 12: 229-242. /. 1, 2. 1912. Whitford, H. N., The genetic development of the forests of northern Michigan; a study in physiographic ecology. Bot. Gaz. 31: 289-325. /. 1-18. 1901. COMPARATIVE LENGTH OF GROWING SEASON OF RING-POROUS AND DIFFUSE-POROUS WOODS FERDINAND W. HAASIS Jenkins, Kentucky The object of these studies was to answer the question: does the growth of so-called diffuse-porous woods continue after that of ring-porous woods has largely ceased; in other words, is the growth of the former distributed over a longer period than that of the latter? The work was done during the 1916 growing season at Jen- kins, Kentucky. A small number of trees of various species were selected growing under essentially identical conditions of site, and of these the growth in length of specific branches was meas- ured, it being assumed that this would be a reasonable indicator of the diameter growth. The specimens were located on a 30 degree southeast slope, with rather rocky thin soil, the bed- rock being a gray conglomerate: litter light, ground cover mod- erate, and including Epigcea repens, Smilax rotundifolia, grasses, moss, lichen, etc. The area was logged in 1911 leaving few older trees, and the specimens were practically in the open. Measurements were made of the following trees with ring- porous wood: Sassafras Sassafras, Quercus Prinus: of the follow- ing with diffuse-porous wood: Nyssa sylvatica, Kalmia latifolia, Acer ruhrum; and of the conifer: Pinus rigida. Two chestnut oaks were used, one situated almost directly on outcrop. Its total height was 43 cm., and it was branched all the way up, but with one distinct niain stem. Measurements were made on a 7-cm. twig at the top. The other was an upright shoot of a semi-prostrate sprout 1.5 m. high and from the same stump as another 4 m. high. The growth was measured of a twig near the top, and 61 cm. in length. The sassafras was one of two seedling sprouts from the same root, and was 15 cm. high. 354 RING-POROUS AND DIFFUSE-POROUS WOODS 355 The red maple was one of about a dozen small sprouts from a 3-cm. stump. Measurements were made on two of three ad- jacent t^\dgs respectively 49, 49 and 52 cm. long, at the end of an inchned sprout 133 cm. long. The* longest was dead at the tip after growing 1 cm. by June 7. The mountain laurel was a bushy plant with two prominent branches. One of these, TABLE 1 Showing the total season's growth at the several dates of measurement o N a g < CO < m "-3 oo m z D •-s o CO 0 o D n S m CI a ID cm. cm. cm. cm,. cm. cm. cm. cm. Sassafras n gr* n gr* n gr* 1 6 7 7 7 7 7 7 Quercus n gr* n gr* n gr* 23 23.0 23 23 23.0 23.0 23.0 23.0 Quercus n gr* n gr* 1.5 cm. o 5.0 5 5 5.2 5.2 5.2 Xvssa n gr* n gr* n gr* 5 27.0 31 32 32.0 32.0 32.0 32.0 Kalmia n gr* n gr* n gr* 13 14.0 14 15.0 15.0 15.0 15.0 16 17.0 17 17 17.0 17.0 dead Acer n gr* n gr* 1 1 1,0 1.0 1.0 1.0 2 2 2.3 2.5 2.5 2.5 . 1.0 t ip dead Pinus n gr* n gr* 2.5 6 . 9.5 12 14.0 14.0 14.0 No growth. TABLE II Showing dates between which growth in length ceased Sassafras June Quercus April 30 Quercus July Nyssa June Kalmia June May Acer July Pinus July 7 June 18 30 May 14 5 August 16 IS July 5 18 July 30 14 June 7 30 August 16 5 July 30 a, at the top, was 28 cm. long. The other, b, a side branch from near the base, was 16 cm. above the last main fork, and bore flower-buds. The black gum measurements were made on the largest of three seedling sprouts from the same root, respectively 40, 75, and 100 cm. long, the shortest being prostrate, the others 356 FERDINAND W. HAASIS erect. The pine was growing on very poor soil, practically outcrop. It had a rather weak stem 95 cm. long bent into an arc of almost 90 degrees. Table 1 shows the results of the measurements, and table 2 the dates between which the growth in length ceased. From the very few data collected, it seems that the plant forming the ring-porous wood does, indeed, finish its wood growth at an earlier date than that producing diffuse-porous wood. If this be true, may there not be some relation between the diffuse- ness of the latter' s growing season and the lack of the extreme differentiation of tissue exhibited by the other? It is to be noted, though, that the diffuse-porous woods grew much faster earlier in the season than later on. In the case of the evergreen conifer the growing season is prolonged as in the diffuse-porous wood. There are needed a larger number of parallel observations on this phenomenon; and the measurements should obviously be more frequent in the very early part of the season. It should not be overlooked that cessation of wood production does not mean that growth has ceased, for bud formation, and in some cases the maturing of fruit, continues considerably later than wood growth. BOOKS AND CURRENT LITERATURE Recent Investigations on Evaporation and Succession. — The appearance of Gates's paper on "The relation between evaporation and plant succession in a given area" has suggested the desirability of examining the conflicting \aews in this field. This task is made easier by the facts that methods and results are essentially in accord throughout. The divergence in the several investigations is limited to the conclusions drawn as to the role of evaporation, and it centers around the question whether evaporation is a cause or an effect. Fuller and Weaver regard evaporation as essentially causal to succession, a view which seems to be shared by Transeau in some degree. On the other hand, Gleason and Gates consider it merely a consequence of the increasing population and the resulting shade. A careful examination of their conclusions readily discloses the source of the disagreement, and serves to harmonize the results more or less completely. Transeau^ was not especially concerned with the dominants of the various communities, and his results do not bear directly upon the serai movement. Moreover, it cannot be said with certainty that he regards evaporation as causal, though the following statements seem to indi- cate this. "With these data in hand it is not difficult to see why seedlings of Trillium, Arisaema and Veratrum are successful in the swamp forest with its 10% relative evaporation; why they fail in the open hillside forest with its 50% rate; and why they are never seen on the near-by gravel slide with its relatives rate of 100% in addition to its unstable character." "In the reforestation of the gravel slides in this locality it vdW be seen that the greatest decrease in the demands for transpiration on the part of seedlings takes place during the first stages. This greatly aids in accounting for the well-known fact that development toward a closed association proceeds with such increasing rapidity when once a few plants gain a foothold. Attention has been frequently called to the importance of pioneers as shade producers, while their effective- ness in reducing transpiration has been underestimated." 1 Transeau, E. X. The Relation of Plant Societies to Evaporation. Bot. Gaz. 45: 217. 1908 357 THE PLANT WORLD, VOL. 20, NO. 11 358 BOOKS AND CURRENT LITERATURE Fuller has made several studies of the relation between evaporation and plant communities, but only two of these deal directly with suc- cession. In Evaporation and Plant Succession, "^ his major conclusion is that "The differences in the rates of evaporation in the various plant associations studied are sufficient to indicate that the atmospheric conditions are efficient factors in causing successions^ It seems signifi- cant that the final comprehensive paper is entitled "Evaporation and soil moisture in relation to the succession of plant associations."'* The conflict in opinions can be traced directly to the statement that "The evaporation thus controlled and changed is one of the principal factors in causing the development of a different vegetation, or in other words, the decreased rate of evaporation caused by the heavier vegetation is the direct cause of succession between different associations" (p. 199). The latter part of this statement would seem to be a slip of the pen if one may judge from the evidence afforded by the general conclusions and summary. "The progressive increase in the water-retaining power of the soil, due largely to its increased humus content, must play no inconsiderable role in causing the succession here culminating in the mesophytic beech-maple forest" (p. 231). "T/iese comparative values of the moisture factors [ratios between evaporation and available water] show such a surprising rate of increase as one proceeds from the pioneer to the climax associations that it cannot be doubted that such a change in water conditions must be one of the chief factors, if not the most important cause, of the succession of associations from the more xero- phytj^ to the more mesophytic" (p. 231). ''The evaporation rates and the amount of growth-water in the various associations vary directly with the order of their occurrence iii the succession, the pioneer being the most xerophytic in both respects. The ratios between evaporation and growth-water in the beech-maple forest, oak-hickory forest, oak dune, pine dune and cottonwood dune associations have been shown to have comparative values. of 100, 65, 20, 17 and 15 respectively, and the differences thus indicated are sufficient to be efficient factors in causing succession." Gleason and Gates,^ working in the same general region as Fuller, 2 Fuller, G. D. Evaporation and Plant Succession. Bot. Gaz. 52: 193. 1911. 3 The italics here and later are the reviewer's. * Fuller, G. D. Evaporation and Soil Moisture in Relation to the Succession of Plant Associations. Bot. Gaz. 58: 193. 1914. ^ Gleason, H. A. and Gates, F. C. A Comparison of the Rates of Evaporation in Certain Associations in Central Illinois. Bot. Gaz. 53: 478. 1912. BOOKS AND CURRENT LITERATURE 359 reached the following conclusions. "Differences in the amount of evaporation in various associations, are due chiefly to the nature of the vegetation, which by its size and density controls the evaporation be- neath it. The observations indicate that successions between associations are not caused by any conditions of evaporation. The more primitive associations have the higher rates of evaporation, while those most nearly like the climax t^^pe have the lowest rates. This is true not only for the forest associations, in which low evaporation is expected, but also for the prairie associations, which are correlated with an arid olimate and consequently high climatic evaporation." Weaver"^ as a result of successional studies in the Palouse region of the Northwest, finds that "A study of the difference of the rates of evaporation in the various plant formations and associations shows that these differences are sufficient to be important factors in causing succession, at least through the earlier stages, where light values are usually high." Later, in a study of edaphic prairip in Minnesota and climatic prairie in Nebraska, Weaver and ThieF summarize the re- actions as follows. "If sufficient Hght is available, there is no question but that the humidity of the air and the soil are the most important factors affecting the establishment of the different plant commimities. The progressive increase of the humidity of the habitat causes a cor- responding increase in the mesophytism of the plant community. The evaporation rates and the amount of soil moisture of the various communities both in Minnesota and Nebraska varj^ in general directly with the order of their occurrence in the succession, the community nearest the climax being the most mesophytic in both respects." Gates^ has directed his attention primarily to the ecesis of the domi- nants of the various stages, and reaches the following results. "Invasion, which is the initial stage of succession, must take place under the conditions already existing. • "The change of conditions coincident with mesophytic succession brings about a decrease in the rate of evaporation in the ground or chamaephytic layer. "In a given area, the differences in the amount of evaporation under " Weaver, J. E. Evaporation and Plant Succession in Southeastern Wash- ington and Adjacent Idaho. Plant World 17: 273. 1914. ^Weaver, J. E. and Thiel, A. F. Ecological Studies in the Tension Zone between Prairie and Woodland. Rep Bot. Surv. Nebr. N. S. 1. 1917. * Gates, F. C. The Relation between Evaporation and Plant Succession in a Given Area. Amer. Jour. Bot, 4: 161. 1917. 360 BOOKS AND CUERENT LITERATURE which' seedlings develop are largely due to the surrounding vegetation, which by its size and density controls the evaporation beneath it. "The complete range of evaporation conditions present in this region, namely, from bare ground to the mature forest, is completely within the physiological limits of the seedlings of Acer saccharum, Pinus strobus, Pinus resinosa and Thuja occidentalis. Given suitable soil conditions, maple seedlings will develop under evaporation conditions at least 2>'i1% more xerophytic than the normal hardwood forest, or 400% more xerophytic than the very dense forest. "Within their soil requirements and in the presence of light, the establishment of the pine, beech-maple and Thuja bog associations is independent of any particular conditions of evaporation. Conse- quently a decrease in evaporation is not a prerequisite to succession. "The change in the rate of evaporation from the chamaephytic layer is produced by the development in density of the invading vegeta- tion. Being coincident with and not antecedent to it, the chavge in evaporation is a result and not a cause of succession." At the beginning of his paper, Gates quotes the opinion of Gleason and Gates, and the first statements of Fuller and We iver, as given above, to show the discrepancy in the views on tliis subject. Fuller (1914, p. 199) evidently feels this also, for he says that "It seems sur- prising that Gleason has reached an opposite conclusion from somewhat similar data." In spite of this, however, the later statements of Fuller, as of Weaver, make it clear that they are thinking of evaporation not as a separate factor but in its normal relation to water content, a general principle with which the work and the conclusions of Gleason and Gates, and of Gates are in full accord. It seems probable, however, that Fuller and Weaver would emphasize the importance of evaporation in the complex of water relations especially in a dry region such as the Palouse, while Gleason and Gates evidently do not. It is clear that evaporation is an indirect or remote cause of succession, since it affects the adequacy of the water-content through transpiration as well as by loss from the soil. The direct or primary causes must be sought in the available water-content, which finally determines absorption and growth, and in light, which controls the food supply, to say nothing of its effect upon transpiration. All of the above investigations have brought us appreciably nearer our goal in the study of succession. They all possess the distinct merit of dealing quantitatively with reactions in their causal relation to the serai sequence. They also serve to bring us closer to the realiza- BOOKS AND CURRENT LITERATURE 361 tion of the fact that future research must deal with the complex of reactions and the exact role of each factor in the complex. The re- viewer^ has already emphasized these requirements of successional research, and it may be helpful to point out here the essentials of thorough-going quantitative study. It is obvious that the reaction- level, in which the seedlings of dominants occur, must be the main objective. In most cases, measurements of water-content and evapora- tion, and of light in the reaction-level of the various zones or stages will suffice, but all of these must be dealt with in the same investigation. ' In the oxysere, aeration and other factors must be studied, while in the halosere the chief attention must be given to the solutes. It is already apparent however that we must soon use the plant as an index of re- action. The transpiration of each dominant will prove by far the best measure of the control of water reactions, just as the amount of pho- tosynthate and growth will be the best measure of serai response to light reactions. Perhaps the greatest need in the study of succession is the use of methods of sequence and experiment in place of the almost universal method of inference. It seems mevitable that the next great step in advance will be made by series of reaction quadrats, in which the interplay of development and reaction may be followed year by year, and where the actual fate of dominants can be checked by reciprocal experunents in ecesis. — Frederic E. Clements. Soil Temperature and Plant Growth. — The effects of soil tem- perature per se, as distinguished from that of the air, on the growth and development of plants, appears not to have received very much atten- tion. The recent study by Halsted and Waksman^ therefore, is of much interest. In this research two lots of corn were placed under observation. Of these one lot was grown between July 30 and August 26, and the other between October 29 and November 29, in a green- house which was not artificially heated. The temperature of the soil was noted twice daily, at 6 o'clock, morning and evening. For the summer the average temperature of the soil was 25.68°C. In the autumn the daily average was 12.87°C. The air temperatures are not given. The title of the study does not give the idea that it is on heredity, 5 Clements, F. E. Plant Succession. Carnegie Inst. Wash. Pub. 1916. Pp. 96, 421. 1 Halsted, B. D., and Waksman, S. A. The Influence of Soil Temperature upon Seedling Corn. Soil Science 3: 393-398, 1917. 362 BOOKS AND CURRENT LITERATURE or variation, as is the fact, and as such it has much interest, but the feature of the work to which the reviewer wishes to direct attention is that correctly connoted by the title, that is, to the influence of the tem- perature of the soil itself on the behavior of the plants without regard to the strains of corn employed. In judging the influence of warm and cool soils on seedling corn the following points were considered: viability, length of mesocotyl, emer- gence, length of plant, weight of seedlings, vigor of seedlings, and vari- ability in lengih of seedlings. Am.ong the leading results and conclu- sions the following can be noted: The sum.mer-grown seedlings were 32.93% m.ore viable than those that were grown in autumn. The meso- cotyl was 10.9% longer in the seedlings grown in summer than in those grown in autumn. In summer the corn seedlings "came up" somewhat over 10 days sooner than in autumn, and the average emergence for the two seasons was 4.06 and 14.63 days, respectively. The length of the plants grown in sum.m.er was found to average 41.6 m.m. wliile the length of plants grown in autumn was 11.7 mm. The average weight of the summer-groAvn seedlings was 4.27 grams while the average weight of the seedlings grown in autumn was 1.27 grams. As to the vigor of the seedlings, that is, "the weight of the crops less the seeds planted," it was found that the seedlings raised in summer averaged n'earty four times as heavy as those grown in autumn. Thus in many respects the seedlings grown in summer are immensely more vigorous than those grown in autumn, but as regards variability, the autumn- grown seedlings ranked first. The variability in length of seedlings of summer was 1.08 per cent, while those that were grown in autumn had a variability in length of 2.32%. Although it is thus shown that the shoots of the corn seedlings vary in development directly with the temperature of the soil, it would be of considerable interest to know whether the development of the roots of the two corn croi:js varied also and to what degree. That this would be the case would be expected, however, from the experience of other writers with other species. Indeed, it might even be not too much to suggest that a close study of root behavior under such conditions as those which obtained in the study in question, may have given results quite as applicable to the case, from, the present point of view at any rate, as the study of the shoots only. The work of Halsted and Waksman recalled to th<^ reviewer a series of analogous experiments which he carried out on cuttings of Opuntia versicolor at the Coastal Laboratory, in which the soil only was heated, BOOKS AND CURRENT LITERATURE 363 and the shoots of the plants were subject to the temperature changes incident to the experimental garden at Carmel. As is well known 0. versicolor is native to southern Arizona and thus, in its proper habitat, is exposed to a warm summer climate. At Carmel, however, the tem- perature of the soil throughout the year is relatively low and so is that of the air. It was not especially surprising, therefore, to learn that shoot growth of the species scarcely ever occurs at the Coastal Labora- tory. This being the case experiments were planned as suggested above, and the apparatus was arranged in the following manner. A root box was devised and constructed in such a manner that heat could be applied continuously at each end by using electric lamps. A part of one side was made of glass and sloped in such a way as would bring about the exposure of the roots. The entire box was well insulated, and the soil was closety covered with heayv' building paper. The tempera- ture of the soil was slightly above the optimum for the Opuntia at the ends of the box, and somewhat under the optimum at the middle, but between the two the temperature was, for the most part, close to 30°C. Several specim.ens were removed from the garden, where they had been quiescent for the entire season, and put in the box in early September. The culture was left under a protecting shade until late November during all of which time the soil was frequently watered and was kept heated in the manner suggested, and the shoots of the plants were exposed to uncontrolled air temperatures, which varied between 3.5° and 30°C. as extremes. Such being the conditions of the experiment, the results can be stated in a word. Root growth of all plants in the soil where the temperature was most favorable was found, when the experiment was terminated, to have been very active, and the roots reached to the bottom of the box, or to a depth of 60 cm. All of the plants were found to have put on new shoots and fresh leaves. The shoots had much the appearance of hav- ing been "forced," and were 8 cm. more or less, in length. Thus it was shown that relatively great vegetative activity of Opuntia versicolor can be induced under unfavorably low conditions of air temperatures if the roots are kept at temperatures favorable for their growth. This result constitutes a rather interesting confirmation of the conclusions of Halsted and Waksman, although having reference to quite a different tj'pe of plant, and further emphasizes the importance of including soil temperatures in any definition of the physical characteristics of the habitat of a species. — W, A. Cannon. NOTES AND COMMENT The receipts of the National Forests for the past fiscal year exceeded those of the previous year by more than $600,000, and reached a total of $3,450,000. This sum is chiefly derived from the nearly equal sources of timber sales and grazing permits, with a small income from permits for water-power development. The cost of operating the forests remained approximately the same as in the preceding year at $4,000,000. The gradually increasing receipts give a basis to the hope that the National Forests will become self-supporting in the course of a few more years. During the last fiscal year the cutting of timber was more active and the number of cattle and sheep given pasturage was raised from 9,600,000 to 9,900,000, with slightly increased fees for grazmg. The careful supervision that has been given to grazing oper- ations in the National Forests for a number of years has resulted in such greatly improved conditions that it was deemed safe to allow an increase in the amount of stock pastured during the past summer as a war emergency measure. Dr. H. C. Cowles and Dr. George D. Fuller, of the University of Chicago, have been engaged in a study of the dunes of Lake Michigan and have an extended publication on this subject in preparation. The younger dunes near the south end of the lake are the ones that have heretofore received the closest study, whereas the present investiga- tion has been largety among the older stabilized dunes of the northern shores of the Michigan side of the lake, some of which bear the highest type of mesophytic forest. In continuation of the series of bulletins on the trees of the Rocky Mountain region, Mr. George B. Sudworth has issued a treatment of the pines (Department of Agriculture, Bull. 460) similar to that of the junipers and cypresses which appeared some months ago. Fourteen species are described and illustrated and small maps are given show- ing their geographical ranges. John Wiley and Sons announce the appearance of a second edition of Dr. Henry Kraemer's Applied and Economic Botany. This book is designed for use in technical and agricultural schools, and for students of pharmacy, medicine, and the chemistry of foods. 