aqirena ceeds prieatied ea gass a suateyate ” ee BEE THE JOHN - CRAIG LIBRARY COLLEGE OF ‘AGRICULTURE Principles of plant culture; an elementar LIBRARY Department of Floriculture and Ornamental Horticulture at CORNELL UNIVERSITY Cornell University The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http:/Awww.archive.org/details/cu31924001725195 PRINCIPLES OF PLANT GULTURE AN ELEMENTARY TREATISE DESIGNED AS A TEXT-BOOK FOR BEGINNERS IN AGRI- CULTURE AND HORTICULTURE BY E. 8S. GOFF PROFESSOR OF HORTICULTURE IN THE UNIVERSITY OF WISCONSIN SECOND EDITION, REVISED Mladison, Wis. PUBLISHED BY THE AUTHOR 1899 CoPpyRIGHT, 1897 By E. 8. GOFF M. J. CANTWELL, Printer Madison, Wis. PREFACE This book has grown out of the author’s experience in the lecture room and laboratory, while giving instruction to students in the Short Course in Agriculture, in the University of Wisconsin. It is intended especially for students who have had little or no previous instruction in botany, and it is hoped that it may also be found interesting and profitable to the general reader who would learn more of the principles that underlie the culture of plants. It is expected that the instructor will amplify the text in proportion to the time at his command, and the ca- pacity of his students. In the author’s practice, the first three chapters have been found sufficient for a term of twelve weeks, and the remaining chapters, supplemented with some special work in horticulture, have served for a second term. A syllabus of laboratory work is added as an appendix. It is hoped that this book may prove as useful to other instructors as it has proved to the author during its evo- lution. i Madison, Wis., Feb. 15, 1897. E. 8. GOFF. Norr.—In the second edition (1899) a number of verbal changes have been made and a few additional paragraphs and illustrations have been inserted. ACKNOWLEDGEMENTS The author desires to express his thanks to Prof. Charles R. Barnes, of the University of Chicago, Prof. F. W. Woll, of the Wisconsin Agricultural Experiment Station and Mr. F. Cranefield, the author’s assistant in horticulture, for revision of the manuscript (of the first edition), and for many valuable suggestions. Figures 14, 15, 18, 19, 20, 21, 22, 28, 29, 30, 34, 46, 47, 48, 49, 53, 54, 55 and 83 were copied from ‘‘Agricultural Botany,’’ with the sanction of the author, Prof. M. C. Potter, of the Durham College of Science, England. Figures 61, 62, 63, 82, 84, 94, 98, 100, 101, 102, 103, 113, 117, 118, 119, 120, 121, 123 and 128 are from ‘The Nur- sery Book,’’ by Prof. L. H. Bailey, and are used by per- mission. Figures 31, 59, 81, 85, 99 and 130 are from “The Amateur Fruit Book,’’ by Prof. 8. B. Green, and are used by permission. Figure 32 is from a photograph kindly loaned by Prof. Green. Figures 37, 39, 40, 41, 42 and 44 are copied by permission of the publishers from ‘‘Barry’s Fruit Garden.” Figures 94 and 95 are from ‘‘How to Make the Garden Pay,’’ by T. Greiner, and are used by permission. Figures 65 and 66 were copied by permission from Bulletin No. 37, of the Rhode Island Agricultural Experiment Station. Figures 77, 78 and 79 are from cuts in the possession of the Wisconsin Agricultural Experiment Station. CONTENTS PAGE Chapter I.— Introductory. .........cee cc ccceec sess eeeeeeeeneees eas Chapter II.—The Round of Plant Life...........00.0.... 22114 Section 1—The Behavior of Seeds toward Water 22— 24 a 2—Germination He 8—The Plantlet........ ug 4—The Inner Stiueeure of the Plantlet... 48— 56 a 5—The Water of Plants and its Nba. TNTOTMES eastern de weeivneds teens auonete vanes waats 57— 64 Ke 6—The Root and the Soil.......... eee 64— 77 ut 7—The Stem...........cccccccssceseecseeeeeneeeseees 78— 80 fe B—— The: Leaves... cccisaicisadgaosacmeisens: eoseansene 81— 84 Of 9 — Phe: Bias scccsvcnuaidoinsodaneeviscendin sethens 84— 93 fe 10—The Flowe............cccccccsecscsccseneeesseees 93—101 ue 11—The Fruit and the Seed..................... 101—104 te 12—The Gathering and Storing of Seeds.. 104—109 ft 183—The Decline of Growth and the Rest POPIOC das esscnttinaunaamasua ve tesnenvereunaectess 109—114 Chapter IIJ.—The Plant as Affected by Unfavorable WO VITOMMON tees seencrecenesensieoutenas 115—180 Section 1— The Plant as Affected by Unfavorable TENT PETA CUTE: sc. avcaneneaiensbne Vegkimanawendans 115—132 A—By Excessive Heat... 115—118 B—By Excessive Cold .............. 118—124 Section 2— Methods of Averting Injury by Cold.. 124—132 A—During the Dormant Period 124—126 B—During the Growing Period 126—122 Section 83— The Plant as Affected by Unfavorable Water Supply 133—140 A—By Excessive Water............ 1383—137 B—By Insufficient Water......... 1387—140 8 Contents. Chapter ITI.— Section 4.—The Plant as Affected by Page. Unfavorable Light............cceeeeeeee 140—144 A—By Excessive Light............ 140—142 B—By Insufficient Light......... 142—144 Section 5— The Plant as Affected by Unfavorable WA 2s stascicytaieesca cuba asauncaadesmiatenemes 144—145 A—By Excessive Wind............ 144 B—By Insufficient Wind ......... 145 Section 6—The Plant as Affected by Unfavorable HOOd Sup ply asc secacecssctess dosnancviocsaes 146—153 A—By Excessive Food..........0... 146—147 B—By Insufficient Food........... 149—153 Section 7— The Plant as Affected by Parasites...... 1538—178 A—By Animal Parasites........... 154—170 B—By Vegetable Parasites........ 170—178 Section 8—The Plant as Affected by Weeds......... 178—180 Chapter IV.— Plant Manipulation 181—257 Section 1— Plant Propagation..... 181—225 A—By Seeds. 182—183 B—By Division, i. e., by parts other than Seeds...........0.. 183—225 Section 2— Transplanting........ cece ceneeeenee rene 225—241 A—Lifting the Plant............... 227—229 B—Removing the Plant............. 