364 THE PENTOSE SUGARS IN PLANT METABOLISM H. A. SPOEHR Desert Laboratory, Tucson, Arizona There is no group of problems more urgent of investigation and pregnant with far-reaching and practical results than those dealing with the more intricate phases of plant metabolism. It is high time that the realization be more generally gained that all products derived from plants, be they sugar, rubber, alka- loids or essential oils, are the result of metabolic activity, and that the study of the mode of formation and increase of these sub- stances is essentially a chemical problem. It is only by means of the most thorough and painstaking investigations, and the employment of the most advanced chemical technique and in- terpretation that any results in this difficult field can be hoped for. Of all the chemical substances found in plants the great group of sugars commands the center of attention in considering the various aspects of plant metaboHsm. All evidence points to the conclusion that sugars are the first products which accumu- late in the process of the photosynthetic appropriation of car- bon dioxide in the chlorophyllous cell, thus forming the starting point for the syntheses of the tremendous number of substances found in the living organism. The manner in which sugars are converted into fats and how they are incorporated into the com- plex protein molecules is a problem on which as yet we have but very little information. The courses of many of the other trans- formations of the sugars still are explained in a purely hypotheti- cal and speculative manner. But not only as synthetic mate- rial are the sugars of importance in the economy of the plant, but especially as sources of energy must they be regarded as of greatest importance in the life of the plant. This latter 365 THE PLANT WORLD, VOL. 20, NO. 12 DECEMBER, 1917 366 H. A. SPOEHR quality is undoubtedly due to the ease and multifarious ways in which the sugars are dissociated as well as to their high free energy. Thus, under aerobic conditions the sugars are easily oxi- dized, and yield a large amount of energy, while under anaerobic conditions also', thanks to their great dissociation, they may un- dergo chemical changes liberating much energy.. In this respect neither the fats nor proteins can be compared with the sugars as to usefulness for the organism. It is evident therefore that the starting point for a rational study of the chemistry of plant metabolism, as well as of the organic constit- uents of protoplasm, is the investigation of carbohydrate synthe- sis, rearrangement and disintegration. The carbohydrates found in plants are in general of two kinds: those in which there are five carbon atoms, the pentoses, and those containing six carbon atoms, the hexoses. Members of the tetrose series, four carbon atom sugars, are exceedingly rare. The pentoses and hexoses appear to some extent in the mono- molecular form, but especially as di- and polysaccharides in which a number of pentose or hexose molecules are condensed to form a large molecule as cane sugar, starch and cellulose. The pentoses are most familiar as pentosans as components of the cell walls and vessels of the plants, and as found in various gums in the form of xylan and araban. While widespread in the vegetable kingdom, they have but recently been regarded in their important bearing, and, in fact, were for a long time not recognized as belonging to a separate group. These sugars occur mainly in the condensed form as pentosans. In fact, the presence of monosaccharide pentoses has been but very recently established. The main point how- ever, is that the five carbon atom sugars have been found in one form or another as a component of almost all plants. On account of their great similarity in chemical composition and reaction, the quantitative separation and individual deter- mination of the hexose and pentose sugars is associated with considerable difficulty, and only by the exercise of great care can reliable data be obtained. It has been found that pentoses PENTOSE SUGARS IN PLANT METABOLISM 367 especially in small quantities can be determined accurately only by first removing all the hexoses by fermentation. ^ The proportion in which these two groups of sugars appear varies greatly in different plants, some containing no pentoses at all; while in others, such as the platyopuntias at times over half of the total sugars present are pentoses. On account of their direct economic value and their great im- portance in animal nutrition, fermentation, etc., special atten- tion has been paid to the hexoses and the chemistry and physio- logical role of this group has been extensively studied. When dissolved in pure water these monosaccharides are comparatively stable substances. Recently it has been found, however, that even small traces of other substances, such as inorganic salts, acids or alkalies in solution induce profound changes. These investigations have aided greath^ in an understanding of the manner in which the sugars are rendered so exceedingly unstable and capable of such multifarious reactions in protoplasm and have throw^n much light on the causes of the instability of living matter. For example, an aqueous solution of dextrose is barely afTected by the oxygen of the air, if however, a trace of an iron salt or of a caustic alkali is added to the solution, oxidation takes place rapidly and with the evolution of much heat. This, very briefly stated, is due to the fact that sugars are actually weak acids, capable of salt formation, that these sugar-salts are far more reactive than the sugars themselves and in aqueous solution spontaneously decompose into smaller molecules capa- ble of oxidation, rearrangement and condensation.- The number of products of such a decomposition is enormous and the nature of the oxidation reaction depends upon tempera- ture, concentration, the inorganic salts present, etc. ^ The complete methods and results as well as a more extensive discussion of this subject are to appear in a publication on "The Carbohydrate Economy of Cacti" now in preparation. See also: W. A. Davis and S. O. Sawyer, The esti- mation of Carbohydrates, IV. The presence of free pentoses in plant extracts and the influence of other sugars on their estimation. Jour. Agri. Sci. 6: 406-412, 1915. 2 Nef, J. U., Dissoziationsvorgonge in der Zuckergruppe. Ann. d. Chem. (Liebig) 357: 214, 1907; 375: 1, 1910; 403: 294, 1918. 368 H. A. SPOEHR In these reactions the inorganic salts play the role of enzymes, and in all probability enzymes act by virtue of their ability to form salts with sugars. Even in these relatively crude experi- ments great differences in the reactions of the various sugars appear; it is therefore not surprising that the far more delicately adjusted enzymatic reactions should exhibit large variations in the reactivity of the various hexose and pentose sugars. That the pentoses are of great physiological importance to the plant becomes evident in the light of recent investigations on the chemistry of the cell nucleus.^ Among the chief compo- nents hereof are the so-called nucleic acids. These are highly com- plex substances consisting roughly of a combination of phos- phoric acid, purines, pyrimidines and several carbohydrate groups. While in the nucleic acids of animal origin the carbo- hydrate is a hexose, the plant nucleic acids so far studied have been found to contain the pentose group. The function and fundamental importance of the nucleus in the metabolism of the plant need no further discussion here; however, a more intimate knowledge of the chemical composition and action will undoubt- edly lead to a clearer understanding of the intricate reactions of this most important organ. As a further illustration of the role of pentoses in the more in- tricate metabolism of certain plants the relation of these sugars to rubber and terpene formation is of special interest. Harries* in his extensive investigations on the constitution of para- caoutchouc has shown that this substance is made up of a large number of groups which have been condensed or polymerized to form an exceedingly large molecule. These individual groups have the composition, CsHg, and thus rubber can be considered as being composed of a number of these groups in a similar man- ner as we think of starch and cellulose as a multi-anhydride of glucose. As the sugars are the first products of the primary or- ganic synthesis in the plant practically all other organic sub- stances found therein must be derived from them more or less directly. Harries considers the CsHs groups as reduction prod- * Levene, J. and W. Jacobs, Ber. d. deutsch. chem. ges. 43: 3147, 3164, 1910. * Harries, C, Ber. d. deutsch. chem. Ges. 38: 1195-1203, 1905. PENTOSE SUGARS IN PLANT METABOLISM 369 ucts of the pentoses, (C5H10O5) and that subsequently the CoHg is condensed to the rubber-hydrocarbon (CioHie)x. Reducing actions are by no means uncommon in plants, es- pecially as the products of intra-molecular respiration and spe- cial types of fermentation. A well known example of the forma- tion of a hydrocarbon is the production of methane from cellu- lose and pentosans by an anaerobic bacillus.^ Harries' conception is further substantiated by the fact that the degradation of caoutchouc yields levulinic acid and levulinic aldehyde which are the same products yielded by the sugars. In the light of the foregoing it seemed therefore not without interest to determine whether a plant which is actually produc- ing rubber would show a condition of its carbohydrate content which might tend to substantiate this theory. The desert rub- ber plant, guayule, (Parihenium argentaium) , offered excellent material for such an investigation. The analyses show that in the youngest parts of the plant, in which the rubber is being formed, an unusually high percentage of the total sugars is in the form of pentoses. To the terpenes and their almost in- numerable derivatives belong many of the most important plant products, more especially many of the essential oils, camphor derivatives, etc. The pentoses have been known for a long time to be common components of the walls and vessels of plants. The several attempts at making alcohol on a commercial scale from wood have not been very successful, apparently because a considerable percentage of the sugar produced by hydrolysis of the wood is unfermentable. The constitution of cellulose, however, has not yet been clearly established and the way in which the pen- tose molecule is united with the other sugar groups is still unsettled. It has long been known that when starch is hydrolysed all of it does not go over into glucose, as is commonly supposed, but there always remains an unfermentable residue. The nature of this residue has been the subject of repeated investigation with- » Omlianski, W., Zentr. Bakt. II, 8, 193, 1902. Koch, Jahresber, 14: 457, 1903. 370 H. A. SPOEHR out however a definite solution having ioeen reached. There is no doubt, however, that starch contains varying quantities of pentoses. This is a fact'' which apparently has been disregarded in most of the studies on the constitution of starch, but which certainly must be of greatest importance in the study of the metabolic relations of starch and the other carbohydrates. The question then naturally arises; is starch really of fixed constitution or is it rather of a heterogeneous nature? Un- doubtedly glucose predominates in its products of hydrolysis. But glucose usually also is present in largest amounts in the plant juices, it does not seem unreasonable to suppose therefore that when the carbohydrates are laid down this sugar should predominate. Could it be that starch is a form (a physical form) in which the various sugars are laid down for storage and that the pentoses should be included herein? If this were so it could be expected that any of the sugars when presented to a starch- free leaf would produce starch therein. It has been shown that this is the case with all the fermentable sugars. Cremer and Bokorny got doubtful results with 1-arabinose and 1-xylose. The writer placed leaves of Ampelopsis quinquefolia which had lost all their starch (by being kept in the dark) on solutions of 1% and 2% pure 1-arabinose (m.p. 160°) in distilled water. After having been kept in these solutions for two days in the dark, the chorophyll was dissolved out by means of hot 80% alcohol, and the leaves were tested for starch with alcoholic io- dine and with chloralhydrate and iodine. The results were un- mistakable; along the main veins and 1 to 2 mm. to either side, the dark blue color of the starch-iodine was visible. Of course, from this experiment it cannot be concluded defi- nitely that the 1-arabinose went directly to form starch in the leaf, for there are other substances (e.g., glycerine) which also form starch in the leaf, and we are certain that these are not directly appropriated. In view of the foregoing, however, the experiment is suggestive, and does indicate that this sugar is « Winterstein, E., Ber. d. deutsch. Chem. Ges. 25: 1237-12-11, 1892. Lintner, C. J., Zeit. angw. Chem. 11: 725-729, 1898. Chem. Zentr. 62: II, 732, 1891. PENTOSE SUGARS IN PLANT METABOLISM 371 utilized in the metabolic processes of the leaf. Careful analyses of starches from various sources and formed under known con- ditions would be desirable information. Similar experiments have been made in order to determine whether the pentoses form glycogen in the liver. The results of various investigators, how- ever, are somewhat contradictory; some having observed an in- crease of glycogen or pseudoglykogen^ others reporting entirely negative results. On critical examination of all the experimental data it becomes evident, however, that in several of the cases where negative results were reported the means employed to re- duce the glycogen in the liver were such as to affect a more dras- tic metabolic disturbance than would be compatible with nor- mal conditions. It is evident then, that the five carbon atom group of sugars is a common component of plants, and is of great importance in some of the most vital metabolic activities of the organism. Nevertheless, the origin and mode of formation of the pentose sugars is still quite obscure. This problem is of special interest because any light thereon would be of great value in gaining a clearer understanding of the process of the photosynthetic ap- propriation of carbon dioxide by the chlorophyllous leaf. The question resolves itself into whether the pentoses are direct prod- ucts of photosynthesis or are derived from other sugars through subsequent metabolic activity. If for instance, the formation of sugar in the green leaf actually takes place by means of a pro- gressive addition of six molecules of formaldehyde the presence of pentoses is to be expected. 2 CH^O^C^H^O^; CH^O^ + CH^O -.C3H6O3 ; C3H6O3 + CHaO-^ C4H8O4; C4H8O4 + CH^O^CsHioOa; C5H10O5 + CH^O-^ C6H12O6 If, again, the sugars are formed by the union of two molecules of glycerine aldehyde, hexoses or their condensation products would be the only substances formed : 2 CH2OH.CHOH.CH: 0->CH20H(CPIOH)4.CH: O ^ Cremer, Ergebnisse der Physiol. 11: 898, 1902. Jaaresber. f. Fortschritte der Tierchem. 38: 446, 1908. v^f^ 372 H. A. SPOEHR This, however, is purely chemical speculation and so far has aided little in the solution of the problem of photosynthesis, the real course of which is probably far more complicated than has been generally assumed. Not enough work has been done with the chlorophyllous leaf to draw valid conclusions, and this in turn has been due to the fact that the methods of separation and determination have not been sufficiently delicate and ac- curate to permit their application to such sensitive material. Most of the work on the pentoses in plants has been done by means of a method which has recently been found to be quite inadequate and liable to yield erroneous results. That is the method depending upon the formation of furfural from pentoses without a previous separation of the other sugars.^ Also little attempt has been made to distinguish between the soluble mono- molecular pentoses and the condensed pentoses present in the plant as pentosans in the cellulose, slimes and gums. For these reasons the question relative to the origin and function of this group of sugars must be considered as not yet definitely answered in spite of the considerable work which has appeared on the subject. Chalmont,-' Tollen,!" Windish and Hasse^^ come to the con- clusion that pentoses are formed from hexoses as first products of oxidation that they are relatively inert and probably are of the nature of waste products. This is based essentially upon their observations that the total pentosan content of seedlings germi- nated and grown in the dark increases with age. The writer made determinations of the total pentoses in seedlings; the re- sults are quite the reverse, however. Wheat seeds were allowed to germinate on glass wool in the dark; at intervals a number of seedlings were removed, dried, ground, hydrolyzed with 1% ^ Davis, W. A., and G. O. Sawyer, 1. c. Kluyver, J., Biochemische Suikerbepolingen. Leiden. 1914. Cunningham, M. and C. Doree, Biochem. Jour. 8: 438-447, 1914. 9 Chalmont, Amer. Chem. Jour. 16: 218, 589, 1894. Ber. d. deutsch. Chem. Ges. 27: 2722, 1894. " Tollens, Chem. Zentr. 69: II, 967, 1898. " Windish and Hasse, Chem. Zentr. 72: II, 1098, 1901. PENTOSE SUGARS IN PLANT METABOLISM 373 HCl, and after determining and fermentating away the hexose sugars the pentose sugars were determined (see table 1). Unquestionably many organisms utilize the pentose sugars as sources of energy. In their physiological effects the differences between the pentoses and hexoses are in many cases less than TABLE 1 Dry weight Total hexose sugar < ^^ [Dry.. Total pentoses < ^^ IDry D.^TS 0 1 3 6 91. so 63.20 54.00 34.80 43.35 25.90 25.10 18.94 47.50 41.00 46.50 54.50 7.60 6.24 1.75 0.57 8.30 3.95 3.24 1.66 21.40 9.95 46.50 0.26 0.05 exist between closely related members of either one of the groups. Many bacteria and molds are capable of utihzing pentoses as the only source of carbon while on the other hand, other organ- isms are quite incapable of doing so. The difference in food value of the various hexoses are well known. Czapek^- gives the following values for Aspergillus niger in weight of jdelds: mg?n. d-fructose 523 . 7 1-Xylose 512.7 d-Galactose 489.3 mgm. d-Glucose 477 . 1 1-arabinose 350.0 d-Mannose 286.8 The high nutritive value of 1-xylose is quite evident, while on the other hand it is well known that the yeasts are quite incapable of utilizing any of the pentose sugars. At the same time it must be remembered that no one of the sugars is universally good nutrient material. For example, as Winogradsky and Omlian- ski^^ have show^n even d-glucose is borne only in very low con- centrations by certain nitrate bacteria, and in this connection the recent investigations of Knudson^* are of great interest. 12 Czapek, F., Biochemie der Pflanzen, I, p. 311, Jena, 1913. 13 Winogradsky and Omlianski, Zentr. f. Bakt., 1899, II, 329-344. >* Knudson, L., Cornell Univ. Agr. Expt. Sta. Mem. 9: 1-57, 1916. 