229—231 C—Replanting.......... cee 231—239 D— ae called growing point. Cc \ These cells divide eC) C very rapidly during ia the growing season, , i Fig. 19. Showing stomato (st.) on leaf of and from them all Oldenburgh apple. Highly magnified. other kinds of cells are evolved. The Inner Structure of the Planttet. 51 68. The Vascular (vas’-cu-lar) Bundles.* While the plantlet remains within the seed-case, it consists largely of cells more or less cubical or globular in outline. But germination scarcely commences before some of the cells begin to increase greatly in length without a correspond- ing increase in thickness.¢ These elongated cells form in groups or bundles (rascular bundles) that extend lengthwise through the stem and roots, and since the individual cells overlap and are in intimate contact, they form threads or fibres. These fibres serve the double purpose of giving strength to the plant and conducting water, with its dissolved food materials, to the different parts. By the absorp- tion of the ends of some of the cells, tubes (ducts) of very considerable ee length are formed. In other cells of cells from stem of rye. vascular bundles, the walls are much tantly masnifed. (AY thickened and strengthened by woody Tschirch). deposits. These groups or bundles of fibres and ducts divide and subdivide in the leaves, forming the so-called veins and veinlets. In the roots they divide in a similar manner, extending lengthwise through all the branches and branchlets. Fig. 21 shows a cross-section of a vascular bundle of the sunflower. The threads in the stalk of Indian corn and the leaf- * Also called jibro-vascular bundles. + Cells of the former class are called Parenchyma (pa-ren’/-chy-ma), and those of the latter class prosenchyma (pro-sen’-chy-ma) (Fig. 20). Fig. 17 shows parenchyma cells from the apple leaf. 52 Principles of Plant Culture. stem of the plantain * furnish examples of well-defined vascular bundles; in most stems the vascular bundles are less clearly de- fined. In woody stems they are Yan closely crowded, which gives the wood its firm text- ure. In some woody plants, as the grape and the elder} a cylinder extending through the center Fig. 21. Showing cross-section of a vascular bundle of the sunflower, (Helianthus annuus). of the stem is free Highly magnified. (After Prantl). See also from vascular vee bundles, forming the pith. The young stems of asparagus, the ball of the kohl-rabi and the roots of turnip are ‘‘stringy’’ when the cells of their vascular bundles become thickened by the deposit of woody material in them. 69. The Cambium (cam’-bi-um) Layer. In most plants having two or more cotyledons (46), a layer of cells in a state of division (15) exists between the bark and the wood, called the cambium or cambium layer (Fig. 22). It is in this layer that growth in diameter of the stem occurs (71). The bark of plants having the cambium layer separates readily from the wood at times when growth is rapid, because the walls of the newly-formed cambium cells are extremely thin and tender. The slimy surface of growing wood, whence the bark has just been re- moved, is due to the protoplasm from the ruptured cam- * Plantago. + Sambucus, The Inner Structure of the Plantlet. 53 bium cells. In plants having more than one cotyledon, the cambium line is usually readily discerned in cross- sections of the stem —though it is rather more distinct and the bark is more readily separable in woody than in herbaceous * stems. In the latter, the part within the Fie. 22, Showing transverse section of corner of a bean stem (Vicia faba). C cambium layer; e epidermis; Cu cuticle; Si stoma. The dark, oval-shaped spots, extending both sides of the cambium layer are the vas- cular bundles; WW wood cells of the vascular bundles. Moderately mag- nified. (After Potter). cambium line corresponds to the wood of woody stems, and that outside of it corresponds to the bark. 70. Portions of Cambium from different plants may Unite by Growth. Ifa section of cambium from one part of a plant is closely applied to the cambium of another part of the same plant or of another closely-related plant, * Herbaceous stems are those that do not have the hard, firm texture of wood, as of the potato, rhubarb etc. 5+ Principles of Plant Culture. the two portions of cambium may unite by growth, a fact of great importance in horticulture since it renders grafting possible (383). Plants having no cambium layer (71) cannot be grafted, because their stems have no layer of dividing cells—the only cells that unite by growth. 7l. How Stems Increase in Diameter. There is no cambium layer in plants having but one cotyledon (46), of which Indian corn, the grasses and the palms are ex- amples. In such plants there is no clear separation be- tween bark and wood; the stem enlarges for a time by growth throughout its whole diameter, after which it ceases to expand. In plants having two or more cotyledons, however, ad- ditions to the bark cells are constantly being made dur- ing the growing season on the outside of the cambium layer, as are additions to the wood cells on the inside of it (Fig. 22). It follows that growth of the bark takes place on its inner surface and growth of the wood takes place on its outer surface. This explains the vertically- furrowed appearance of the bark of old trees which is being constantly split during the growing season by the forming layer within. It also explains the ringed ap- pearance of a cross-section of a woody stem. A new ring of wood is formed each season on the outside of that previously formed, and the line separating the rings marks the point where growth in autumn ceased and was renewed the following spring. The age of a given part of the stem of a woody plant is approximately in- dicated by the number of its wood rings.