374 H. A. SPOEHR Such specific action of enzymes is one of the most complex and subtle questions in chemistry. Little is known of the role of the pentoses in the metabolism of the higher plants. The pentosans in the walls and vessels have been very extensively investigated, but, as has been indi- cated above very little is known of the origin and physiological role of these substances in the plant. In the mammalian body the pentoses have been found to be about isodynamic in food value with the fats but are not pro- tein sparers as the hexoses are. In carnivorous animals as high as 50 to 60% of the amount fed has been observed excreted in the urine; in omnivorous animals the percentage is less while the herbivorous are capable of utilizing relatively large quantities. ^^ Although physiological work with plants has some advantages over the use of animals in metabolism studies, the former never- theless is associated with obstacles which are exceedingly difficult to overcome. The non-existence of great functional differentia- tion, the impracticability of injecting substances, the lack of any but gaseous excreta, and the high synthetic power of almost all plant cells, make the study of the intermediate steps in plant metabolism an exceedingly difficult experimental investigation. The fleshy joints of the cacti have been found to offer splendid material for various phases of these studies. With the develop- ment of new and special methods of analysis it has been possible to gather data which it is believed may offer added light to these important problems. In the experiments here recorded Opuntia sp. was used exclusively. During March the new joints develop, these grow quite rapidly, so that within about one month the new ovoid joints have attained their full size of 100 to 125 cm. Apparently the young joints are autonomous very early in their development; when cut from the plant with but a very small portion of the parent joint, and placed with the base in tap water, the young joints grow to full size and develop '5 Schirokich, P., Biochem. Zeit. 55: 370, 1913. Magnus-Levy, Oppenheimers Handbuch der Biochem, IV, 1: 399. PENTOSE SUGARS IN PLANT METABOLISM 375 normally. The analyses are given in table 2 in terms of the per cent of the dry material. The first young joints were 2 to 4 cm., about fifteen days old. It is evident that the amount of pentose sugar is considerable even in this very early stage, al- TABLE 2 The carbohydrate content of young and mature Opuntia Joints. percentages of the dry material Values given in March 27 1 April 3 April 16 ( JOINTS , to '^ to TOTAL PENTOSE SUGARS PENTOSE TO TOTAL SUGARS is is P w J to J o W J o Young 14.35 31.22 6.23 0.199 2.74 7.24 Parent 18.62 22.44 5.21 0.232 3.22 11.35 Young 12.70 33.60 9.57 0.285 3.37 6.96 Parent 18.90 20.18 10.04 0.495 5.32 11.86 Young 11.60 36.68 7.48 0.204 4.43 7.22 Parent 18.22 28.40 5.23 0.185 5.00 12.08 a IB < 6.88 12.60 7.51 14.40 10.71 13.95 though the proportion to the total sugars is somewhat higher in the parent joints. An analysis made in October comparing the young joints, then fully matured, with joints three years old show that there TABLE 3 Carbohydrate content of young and old joints of the same plant CO a z s z M a* M 1916 1913 si g§ TOTAL POLYSAC- CHARIDES TOTAL HEXOSE SUGARS !0 1 H CO a CO O w K TOTAL PENTOSE SUGARS to a CO 0 H z a < to O z H P. TOTAL SUGARS TO TOTAL PENTOSE 17.85 20.45 17.94 10.10 1.18 1.27 9.78 0.23 9.55 0.478 20.11 16.60 14.45 9.10 0.51 1.22 7.10 0.40 6.70 0.428 D a ■J to a J 9.10 10.26 TABLE 4 Daily variation in carbohydrate content of Opuntia sp. in October 5.00 p.m. 7.30 a.m. 5.00 p.m. DRY WEIGHT TOTAL SUG.\RS DISAC- CHAHIDES HEXOSES TOT.\L PENTOSE SUGARS PEN- TOSANS PEN- TOSES 17.58 18.80 17.85 16.18 19.40 20.45 0.58 0.34 1.18 1.06 0.83 1.27 8.60 8.33 9.78 8.34 8.22 9.55 0.26 0.20 0.23 TOTAL SUGAR.S TO TOTAL PENTOSE 0.531 0.430 0.478 376 H. A. SPOEHR is no accumulation of either pentose sugars or of pentosans in the old material. In fact, in several other determinations the proportion of pentose sugars in the young was sHghtly higher than in the old joints. There is, therefore, no evidence here which supports the opinion that pentoses and pentosans are end or waste products which accumulate in the older portions of the plant. In the cacti the daily variation in the carbohydrate content is slight. Davis, Daish and Sawyer note that the pentoses and pentosans rise steadily during the night in the mangold leaf (mangel wurzel). This was not observed in the cacti, but rather a slight diminution of these sugars during the night. During the course of the year there is considerable variation in the total carbohydrate content of the cactus as well as in the proportion of the various kinds of sugars. These variations are the result of environmental influences; especially the amount of available water and temperature. A rational conception of the carbohydrate metabolism of a plant can be gained only through the study of the equilibrium of the various sugar components and the factors which influence these equilibria. This paper is confined to a brief consideration of the pentose sugars. These show a decided increase both in actual amount and in the pro- portion to the total sugars as the water content of the plant de- creases. In table 5 are given the results of monthly analyses of joints of Opuntia sp. of the same age and from the same plant growing out of doors. The first analyses were made during the dry fore-summer— the pentose and hexose sugars are present in about equal pro- portion. The summer rains began the middle of July and con- tinued through August. During this period of rain the total sugars are reduced, and especially the pentoses, bringing the pro- portion of hexose sugars considerably higher. September, October and November were very dry months (less than 1 inch rainfall) with a httle rain to December 20. The increase in pentoses during these dry months is very noticeable. There was regular rainfall during the last week in December and January. The March samples were taken a few days after a PENTOSE SUGARS IN PLANT METABOLISM 377 rain, thereafter the dry fore-summer conditions set in. The effects of these periods of rainfall on the relative sugar content and especially on the pentoses are striking. Changes in temper- ature also affect the equilibrium, and — as separate experiments have shown — in such a manner that at higher temperatures the proportion of monosaccharides is reduced in favor of the poly- saccharides. However, this applies particularly to the hexose sugars, the effect of temperature on the pentose-pentosan equilib- rium is slight. TABLE 5 Seasonal variations in sugar content of Opuntia sp. Dry weight. . . Total sugars.. Total hexose sugars Total pentose sugars Pentosans Pentoses Total pentose sugars to total sugars . Total hexose sugars to total sugars . 36.38 20.03 10.45 9.26 9.04 0.20 0.462 0.522 3 16.45 13.24 8.60 4.39 19.66 18.44 8.83 9.08 8.86 0.24 0.332 0.492 0.524 0.650 J3 O 20.30 20.90 9.32 10.95 10.47 0.48 X! S o > o 0.479 0.446 23.05 18.75 5.50 12.50 11.35 0.82 0.667 0.293 30.10(?) 18.95 7.90 10.45 10.10 0.35 0.551 0.417 C3 3 C 22.20 19.10 14.95 4.73 4.40 0.43 0.248 0.783 3 u 22.33 21.32 14.90 6.07 5.51 0.65 0.283 0.698 19.50 28.05 22.16 5.55 4.75 0.82 0.198 a 24.30 32.40 22.70 9.15 8.68 0.48 0.283 0.7910.702 25.25 .30.15 17.08 12.34 12.17 0.16 0.409 0..567 It was possible to reproduce experimentally the effect of the water content on the pentose sugars. Two sets of Opuntia joints, taken from the same plant, under identical conditions were placed in a dark room at constant temperature, 28°. One set (A) was kept with the base of the joints in water, the other set (B) was kept dry; the experiment continued for a month. (A) produced a few small roots, 5 to 10 cm. long, the water was tested from time to time, but not a trace of sugar could be de- tected. The results are given in table 6. 378 H. A. SPOEHR TABLE 6 The effect of the water content upon the proportion of total pentose sugars A B DRY WEIGHT 16.34 23,25 TOTAL SUGARS 8.29 11.90 TOTAL HEX- OSE SUGARS 6.70 6.36 TOTAL PEN- TOSE SUGARS 1.50 5.22 TOTAL PEN- TOSE SUGARS TO TOTAL SUGARS 0.181 0.439 TOTAL HEX- OSE SUGARS TO TOTAL SUGARS 0.808 0.534 It is highly probable that this fact explains the observation of various workers that the total pentoses increase with advancing age of the plant, as in general the water content decreases as the plant grows older. Unfortunately, however, in these older in- vestigations no data are given concerning the amount of water. Furthermore, in using the old methods the cellulose of the walls and vessels is usually also hydrolysed; this fibrous material in- creases with age in the plant and is known to contain a high per- centage of pentose. The fact that the pentose sugars tend to disappear with increasing water content is of special interest in considering the theory previously mentioned of the formation of rubber from pentoses in the rubber plants. In the commercial culture of these plants the effect of water is best expressed in a proverb used by the Mexicans of the Guay- ule rubber country: "much water, little rubber."!^ This, of course, must be regarded as rather circumstantial evidence in favor of the pentose origin of rubber. The salient feature of these experiments is that the pentose sugars accumulate only under conditions of low water content. Little light is thrown on their origin. While Davis, Daish and Sawyer in the mangold leaf observed a rise in the pentoses ap- parently at the expense of the hexoses, the large number of experiments with cacti are not univocal herein. The problem, however, is very complex involving factors some of which are impossible to control. The course of carbohydrate consumption during starvation of joints of Opuntia sp. throws some light on the utilization of the various sugars. A large number of joints of the same age and cut from the same plant were kept in the dark at a constant '^ From a private communication of Dr. W. B. MacCallum. PENTOSE SUGARS IN PLANT METABOLISM 379 temperature, 28°. It is a very striking fact that although the joints are constantly losing water through transpiration, the water content after about the first month remains fairly con- TABLE 7 The course of carbohydrate depletion during starvation of Opuntia sp. Dry weight Total sugars Total polysaccharides Total hexose sugars Hexose polysaccharides Disaccharides Hexoses "Total pentose sugars Pentosans Pentoses Monosaccharides Monosaccharides to total polysacchar ides Total pentoses to total sugars Decem- ber 20 31.50 22.86 20.38 19.74 17.64 1.63 0.62 2.93 2.67 0.36 0.98 0.048 0.128 Febru- ary 12 36. 16. 14. 14. 13, 0. 0. 1, 1. 0. 0. 0. 0. 80 62 22 85 ,72 72 49 68 33 34 83 058 101 March 2 36.20 13.71 12.30 12.25 11.15 0.73 0.45 1.38 1.08 0.30 0.75 0.061 0.101 March 22 40.13 15.23 14.10 13.27 12.41 0.70 0.21 1.84 1.55 0.25 0.46 0.033 0.121 April 20 40.50 14.54 13.52 12.24 11.48 0.55 0.26 2.17 ,2.02 0.15 0.31 0.023 0.149 May 12 37.60 13.52 12.46 11.70 10.87 0.59 0.30 1.72 1.50 0.22 0.52 0.042 0.127 stant.^" Thus also the proportions of the various sugars to each other maintain a surprising regularity as the depletion proceeds; hexose and pentose sugars are consumed at about the same rela- tive rates (table 7). It is quite evident that not only is there no accumulation of pentoses but these sugars are used up at a very appreciable rate. '" Mac Dougal, D. T., E. R. Long and J. C. Brown, End results of the desicca- tion and respiration in succulent plants. Physiol. Res. 1: 289-325, 1915. THE VEGETATION OF CONGLOMERATE ROCKS OF THE CINCINNATI REGION E. LUCY BRAUN University of Cincinnati, Cincinnati, Ohio On the limited areas of conglomerate rock within the Cin- cinnati region, is a vegetation so unique for this region, so dif- ferent from all the surrounding vegetation, that it has no place in the major plant formations of the region. On these rocks there is an independent succession in progress which only in its latest stages, begins to merge with the surrounding associations. Location and extent of rock outcrop. Conglomerate rocks in the Cincinnati region are exposed mostly in the little Miami valley, and in that part of the Ohio valley just above the mouth of the Little Miami river. A few areas also are found in the Miami valley. The outcrops occur in groups, so that there is usually a number of outcrops very close together. These groups or areas may be several miles apart. Rock exposures vary from a few square feet to hundreds of square feet in area. All the outcrops are found on hillsides where there are remnants of glacial terraces. Origin of the conglomerate. The conglomerate was made by the cementation of outwash gravels of the Illinoian and Earlier Wisconsin glacial stages. In most of the Cincinnati region, these gravels — especially those of Wisconsin age — are loose and unconsolidated, or only partially cemented. In places they have been so well cemented as to form a very firm and resistant conglomerate. Composition and texture. The pebbles and bowlders of the conglomerates are of various materials — limestone, quartz, and igneous rocks. Limestone everywhere predominates so that the rock may be considered a limestone conglomerate. The cement is calcareous, locally ferruginous. The texture of .380 VEGETATION OF CONGLOMERATE ROCKS 381 the rock varies from a coarse conglomerate to a sandstone with few pebbles. Within the same rock mass, the gravel varies greatly in size, from particles the size of coarse sand grains to bowlders several inches in diameter. The larger bowlders are embedded in a matrix of smaller particles. The rock is extremely porous. The weathered sur- face is very irregular due to numerous projecting bowlders, and to small depressions or pockets formed when bowlders weather out. Comparison ivith bed-rock of region. The conglomerates of the Cincinnati region everyw^here tend to be more massive than the bed-rock. Because of this there is a difference in the man- ner, possibly also in the rate of weathering of the two types of rock. Weathering of the conglomerates is due to the action of surface agencies and ground water, resulting in the gradual reduction of surface, wdth the accompanying formation of soil on the rock surface, and the occasional loosening of surface bowlders. In the weathering of bed-rock, there is, in addition to the above factors, a pronounced sapping of limestone layers due to the rapid disintegration of the interbedded shales. This results in sudden and relatively great changes in the surface of the rock exposed, and yields instead of fine soil, numbers of large slabs of limestone which are relatively soon covered with soil from the surrounding slopes. Decomposition is more ef- fective in the weathering of the conglomerates than is disin- tegration. In the case of the bed-rock the reverse is true. The hillside around the conglomerate rock is frequently reduced to a fairly gentle slope from which the rock mass projects. For this reason, the conglomerates usually project as huge masses from the hillside (fig. 1). ECOLOGICAL FACTORS Moisture, Except during and for a short time after rains, much of the surface of these rocks is dry. Some water is held for a time in the surface pockets. The accumulation of soil in the pockets, and the deep moss mat are important in lessen- ing run-off. The irregularities of the surface and the porous THE PLANT WORLD, VOL. 20, NO. 12 382 E. LUCY BRAUN nature of the matrix, facilitate the entrance of rain water. The fine-grained parts of the masses serve as reservoirs to retain and gradually feed out the water after the surface portions become dry. Part of the rock, too, is buried deep in the soil of the hill- side where there is always a constant supply of moisture. The amount of water available to the vegetation of these rocks depends directly on the steepness of slope of the surface Fig. 1. Conglomerate rock outcrop on hillside; patches of moss and Sedum are prominent, with shrubs on the ledges. and on the texture of the material, and indirectly on the direc- tion of slope. The influence of steepness of slope is seen in the distribution of plant communities (fig. 4). We find the most xerophytic communities on the vertical faces and edges of shelves, the xero-mesophytic communities on gently sloping and irregular parts of the rock, and the most mesophytic communities in deep and sheltered angles where both surface water and water drain- VEGETATION OF CONGLOMERATE ROCKS 383 ing from the rock pores is collected. A few places are almost constantly wet, due to a gradual seepage of water from the in- terior of the rock. Direction of slope is important because of differences in ex- posure to sunlight resulting in differences in evaporation (figs. 4 and 5). The effect is indicated in the progress of the plant successions and the character of the final closed associations found on different slopes. The texture of the rock material determines the volume of water which may be held in the pores of the rock, and the rapidity with which water may enter from the outside. Measurements of the water content of small pieces of the conglomerate from the surface of the rock mass showed an aver- age of 4.45 grams water to 100 grams dry weight of rock. Rock weathering. The character of the weathering of these Pleistocene conglomerates — slow surface decomposition without sapping — is probably the most important factor in determining the nature and completeness of the marked plant succession on these rocks. It is chiefly because of this physical character- istic of the habitat that the very marked plant communities are developed. Soil. As a result of rock weathering and plant decay there is accumulated in the irregularities of the surface, a very black sandy humus. This soil is strongly calcareous, due to the pres- ence in it of numerous minute grains of limestone produced by the disintegration of the conglomerate upon decomposition of its cement. The soil is extremely light, fine grained, and spongy when wet, and does not bake on drying. The average capillary water content as determined from a number of tests is 62.26 grams water to 100 grams of air dry soil. Isolation. Isolation of any area is an ecological factor be- cause of the effect on plant distribution. Outcrops or groups of outcrops of conglomerate rocks are frequently several miles apart. The intervening space is forest, cultivated, or waste land, usually having little in common \vith the rock habitat. Outcrops of the limestone and shale bed-rock of the region are seen (1) along stream banks, (2) in ravines, (3) in quarries, 384 E. LUCY BRAUN and (4) occasionally near the tops of the higher hills. Slabs of limestone weathered out from the bed-rock are numerous on the steeper hillsides. In the first two types of locations, the rocks are subjected usually several times annually, to the erosive action of streams. In the third type, conditions of light and moisture are extreme, especially in those quarries recently worked. When the quarry has been long abandoned, the face is almost covered with soil and small rock fragments, thus giv- ing adequate foothold for herbaceous and even tree growth. The fourth type of location, rock outcrops near the tops of the higher hills, is somewhat similar to the conglomerate out- crops under consideration. Even here, the rock succession^ is very incomplete, only the earliest lichen and moss stages being represented before the advent of herbaceous and woody plants, which appear relatively early because of the many crevices. Because of the position, high up on slopes, the rocks are always exposed to direct sunlight, until shaded by their own vegetation. The limestone slabs lying on the surface of steeper hillsides are so small that they can only support a very meager flora. The character and frequency of rock outcrops in the Cincin- nati region has been given here in order to make clear the de- gree of isolation of the conglomerate rock areas in the region. The vegetation of these rocks is of interest chiefly because of its unusualness in the region. It is of a character to be expected in a rocky region, where migration from area to area is easy. It is remarkable in a region of few stable rock outcrops, where distance becomes an obstacle to migration. VEGETATION The plant succession of the conglomerate rocks of the Cincin- nati region is the only typical rock succession in the region. The succession passes through various lichen and moss stages before the advent of herbaceous and shrub stages. 1. Lichen stages. The lichen stages of the succession are two 1 Braun, E. Lucy. The Physiographic Ecology of the Cincinnati Region. Ohio Biol. Survey, Bulletin 7, 1916. i VEGETATION OF CONGLOMERATE ROCKS 385 ill number, one dominated by crustose lichens, the other by fohose Uchens. The first or crustose hchen stage is seen on the smoother and more exposed rock faces. The patches of crustose hchens are separated by spaces of bare rock, or rarely nearly cover the surface. The lichens most commonly found are Lecidea sp., Pertusaria communis, Staurothele umbrina, Verrucaria muralis, Fig, 2. The foliose lichen, Dermatocarpon miniatum, on steep rock surface facing 825° W; scattered herbaceous plants in pockets. Both transects, figures 4 and 5, cross this area. and Placodium citrinum. With these crustose lichens, but of only minor importance in this lichen community, is the xero- phytic moss, Grimmia apocarpa. Foliose lichens begin to ap- pear early in the crustose lichen stage, but reach their cul- mination only on partially shaded rocks. The second or foliose lichen stage is dominated by Dermato- carpon miniatum. Where best developed the large gray thalli of this plant nearly cover the rock surface (fig. 2). A few 386 E. LUCY BRAUN secondary species of lichens are present, most prominent of which is the gelatinous lichen, Omphalaria sp. Mosses become more important, both in numbers and species, than in the crus- tose lichen stage. Grimmia apocarpa, Anomodon attenuatus, and Leskea sp. are represented, and in places become so abun- dant as to interfere with the lichens, thus indicating the next stage in the succession. The aspect of the foliose lichen stage changes from place to place. Omphalaria is sometimes the facies of the association. In places the foliose lichens are not well represented, and the mosses of this stage assume greater prominence, though scarcely more abundant. Fruticose lichens are entirely absent from the succession, which in this respect differs from rock successions described elsewhere. 