* * More than one wood ring is sometimes formed inaseason. If growth ceases during the summer from severe drought or other cause, and is re- newed the same season, an extra ring is formed. The Inner Structure of the Plantlet. 5: oo 72. The Vital Part of Woody Stems in plants having more than one ? eoupledon (46) is limited to a rather thin A Z Zz Zz E 'zZ is 2 B Zz Zz z Bg zB Z ee Stee ao TLS SS 8 | wersere Te Fig. 23. Live poplar tree with hollow trunk, showing to what extent the heart-wood may decay without destroying the life of a tree. layer of bark and wood, of which the cambium (69) for mis the center. The cells of the so-called heart-wood and those of the dry and furrowed outer bark, have lost their proto- plasm, and hence are no longer alive, though they serve a useful purpose in adding strength and protection to the vital layer. The heart-wood of a tree may largely decay ° without materially interfering with the vital processes (Fig. 23). 73. The Healing of Wounds. Cambium cells exposed to the air by partial or complete re- moval of the bark, soon per- ish, as a rule, hence growth ceases in a part of the stem thus injured. The uninjured cambium cells on the borders of the wound may, however, by division (15), form a cush- ion of new material that grad- ually extends over the injured part. A new cambium layer may thus be formed over the wound it it be not too large, so that growth of the stem may be resumed at this place. The same process occurs when a branch is cut off 56 Principles of Plant Culture. near its union with the stem. The wound, if not too large, is ‘‘healed’’? by new growth from the adjacent, uninjured cambium cells (Fig. 24). In planted cuttings, the uninjured cam- bium cells at the base form the callus (eal’-lus) by con- tinned division. (Fig. 25). Exposure of the bark to undue heat or cold may destroy the cambium, caus- ing sunseald (186). : In periods of very a eee eee rapid growth, when ae 4 fee off a branch (A). the cambium cells winow cutting. are unusually active, large areas of bark, even extending clear around the stem and as deep as the cambium layer, may sometimes be removed from trees without destroy- ing their life, provided the recently- formed wood layer is not injured (71). In this case, the outer cells of the thin layer of cambium that remains on the surface of the wood promptly change to bark cells, hence a new bark layer forms over the exposed surface the same season. Several successive crops of bark are sometimes removed from the trunk of the cork oak,* but in this case, the- cambium layer is usually not injured. * Quercus suber. The Water of Plants and its Movements. 57 SECTION V. THE WATER OF PLANTS AND ITS MOVE- MENTS 74. Plants Contain Large Amounts of Water. We have seen that the cell-walls of living plants are constantly saturated with water (63), and that the cells of the grow- ing parts are always more or less distended with it. The proportion of water contained in living plants is gener- ally very large. In the root of the turnip and in some fruits, it may exceed ninety per cent of the whole weight. It is greatest in young plants and in the younger and growing parts of older plants. The proportion of water is not constant in the same plants, but varies somewhat with the water content of the soil and with meteorologi- cal conditions. 75. Transpiration (trans-pi-ra’-tion). The water of plants passes off more or less rapidly from parts exposed to the air— usually as an invisible vapor. This invisi- ble escape of water from plants is called transpiration. It is mainly due to evaporation of water from the plant, the same as takes place from other moist material. But fluctuations oceur in the amount of transpiration from living plants that do not occur in dead organic material under similar conditions. For example, transpiration is more rapid in light than in darkness, because the stomata (66) are open in the light and thus facilitate the escape of water from the intercellular spaces. Plants poorly supplied with nourishment transpire more freely under the same conditions than those well supplied. The amount of transpiration varies greatly in different plants and depends upon the leaf surface, the nature of the epi- 4 58 Principles of Plant Culture. dermis and cuticle (65), the number of stomata (66) ete. Some plants, as purslane, the sedums, cacti ete., have special water-storing tissue, from which transpiration is extremely slow. Experiments indicate that the transpiration from most leaves is between one-third and one-sixth as much as the evaporation from an equal area of water. When we take into account the immense leaf surface of a large tree, it is evident that the aggregate transpiration must be very great, as is often illustrated by the dwarfing in- fluence of trees upon adjacent crops in dry weather (Fig. 26). Transpiration is much more rapid during dry Fra. 26, Showing how a spruce hedge dwarfs an adjacent corn crop in dry weather. than during wet weather, and in the rare atmosphere of high altitudes than in the denser atmosphere of low lands. Excessive transpiration, as occurs in very dry weather, is detrimental to plants, since it reduces the water pres- sure within the cells below the point where healthful growth can take place (63); but normal transpiration, i. e., not sufficient in amount to interfere with healthful growth, is doubtless beneficial, since it aids in carrying The Water of Plants and its Movements. 59 food materials from the soil into the leaves (59). For this reason, plants native to regions having a rather dry atmosphere, do not thrive in greenhouses unless abund- ant ventilation is given to encourage transpiration. 