2 On the undersides of overhanging ledges and on many rock faces protected from direct light, none of the characteristic lichens of the two preceding stages are seen. In their places, is the pale powdery lichen, Amphiloma lanuginosum, and rarely a light green moss, Plagiothecium sp. The sharp color contrast between the dull grey-greens of the lichen communities or the dark rich green of the moss mats, with the pale yellowish green of this lichen is often very striking. In very sheltered spots the Amphiloma sometimes grows with the mesophytic mosses and occasionally overruns them. 2. Moss stages. The first mosses appear early in the lichen stages of the succession, but it is not until after the foliose lichen stage is well advanced, that they become prominent. The first well marked moss stage is dominated by Anomodon attenuatus, with Leskea sp., Anomodon minor, Grimmia apocarpa, and the liverwort, Porella platyphylla, as secondary species. Crustose and foliose lichens persist in spots. Grimmia is the 2 Cooper, W. S. The ecological succession of mosses, as illustrated upon Isle Royale, Lake Superior. Plant World 15: 197-213. 1912. Cooper, W. S. The climax forest of Isle Royale, Lake Superior, and its de- velopment. Pt. II, The successions. Bot. Gaz. 55: 1L5-140. 1913. Fink, Bruce. A lichen society of a sandstone riprap. Bot. Gaz. 38: 265-284. 1904. VEGETATION OF CONGIiOMERATE ROCKS 387 most xerophytic of the mosses and is really a relict of an earlier stage; Anomodon minor seems to be the most mesophytic of the mosses here represented, and indicates an advance to more mesophytic conditions. It is usually found in more sheltered spots or on gentler slopes as a constituent of the ever thickening moss mat. On flat ledges and in sheltered and shaded spots, the mosses of the first stage are replaced by more mesophytic kinds. A second moss stage, much more mesophytic than the first, becomes e\ddent. This is characterized by a very dense and deep moss mat, in which Mnium cuspidatum is the facies, and Rhodohryum roseum, Catharinea crispa, Entodon seductrix, Brachy- thecium salebrosum, Fissidens incurvus and the mosses of the pre- vious stage, except Grimmia, are secondary species. The foliose lichen, Peltigera apthosa, and the liverwort, Conocephalum coni- cum, are important locally. The mosses of this stage vary in importance at different periods of development and in different parts. Mnium — always characteristic of this community — becomes increasingly important with the development of the succession. The series from Anomodon as the dominant plant, to Mnium as the dominant is well marked in a number of places. Beneath the moss mat of this stage there is being accumulated h thick layer of humus, preparing the way for the advent of the herbaceous plants which follow. 3. Herhaceous stages. Herbaceous plants begin to appear as soon as there is some soil accumulated in the irregularities of the surface. The usual distinction between crevice and sur- face plants is scarcely applicable here. The first herbaceous plants grow in the shallow soil of the pockets, which unlike crevices, do not permit of deep rooting. With the accumulation of soil in the pockets, and the growth of the moss mat, there begins an open herbaceous stage, which on sunny south rock slopes may telescope the second moss stage. The first herbaceous plants of the pockets appear in the foliose lichen stage (fig. 2). The pioneer herbs are Aquilegia canadensis (wild columbine), Cystopteris fragilis, Woodsia obtusa, and Poa compressa. As the mosses spread over the surface and 388 E. LUCY BRAUN furnish soil and a foothold for herbaceous plants, the presence of pockets comes to be of less importance. Late in the first moss stage patches of herbaceous plants, among which Sedum ter- naium is most prominent (fig. 1), begin, to compete with the mosses. The most rapid advance of herbaceous plants is made on gentle slopes and ledges. On southerly slopes and in all dryer situations, the most Fig. 3. V.'alking fern and Mitella on a northward facing moss-covered rock. advanced herbaceous stage seen is a xero-mesophytic closed association in which Sedum is dominant throughout the year. With the Sedum, and of varying importance at different seasons, are Cystopteris fragilis, Aquilegia canadensis, Silene virginica, Aster Shortii, Viola Rafinesquii and V. striata, Arabis Drum- mundi, Heuchera americana, and a few individuals of a number of other less characteristic plants. On northerly slopes the earlier herbaceous stages are con- temporaneous with the lichen and moss stages. Throughout VEGETATION OF CONGLOMERATE ROCKS 389 the moss stages the number of herbaceous plants steadily increases. On north slopes, after a short succession with numerous in- stances of telescoping, and on east and west slopes, after a much longer and more complete succession, the most advance her- baceous stage of the rock succession is reached. This is a meso- phytic closed association dominated by walking fern, CaMpto- sorus rhizophyllus (fig. 3). Where best developed, this fern grows in dense tangled masses in a moss mat composed of the mosses of the second or Mnium moss stage. With the walking ferns are a large variety of other herbs, most characteristic of which are Mitella diphylla and Cystopteris bulbifera. Other plants of the association are maidenhair fern {Adiantum peda- tum), great chickweed {Stellaria pubera), rue anemone {Anemo- nella thalictroides) ,Corydalis fiavula, Carda?nine Douglassii, Dutch- man's breeches {Dicentra Cucullaria) tall bellflower {Campanula americana), and a number of the plants of the preceding stage. 4. Shrub stages. On shelves, on the upper surface of the rocks, and in large pockets wherever several inches of soil have accumulated, are a number of shrubs — bladder nut {Staphylea trifolia), gooseberry {Ribes gracile), fragrant sumac (Rhus cana- densis), nine-bark {Physocarpus opidif alius), and poison ivy {Rhus Toxicodendron) in dry parts, and wild hydrangea {Hy- drangea arborescens) in damp places. In only a few rock areas, the shrubby plants form definite communities with a well es- tablished place in the rock succession. A shrub stage when represented, may follow either of the closed herbaceous associa- tions. The shrubs of dryer parts of the rocks, only one or two of which are usually represented in any one rock area, follow the Sedum association (fig. 1). The hydrangea shrub stage is seen only in very moist places, and follows some phase of the mesophytic closed herbaceous association. Transition to surroundiiig forest. Only on the tops of the rocks, where the accumulated soil is relatively deep, does the vegetation show any transition to that of the surrounding hill- sides. Herbaceous plants of the hillsides, and occasional sap- lings, grow in the deep soil on the rocks. But the covering of the 390 E. LUCY BRAUN ''',' l'^', U :J'% ' m-^Sk%.^/^ii^t^^^3i^' 3 _ £, 0- ; ^ s. . " T Gy V/? rl^D 7 / ^',; ^®y^4D7:' S Kd / iA-''j'.\/ a ,; •/' ■ /\ /t \a^at. '•/^ •rs THICK MAT }\Anf^i A% ' ■■ ■■ ,; • ■ • '^ I ■■ L ^"T ^ WK W'o A-Anomodon a ttenua res An-ANO/^ODON niNOR AS-ASTER SHORTII B-CAMRANULA AMERICANA C-AauiLEG/A CANADENSIS CrZ-CrSTOPTERIS auLBireRA D-Bermatocarpon miniatum G-Galium Aparine Qv-Geum vernum H-HysTRix. patula L -LESKEA SP /1-MA/IUn CUSPIOA TUM 0-OmPHALARIA 5P p- poa comrressa Po-Porella platyphylla P- RHAPIDOSTEGIUM SP i r-/?Ri/S TOy^lCODENORON S-Sedum ternatum v- verrucar/a r^uralis Vr-Viola Rafine:so.uii ^ w- woodsia obtusa wp-Camptosorus phizophyllus '/'- Grimm I A apocarpa y-LEC/o/A SP. -AMPHILOMA LANU&INOSUr^ r\- Patch (.j-PATCH,//VDEr/^ir£ OUTLINE • -Plant in patch ^'.-pleurococcus ^ Ol R£C TION OF SL OPC ^ -Placooium citrinum F g. 4. Belt transect showing relation of vegetation to steepness of slope; direction of slopes, S25° W and N; transect follows rock profile shown above. rocks by a deep soil, and the consequent appearance of plants from the surrounding forest, does not represent a step in the rock succession, but rather the elimination of the rock habitat, and .with it, of its characteristic vegetation. VEGETATION OF CONGLOMERATE ROCKS 391 Effect of slope on vegetation. Throughout the progress of the rock succession, the effect of steepness and direction of slope is very marked. Change in the angle of slope is always accom- V a ^' s se'w 6M ScAL£ OF Rock Outline o ./ .2 M J) M} VSKI ■ ■■■■4- V. J'.'' ', u ^/ <^'X i^'t\m\ » "^^m'' 'p? ■ r^ w^W Mfr! C \^ '^^ Wf\ Mat ^FWr c- Q^ W-f :'C. ': ^AT ^^■^^S c- '.CI Fig. 5. Horizontal belt transect showing relation of vegetation to direction of slope; angle of slope, 55° to 65°; transect follows rock outline shown above. Abbreviations as in figure 4. panied by some change in vegetation. Slopes of the same steep- ness but of different direction show very great differences in the character of the vegetation. The accompanying transects, figures 4 and 5, illustrate these effects of direction and steepness of slope. 392 E. LUCY BRAUN Plants confined to conglomerate rock areas. A few of the plants of the conglomerate rocks are confined to this habitat within the Cincinnati region; others are usually confined to the sandy or gravelly soil of terraces; and still others are of rather general distribution. The most characteristic plants of the various stages are the plants of most limited distribution. Dermato- carpon minidtum is known from only one rock area with out- crops at short intervals over a distance of about a mile. Walk- ing fern {Camptosorus rhizophyllus) and Cystopteris bulbifera are confined to conglomerate rocks within this region. These are characteristic plants of limestone cliffs throughout a wide geo- graphical range, and have been recorded from stations 50 to 100 miles from here, but are not known to occur in the intervening area. Many of the secondary species, and a few of those deter- mining the facies, are of less limited distribution, but by no means general in the region. Thus Mitella diphylla, Woodsia obtusa, Aquilegia canadensis, Arabis Drummundi, Physocarpus opuli- f alius, and Silene virginica (usually) are confined to the relatively small areas of sandy or gravelly soil ^\dthin the Cincinnati region. The vegetation of the conglomerate rocks of the Cincinnati region represents an isolated plant community deriving some of its members from the ordinary vegetation of the region; others from the vegetation of the nearest related soil areas of the region; and still others — the most characteristic elements in this rock succession — are not represented elsewhere in the re- gion, and must have been derived from distant similar habitats. BOOKS AND CURRENT LITERATURE Absorption and Secretion. — Even though an enormous volume of experimentation bearing upon absorption and secretion has come from both animal and plant physiologists, some fundamental facts relative to these phenomena are too little understood, as indicated by text books dealing with these subjects and by a number of recent researches. Fur- thermore, the animal physiologist has failed to familiarize himself with the investigations of the plant phj^siologist and vice versa, so that there has been in some instances a duplication of effort to no purpose and a failure to coordinate similar problems in the two fields of stud3^ A re- cent book by Fischer,^ written by one who has employed animal tissues throughout his investigations, is the most lucid and illuminating account which has ever been written on the subject of absorption and its mirror image secretion, and the relation of these two phenomena to the patho- logical states called oedema, nephritis, glaucoma, etc. It should be read with equal enthusiasm by both plant and animal physiologist and should be far reaching in its influence in eradicating many misconcep- tions which are now being promulgated by teachers of physiology It is idle to suppose that any adequate notion can be given of Dr. Fischer 's treatment of the subject in a brief review, but it is hoped by this means to call the attention of physiologists and pathologists to a stimulating and meritorious work whose presence is not generally known to them. The subject matter of a book on oedema published several years earlier by the same author has been enriched by subsequent experimen- tation, and he has combined with it his studies upon other pathological states following abnormal absorption or secretion. He has summarized in the form of a resume, occupjang the first thir- ty-four pages, his conclusions, based upon observations and clinical data presented in detail in the remainder of the book. His conclusions all center around the view that the absorption of water, whether normal or abnormal, by the living organism is determined by the colloids con- thesia, how salines decrease generalized oedema and relieve uremia, tained in it and their state. The acceptance of this view constitutes ipischer, Martin H. Oedema and Nephritis: A critical, experimental and clinical study of the physiology and pathology of water absorption in the liv- ing organism. Second and enlarged edition, pp. 695, New York, 1915. .39.3 394 BOOKS AND CURRENT LITERATURE a tacit dismissal of the osmotic theory of Pfeffer and De Vries, the lipoid membrane theory of Overton, the mosaic thoery of Nathansohn, and the pressure theory of Pfeffer and his students. All of these theories depend for their operation, upon the presence of a membrane through which water and the dissolved substances pass. Difficulty arises when one attempts to explain by these theories, how both water and dissolved substances move into the cell at the same time or out at the same time, or in opposite directions, either into the cell or out of the cell at the same time, yet this must be possible within living cells. By the theory which regards the protoplast as a colloid-chemical complex, there is no need for membranes about the cells. This colloid complex cannot only absorb and secrete water, but it can absorb and secrete any dis- solved substance at the same time, the two processes being directed either in the same or opposite directions. The laws governing hydra- tion and dehydration of lyophilic colloids then govern their absorp- tion and secretion. The differences in concentration within and without the cell can thus be accounted for by differences in solubility, differences in adsorption, and differences in chemical constitution. The problem of oedema is regarded as dependent upon an increased or heightened hydration of the body colloids and the cause of which in- crease exists within the tissues themselves. This increased hydration, he maintains, is caused by the accumulation of .acids within the tissues, brought about either through their abnormal production, or through their inadequate removal, though some of it may be due to the produc- tion or accumulation of substances of the type or urea, pyridin, certain amins, etc., which hydrate colloids as do acids, or even to the conver- sion of colloids having little capacity for water to those having a greater hydrophylic capacity. The bearing of the problem of oedema in ani- mals to such states in plants as are described as overgrowths, excres- cences, galls, cankers, intumescences, crown gall, knots, etc .are not far to be sought. Furthermore, the author 's experimental procedure on oede- ma is such that it could in many cases be duplicated in work of instruc- tion in the classroom and laboratory. The studies in secretion are for the most part concerned with the kid- ney but here again many related problems suggest themselves and both the investigator and the teacher will find a lively interest in Dr. Fischer 's treatment of the fundamentals of the process. Such interesting vital questions as the reason for a decreased urinary output following anaes- why blood remains in the vessels, are all included in the problem of se- cretion and are presented with a body of clinical and experimental data, Frederick A. Wolf. BOOKS AND CURRENT LITERATURE 395 Natural History op Costa Rica. — This is a record of a year's travel, collecting and study of the natural history of Costa Rica, from May 1910 to May 1911.' The attention of the authors was especially directed to the insect life of the regions visited. The book is essentially a record of their personal experiences, and is far too much taken up with the details of travel, data of accommodations, and kindred other un- important incidents common to living and travel in Central America, that may be interesting to the tourist but of no value to the naturalist. The valuable parts of the book are the author's observations upon the life histories, habits and distribution of the organisms studied by them; their data of climate and topography, and their excellent and numerous photographs of plants and animals, especially the insects. There is a conspicuous lack of any broad conceptions of the distribution of the species studied, or of their ecological relations, and the book would have been much improved by some general summary and discussion of the results secured. The observations recorded are valuable, how- ever, and will certainly find their place in subsequent general consid- erations of the biology of Costa Rica. In this respect the book is a welcome and distinct contribution. Appendices contain a record of the authors' itinerary, with notes upon the "weather," "weather" records at Cartago, bibliographj^, and a list of the plants and animals men- tioned in the text. The book will stand with Belt's A Naturalist in Nicaragua, as a record of observations, but is not the equal of Belt's work in insight into the ecological relations of the organisms studied, and understanding of the problems of tropical biology, and it is hoped that in some subsequent publication the authors will give us this summation of their work. — W. L. Tower. ^ Calvert, Amelia Smith, and Philip Powell. A Year of Costa Rican Natural History. Pp. 577, figs. 137, 5 maps. The Macmillan Company, New York, 1917 ($3.00). NOTES AND COMMENT Every day brings fresh evidence of the detennination of the United States to win the great war. We enjoy a grim sense of satisfaction in every sacrifice we make that contributes to this end. The scientific men of the country are giving their ripest ideas and their best efforts to aid in the struggle. It must give profound satisfaction to every one of these men, however ardent his patriotism, to reahse that we have not yet had in this country an outbreak of the folly of renouncing German degrees, melting German medals, and repudiating scientific literature and generalizations of German origin. We are not engaged in a com- bat with Intellectual Germany. If there were no other Germany than tliis there would be no war in progress. It is Political Germany which we are bound to crush, cliiefly for the sake of our own political safety. In doing so we may aid in the rescue of Intellectual Germany from the noi- some militaristic infections that have sometimes attacked it. A pro- gramme of renunciation and repudiation would mar our future relations with Intellectual Germany, would belittle American science, and would contribute nothing toward wimiing the war. A text entitled Genetics in Relation to Agriculture is in an advanced state of preparation by Dr. Ernest B. Babcock and Dr. Roy E. Clausen, of the University of California. The work will consist of about 600 pages, with numerous illustrations, glossary and bibliography, and the publishers will be the McGraw Hill Book Company of New York. The first half of the book will treat the fundamental principles of genet- ics, with an up to date exposition of Mendelism, and chapters on varia- tion, biometry, pure lines and mutations. The second half is devoted to applied genetics, with respect to both plants and animals, and is de- signed to form a clear and practical exposition for the layman. On the attainment of his seventieth year, in February, Prof. Hugo De Vries will retire from the professorship of botany at the University of Amsterdam. As a testimonial of their esteem the Dutch botanists are preparing to issue a set of six volumes containing the essays and papers of Professor De Vries which it is now impossible or difficult to obtain. Persons desirous of securing these volumes should communicate with Prof. Theo. J. Stomps, Weesperzijde 29, Amsterdam. 396 VOLUME 20 NUMBER 1 JANUARY, 1917 CONTAINING A Quarter-Century of Growth in Plant Physiology <- • - * ^' *-* '-^ "^ ^ Burton Edward Livingston 1 Notes on the History of the Willows and Poplars Edward W, Berry 16 Books and Current Literature 29 Notes and Comment 32 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmount Ave. baltimore, md. EDITORIAL OFFICE TUCSON, ARIZONA Entered as second-class matter March 9. 1912, at the post office at Baltimore, Maryland, under the Act of July 15, 1834 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Charles Louis Pollard, Founder Otis William Caldwell University of Chicago William Austin Cannon Desert Laboratory J. Arthur Harris Station for Experimental Evolution Burton Edward Livingston Johns Hopkins University Francis Ernest Lloyd McGill University Daniel 'Trembly MacDouoal Carnegie Institution of Washingtoi* James Bertram Overton University of Wisconsin George James Peircb Stanford University Herbert Maule Richards Columbia University Forrest Shreve Desert Laboratory John James Thohnbeb University of Arizona Edgab Nelson Transeau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without covers with covers First 100 Additional 100 First 100 Additional 100 Four pages S2.6S 4.32 4.80 $0.72 1.20 2.00 $4.68 6.32 6.80 $1.72 Kifirht Daees 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. METABOLISM THE GANONG WATER CULTURE SUPPORT is correct in principle and simple in operation. The plants are securely supported both above and below the seeds by the two aluminum disks whose perforations are closed with paraffin, proper openings being made to accommodate the seedlings. A double screw keeps the disks parallel and serves to regulate the distance between them. An opaque sleeve keeps light from the tumbler containing the culture solution. Professor Ganong grew ten corn plants in this Support to a height of four feet, the mass of healthy roots filling the tumbler as a mold. Price, complete, $1.10 Our catalog of Ganong Botanical Apparatus describes in detail 26 different pieces of apparatus. Every teacher should have a copy. Bausch &" ipmb Optical @. HEW YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON ntOCHESTEn,N.Y. ^•^ANKFORT Leading American Manufacturers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Engineering Instruments, Range Find- ers, Binoculars, Ophthalmic Lenses and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 1. Chemical Plant Physiologist. Candidate for degree of Ph.D. in plant physiology in 1917 at a leading university desires to acquire a position offering opportunity for research. Graduated from a leading agricultural college. Twelve years of experience in research and teaching in agricultural chemistry and plant physiology. Special attention given to nutrition and metabolism of plants and development of a course in physiological plant c*hemistry. Author or joint author of several research papers and two text- books. No. 2. Plant Physiologist. Candidate for Ph.D. degree (major in plant physiology) at a leading university desires teaching position with oppor- tunity for research. Has degrees of Ph.B. and A.M. from college of good standing. Has had special training in physics ; has had experience in teach- ing and in assisting in laboratories at college and university. No. 3. Successful Teacher. Associate Professor of Biology in a large normal school desires a position in a university, large college or normal school, preferably where there is opportunity for earning Ph.D. degree. Holder of A.B. and A.M. from two leading universities. Highly successful in teaching large beginning classes in college botany (general), in elementary ecology and physiology, and in the courses for the training of teachers. Capable of supervising or organizing departments of biology in colleges or normal schools. Especially efficient in arousing the interest ot the students of required courses in biological thought and methods. Capable research worker in ecology. THE PLANT WORLD Tucson, Arizona EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We manufacture thia Journal. In addition we produce 25 other scientific and teohnloal publications and a large number of books and catalogues. All are handled on a definiti $eh*duU maintaining the highest standard of meehanloai workmanship. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 2419-2421 Greenmount Aye.. Baltimore. Md.. U. S. A [CE Each Price Per Ten $ .60 $5.00 1.40 11.00 .50 4.50 2.25 20.00 2.75 25.00 2.25 20.00 2.75 25.00 PRICE LIST OF ATMOMETER CUPS AND OTHER APPARATUS Prices in Effect January 1, 1917 In placing telegraphic orders the list numbers may be used. List No. 1 Natural Cylindrical Cups, no number, no coating (3x13 cm.) lA Standardized Cylindrical Cups, numbered and shel- lacked at base. 4 Used Cups and Seconds (when in stock) 5 Bellani Plates (porous disc attached to a glazed hemi- spherical funnel.) 5A Bellani Plates, standardized and numbered. 6 White Spherical Cups, with glazed neck. 6A White Spherical Cups, standardized and numbered. 7 Transeau Vaporimeter Cups (1.5x25 cm.), no num- ber, no coating. .60 5.00 8 Large Cylindrical Cups (5 x 35 cm.), for use as Auto- Irrigators. .80 7.00 17 Rotating Table, for standardizing atmometers or equalizing conditions for growing plants, 4 ft. in diameter. 20.00 18 Tops for Rotating Tables, 3-ply, unpainted. ' 4.50 19 Iron Tripods for Rotating Tables, unpainted. 4.50 20C Shive Non-Absorbing Atmometer Mounting (without cup), for use with Cylindrical Cup. 6.00 55.00 20S Shive Non-Absorbing Atmometer Mounting (without cup), for use with Spherical Cup. 6.00 55.00 21 Collar Clamps, for holding stopper in Cylindrical Atmometer Cup. 22 Pans for water-retaining power of soils. 23 Clips for Cobalt Paper Transpiration method. 24 Selected Cobalt Paper for Transpiration method. Circles 11 cm. in diameter. 25 Tripartite Cobalt Paper Slips. 30 MacDougal Direct Reading Precision Auxograph. Restandardizing Atmometer Cups. Cleaning Atmometer Cups. Please notify us before shipping cups for restandardization. Eastern orders may be filled by addressing: Eastern Branch, The Plant World, 2753 Maryland Ave., Baltimore, Md. Further information regarding any of the above items will be furnished on application THE PLANT WORLD TUCSON, ARIZONA 3.50 33.00 1.50 12.50 .30 2.50 .30 2.50 .12 1.00 75.00 .40 4.00 .60 6.00 Farmers of Forty Centuries A History of the Permanent Agriculture in China, Korea, and Japan By F. H. KING, D.Sc. Late Professor of Agricultural Physics, University of Wisconsin Written by one of America's foremost Agriculturists, who made a close study of the methods by which the Chinese have supported 500,000,000 people for four thousand years on an area smaller than the improved farm land of the United States. "No more important practical contribution to geographic knowledge has been published in many years than 'Farmers of Forty Centuries.' " — Review. A book of strong interest for the botanist and agriculturist, as well as for the practical man and the student, containing 450 pages and 248 illustrations. The price, postpaid, is $2.50. Orders should be sent to Mrs. F. H. King, Madison, Wisconsin. LETTERING SHEETS We offer a series of six sheets of letters, figures, words, and symbols for the lettering of diagrams and drawings for line cut reproduction. The lettering is in bold type in two sizes, and in italics. The sheets are Dennison's best quality white gummed paper. A wealth of words and abbreviations relative to time, weights, measures, climate, and experimental results, as well as chemical symbols, abbrevi- ations used in morphology; etc., will give these sheets a wide utility. Sample on request Per sheet 10c Set of 6 sheets 50c Six sets $2.00 THE PLANT WORLD TUCSON, ARIZONA KODAK FINISHING We Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON, ARIZONA TUCSON IS THE METROPOLIS OF ARIZONA! Finest Climate on Earth Elevation 2369 feet Ideal Tourist Resort No Fogs, No Fleas No Sunstrokes, No Cyclones "The Sunshine City" Railway and Commercial Center Seat of Arizona University Center Rich Mining District Rich Agricultural Lands Splendid Business Opportunities Why Not Invest? YOUR FRIENDS Would be Interested in the Growth of this Enterprising and Progressive City Send Their Names and Addresses to The Tucson Chamber of Commerce A FREE ILLUSTRATED BOOKLET WILL BE MAILED TO THEM Albert Steinfeld & Co. Tucson, Arizona 1 WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOTJR opportunities by means of a savings bank account. In this kind of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA / » ^ — * •«*'^'W '*-■ The Pi ant World A Magazine of General Botany VOLUME 20 NUMBER 2 FEBRUARY, 1917 CONTAINING Observations on a New Type of Artificial Osmotic Cell Joshua Rosett 37 Some Undescribed Prairies in Northeastern Arkansas Roland M. Harper 58 Books and Current Literature 62 Notes and Comment 65 PtTBLISHBD MONTHLT OFFICE OF PUBLICATION 2419-21 Greenmount Ave. BALTIMORE, MD. EDITORIAL OFFICE TUCSON, ARIZONA 'yV Entered bb Becond-cla«« matter March 9, 1912, at the post office at Baltimore, Maryland, under the Act of July 16, 18S4 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chables Louis Pollabo, Founder Oti8 William Caldwell University of Chioago William Austin Cannon Desert Laboratory J. Abthub Habbis Station for Experimental Evolution BuBTON Edwabd Livingston Johns Hopkins University Fbancis Ebnest Llotd McGill University Daniel Trembly MacDouqal Carnegie Institution of WaahlDgton James Bebtbam Ovebton University of Wisconsin Geobge Jamb!i Peibcb Stanford University Hebbebt Mauls Richabds Columbia University FoBBE3T ShBEVB Desert Laboratory John James Thornbeb University of Arizona Edgab Nelson Tbanseau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: WITHOUT COVEBS WITH C0VEB8 « First 100 Additional 100 First 100 Additional 100 Four pages $2.68 4.32 4.80 $0.72 1.20 2.00 $4.68 6.32 6.80 $1.72 Eieht pages 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 ran be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. METABOLISM THE GANONG WATER CULTURE SUPPORT is correct in principle and simple in operation. The plants are securely supported both above and below the seeds h by the two aluminum disks whose perforations are closed with paraffin, proper openings being made to accommodate the seedlings. I ft I A double screw keeps the disks parallel and serves to regulate the distance between them. An opaque sleeve keeps light from the tumbler containing the culture solution. Professor Ganong grew ten corn plants in this Support to a height of four feet, the mass of healthy roots filling the tumbler as a mold. Price, complete, $1.10 Our catalog of Ganong Botanical Apparatus describes in detail 26 different pieces of apparatus. Every teacher should have a copy. . B^usch £5 ipmb Optical (o. NtW YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON R,oCHESTEn,N.Y. fi^ANKroar Leading American Manufacturers of Microscopes, Projection Apparatus (Balopticons) , Photographic Lenses, Engineering Instruments, Range Find- ers, Binoculars, Ophthalmic Lenses and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 Avords. They will be inserted once for 50 cents, three insertions for $1.00. No. 2. Plant Physiologist. Candidate for Ph.D. degree (majoi plant phj^siology) at a leading university desires teaching position with oppor- tunity for research. Has degrees of Ph.B. and A.M. from college of good standing. Has had special training in physics; has had experience in teach- ing and in assisting in laboratories at college and university. No. 3. Successful Teacher. Associate Professor of Biology in a large normal school desires a position in a university, large college or normal school, preferably where there is opportunity for earning Ph.D. degree. Holder of A.B. and A.M. from two leading universities. Highly successful in teaching large beginning classes in college botany (general), in elementary ecology and physiology, and in the courses for the training of teachers. Capable of supervising or organizing departments of biology in colleges or normal schools. Especially efficient in arousing the interest ot the students of required courses in biological thought and methods. Capable research worker in ecology. No. 4. A young, ummarried man, with a Ph.D. degree in Mycology from one of the large state universities, desires a position in Botany Depart- ment of college or university, preferably where an opening in Cryptogamic Botanic, especially Mycology and Plant Pathology, is offered. At present Instructor in Botany in one of the largest state universities temporarily, during the leave of. absence of one of the members of the regular staff. No. 5. Ecologist and systematic botanist with degree of Ph.D-. in ecology desires position in either or both of these branches. Training mainly sys- tematic, morphological, and ecological. Eleven years systematic study of higher plants; four years research work in field ecology. Holds permanent position in a leading university, but necessity demands securing more remun- erative place. No. 6. A young woman trained in mycology and pathology, with degrees of B.A. and M.A., wishes position in a university or experiment station. Prefers a laboratory position in purely investigative work but is willing to teach also. THE PLANT WORLD Tucson, Arizona EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We znanufabcure this Journal. In addition we produce 25 other scientific and teohntcal publications and a large number of books and catalogues. All are handled on a definit* aehtduU maintaining the highest standard of mechanical worlunansblp. WAVERLY PRESS WILLIAMS & WILRINS COMPANY 2419-2421 Greenmount Ave., Baltimore. Md.. U. S. A. ICE Each Price Per Ten $ .60 $5.00 1.40 11.00 .50 4.50 2.25 20.00 2.75 25.00 2.25 20.00 2.75 25.00 PRICE LIST OF ATMOMETER CUPS AND OTHER APPARATUS Prices in Effect January 1, 1917 In placing telegraphic orders the list numbers may be used. List No. 1 Natural Cylindrical Cups, no number, no coating (3 X 13 cm.) lA Standardized Cylindrical Cups, numbered and shel- lacked at ba.se. 4 Used Cups and Seconds (when in stock) 5 Bellani Plates (porous disc attached to a glazed hemi- spherical funnel.) 5A Bellani Plates, standardized and numbered. 6 White Spherical Cups, with glazed neck. 6A White Spherical Cups, standardized and numbered. 7 Transeau Vaporimeter Cups (1.5x25 cm.), no num- ber, no coating. .60 5.00 8 Large Cylindrical Cups (5 x 35 cm.), for use as Auto- Irrigators. ,80 7.00 17 Rotating Table, for standardizing atmometers or equalizing conditions for growing plants, 4 ft. in diameter. 20.00 18 Tops for Rotating Tables, 3-ply, unpainted. 4.50 19 Iron Tripods for Rotating Tables, unpainted. 4.50 20C Shive Non-Absorbing Atmometer Mounting (without cup), for use with Cylindrical Cup. 6.00 55.00 20S Shive Non-Absorbing Atmometer Mounting (without cup), for use with Spherical Cup. 6.00 55.00 21 Collar Clamps, for holding stopper in Cylindrical Atmometer Cup. 22 Pans for water-retaining power of soils. 23 Clips for Cobalt Paper Transpiration method. 24 Selected Cobalt Paper for Transpiration method. Circles 11 cm. in diameter. 25 Tripartite Cobalt Paper Slips. 30 MacDougal Direct Reading Precision Auxograph. Restandardizing Atmometer Cups. Cleaning Atmometer Cups. Please notify us before shipping cups for restandardization. Eastern orders may be filled by addressing: Eastern Branch, The Plant World, 2753 Maryland Ave., Baltimore, Md. Further information regarding any of the above items will he furnished on application THE PLANT WORLD TUCSON, ARIZONA 3.50 33.00 1.50 12.50 .30 2.50 .30 2.50 .12 1.00 75.00 .40 4.00 .60 6.00 Farmers of Forty Centuries A History of the Permanent Agriculture in China, Korea, and Japan By F. H. KING, D.Sc. Late Professor of Agricultural Physics, University of Wisconsin Written by one of America's foremost Agriculturists, who made a close study of the methods by which the Chinese have supported* 500,000,000 people for four thousand years on an area smaller than the improved farm land of the United States. "No more important practical contribution to geographic knowledge has been published in many years than 'Farmers of Forty Centuries.' " — Review. A book of strong interest for the botanist and agriculturist, as well as for the practical man and the student, containing 450 pages and 248 illustrations. The price, postpaid, is $2.50. Orders should be sent to Mrs. F. H. King, Madison, Wisconsin. STOPPER CLAMPS For Holding Stopper in Cylindrical Porous Cup A BRASS collar purrouiids the cup and rests against the flange of -^^ the latter, and a brass plate is drawn toward this by three bolts with knurled nuts. The plate rests on top of stopper and has an opening for tube. ]t compresses the stopper and forces it into the cup, thus holding it firmly in place. Especially for use when pressure is applied inside the cup, as when the latter is used as a Pfeffer osmotic cell, but generally use- ful to insure a tight joint between stopper and cup and between stopper and tube. Each $3.50— Per Ten $33.00 THE PLANT WORLD _ _ . Tucson, Arizona KODAK FINISHING We Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON, ARIZONA TUCSON IS THE METROPOLIS OF ARIZONA! Finest Climate on Earth Elevation 2369 feet Ideal Tourist Resort No Fogs, No Fleas No Sunstrokes, No Cyclones "The Sunshine City" Railway and Commercial Center Seat of Arizona University Center Rich Mining District Rich Agricultural Lands Splendid Business Opportunities Why Not Invest? YOUR FRIENDS Would be Interested in the Growth of this Enterprising and Progressive City Send Their Names and Addresses to The Tucson Chamber of Commerce A FREE ILLUSTRATED BOOKLET WILL BE MAILED TO THEM Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In this kind of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA J iU^^ A Magazine of General Botany VOLUME 20 NUMBER 3 _ MARCH, 1917 CONTAINING The Effect of Surface Films of Bordeaux Mixture on the Foliar Trans- piring Power in Tomato Plants. John W. Shive and William H. Martin 67 Seeding Habits of Spruce as a Factor in the Competition of Spruce with its Associates. Louis S. Murphy 87 Books and Current Literature 91 Notes and Comment 95 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmount Ave. baltimoiie, md. EDITORIAL OFFICE TUCSON, ARIZON.^ Entered as eeoond-clase matter March 9. 1912, at the post oflSce at Baltimore, Maryland, under the Act of July 16, 1894 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chableb Louis Pollard, Founder Otib William Caldwell University of Chicago William Austin Cannon Desert Laboratory J. Abthub Habbis Station for Experimental Evolution BuBTON Edwabd Livingston Johns Hopkins University Fbancis Ebnest Lloyd McGill University Daniel Tbembly MacDougal Carnegie Institution of Washington James Beeteam Overton University of Wisconsin Geoege James Peirce Stanford University Herbebt Maulb Richabds Columbia University Fobbest Shbeve Desert Laboratory John James Thornbeb University of Arizona Edgab Nelson Tbanseau Eastern Illinois Normal School All manuscripts submitted for publication should be tjrpe-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without covebs with covers First 100 Additional 100 First 100 Additional 100 Four pages J2.68 4.32 4.80 $0.72 1.20 2.00 $4.68 6.32 6.80 $1.72 Eicht nages 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. METABOLISM \ THE GANONG WATER CULTURE SUPPORT is correct in principle and simple in operation. The plants are securely supported both above and below the seeds by the two aluminum disks whose perforations are closed with paraffin, proper openings being made to accommodate the seedlings. A double screw keeps the disks parallel and serves to regulate the distance between them. An opaque sleeve keeps light from the tumbler containing the culture solution. Professor Ganong grew ten corn plants in this Support to a height of four feet, the mass of healthy roots filling the tumbler as a mold. Price, complete, $1.10 Our catalog of Ganong Botanical Apparatus describes in detail 26 different pieces of apparatus. Every teacher should have a copy. Bausch ^ Ipmb Optical®. new YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON riOCHESTEa,N.Y. f^l^ANKFORT Leading American Manufacturers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Engineering Instruments, Range Find- ers, Binoculars, Ophthalmic Lenses and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 2. Plant Physiologist. Candidate for Ph.D. degree (majoi in plant physiology) at a leading university desires teaching position with oppor- tunity for research. Has degrees of Ph.B. and A.M. from college of good standing. Has had special training in physics; has had experience in teach- ing and in assisting in laboratories at college and university. No. 3. Successful Teacher. Associate Professor of Biology in a large normal school desires a position in a university, large college or normal school, preferably where there is opportunity for earning Ph.D. degree. Holder of A.B. and A.M. from two leading universities. Highly successful in teaching large beginning classes in college botany (general), in elementary ecology and physiology, and in the courses for the training of teachers. Capable of supervising or organizing departments of biology in colleges or normal schools. Especially efficient in arousing the interest ot the students of required courses in biological thought and methods. Capable research worker in ecology. No. 4. A young, unmarried man, with a Ph.D. degree in Mycology from one of the large state universities, desires a position in Botany Depart- ment of college or university, preferably where an opening in Cryptogamic Botanic, especially Mycology and Plant Pathology, is offered. At present Instructor in Botany in one of the largest state universities temporarily, during the leave of absence of one of the members of the regular stafj. No. 7. Instructor in Botany. Candidate for M. S. degree in botany in 1917 at eastern agricultural college desires a position as an instructor in botany. Graduate of a leading eastern universit3^ Three years experience teaching general botany and forestry in agricultural college. Special work done in dendrology and agricultural botany at present location. THE PLANT WORLD Tucson, Arizona EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We msDufaiicure this Journal. In addition we produce 25 other scientific and teohnioal publications and a large number of books and catalogues. All are handled on a definite tchtduli maintaining the highest standard of mechanical workmanship. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 2419-2421 Greenmount Ave.. Baltimore. Md.. U. S. A. BOTANICAL JOURNALS, BOOKS, AND SEPARATES Bulletin of the Torre y Botanical Club, 1870-1910; 41 years, beauti- fully bound in half morocco in 26 volumes $90.00 Annual Report of the Missouri Botanical Garden, 22 vols., cloth. . 22.00 Edward Tuckerman. Synopsis of the Lichens of North America, 2 parts complete. With introduction to the study of Lichens, by Henry Willey, bound in. Half morocco. Very scarce 25.00 Thornton, British Flora. Published 1812. Vol. 1, text, 536 pp. Vol. 2, 347 plates. Handsomel}^ bound in red half morocco 22. 50 BrlTTEN and Holland. Dictionary of English Plant Names. Published by the English Dialect Society. Three parts in one, half morocco. . . 12.50 Britton and Brown. Illustrated Flora of the Northeastern States. First Edition, three volumes 8. 50 Robert Brown. Miscellaneous Botanical Writings. Two vols. Text, one vol. Plates, cloth 7.00 Payer. Botanique Cryptogamique. Half morocco. Scarce 5.50 Ralph. Icones Carpologicae. Leguminosae, 40 plates. The complete work, in half morocco 4 . 50 George Goodale. Physiological Botany. Half morocco 3.75 Rabenhorst. Die Slisswasser Diatomaceen. Ten plates. Half morocco. 3.50 Reginald R. Gates. The Mutation Factor in Evolution. 1915 2.00 MacDougal, Vail, Shull, and Small. Mutants and Hybrids of the Oenotheras. 1905. Out of print. Paper 1.25 Marshall A. Howe. The Marine Algae of Peru. Paper 2.00 Barnes and Heald. Keys to the Genera and Species of North American Mosses. 1896 ; . . . 1 . 50 F. E. AND E. S. Clements. Rocky Mountain Flowers. Cloth, 400 pp., profusely illustrated in color 3 . 00 J. C. Arthur and D. T. MacDougal. Living Plants and their Properties. Cloth, 234 pp., illustrated 1 . 