76. Trees are Detrimental to Crops in their vicinity not only by the shade they cause, but also by their ex- exhausting effect upon the soil moisture in dry weather. The area affected by a group of trees is often much larger than is supposed. The illustration on page 58 (Fig. 26) shows how an evergreen hedge may restrict the growth of corn in an adjoining field. We should not infer from this, however, that trees are on the whole detrimental to agriculture. They serve many useful purposes. Experimental crops intended to be comparable with each other should not be planted near growing trees. 77. The Brittleness of Young Plant Tissues depends upon the degree of water pressure within the cells. Fo- liage is usually most brittle during the morning and least brittle during the latter part of the day, because trans- piration is most active during the warm hours of the day. Lettuce and other salad‘ plants are, therefore, apt to be most crisp and tender when cut in the morning. Tobacco, in which breaking of the leaves is detrimental, is preferably cut in the afternoon. Young hoed crops are generally less injured by the smoothing harrow in the afternoon than in the morning, and grass intended for hay usually dries soonest when cut in the afternoon. Lawn grass generally cuts easier in the morning than in the afternoon. Slightly withered vegetables may have their crispness partially restored by soaking them in water for a time. 60 Principles of Plant Culture. 78. The Evaporation Current. Since the water of plants is taken in from the soil through the root-hairs (101), and escapes more or less rapidly by transpiration (75), it is clear that in leafy plants a current of water must pass from the roots through the stem and branches into the leaves, and that the rate of this current will depend much upon the rate of transpiration from the foliage. When the soil moisture is reduced and transpiration is excessive, this upward current of water is not always. snfficient to maintain the normal pressure within the cells (63), hence the foliage wilts, or the leaves roll up, as in Indian corn and some other plants of the grass family. This current passes chiefly through the younger vascular bundles (68), which in trees constitute the so- called sap-wood, since the cells of these are less obstructed. by woody deposits than those of other tissues. The physical forces that cause the soil water to rise to the tops of the tallest trees are not well understood, but osmosis* and the pull produced by the evaporation of water from the leaves, play important parts. 79. The Flow of Sap in Spring. In the temperate zones, evaporation from the leafless stems of deciduous. trees and shrubs nearly ceases during winter. The por- tion of the roots of these plants, however, that lies below the frost line, continues to absorb water, which gradu- ally accumulates in the stems and branches. On the return of spring weather, the rise in temperature causes. * Osmosis is the tendency that causes two liquids of different densities to mix with each other when separated by a permeable membrane. The less dense liquid tends to flow into the denser one with a force correspond- ing to the difference in their densities. Ccll contents are denser than soil water, hence the latter tends to flow into the cells, and thus to rise in the plant. The Water of Plants and its Movements. 61 expansion of the tissues of the stem, as well as of the air and water within it. This creates so much pressure in some trees and shrubs that water flows freely from wounds in the wood, bearing with it, of course, the ma- terials it holds in solution. This happens when we tap a sugar maple tree in spring. Alternate rise and fall of temperature increase the flow of sap, because with each contraction, new supplies of water or air are drawn into the stem, and thus the pressure is maintained. Sap ceases to flow on the opening of the buds, because trans- piration from the foliage (75) quickly relieves the ab- normal pressure. The popular idea, that the flow of sap in spring is due to a rapid rise of water through the stem at that season, is erroneous. The sap is really rising through the stem much faster in midsummer than in early spring. 80. The Current of Prepared Food. The food of the protoplasm in the different parts of the plant is prepared almost wholly in the leaves (121). We know, however, that growth occurs in the stem and roots as well as in the leaves. It is clear, therefore, that when the stem and roots are growing, a inovement of food matter must occur from the leaves into these organs. This movement may be demonstrated by a simple experiment. If a notch deep enough to pass through the bark and a little into the wood, is cut into the stem of any of our common woody plants during spring or summer, a callus or cush- ion of new cells (73) will soon form on the upper side of the notch, but not on the lower, showing that the ma- terial from which new cells are formed is passing down- ward. Close examination will show that this callus 62 Principles of Plant Culture. forms just outside the union of the bark and wood. In all plants having more than one cotyledon (46), this cur- rent is through the inner layers of the bark. The pre- pared food matter is dissolved in the water that saturates the cell-walls, and passes from the leaves to other parts of the plant by diffusion (64). 8I. Killing Trees by Girdling. To destroy the life of a tree that can not be conveniently removed, we girdle it by cutting a notch about the trunk beneath the lowest branch. This cuts off the downward food current and so starves the protoplasm of the roots. If the notch is made after the leaves have expanded in spring, and ex- tends only through the bark, the leaves may remain fresh for several weeks, for the transpiration current passing through the sap-wood (78) may continue. Since the roots receive no nourishment however, they will soon cease to grew and will usually die from starva- tion before the following spring. If the notch is eut deep enough to reach through the sap-wood, thus cutting off both the ascending and descending currents, death of the tree soon follows. 