25 Grace J. Livingston. Bibliography of Evaporation. Paper, 121 pp. . . . 1.25 B. E. Livingston. Atmometry and the Porous Cup Atmometer. Paper, 64 pp., illustrated .75 E. E. Free. Studies in Soil Physics. Paper, 42 pp .75 B. E. Livingston and Edith B. Shreve. Lnprovements in the Method for Determining the Transpiring Power of Plant Surfaces by Hygro- metric Paper. Paper, 24 pp .40 Forrest Shreve. A Map of the Vegetation of the United States. With map in color and descriptive text .50 D. T. Ma.cDougal. The Deserts of Egypt. Paper, 27 pp., illustrated. . .40 D. T. MacDougal. The Desert Basins of the Colorado River. Paper, 25 pp., illustrated, map .40 J. W. Shive. An Lnproved Non-Absorbing Porous Cup Atmometer, Paper, 4 pp .20 D. T. MacDougal. Hybridization of Wild Plants. Paper, 16 pp .30 THE PLANT WORLD TUCSON, ARIZONA Farmers of Forty Centuries A History of the Permanent Agriculture in China, Korea, and Japan By F. H. KING, D.Sc. Late Professor of Agricultural Physics, University of Wisconsin Written by one of America's foremost Agriculturists, who made a close study of the methods by which the Chinese have supported 500,000,000 people for four thousand years on an area smaller than the improved farm land of the United States. "No more important practical contribution to geographic knowledge has been published in many years than 'Farmers of Forty Centuries.' " — Review. A book of strong interest for the botanist and agriculturist, as well as for the practical man and the student, containing 450 pages and 248 illustrations. The price, postpaid, is $2.50. Orders should be sent to Mrs. F. H. King, Madison, Wisconsin. BACK NUMBERS WANTED We wish to purchase whole copies of the following issues of The Plant World : Vol. X 1907 Feb., Mar., June, July, Oct., Nov., Dec. Vol. XI 1908 Feb., Mar., Apr., May, Sept., Nov. Vol. XIV 1911 Oct. Vol. XV 1912 Feb. W^'e will pay thirty cents each for these numbers at any time. THE PLANT WORLD Tucson, Arizona KODAK FINISHING We Guarantee to get the best possible res-ults from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON, ARIZONA TUCSON IS THE METROPOLIS OF ARIZONA! Finest Climate on Earth Elevation 2369 feet Ideal Tourist Resort No Fogs, No Fleas No Sunstrokes, No Cyclones "The Sunshine City" Railway and Commercial Center Seat of Arizona University Center Rich Mining District Rich Agricultural Lands Splendid Business Opportunities Why Not Invest? YOUR FRIENDS Would be Interested in the Growth of this Enterprising and Progressive City Send Their Names and Addresses to The Tucson Chamber of Commerce A FREE ILLUSTRATED BOOKLET WILL BE MAILED TO THEM Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In this Mnd of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA ^. f CPC^-Cf^ A Journal of General Botany V O L U M Ei 2 0 JSr U M B E R 4 APRIL, 1917 CONTAINING Plant Association of Western Pennsylvania with Special Reference to Physiographic Relationship. J. E. Cribbs 97 Critical Flowering and Fruiting Temperatures for Phytolacca decandra. Francis E. Lloyd 121 Books and Current Literature 127 Notes and Comment 132 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmotjnt Ave. BALTIMORE, MD. EDITORIAL OFFICE TUCSON. ARIZONA £nt«red as eeoond-class matter March 9^ 1912, at the post office at Baltimore, Maryland, under the Act of July 16, 1804 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chableb Louis Pollakd, Founder Joseph Chakles Arthdb - Purdue University Otib William Caldwell University of Chioago William Austin Cannon Desert Laboratory J. Arthdb Harbis Station for Experimental Evolution Burton Edward Livingston Johns Hopkins University Francis Ernest Llotd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Tbemblt MacDouoal Carnegie Institution of Washington James Bertbam Ovebton University of Wisconsin Geobqe Jame? Peirce Stanford University Hebbebt Maule Richabds Columbia University FOBBEST ShBEVE Desert Laboratory John James Thornbeb University of Arizona Edgab Nelson Tbanseau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: WITHOUT COVEBS WITH COVEBS First 100 Additional 100 First 100 Additional 100 Four pages $2.63 4.32 4.80 $0.72 1.20 2.00 $4.68 6.32 6.80 S1.72 £ieht Daces 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be suppUed incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. Wollaston Camera Lucida Bly Model INFLUENCED by the inability of biologists and illustrators to secure this useful instru- • ment, we have made a Wollaston Camera Lucida that wall give maximum convenience in use. By use of this instrument a laboratory or field specimen can be copied in reduced, enlarged, or natural size. The eye looks into the prism, placed above the drawing paper, and sees the specimen apparently projected on the paper. The image thus seen is simply traced. The ad- vantage of this camera lucida lies in its simplicity and the accuracy and rapidity with which a spec- imen can be copied. It also permits important features to be emphasized and unessentials to be omitted. The stand telescopes in three sections and has a table clamp with inclination joint. The prism has all necessary adjustments. Price, $25.00 Bausch {5 Ipmb Optical Xo. NEW YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON iiOCHESTEa,N.Y. ^I^ANKFORT Leading American Manufacturers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Engineering Instruments, Range Find- ers, Binoculars, Ophthalmic Lenses and other High Grade Optical Products This column serves as a place in which it is possible foi' men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 4. A young, unmarried man, with a Ph.D. degree in Mycology from one of the large state universities, desires a position in Botany Depart- ment of college or university, preferably where an opening in Cryptogamic Botanic, especially Mycology and Plant Pathology, is offered. At present Instructor in Botany in one of the largest state universities temporarily, during the leave of absence of one of the membeis of the regular staff. No. 7. Instructor in Botany. Candidate for M. S. degree in botany in 1917 at eastern agricultural college desires a position as an instructor in botany. Graduate of a leading eastern university. Thi-ee years experience teaching general botany and forestry in agricultural college. Special work done in dendrology and agricultural botany at present location. research desired No. 9. Position desired for summer oF 1917 as teacher or research assist- ant in plant ecology, plant physiology, classroom, laboratory, or field. Ex- perienced. Free early June to late September. No. 10. Graduate of leading agricultural school and candidate at a lead- ing university for Ph.D. in Botany in 1917 desires a position. Training in plant physiology, mycology and pathology, agriculture. Experience in teach- ing and research. Would prefer a place offering opportunity for research. THE PLANT WORLD Tucson, Arizona EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We manufacture this Journal. In addition we produce 25 other scientific and technical publications and a large number of books and catalogues. All are handled on a definitt schtdule maintaining the highest standard of mechanical worlcmanshlp. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 2419-2421 Greenmount Atc, Baltimore, Md.. U. S. A. SPHERICAL ATMOMETER CUPS A spherical evaporating surface, 5 cm. in diameter, presenting the same external ex- posure in all directions, with glazed cyUndri- cal neck 3 cm. long and 2 cm. inside diameter. They are composed of very resistant material, of proper porosity for atmometric work, and are to be mounted on rubber stoppers as in the case of cyUndrical cups. The spheres may be cleaned with brush and distilled water, may be treated with acid, and even heated to red heat. They should thus be capable of many years of use, without permanent alteration of the coefficient. They are not easily broken. These new spheres are suppHed either standardized or unstandardized. Stand- ardization is carried out with reference to a newly adopted spherical standard; spheres cannot be satisfactorily standardized to the cyUndrical standard cup. Therefore readings from spheres are not satisfactorily reducible to terms of readings from cylin- ders (see Plant World, Vol. 18, pp. 21, 51, 95, 143). Unstandardized White Spheres, $2.25 each, $20.00 per ten • Standardized White Spheres, $2.75 each, $25.00 per ten THE PLANT WORLD - - TUCSON, ARIZONA A MAP OF THE VEGETATION OF THE UNITED STATES A colored map 20 x 12 inches in size showing the 18 major types of vegetation in the United States. Prepared hy Di . Forrest Shreve, and reprinted fi(jni the Geographical Review. Accompanied Ijy a !)rief descriptive text. Text, with Folded Map $.50 each, $4.00 per ten Text, with Rolled Map $.60 each, $4.10 per ten THE PLANT WORLD Tucson, Arizona KODAK FINISHING Wtf Guarantee to i^et the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free . The Smith Sporting Goods Company TUCSON, ARIZONA Two Camiiosco Instruments 32-254 TRANSPIRATION App. Detmer P. 214. Garreau's To determine the amount of transpiration from the upper and lower sides of a leaf at the same time. Complete, . . . $4.50 32-256 TRANSPIRATION CHAMBER, Dclmcr, P. 219. To show that the amount of transpiration depends upon the degree of moisture in the air and that a rising temperature accelerates 32-2S4 transpiration. The m/e of transpiration in (/ry 32.256 air and in moist is easily determined. Without burner or thermometer, $5.00. SEE Botanical Catalog, 91, P. 49, for complete information. CAMBRIDGE BOTANICAL SUPPLY COMPANY WAVEKLKY, MASS. Leading American Makers of Physiological Apparatus Laboratory Equipment for all the Sciences HsinhlisluMl ISSl Catalogue Free Mention Plan* World ll University of Colorado l^ountain Laboratory Located at Tolland, Colorado, in the Rocky Mountains in an open park surrounded by coniferous forest. Rich and varied flora from foothills to alpine i)eaks easily accessible. Courses in Field Botany and Field Zoology; especially taxonomy oi seed i)lants. Work suitable for high-school and college instructors in botany or zoology. No elementary students received. Ninth Annual Session June 25 to August 4, 1917. Fees moderate. Expenses reasonable. An ojiportunity to learn much with little expenditure of time and money. Additional Information may be obtained by addressing Professor Francis Ramaley, University of Colorado, Boulder, Colorado. TUCSON IS THE METROPOLIS OF ARIZONA! Finest Climate on Earth Elevation 2369 feet Ideal Tourist Resort No Fogs, No Fleas No Sunstrokes, No Cyclones "The Sunshine City" Railway and Commercial Center Seal of Arizona University Ct-nter Rich Mining District Rich Agricultural Lands Splendid Business Opportunities Why Not Invest? YOUR FRIENDS Would be Interested in the Growth of this Enterprising and Progressive City Send Their Names and Addresses to The Tucson Chamber of Commerce A FREE ILLUSTRATED BOOKLET WILL BE MAILED TO THEM Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank accotmt. In this kind of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA r-jJ^^-^^..^^C^^ A Journal of General Botany VOLUME 20 NUMBER 5 MAY, 1917 CONTAINING The Physical Control of Vegetation in Rain-Forest and Desert Mountains Forrest Shreve 135 Plant Associations of Western Pennsylvania with Special Reference to Physiographic Relationship. II J. E. Cribbs; 142 Books and Current Literature 158 Notes and Comment 161 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmount Ave. baltimore, md. EDITORIAL OFFICE TUCSON, ARIZONA Ent«red as second-class matter March 9, 1912, at the post oflBce at Baltimore, Maryland, under the Act of July 16, 1894 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Charles Lours Pollahd, Founder Joseph Charles Arthur Purdue University Otis Willi.4.m Caldwell University of Chicago WiLLLAM Austin Cannon Desert Laboratory J. Arthur Harris Station for Experimental Evolution Burton Edward Livingston Johns Hopkins University Francis Ernest Lloyd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Trembly MacDougal Carnegie Institution of Washington James Bertram Overton University of Wisconsin George James Peiece Stanford University Herbert Maule Richards Columbia University Forrest Shbeve Desert Laboratory John James Thornber University of Arizona EodAB Nelson Transeau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without covers with covers First 100 Additional 100 First 100 Additional 100 Four pages $2.68 4.32 4.80 $0.72 1.20 2.00 $4.68 6.32 6.80 $1.72 Eight pages 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. Wollaston Camera Lucida Bly Model INFLUENCED by the inability of biologists and illustrators to secure this useful instru- ment, we have made a Wollaston Camera Lucida that will give maximum convenience in use. By use of this instrument a laboratory or field specimen can be copied in reduced, enlarged, or natural size. The eye looks into the prism, placed above the drawing paper, and sees the specimen apparently projected on the paper. The image thus seen is simply traced. The ad- vantage of this camera lucida lies in its simphcity and the accuracy and rapidity with which a spec- imen can be copied. It also permits important features to be emphasized and unessentials to be omitted. The stand telescopes in three sections and has a table clamp with inclination joint. The prism has all necessary adjustments. Price, $25.00 Bausch £5 Ipmb Optical (p. HCW YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON R,OCHESTEIl,N.Y. f^I^ANKFORT Leading American Manufacturers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Engineering Instruments, Range Find- ers, Binoculars, Ophthalmic Lenses and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches- The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 7. Instructor in Botany. Candidate for M.S. degree in botany in 1917 at eastern agricultural college desires a position as an instructor in botany. Graduate of a leading eastern university. Three years experience teaching general botany and forestry in agricultural college. Special work done in dendrology and agricultural botany at present location. No. 8. Instructor in botany in western university desires a university or college professorship. Has a Ph.D. and has had many years teaching experience. Competent to give courses in General Botany, Biology, Mor- phology of the Great Groups of Plants and Cytology. Some opportunity for research desired. No. 10. Graduate of leading agricultural school and candidate at a lead- ing university for Ph.D. in Botany in 1917 desires a position. Training in plant physiology, mycology and pathology, agriculture. Experience in teach- ing and research. Would prefer a place offering opportunity for research. No. 11. A man having wide experience and training in museum and scientific work seeks appointment as curator of a university or college museum. He is experienced in the preparation of modern museum exhibits which seek to portray the life of animals and plants as they occur in natural ecological groups. For a number of years carried on educational museum extension work among the public schools of a large city. Would also consider position in charge of a research museum in an educational institution carrying on biological survey work, either scientific or economic, in both of which he has had wide experience. Has published numerous scientific papers. THE PLANT WORLD Tucson, Arizona EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We manufacture this Journal. In addition we produce 25 other scientific and technical publications and a large number of books and catalogues. All are handled on a definitt tch*duU malntalnlne the hlehest standard of mechanical workmanship. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 2419-2421 Greenmcunt Ave., Baltimore. Md.. U. S. A. LIGHT FILTERS We are able to supply a series of g^ass screens which absorb or transmit various parts of the spectrum and are useful for experimental work in growth, photo- tropism, and photosynthesis. These glass screens were developed by Dr. D. T. MacDougal, and are now available in bell-jars 36 x 36 cm. in size, with perforated top, or in plates 16.5 cm. square. Red Plates. A good monochrome transmitting to .610 u $1.50 each Blue Plates. Transmitting wave lengths less than .510 u SI. 50 each Orange Plates. High transmission in red and green to .530 u. Bridges the spectrum from red to blue SI. 00 each Heat-Absorbing Plates. Absorb most of the infra-red and 97% of the heat of a Nernst lamp. Give a pyrheUometer reading about half that of good window glass. Transmit 65% of inci- dent white light. In plates only SlOO each Uviol Plates. Transparent to visible spectrum, transmitting ultra-violet to .310 u. in sheets 6 mm. thick to .300 u. in sheets 3 mm. thick. In plates only $1.00 each Terms for bell-jars furnished on request. Additional information cheerfully given THE PLANT WORLD TU.CSON, ARIZONA A MAP OF THE VEGETATION OF THE UNITED STATES A colored map 20 x 12 inches in size showing the 18 major types of vegetation in the United States. Prepared by Di. Forrest Shreve, and reprinted from the Geographical Review. Accompanied by a brief descriptive text. Text, with Folded Map $.50 each, $4.00 per ten Text, with Rolled Map $.60 each, $4.10 per ten THE PLANT WORLD Tucson, Arizona KODAK FINISHING We Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON, ARIZONA Two Cambosco Instruments 32-254 TRANSPIRATION App. Ganeau's Detmer P. 214. To determine the amount of transpiration from the upper and lower sides of a leaf at the same time. Complete, . . . $4.50 32-256 TRANSPIRATION CHAMBER, Detmer, P. 219. To show that the amount of transpiration / -va. depends upon the degree of moisture in the / ^°*-^**- '^\ air and that a rising temperature accelerates 32-254 transpiration. The m/e of transpiration in (ir); 32.255 air and in moist is easily determined. Without burner or thermometer, $5.00. SEE Botanical Catalog, 91, P. 49, for complete information. CAMBRIDGE BOTANICAL SUPPLY COMPANY WAVERLEY, MASS. Leading American Makers of Physiological Apparatus Labpratory Equipment for all the Sciences Established 1884 Catalogue Free Mention Plant World University of Colorado Mountain Laboratory Located at Tolland, Colorado, in the Rocky Mountains in an open park surrounded by coniferous forest. Rich and varied flora from foothills to alpine peaks easily accessible. Courses in Field Botany and Field Zoology; especially taxonomy of seed plants. Work suitable for high-school and college instructors in botany or zoology. No elementary students received. Ninth Annual Session June 25 to August 4, 1917. Fees moderate. Expenses reasonable. An opportunity to learn much with little expenditure of time and money. Additional Information may be obtained by addressing Professor Francis Ramaley, University of Colorado, Boulder, Colorado. Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In this kind of insurance you are PAID dividend! instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA TUCSON IS THE METROPOLIS OF ARIZONA! Finest Climate on Earth Elevation 2369 feet Ideal Tourist Resort No Fogs, No Fleas No Sunstrokes, No Cyclones "The Sunshine City" Railway and Commercial Center Seat of Arizona University Center Rich Mining District Rich Agricultural Lands Splendid Business Opportunities Why Not Invest? YOUR FRIENDS Would be Interested in the Growth of this Enterprising and Progressive City Send Their Naiies and Addresses to The Tucson Chamber of Commerce A FREE ILLUSTRATED BOOKLET WILL BE MAILED TO THEM \* A Journal of General Botany VOLUME 20 NUMBER 6 JUNE, 191T 00??TAININQ An Enumeration of the Pteridophytes and Spermatophytes of the San Bernardino Mountains, California S. B. Parish 163 Redwoods, Rainfall and Fog W illiam S. Cooper 179 Books and Current Literature 190 Notes and Comment 192 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmount Ave. BALTIMORE, MD. EDITORIAL OFFICE TUCSON. ARIZO^''A Entered as second-class matter March 9, 1912, at the poat ofSce at Baltimore, Maryland, under the Act of July 16, 1894 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chables Louib Pollard, Founder Joseph Chahles Arthur Purdue University Otm William Caldwell University of Chicago^ WiLLiAU Austin Cannon Desert Laboratory J. Arthur Harris Station for Experimental Evolution Burton Edward Livingston Johns Hopkins University Francis Ernest Llotd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Trembly MacDouqal Carnegie Institution of Washington James Bertram Overton University of Wisconsin George James Peirce Stanford University Herbert Maule Richards Columbia University Forrest Shreve Desert Laboratory John James Thornbeb University of Arizona Edgar Nelson Transeau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without covers wrra covers First 100 Additional 100 First 100 Additional 100 $2.68 4.32 4.80 $0.72 1:20 2.00 $4.68 6.32 6.80 $1.72 £iEht Das63 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. FOR FIELD EXCURSIONS A PORTABLE MICROSCOPE is required that is really portable and sacrifices none of the efficiency of the bulkier instruments. Microscope APS has all the adjustments of our laboratory instruments, with all their [ accuracy and convenience of manipulation — and the cost is practically the same. APS 6 in carrying case weighs 8 lbs., 5 oz. The carrying case is less than one-half the size of a regular microscope case. The folding base is the only collap- sible feature and there is no inclination joint. APS has the lever side fine adjustment (two heads) which is simple in design and responds instantly. It ceases to operate when the objective touches the specimen. Microscope APS 6 Equipped with screw substage having iris diaphragm with protective locking device, Abbe condenser, 1.20 N.A., in iris mount; 5 X and 10 X eyepieces; 16 mm and 4 mm objectives on dust-proof nosepiece; com- plete in carrying case _ _ - $48.00 Bausch ^ Ipmb Optical ®. NEW YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON ROCHLSTEn, NX ^Rankfort. Leading American Makers of Microscopes, Projection Lanterns (Balopticons), Photographic and Ophthalmic Lenses, Binoculars and other High Grade Optical Products. PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 8. Instructor in botany in western university desires a university or college professorship. Has a Ph.D. and has had many years teaching experience. Competent to give courses in General Botany, Biology, Alorphology of the Great Groups of Plants and Cytology. Some opportunity for research desired. No. 10. Graduate of leading agricultural school and candidate at a leading univer- sity for Ph.D- in Botany in 1917 desires a position. Training in plant physiology, mycology and pathology, agriculture. Experience in teaching and research. Would prefer a place offering opportunity for I'esearch. No. 11. A man having wide experience and training in museum and scientific work seeks appointment as curator of a university or college museum. He is experienced in the preparation of modern museum exhibits which seek to portray the life of animals and plants as they occur in natural ecological groups. For a number of years carried on educational museimi extension work among the public schools of a large city. Would also consider position in charge of a research museum in an educational institution carrying on biological survey work, either scientific or economic, in both of which he has had wide expsrience. Has published numerous scientific papers. No. 12. Botanist. Woman, Doctor of Philosophy of a leading university (1915). Chief training in plant morphology and physiology; has also done work in zoology and bacteriology. Has done research in cytology and phsiology. The present year is being spent in research. THE PLANT WORLD Tucson, Arizona DrkTATTXTr" TADT17 for equalizing the exposure KUlAllilVJ 1 AD LEi OF A SERIES OF PLANTS ^ .? This becomes an indispensable de- vice in every physiological laboratory after its- first trial. It is impossible to give equal conditions to all plants in a standing series of cultures. For the proper standardization of Atmometer Cups it has been found absolutely nec- essary. The table-top is circular, 4 feet in diameter, of 5-ply wood, and is mounted on a bicycle wheel, which is supported on a heavy iron tripod base. It is rotated by a belt from a reducing gear, which is operated by a 1/20 H. P. electric motor or other sources of power. A hot-air engine or small gas engine would also serve. A good speed of rotation for most purposes is from 1/5 to 5 revolutions per minute. See Plant World 15: 157-162, 1912; Physiological Researches 1: 345- 1915. WEIGHT READY FOR SHIPMENT, ABOUT 150 LBS. Price of Rotating Table Complete, $25.00; Per Ten, $225.00 Table Top Alone, $6.00; Tripod Base Alone, $6.00 THE PLANT WORLD TUCSON, ARIZONA BOTANICAL JOURNALS, BOOKS, AND SEPARATES Bulletin of the Torrey Botanical Club, 1870-1910; 41 years, beauti- fully bound in half morocco in 26 volumes S90. 