82. Root Starvation may occur Without Girdling. In seasons of extreme drought, when the leaves are poorly supplied with crude food materials from the soil, the amount of prepared food may be so meagre that the food current will be exhausted before it reaches the roots. In such cases the roots perish, and the tree is found dead the following spring. This most frequently oceurs with trees on poor soil, that have suffered from insect attacks as well as from a dearth of water. It often occurs also in recently-transplanted trees that fail to make satisfac- tory growth the first season. The Water of Plants and its Movements. 63 83. To Destroy the most persistent Weeds we starve the roots by preventing all leaf growth (339). 84. Restriction of the Growth Current Promotes Fruit- fulness by causing an accumulation of prepared food in the stem and branches (135 B). _ 85. The Storage of Reserve Food. In healthy plants, food is usually prepared faster than it is consumed by growth. The surplus may be in the form of starch, as in the potato (Fig. 16), wheat and sago; sugar, as in the sugar cane, sugar maple and beet; or oil, as is cotton seed, flax seed and rape. Aside from the seeds, which are always stocked with reserve food, certain plants liv- ing more than one year, as the potato, beet, onion, kohl- rabi ete., have special accumulations of food in certain parts, and the parts of plants that contain such reserve food are most valuable as food for man or animals. The proportion of starch stored in potato tubers is not con- stant, hence the food value of different samples of pota- toes may vary greatly. In woody plants, the surplus food is more evenly distributed through the different parts, though the older leaf-hearing wood is usually best supplied. 86. Plants Use their Reserve Food in the production of flowers and seeds (135 A), and in repairing damages, as the healing of wounds (73), or the replacement of leaves destroyed by insects or otherwise. Annual plants (337) expend all their reserve food in flower and seed produc- tion and then perish as soon as the seed is ripe. Bien- nial plants devote the first season of their life to storing an abundant food supply, which is expended in flower and seed production the second year. Our seed crops, 64 Principles of Plant Culture. as oats, corn, peas and beans, are mostly annuals; our vegetables other than seeds, as beets, cabbage, parsnips and celery, are mostly biennials. Perennial plants, in normal condition, expend only a part of their reserve food in any one season for the production of flowers and seeds, withholding the remainder for nourishment through the winter and to develop leaves the following spring. The reserve food in dormant cuttings (358) en- ables them to form roots and expand their buds. Section VI. THe Root aNnD THE SOIL With the out-door cultivator, the part of the plant environment that lies beneath the soil surface is more under control than the part that lies above it. He can do little to change the composition or temperature of the air or the amount of sunlight; he may do much to influ- ence the fertility, the texture, the drainage and the aera- tion of the soil. A knowledge of the roots of plants and of the soil in which they grow and feed, is therefore, of the utmost practical importance. 87. The Office of the Root. The roots of land plants serve (a) to anchor the plant in the soil, enabling the stem or stems of erect species to grow upright, and (b) to supply the plant with water with its dissolved food materials (63). 88. The Root Originates in the Stem. As we have seen the primary root develops from the lower or ‘‘root-end’?’ of the hypocotyl (45). But lateral roots may develop freely from other parts of the stem. Jf we examine the base of the stein of a plant of Indian corn a few weeks The Root and the Soil. 65 after planting, we may sce that the main roots start above the point at which the stem was originally attached to the seed; and if we pull up a pumpkin vine or an un- trellised tomato plant late in summer, we often find it rooted from the stem at some distance from the original root. Lateral roots originate in the internal tissues of the stem or root and not close to the surface, as do buds (182). 89. Moisture Excites Root Growth. Roots develop, as a rule, from portions of the stem that are maintained for a certain time in contact with abundant moisture. In the pumpkin vine and tomato plant above mentioned, nearness to the soil furnishes a moist atmosphere. A corn-stalk pegged down to the ground for some distance will usually root at all joints of the stem in contact with the soil. A potato plant grown under a bell-jar, where the air is nearly saturated with water, will form roots at any joint of the stem. In parts of the tropics where the air is very moist, certain plants, as orchids and the Ban- yan tree,* emit roots freely from the stem above ground. Cuttings (858) and layers (349) form roots because they are maintained in contact with abundant moisture and at a suitable temperature. Cuttings of some plants, as the willow and nasturtium,+} root promptly when their stems are immersed in water. 