00 Annual Report of the Missouri Botanical Garden, 22 vols., cloth. . 22.00 Edward Tuckerman. Synopsis of the Lichens of North America, 2 parts I complete. With introduction to the study of Lichens, by Henry f Willey, bound in. Half morocco. Very scarce 25.00 Thornton, British Flora. Published 1812. Vol. 1, text, 536 pp. Vol.2, I 347 plates. Handsomely bound in red half morocco 22 . 50 Britten and Holland. Dictionary of English Plant Names. Published by the English Dialect Society. Three parts in one, half morocco ... 12 . 50 Britton and Brown. Hlustrated Flora of the Northeastern States. First Edition, three volumes 8 . 50 Robert Brown. Miscellaneous Botanical Writings. Two vols. Text, one vol. Plates, cloth 7 . 00 Payer. Botanique Cryptogamique. Half morocco. Scarce 5.50 Ralph. Icones Carpologicae. Leguminosae, 40 plates. The complete work, in half morocco 4 . 50 George Goodale. Physiological Botany. Half morocco 3 . 75 Rabenhorst. Die Slisswasser Diatomaceen. Ten plates. Half morocco. 3.50 Reginald R. Gates. The Mutation Factor in Evolution. 1915 2.00 MacDougal, Vail, Shull, and Small. Mutants and Hybrids of the Oenotheras. 1905. Out of print. Paper 1.25 Marshall A. Howe. The Marine Algae of Peru. Paper 2.00 Barnes and Heald. Keys to the Genera and Species of North American Mosses. 1896 1. 50 F. E. and E. S. Clements. Rocky Mountain Flowers. Cloth, 400 pp., profusely illustrated in color 3 . 00 J. C. Arthur and D. T. MacDougal. Living Plants and their Properties. Cloth, 234 pp., illustrated 1 . 25 Grace J. Livingston. Bibliography of Evaporation. Paper, 121 pp. . . . 1.25 B. E. Livingston. Atmometry and the Porous Cup Atmo meter. Paper, 64 pp., illustrated .75 E. E. Free. Studies in Soil Physics. Paper, 42 pp .75 B. E. Livingston and Edith B. Shreve. Improvements in the Method for Determining the Transpiring Power of Plant Surfaces by Hygro- metric Paper, Paper, 24 pp .40 Forrest Shreve. A Map of the Vegetation of the United States. With map in color and descriptive text .50 D. T. MacDougal. The Deserts of Egypt. Paper, 27 pp., illustrated. . .40 D. T. MacDougal. The Desert Basins of the Colorado River. Paper, 25 pp., illustrated, map .40 J. W. Shive. An Improved Non-Absorbing Porous Cup Atmometer. Paper, 4 pp .20 D. T. MacDougal. Hybridization of Wild Plants. Paper, 16 pp 30 THE PLANT WORLD TUCSON, ARIZONA Two Cambosco Instruments 32-254 TRANSPIRATION App. Garreau's Detmer P. 214. To determine the amount of transpiration from the upper and lower sides of a leaf at the same time. Complete, . . , $4.50 32-256 TRANSPIRATION CHAMBER, Detmer, P. 219. To show that the amount of transpiration depends upon the degree of moisture in the air and that a rising temperature accelerates 32-254 transpiration. The m/e of transpiration in c?/-^/ 32.255 air and in moist is easily determined. Without burner or thermometer, $5.00. SEE Botanical Catalog, 91, P. 49, for complete information. CAMBRIDGE BOTANICAL SUPPLY COMPANY WAVERLEY, MASS. Leading American Makers of Physiological Apparatus Laboratory Equipment for all the Sciences Established 1884 Catalogue Free Mention Plant World University of Colorado IVIountain Laboratory Located at Tolland, Colorado, in the Rocky Mountains in an open park surrounded by coniferous forest. Rich and varied flora from foothills to alpine peaks easily accessible. Courses in Field Botany and Field Zoology; especially taxonomy of seed plants. Work suitable for high-school and college instructors in botany or zoology. No elementary students received. Ninth Annual Session June 25 to August 4, 1917. Fees moderate. Expenses reasonable. An opportunity to learn much with little expenditure of time and money. Additional Information may be obtained by addressing Professor Francis Ramaley, University of Colorado, Boulder, Colorado. Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, ?old a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In tliis kind of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA *>^ Make the Acquaintance of TUCSON THE METROPOLIS OF ARIZONA AND NEW MEXICO Both the oldest and the newest City of the Southwest It combines the picturesqueness of its ancient missions and the quaintness of its Mexican quarter with the modern features of a progressive American City. It is an important railway and banking centre, a wholesale distributing point, the focus of a rich mining and grazing region, and an agricultural oasis of a imique and successful character. It is the seat of the University of Arizona, the State Agricultural Experiment Station, the Desert Laboratory of the Carnegie Institution, the Magnetic Observatory of the Coast and Geodetic Survey, and other state and national institutions. The environs of Tucson are extremely attractive, in its setting of lofty and rugged mountains. The excellent roads make it easy to visit the numerous localities of historic and prehistoric interest, and to enjoy the varied natural features of the surrounding region. Desert valleys, grassy plains, groves of oaks and forests of pines are all available by automobile and pack train. The hunting is ^ood The botanizing is ^ood The summer is more comfortable in Tucson than it is in New York or Washington Illustrated booklets and information will be gladly furnished to you and your friends THE CHAMBER OF COMMERCE TUCSON, ARIZONA EFFICIENCY The Principles of Scientific Siiop Management are Applied by us to the Printing Business We manufacture this Journal. In addition we produce 25 other aclentlfio and teohnloal publications and a large number o{ books and catalogues. All are handled on a d*finit* Mchedul* maintaining the highest standard of meehanloal workmanship. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 2419-2421 Greenmount Are., Baltimore, Md., U. S. A. KODAK FINISHING Wg Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith SportiRg Goods Company TUCSON, ARIZONA /L.OCC'C^M A Journal of General Botany VOLUME 20 NUMBER 7 JULY, 1917 CONTAINING The Revegetation of Taal Volcano, Philippine Islands Frank C. Gates , 195 An Enumeration of the Pteridophytes and Spermatophytes of the San Bernardino Mountains, California S. B. Parish 208 Books and Current Literature 224 Notes and Comment 227 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmoxjnt Ave. BALTIMORE, MD. EDITORIAL OFFICE TUCSON, ARIZONA ^\ 1 LISRA?^ Ent«red bb seoond-claea matter March 9. 1912, at the post office at Baltimore, Maryland, under the Act of July 10, 1804 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chajiles Louis Pollabd, Founder Joseph Chables Abthur Purdue Univeraity Gin WnxiAM Caxdwell University of Chicago WnxiAM Austin Cannon Desert Laboratory J. Abthub Habbis Station for Experimental Evolution BuBTON Edwabd Livingston Johns Hopkins University ^ Fbancib Ebnebt Llotd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Tbemblt MacDouqal Carnegie Institution of Washington James Bebtbam Ovbbton University of Wisconsin Geobge James Pbibcb Stanford University Hebbebt Mauxe Richabds Columbia University Fobbest Shbevb Desert Laboratory John James Thornbeb University of Arizona EoQAB Nelson Tbansbau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without covEas WITH COVERS First 100 Additional 100 First 100 Additional 100 Four pages $2.68 4.32 4.80 $0.72 1.20 2.00 $4.68 6.32 $1.72 Eieht oasee 2.20 Sixteen pages 6.80 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. B ausc land* I h |omb Binocular Microscope For Single Objectives MICROSCOPE CAE is our newest model, designed to give the advantages of binocular vision with objectives of all powers. It has parallel eye- piece tubes. The advantages are: 1. Apparent stereoscopic effect. 2. Increased penetrating power. 3. Brilliancy and increase in quality of image. 4. Resting effect conducive to prolonged examinations. The exact interpupillary dis- tance is obtained by a convenient adjustment with numbered, mil- limeter scale. One tube is ad- justable for differences in vision between the observer's eyes. The stand has appointments for research work. Write for special circular Bausch ^ Ipmb Optical (o. HEW YOIiK WASHINGTON CHICAGO SAN FRANCISCO LONDON riOCHESTEn, N.Y. f^RANKFORT Leading American Makers of Microscopes, Projection Apparatus (Balopticons), Photographic and Ophthalmic Lenses, Engineering Instruments, Stereo Prism Binoculars and other High Grade Optical Products Completely Equipped $156.50 PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 11. A man having wide experience and training in museum and scientific work seeks appointment as curator of a university or college museum. He is experienced in the preparation of modern museum exhibits which seek to portray the life of animals and plants as they occur in natural ecological groups. For a number of years carried on educational museimi extension work among the public schools of a large city. Would also consider position in charge of a research musemn in an educational institution carrying on biological survey work, either scientific or economic, in both of which he has had wide experience. Has published numerous scientific papers. No. 12. Botanist. Woman, Doctor of Philosophy of a leading university (1915). Chief training in plant morphology and physiology; has also done work in zoology and bacteriology. Has done research in cytologj^ and physiology. The prescmt year is being spent in research. THE PLANT WORLD Tucson, Arizona DHTATTXTr TAT^TT? ^^^r equalizing the exposure IVU 1 A 11 11 VJ 1 /ID l^Ei OF A series OF PLANTS ^ ^ Thiis becomes an indispensable de- vice in ever\' physiological laboratory after its first trial. It is impossible to give equal conditions to all plants in a standing series of cultures. For the proper standardization of Atmometer Cups it has been lound absolutely nec- essary. The table-top is circular, 4 feet in diameter, of 5-ply wood, and is mounted on a bicycle wheel, which is supported on a heavy iron tripod base. It is rotated by a belt from a reducing gear, which is operated by a 1/20 H. P. electric motor or other sources of power. A hot-air engine or small gas engine would also serve. A good speed of rotation for most purposes is from 1/5 to 5 revolutions per minute. See Plant World 15: 157-162, 1912; Physiological Researches 1 : 345- 1915. WEIGHT READY FOR SHIPMENT, ABOUT 150 LBS. Price of Rotating Table Complete, $25.00; Per Ten, $225.00 Table Top Alone, $6.00; Tripod Base Alone, $6.00 THE PLANT WORLD TUCSON, ARIZONA ORNAMENTAL CACTI Learn to know the delights of cactus culture by securing some of these plants, celebrated for their grotesque forms and beautiful flowers. We offer robust desert-grown plants or vigorous cuttings of species which are capable of outdoor growth in a temperate climate, with winter protection in the north. Opuntia spiiiosior, arborescent, flowers crimson $ .60 Opuntia versicolor, arborescent, flowers terra-cotta .30 Opuntia vivipara, a rare, slender, bushy plant .40 Opuntia fulgida, covered with shining straw-colored spines .35 Opuntia leptocaulis, very slender, with persistent red fruit .30 Opuntia microdasys, flat joints with velvety covering .40 Opuntia santa-rita, round joints with strong red coloration .50 Opuntia linguiformis, remarkable elongated joints ,40 Opuntia castillae, a rapid grower, nearly spineless .35 Cereus giganteus, plants according to size from $1.00 to 50.00 Echinocactus wislizeni, Barrel Cactus, heavy hooked spines 1.00 Echinocactus erectocentrus, large pink flowers .50 Echinocereus fendleri, magnificent magenta flowers .35 to 1.00 Echinocereus rigidissimus, the beautiful Rainbow cactus .75 to 1.00 Mamillaria grahami, hoary spines and pink flowers .35 Mamillaria arizonica, large pink flowers .40 ASSORTED LOTS OF CACTI Lot a. Four species, including Mamillaria, Echinocereus and two types of Opuntia $1 -00 Lot B. Four species, all Opuntias of different types 1.00 Lot C. Four species of larger Cacti, including Cereus giganteus 2.50 Lot D. Four species selected for the size and unusual beauty of their flowers 2.50 Lot E. Four species selected for their hardiness, all being capable of standing short periods of zero 1 . 25 Lot F. Four species of Opuntia capable of rapid growth in a warm moist climate 1.25 Lot G. Twelve species. Includes A, B, and C 4.00 Lot H. Twelve species of Opuntia. A diversified lot 4 . 00 Lot K. Twenty species of Cacti, including Cereus giganteus, Mamillaria Grahami and Echinocereus rigidissimus 10 . 00 Lot L. Forty species of Cacti. A fine collection in itself, including members of all genera Ksted above. DupHcates Lot K in part. A bargain at 20.00 Special prices on large plants. Special discounts on large orders SEND FOR OUR COMPLETE CATALOGUE THE PLANT WORLD TUCSON, ARIZONA Two Cambosco Instruments 32-254 TRANSPIRATION App. Garreau's DetmerP. 214. To determine the amount of transpiration from the upper and lower sides of a leaf at the same time. Complete, . . . $4.50 32-256 TRANSPIRATION CHAMBER, Defmer, P. 219. To show that the amount of transpiration depends upon the degree of moisture in the air and that a rising temperature accelerates 32-254 transpiration. The m/g of transpiration in ^^^3; 32.256 air and in moist is easily determined. Without burner or thermometer, $5.00. SEE Botanical Catalog, 91, P. 49, for complete information. CAMBRIDGE BOTANICAL SUPPLY COMPANY WAVERLEY, MASS. Leading American Makers of Physiological Apparatus Laboratory Equipment for all the Sciences Established 1884 Catalogue Free Mention Plant World SPHERICAL ATMOMETER CUPS A spherical evaporating surface, 5 cm. in diameter, presenting the same external ex- posure in all directions, with glazed cylindri- cal neck 3 cm. long and 2 cm. inside diameter. They are composed of very resistant material, of proper porosity for atmometric work, and are to be mounted on rubber stoppers as in the case of cylindrical cups. The spheres may be cleaned with brush and distilled water, may be treated with acid, and even heated to red heat. They should thus be capable of many years of use, without permanent alteration of the coefficient. They are not easily broken. These new spheres are supplied either standardized or unstandardized. Stand- ardization is carried out with reference to a newly adopted spherical standard ; spheres cannot be satisfactorily standardized to the cylindrical standard cup. Therefore readings from spheres are not satisfactorily reducible to terms of readings from cylin- ders (see Plant World, Vol. 18, pp. 21, 51, 95, 143). Unstandardized White Spheres, $2.25 each, $20.00 per ten Standardized White Spheres, $2.75 each, $25.00 per ten THE PLANT WORLD TUCSON, ARIZONA Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being; prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In this kind of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA Make the Acquaintance of TUCSON THE METROPOLIS OF ARIZONA AND NEW MEXICO Both the oldest and the newest City of the Southwest It combines the picturesqueness of its ancient missions and the quaintness of its Mexican quarter with the modern features of a progressive American City. It is an important railway and banking centre, a wholesale distributing point, the focus of a rich mining and grazing region, and an agricultural oasis of a unique and successful character. It is the seat of the University of Arizona, the State Agricultural Experiment Station, the Desert Laboratory of the Carnegie Institution, the Magnetic Observatory of the Coast and Geodetic Survey, and other state and national institutions. The environs of Tucson are extremely attractive, in its setting of lofty and rugged mountains. The excellent roads make it easy to visit the numerous localities of historic'and prehistoric interest, and to enjoy the varied natural features of the surrounding region. Desert valleys, grassy plains, groves of oaks and forests of pines are all available by automobile and pack train. The hunting is good The botanizing is good - ■ The summer is more comfortable in Tucson than it is in New York or Washington Illustrated booklets and information will be gladly furnished to you and your friends THE CHAMBER OF COIMERCE TUCSON, ARIZONA EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We manufacture thU Journal. In addition we produce 26 other ■ctenttfio and teohnloal ynbllcatloni and a laree number of booki and catalogues. All are handled on a d4finit$ lehsdult maintatninE the hlgheet standard of meahanloal workmanship. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 3419-3431 Greenmount Are., BalUmor*. Mil., U. S. A. KODAK FINISHING We Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON, ARIZONA ^ iX s A Journal of General Botany VOLUME 20 NUMBER 8 AUGUST, 19 17 CONTAINING Soil Temperatures as a Factor in Ph3rtopathology L. R. Jones 229 The Beginnings and Physical Basis of Parasitism D. T. MacDougal 238 An Entraieration of the Pteridophytes "and Spermatophytes of the San Bernardino Mountains, California S. B. Parish 245 Books and Current Literature 260 Notes and Comment 284 PUBLISHED MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmottnt Ave. BALTIMORE, MD. EDITORIAL OFFICE TUCSON, ARIZONA Entered as second-class matter March 9^ 1912, at the post office at Baltimore, Maryland, under the Act of July 16, 1894 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chableb Louib Pollabd, Founder Joseph Chablbs Abthcb Purdue University Otib William Caldwell University of Chicago William Austin Cannon Desert Laboratory J. Abthub Habbis Station for Experimental Evolution Bdbton Edwabd Livingston Johns Hopkins University Fbancib Ebnebt Llotd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Tbembly MaoDouoal Carnegie Institution of Washington James Bertbam Ovebton University of Wisconsin Geobqe Jame? Peibce Stanford University Hebbebt Maule Richabdb Columbia University FOBBBST ShBEVB Desert Laboratory John Jameb Thoenbeb University of Arizona Edqab Nelson Tbanseatj Eastern Illinois Normal School All manuscripts submitted for publication should be tj^je-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: WITHOUT COVEBS WITH COVEBS First 100 Additional 100 First 100 Additional 100 Four pages $2.63 4.32 4.80 JO. 72 1.20 2.00 $4.68 6.32 6.80 $1.72 Eieht naees 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date pf issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. The Bausch & Lomb Auxograph For Demonstrating and Recording Plant Growth is a practical instrumeDt for educational use which possesses the following advantages: Prominence of Record Ease and Simplicity of Adjustment Comparative Accuracy DurabiUty Ready Portability Principle and Operation Perfectly Apparent PRICE, complete, $25.00 Ask for Catalog Bausch J5* Ipmb Optical (o. WEW YOUK WASHINGTON CHICAGO SAN FR.ANCISCO LONDON iiOCHESTEri,N.Y. ^i^ankfort Leading American Makers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Binoculars and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 11. A man having wide experience and training in museum and scientific work seeks appointment as curator of a university or college museum. He is experienced in the preparation of modern museum exhibits which seek to portray the life of animals and plants as they occur in natural ecological groups. For a number of years carried on educational museimi extension work among the public schools of a large city. Would also consider position in charge of a research museum in an educational institution carrying on biological survey work, either scientific or economic, in both of which he has had wide experience. Has published numerous scientific papers. No. 12. Botanist. Woman, Doctor of Philosophy of a leading university (1915), Chief training in plant morphology and physiology; has also done work in zoology and bacteriology. Has done research in cytology and physiology. The present year is being spent in research. THE PLANT WORLD Tucson, Arizona DHTATTlVFr TARTT? for equalizing the exposure RUlrVlliiVJ 1 i\D JLEi of a series of plants >?? ^? This becomes an indispensable de- vice in every physiological laboratory after its first trial. It is impossible to give equal conditions to all plants in a standing series of cultures. For the proper standardization of Atmometer Cups it has been found absolutely nec- essary. The table-top is circular, 4 feet in diameter, of 5-ply wood, and is mounted on a bicycle wheel, which is supported on a heavy iron tripod base. It is rotated by a belt from a reducing gear, which is operated by a 1/20 H. P. electric motor or other sources of power. A hot-air engine or small gas engine would also serve. A good speed of rotation for most purposes is from 1/5 to 5 revolutions per minute. See Plant World 15: 157-162, 1912; Physiological Researches 1: 345- 1915. WEIGHT READY FOR SHIPMENT, ABOUT 150 LBS. Price of Rotating Table Complete, $25.00; Per Ten, $225.00 Table Top Alone, $6.00; Tripod Base Alone, $6.00 THE PLANT WORLD TUCSON, ARIZONA Phice Each Price Per Ten $ .60 $5.00 1.40 11.00 .50 4.50 2.25 20.00 2.75 25.00 2.25 20.00 2.75 25.00 PRICE LIST OF ATMOMETER CUPS AND OTHER APPARATUS Prices in Effect January 1, 1917 In placing telegraphic orders the list numbers may be used. List No. 1 Natural Cylindrical Cups, no number, no coating (3 X 13 cm.) lA Standardized Cylindrical Cups, numbered and shel- lacked at base. 4 Used Cups and Seconds (when in stock) 5 Bellani Plates (porous disc attached to a glazed hemi- spherical funnel.) 