90. Oxygen is Necessary to the Life of Roots. Since the cells of newly-formed roots are filled with proto- plasm, they must have access to the oxygen of the air, or they can neither live nor grow. This is shown by a simple experiment. Boil a quantity of water fifteen * Ficus Indica. + Tropeeolum, 66 Principles of Plant Culture. minutes or longer, to exhaust it of free oxygen, and then cool it quickly by setting the dish containing it in cold water. Now place a healthy cutting (358) of some plant that roots freely in water, as willow, nasturtium or wandering jew,* in each of two tumblers. Pour a part of the cool, boiled water into one of the tumblers and add a little olive oil to form a film over the liquid thus preventing it from absorbing more air. Then agitate the rest of the water vigorously to impregnate it again with oxygen, and pour some of this into the second tum- bler. Set both tumblers ina light, warm place. Ina tew days roots will start freely from the slip in the tum- NS as bler in which the wy 4 water has access to sf SL ve =¢ \, the air, but not in the e other (Fig. 27). If now the rooted cut- ting is placed in oil- covered water that , has been exhausted of its oxygen by boiling, the roots will soon die. The copious forma- tion of root-hairs (101) that reach out into the moist atmos- | phere of the seed- il = IL tester (39), and that h so often fills the soil Fra. 27. Slips of Tradescantia in water con- cavities with a deli- taining oxygen (left glass) and in water con- taining no oxygen (right glass). From nature, Cate, cottony down, 1S i | * Tradescantia. The Root and the Soil. 67 further proof that roots search for air as well as water. The total absence of live rootlets in the puddled clods of badly-tilled fields shows that roots will not penetrate soil from which the air has been expelled by undue compres- sion while wet. Plants in over-watered greenhouse pots sometimes send rootlets into the air above the soil to secure the oxygen from which their roots have been deprived. 91. The Ideal Soil for Land Plants must contain enough plant food and water to fully supply the plants, and yet be so porous that air can circulate through it and come in contact with the roots. Each particle of such a soil is surrounded by a thin film of water, while between the particles are spaces connected with each other, and filled with moist air that is in communication with the air above the soil. The root-hairs (101) apply themselves intimately to the wet surfaces of the soil particles, or reach out into cavities filled with saturated air, and are thus able to draw in the well-aerated soil water, with its dissolved food constituents, in sufficient quantity to re- store the loss from transpiration (75) and to distend the newly-formed cells (63). 92. The Soil is a Scene of Constant Changes. The part of the soil in which the roots of plants grow is the field of most potent vital and chemical activities. The dead remains of plants and animals it chances to contain are undergoing decomposition during the warm season, by serving as the feeding ground of myriads of microscopic plants (bacteria). Through their agency nitric acid, which supplies the higher plants with their most valu- able food element — nitrogen (255), is formed in the soil. 68 Principles of Plant Culture. The carbonic acid these remains took from the air during growth is also set free to slowly disintegrate the mineral soil constituents, rendering these soluble and thus avail- able as plant food. In winter, the frost separates the compacted particles of clods, making the latter perme- able to air and rootlets, or flakes off new fragments of rock, thus unlocking new supplies of mineral fertility. 93. The Importance of Organic Matter in the Soil. Crops secure a large part of their nitrogen, as well as of other food substances, from dead organic matter, i. e., animal or vegetable materials. The application of such matter to the soil is, therefore, of great importance, where large erops are expected. Stable and barn-yard manure, the offal from slaughter-houses, tanneries, breweries ete., are all valuable for this purpose, when wisely used. Not only does organic matter in the soil furnish plant food, but while in a partially decomposed state (humus), it renders the soil porous and greatly increases its water- holding power. 94. The Soil Needs Ventilation. The roots of growing plants and the decomposition of organic matter in the soil tend constantly to exhaust the latter of its free oxygen, and to replace this with carbonic acid, which is not used by the roots. Hence, without some interchange between the contents of the soil cavities and the atmosphere above, the roots sooner or later become smothered and perish. In sufficiently porous soil, changes in tempera- ture and in atmospheric pressure, aided by wind and rain, furnish the needed soil ventilation, but in poorly-drained soils, and soils not thoroughly tilled, the roots of plants often suffer from insufficient oxygen. A puddled crust The Root and the Soil. 69 on the surface of clayey soil, due to the compacting influ- ence of rain, is a great hindrance to its ventilation. Earthworms and other animals that burrow in the soil aid in aerating it. 95. Hotbeds Require Especial Care in Ventilation (365), since they usually contain large quantities of decompos- ing organic matter (manure),-which rapidly absorbs oxygen from the soil, replacing it with carbonic acid. 96. Drainage Promotes Soil Aeration by forming an outlet for the surplus water that would otherwise fill the cavities. Although moisture is essential to root growth, land plants do not prosper with their roots immersed in water. True, most plants may be grown in ‘‘ water cul- ture,’’ i. e., with their roots from germination grown in water that is freely exposed to the air; but the roots of land plants soon smother for want of free oxygen when the soil cavities are filled with water, because the soil tends to prevent the water within its cavities from ab- sorbing air. 97. Potted Plants Require Drainage (412), and the out- side of the pots should be kept clean, to admit air through their walls. Potting soil should contain suffi- cient sand and humus (93), so that it does not readily become puddled by watering (31). 98. Potted Plants should be Watered with Care (219). They should receive sufficient water so that the soil par- ticles are constantly surrounded with a film of water, but not so much that the soil cavities remain filled. 99. How the Root-Tip Penetrates the Soil. Darwin made the interesting discovery that the root-tip, in ad- vancing through the soil, does not move in a straight 70 Principles of Plant Culture. line, but has an oscillating motion, which enables it to take advantage of openings between the soil particles. The force with which the root-tip is pushed forward was calculated by Darwin to be at least a quarter of a pound in some cases, while the increase of the root in diameter may exert a much greater force. The root-tip is pro- tected in its passage through the soil by a thimble-lke covering called the root-cap.* 100. Growth of Roots in Length. Since the soil offers more or less resistance to the growth of roots, it is evi- dent that the roots of land plants can- not elongate through their whole length at once. On the contrary, the part that increases in length is limited to a short portion just behind the root-tip. Sachs found that the part of the rootlet of the broad bean that increased in length by growth scarcely exceeded half an inch long. In Fig. 28, the parts that are increasing in length are considerably shorter than the root-tips (RT). 101. The Root-Hairs (Fig. 29 B.) de- velop just behind the elongating part of the rootlet and are present in nearly awa iaite cae plants. Their object is to absorb wheat plant. The parts Water, with the food materials it con- AUS main ce Oa tains. The root- hairs greatly increase hairs. RT, root-tips; e, the absorbing surface of the roots, older parts of root. One- just as leaves increase the absorbing fourth natural size. After Frank and Tschireh. surface of the plant above ground. * The root-cap is readily seen without a magnifying glass when a bean plant is grown in water. The Root and the Soil. 71 Each root-hair consists of a single elongated cell (Fig. 30), and is filled with protoplasm, as are the cells in other living parts of the plant (13). As the ex- tremity of the root advances through the soil by growth, new root-hairs are formed in front of the older ones, while those farthest back as “3 rapidly die off, so that only a short portion of a rootlet bears root-hairs at any one time. In * Fig. 27 root-hairs are visible in the left glass, i and in Fig. 6 they may be seen on the hypo- cotyl of some of the germinating corn grains. In Fig. 29A and in Fig. 28 the parts of the root bearing root-hairs are indicated by the sand which adheres to these parts. It is usually difficult to see the root-hairs of plants grow- Fre.29, Sea. Mg in the natural soil, but they may some- lingsofturnip times be discovered with the help of a pocket ae magnifying glass by carefully removing the Frank ana soil particles about the younger roots, when Tscbirch). the silky network of root-hairs may be seen filling the smaller pores of the soil or enveloping the soil particles. Fig. 30 shows a magnified root-hair DTS. Fia@. 30. Magnified root-hair of wheat, in contact with soil particles. (After Sachs). of the wheat plant, closely attached to some particles of soil. The root-hairs are able to take up water freely, even from soil that does not appear very wet, because each soil particle is enveloped in a thin layer of water (91). Still more interesting is the fact, that root-hairs 72 Principles of Plant Culture. are able to dissolve mineral matters in the soil, by their excretions most important of which is carbonic acid, thus permitting the plant to use these matters as food. 102. Root-Hairs Absorb Water with considerable force. It is the absorptive power of the root-hairs that causes water (sap) to flow so freely from injured stems of grape vines* and some other plants in spring, and from wounds in the trunks of some trees in summer. This force is probably due to the absorptive power of the protoplasm in the very active young root cells. It is affected by the temperature of the soil within certain limits, lessening as the temperature falls, and increasing as it rises. Sachs found that the foliage of plants of tobacco and pumpkin drooped when the temperature of the soil in which they were growing was reduced much below 55° F., showing that the roots did not absorb enough water at that temperature to compensate for the loss by transpiration (75). When the soil is warm, on the other hand, the absorptive power of roots may be sufficient to force water from the tips of leaves during cool nights when tran- spiration is slight (63). 103. Only the Youngest Parts of Roots are Active in Absorption. The part from which the root-hairs have perished absorbs little water, but is chiefiy useful in giving strength to the plant and in conducting the plant fluids. The absorbing part of any given rootlet is, therefore, comparatively short. It follows that the amount of nourishment a given plant can receive will depend upon the number of its root-tips. Our treatment * Hales found the absorbing force of the roots of a grape vine equal to the weight of a column of mercury thirty-two and one-half inches high. The Root and the Soil. 73 of the plant should, therefore, be aimed at promoting the formation of root-tips. In other words, we should encour- age root branching.