5A Bellani Plates, standardized and numbered. 6 White Spherical Cups, with glazed neck. 6A White Spherical Cups, standardized and numbered. 7 Transeau Vaporimeter Cups (1.5x25 cm.), no num- ber, no coating. .60 5.00 8, ' Large Cylindrical Cups (ox 35 cm.), for use as Auto- Irrigators. .80 7.00 17 Rotating Table, for standardizing atmometers or equalizing conditions for growing plants, 4 ft. in diameter. 20.00 18 Tops for Rotating Tables, 3-ply, unpainted. 4.50 19 Iron Tripods for Rotating Tables, unpainted. 4.50 20C Shive Non-Absorbing Atmometer Mounting (without cup), for use with Cylindrical Cup. 6.00 55.00 20S Shive Non-Absorbing Atmometer Mounting (without cup), for use with Spherical Cup. 6.00 55.00 21 Collar Clamps, for holding stopper in Cylindrical Atmometer Cup. 22 Pans for water-retaining power of soils. 23 Clips for Cobalt Paper Transpiration method. 24 Selected Cobalt Paper for Transpiration method. Circles 11 cm. in diameter. 25 Tripartite Cobalt Paper Slips. 30 MacDougal Direct Reading Precision Auxograph. Restandardizing Atmometer Cups. Cleaning Atmometer Cups. Please notify us before shipping cups for restandardization. Eastern orders may be filled by addressing: Eastern Branch, The Plant World, 2753 Maryland Ave., Baltimore, Md. Further information regarding any of the above items will be furnished on application THE PLANT WORLD TUCSON, ARIZONA 3.50 33.00 1.50 12.50 .30 2.50 .30 2.50 .12 1.00 75.00 .40 4.00 .60 6.00 Two Cambosco Instruments 32-254 TRANSPIRATION App. Detmer P. 214. Garreau's To determine the amount of transpiration from the upper and lower sides of a leaf at the same time. Complete, . . . $4.50 32-256 TRANSPIRATION CHAMBER, Detmer, P. 219. To show that the amount of transpiration depends upon the degree of moisture in the air and that a rising temperature accelerates 32-254 transpiration. The m/e of transpiration in c^/-^; 32.256 air and in moist is easily determined. Without burner or thermometer, $5.00. SEE Botanical Catalog, 91, P. 49, for complete information. CAMBRIDGE BOTANICAL SUPPLY COMPANY WAVERLEY, MASS. Leading American Makers of Physiological Apparatus Laboratory Equipment for all the Sciences Eiitablished 1884 Catalogue Free Mention Plant World SPHERICAL ATMOMETER CUPS A spherical evaporating surface, 5 cm. in diameter, presenting the same external ex posure in all directions, with glazed cylindri- cal neck 3 cm. long and 2 cm. inside diameter. They are composed of very resistant material, of proper porosity for atmometric work, and are to be mounted on rubber stoppers as in the case of cylindrical cups. The spheres may be cleaned with brush and distilled water, may be treated with acid, and even heated to red heat. They should thus be capable of many years of use, without permanent alteration of the coefficient. They are not easily broken. • These new spheres are suppUed either standardized or unstandardized. Stand- ardization is carried out with reference to a newly adopted spherical standard; spheres cannot be satisfactorily standardized to the cylindrical standard cup. Therefore readings from spheres are not satisfactorily reducible to terms of readings from cylin- ders (see Plant World, Vol. 18, pp. 21, 51, 95, 143). Unstandardized White Spheres, $2.25 each, $20.00 per ten Standardized White Spheres, $2.75 each, $25.00 per ten THE PLANT WORLD TUCSON, ARIZONA Make the Acquaintance of TUCSON THE METROPOLIS OF ARIZONA AND NEW MEXICO Both the oldest and the newest City of the Southwest It combines the picturesqueness of its ancient missions and the quaintness of its Mexican quarter with the modern features of a progressive American City. It is an important railway and banking centre, a wholesale distributing point, the focus of a rich mining and grazing region, and an agricultural oasis of a unique and successful character. It is the seat of the University of Arizona, the State Agricultural Experiment Station, the Desert Laboratory of the Carnegie Institution, the Magnetic Observatory of the Coast and Geodetic Survey, and other state and national institutions. The environs of Tucson are extremely attractive, in its setting of lofty and rugged mountains. The excellent roads make it easy to visit the numerous localities of historic and prehistoric interest, and to enjoy the varied natural features of the surrounding region. Desert valleys, grassy plains, groves of oaks and forests of pines are all available by automobile and pack train. The hunting is good The botanizing is good The summer is more comfortable in Tucson than it is in New York or Washington Illustrated booklets and information will be gladly furnished to you and your friends THE CHAMBER OF COMMERCE TUCSON, ARIZONA EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We manufacture thU Journal. In addition we produce 25 other lolentlfio and teohnloal publications and a lare* number o{ booki and oataloguea. All are bandied on a itfiniU »eh*iuU maintalnlnt; the highest itandard of meohanloal workmanahlp. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 2419-2421 Greenmount Atc, Baltlmor*. Md., U. S. A. K.ODAK FINISHING We Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON. ARIZONA Albert Steinfeld & Co. Tucson, Arizona WHOLESALE AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now, past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In this kind of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA VOLUME 20 NUMBER 9 SEPTEMBER, 1917 OONTAININQ The Indicator Significance of Native Vegetation in the Determination of Forest Sites Clarence F. Korstian 267 The Adaptation of Truog's Method for the Determination of Carbon Diox- ide to Plant Respiration Studies A. M. Gurjar 288 Environment of Seeds and Crop Production Byron D. Halsted and Earle J. Owen 294 Books and Current Literature 298 Notes and Comment » 301 PTTBLI8HBD MONTHLY OFFICE OF PUBLICATION 2419-21 Greenmount Ave. BALTIMORE, MD. EDITORIAL OFFICE TUCSON. ARIZONA Ent«r«d aa B«oond-clas9 matter March 9, 1912, at the post oflace at Baltimore, Maryland, under the Act of July 16, 1894 The Plant World A Monthly Journal of General Botany Established 1897 Edited by Forrest Shreve Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chables Loub Pollabd, Founder JoBBPH Charles Arthur Purdue University Otm William Caldwell Univerrity of Chicago William Austin Cannon Desert Laboratory J. Arthur Habrib Station for Experimental Evolution Burton Edward LrviNasTON Johns Hopkins University FsANcm Ebnest Llotd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Tbeublt MacDougal Carnegie Institution of Washington James Bertram Ovebton University of Wisconsin Geobge Jambs Pbibcb Stanford University Hbbbbbt Maulb Richabds Columbia University Fobbest Shbgvb Desert Laboratory Jo£[N James Thornbbr University of Arizona Edqar Nelson Transeau Eastern Illinois Normal School All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: WITHOUT cover* WITH COVERS First 100 Additional 100 First 100 Additional 100 Four pages S2.es tO.72 $4.63 6.32 $1.72 Eight pages 4.32 1.20 4.80 2.00 2.20 Sixteen pages 6.80 ' 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is $2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are $2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. The Bausch & Lomb Auxograph For Demonstrating and Recording Plant Growth is a practical instrument for educational use which possesses the followdng advantages: Prominence of Record Ease and Simplicity of Adjustment Comparative Accuracy Durabihty Ready Portability Principle and Operation Perfectly Apparent PRICE, complete, $25.00 Ask for Catalog Bausch {5" Ipmb Optical (o. MEW YOriK WASHINGTON CHICAGO SAN FRANCISCO LONDON R,oCHESTEri,N.Y. ^i^ankfort Leading American Makers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Binoculars and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. No. 11. A man having wide experience and training in museum and scientific work seeks appointment as curator of a university or college museum. He is experienced in the preparation of modern museum exhibits which seek to portray the life of animals and plants as they occur in natural ecological groups. For a nimiber of years carried on educational musemn extension work among the public schools of a large city. Would also consider position in charge of a research museum in an educational institution carrying on biological survey work, either scientific or economic, in both of which he has had wide experience. Has published numerous scientific papers. No. 12. Botanist. Woman, Doctor of Philosophy of a leading university (1915). Chief training in plant morphology and physiology; has also done work in zoology and bacteriology. Has done research in cytology and physiology. The present year is being spent in research. THE PLANT WORLD Tucson, Arizona PnTATTXir TAPTT7 foR equalizing the exposure iVU li\l lilVJ lilDL/ Hi OF A SERIES OF PLANTS ^ >i? This becomes an indispensable de- vice in every physiological laboratory after its first trial. It is impossible to give equal conditions to all plants in a standing series of cultures. For the proper standardization of Atmometer Cups it has been found absolutely nec- essary. The table-top is circular, 4 feet in diameter, of 5-ply wood, and is mounted on a bicycle wheel, which is supported on a heavy iron tripod base. It is rotated by a belt from a reducing gear, which is operated by a 1/20 H. P. electric motor or other sources of power. A hot-air engine or small gas engine would also serve. A good speed of rotation for most purposes is from 1/5 to 5 revolutions per minute. See Plant World 15: 157-162, 1912; Physiological Researches 1 : 345- 1915. WEIGHT BEADY FOR SHIPMENT, ABOUT 150 LBS. Price of Rotating Table Complete, $30.00 Table Top Alone, $7.50; Tripod Base Alone, $8.50 THE PLANT WORLD TUCSON, ARIZONA DIRECT READING PRECISION AUXOGRAPH The improved form of this instrument, originaUy designed and perfected by Dr. D. T. MacDougal, has a compound lever by which changes in length or thickness of plant organs may be multiplied twenty to fifty times, and the variations traced con- tinuously on paper ruled to 1 mm., making possible readings to 0.01 mm. The recording drum carries a seven-day chart (one day if desired), and is driven by reliable clockwork. The records are not integrated but consist of inked tracings on sheets of the same length as thermograph charts, so that the course of growth and temperature may be connected directly. The drum may be swung away from the pen lever and also adjusted vertically on its support by a sliding sleeve. The lever system may b3 moved vertically l^y a rack and pinion to secure adjustment to varying lengths of a plant organ. This apparatus is designed for the study of the general course of growth, of the influence of external conditions on the rate, the analysis of the "Stoss- weise Anderungen" of Sachs, retractions, and changes of form in both limp and rigid organs. A small number of tested instruments now ready for delivery at $75.00 each THE PLANT WORLD, Tucson, Arizona Two Cambosco Instruments 32-254 TRANSPIRATION App. Detmer P. 214. Garr call's To determine the amount of transpiration from the upper and lower sides of a leaf at the same time. Complete, . . . $4.50 32-256 TRANSPIRATION CHAMBER, Detmer, P. 219. To show that the amiount of transpiration depends upon the degree of moisture in the air and that a rising temperature accelerates 32-254 transpiration. The m/e of transpiration in ^r^' 32.256 air and in moist is easily determined. Without burner or thermometer, $5.00. SEE Botanical Catalog, 91, P. 49, for complete information, CAMBRIDGE BOTANICAL SUPPLY COMPANY M AVERLEY, MASS. Leading American Makers of Physiological Apparatus Laboratory Equipment for all the Sciences Catalogue Free Mention Plant World Established 1884 LIGHT FILTERS We are able to supply a series of glass screens which absorb or transmit various parts of the spectrum and are useful for experimental work in growth, photo- tropism, and photosynthesis. These glass screens were developed by Dr. D. T. MacDougal, and are now available in bell-jars 36 x 36 cm. in size, with perforated top, or in plates 16.5 cm. square. Red Plates. A good monochrome transmitting to .610 u $1.50 each Blue Plates. Transmitting wave lengths less than .510 u SI. 50 each Orange Plates. High transmission in red and green to .530 u. Bridges the spectrum from red to blue ' -$1.00 each Heat-Absorbing Plates. Absorb most of the infra-red and 97% of the heat of a Nernst lamp. Give a pyrhehometer reading about half that of good window glass. Transmit 65% of inci- dent white light. In plates only SI 00 each Uviol Plates. Transparent to visible spectrum, transmitting ultra-violet to .310 u. in sheets 6 mm. thick to .300 u. in sheets 3 mm. thick. In plates only SI. 00 each Terms for bell-jars furnished on request. Additional information cheerfully given THE PLANT WORLD TUCSON, ARIZONA Make the Acquaintance of TUCSON THE METROPOLIS OF ARIZONA AND NEW MEXICO Both the oldest and the newest City of the Southwest It combines the picturesqueness of its ancient missions and the quaintness of its Mexican quarter with the modern features of a progressive American City. It is an important railway and banking centre, a wholesale distributing point, the focus of a rich mining and grazing region, and an agricultural oasis of a unique and successful character. It is the seat of the University of Arizona, the State Agricultural Experiment Station, the Desert Laboratory of the Carnegie Institution, the Magnetic Observatory of the Coast and Geodetic Survey, and other state and national institutions. The environs of Tucson are extremely attractive, in its setting of lofty and rugged mountains. The excellent roads make it easy to visit the numerous localities of historic and prehistoric interest, and to enjoy the varied natural features of the surrounding region. Desert valleys, grassy plains, groves of oaks and forests of pines are all available by automobile and pack train. The hunting is ^ood The botanizing is ^ood The summer is more comfortable in Tucson than it is in New York or Washington Illustrated booklets and information will be gladly furnished to you and your friends THE CHAMBER OF CX)MMERCE TUCSON, ARIZONA EFFICIENCY The Principles of Scientific Shop Management are Applied by us to the Printing Business We manufacture this Journal. In addition we produce 25 other aetenttfio and teohnloal pnbllcBtloni and a lars* number of booki and cataloeuet. All are handled on a dsfiniU »eh»duh matntalnlne the blgbeat standard of meahanloal workmanahlp. WAVERLY PRESS WILLIAMS & WILKINS COMPANY 3419-3431 Greenmount Are., Baltimor*. Md., U. S. A. KODAK FINISHING We Guarantee to get the best possible results from your exposures. Mail orders attended to promptly. Catalogue and Price List Free The Smith Sporting Goods Company TUCSON. ARIZONA Albert Steinfeld & Co. Tucson, Arizona WHOLESALE . AND RETAIL GENERAL MERCHANDISE Pumping Machinery for Reclaiming Desert Lands OPPORTUNITY INSURANCE Many a man has lost good business opportunities by not being prepared financially to grasp them. In an eastern city a skilled machinist, 50 years old, who had always earned a good salary, sold a valuable invention for a small amount because he had not saved any money and had not capital to float it. He said that if he had had even a small amount of capital he could have made a fortune out of the de- vice. Now. past middle life, he must keep on working, when he might have retired in comfort. Insure YOUR opportunities by means of a savings bank account. In this land of insurance you are PAID dividends instead of having to PAY premiums. At this bank your dividends come in the form of FOUR per cent semi-annually compounded interest. SOUTHERN ARIZONA BANK & TRUST CO. TUCSON, ARIZONA J ciuZi A Journal of General Botany VOLUME 20 NUMBER 10 OCTOBER, 1917 CONTAINING The Interpretation and Application of Certain Terms and Concepts in the Ecological Classification of Plant Communities George E, Nichols 305 Relation of the Rate of Root Growth in Seedlings of Prosopis Velutina to the Temperature of the Soil W. A. Cannon 320 Books and Current Literature 334 Notes and Comment 339 PUBLISHED MOIWHLT OFFICE OF PUBLICATION 2419-21 Greenmount Ave. baltimore, md. EDITORIAL OFFICE TUCSON, ARIZONA Entered as second-class matter March 9, 1912, at the post office at Baltimore, Maryland, under the act of July 16, 1894 The Plant World A Monthly Journal of General Botany Established 1897 Edited by FOEREST ShREVB Published by The Plant World Association COMPOSED OF THE FOLLOWING MEMBERS: Chables Louis Pollard, Founder Joseph Chables Arthur Purdue University Otis William Caldwell Teacher's College, Columbia University William Austin Cannon Desert Laboratory J. Abthub Habrib Station for Experimental Evolution Bubton Edwabd Livingston Johns Hopkins University Fbancis Ernest Lloyd McGill University Edwin Bennett McCallum Continental Rubber Company Daniel Tbembl; MacDouoal Carnegie Institution of Washington James Berteam Overton University of Wisconsin G&ORQE Jambs Peirce Stanford University Herbert Maule Richards Columbia University Forrest Shreve Desert Laboratory John James Thornber University of Arizona Edgar Nelson Tbanseatj Ohio State University All manuscripts submitted for publication should be type-written and in good order. Galley proof is submitted to the author who should return it as early as possible to the Editor. Reprints should be ordered on a blank for that purpose which accompanies the galley proofs. Reprints will be supplied at cost, at approximately the following rates: without COVEB9 with COVERS First 100 Additional 100 First 100 Additional 100 Four pages $2.08 *n.72 $4.68 6.32 6.80 $1.72 Eight pBgw 4.32 1 i.20 4.80 1 2.00 2.20 Sixteen pages 3.00 Advertising rates will be furnished on application. Address all correspondence regarding contributions and reprints, and all books for review to The Editor, The Plant World, Tucson, Arizona. The subscription price is S2.50 per annum in the United States, its overseas dependencies, and Canada and Mexico; $3.00 to other countries. Single copies are 30 cents each. Volumes 1 to 7 inclusive can not be supplied; Volumes 10 and 11 can be supplied incomplete; Volumes 8 and 9, and Volumes 12 to 20 are S2.50 each. Missing numbers lost in the mails will be replaced gratis only when notice is received within one month of date of issue. Make all remittances payable to The Plant World. Address all correspond- ence regarding subscriptions, discontinuances, changes of address, back num- bers and early volumes to: The Waverly Press, Williams & Wilkins Company, 2419-21 Greenmount Avenue, Baltimore, Md., or to The Plant World, Tucson, Arizona. B |omb ausc Lar^e Dissecting Stand A new design which meets every requirement by reason of its large size and wide range of usefulness. Accommodates interchange- ably Binocular Microscope body (illustrated), Monocular erecting body using medium high power objectives, or simple lens in jointed arm — all focused by rack and pinion. The microscope bodies may be mounted on a sliding track permitting the entire width of the stage to be covered. Stage, 8x7 inches, is provided with glass and metal plates, 4| inches in diameter, and with adjustable background stops beneath. With 38 and 19 mm. doublet lenses $26.50 With Binocular Microscope body, 40 mm. objectives and lOX eyepieces. 70.00 Write for Complete Illustrated Circular Bausch f/ Ipmb Optical (o. bEW YORK WASHINGTON CHICAGO SAN FRANCISCO LONDON iiOCHESTEa,N.Y. ^Rankfort Leading American Makers of Microscopes, Projection Apparatus (Balopticons), Photographic Lenses, Binoculars and other High Grade Optical Products PROFESSIONAL ADVANCEMENT COLUMN This column serves as a place in which it is possible for men to insert brief notices with a view to securing positions or securing men, either in botany or any of its related and applied branches. The identity of advertisers may be learned from the Editor of the Plant World. Notices should not exceed 100 words. They will be inserted once for 50 cents, three insertions for $1.00. THE PLANT WORLD Tucson, Arizona LARGE AUTO-IRRIGATORS For the automatic watering of large pots or beds of soil we offer an Auto- Irrigator Cup which is similar to the ordinary Atmometer in its form and proportions, but is 14 inches in length and U inches in diameter. These large cups are installed and operated in the same manner as the smaller Auto-Irrigators which are now in general use, and also lend themselves to various other purposes. Each .80, per ten $7.00. Directions for the use of Auto-Irrigators will be sent on request. THE PLANT WORLD - - Tucson, Arizona DATATTXTr' TADTT? for equalizing the exposure J\UlAlli>VJ 1 AD L