** How may we do this? 104. The Branching of Roots in land plants appears to depend much upon the amount of free oxygen (31) and available plant food which the soil contains, so long as the moisture supply is sufficient. In cultivated grounds having a compact sub-soil the roots of annual crops usually branch most freely just at the bottom of, or a little below, the layer of soil stirred by the plow, this being the point at which the supply of oxygen, plant food and moisture are ‘probably best suited to root growth. As the depth of tillage is increased, roots branch freely at a greater depth. Masses of decomposed manure beneath the surface of the soil are usually penetrated through and through with finely-branched roots; and fragments of bone in the soil are often inclosed in a mat of delicate rootlets. These materials furnish plant food in abundance. Roots that penetrate the deeper and more compact layers of soil, on the other hand, and those in poor and dry soils, are usually little branched. It is clear, therefore, that unless a Fig. 31. Showing how root soil is well aerated (94) by a pruning stimulates root branching. proper system of tillage, and by * Root branches must not be confounded with root-hairs. In Fig. 28, branches of the roots appear at e. e.e. The branches bear root-hairs when of sufficient length, but root-hairs never develop into branches. 5 74 Principles of Plant Culture. draining if need be, and unless it contains abundant soluble plant food in the aerated part, the roots of plants growing upon it will not branch freely and hence the plants cannot be well nourished. 105. Transplanting (400) and Root Pruning (416) Stimulate Root Branching. Removing the growing points of either the stem or root (67) stimulates the development Fia. 32. Showing effects of transplanting on root growth of celery plants. The left two plants were transplanted when quite small; the right two were not. (After Green.) of other growing points farther back. Transplanting or root pruning accomplishes this in the case of roots (Fig. 31, p.73). While these operations may not often increase the total number of root-tips,and hence may not enable the plant to take up a greater amount of nourishment, they do cause the development of a more compact root system, which is of great advantage to young plants grown in the seed-bed or nursery for subsequent transplanting. The Root and the Soil. 1D 106. Pricking Off Young Seedlings, i. e., transplanting them from the soil in which they grew to other soil, where they have more room, is an important preparation for their final transplanting. They should receive as good care after pricking off as before, with which they soon develop many new rootlets near the base of the stem, that need be little injured in the later removal (Fig. 32, p. 74). 107. Nursery Trees are Benefited by Transplanting them once or twice before the final planting out, for the rea- sons named above. 108. Root Pruning (416 k) is sometimes employed as a substitute for transplanting, and is especially useful to trees that form few branch roots, as the hickory and walnut. In this case, the tap root is cut off a few inches below the surface of the soil the year before transplanting. 109. The Horizontal Extent of Roots is usually greater than is generally supposed. In upright-growing plants, the area occupied by the roots, as a rule, exceeds that covered by the foliage, while in spreading and trailing plants, the roots are probably not often less in extent than the branches. It appears from the observations recorded that even in such plants as the melon and squash, the horizontal extent of the roots usually equals or exceeds that of the runners. As the diffusion of solu- ble matters in the soil water is probably much hindered by the soil particles, the roots of plants need to travel farther after food than do the branches, which develop in a freely circulating medium. Especially is this true of plants growing in poor soil. 110. The Depth of Roots in the Soil. It appears from the observations recorded that the extreme depth reached 76 Principles of Plant Culture. by roots is generally less than their greatest horizontal extent. The distance reached by the deeper roots is probably governed largely by the nature of the subsoil and the depth of free ground water. But in most annual crops a comparatively small part of the root system de- velops much below the plow line. At the Geneva Ex- periment Station * the chief root-feeding ground of the field and garden crops grown in that locality appeared to be from three to ten inches below the surface, while that of crops making large development of stem and foli- age during summer, as Indian corn, sorghum, tobacco and the Cucurbiiw, appeared to be shallower than in slower-growing crops. A portion of the roots of many crops grow very near the surface of the ground. Branches from the main horizontal roots often grow upward as well as in other directions. At the Geneva Experiment Station, numer- ous roots of sweet corn were found within an inch of the surface, and in a tall-growing southern corn, roots of con- siderable size started at a depth of only half an inch. The main root of a Hubbard squash vine was traced a distance of ten feet, in which its depth varied from two to five inches. In tobacco fields, the rootlets sometimes literally protrude from the surface of the soil in warm, wet weather (232). (1. The Rate of Root Growth in rapidly developing plants is often extremely fast. President Clark, formerly of the Massachusetts Agricultural College, concluded from very careful examinations and measurements of the roots of a squash vine grown under glass, that rootlets ~~ * See Report of New York Agricultural Experiment Station, 1886, p. 165. The Root and the Soit. HE must have been produced at the rate of at least one thousand feet per day during the latter part of the growth period. 112. Relation of Roots to Food Supply. In the extent of ground occupied, root growth is relatively less in moist and fertile soils than in poorer and drier ones, but the roots are proportion- ally more branched. In wet seasons, a given plant has less extensive root development than in drier seasons, because the roots may then se- cure the needed food and water from a smaller area. Nursery trees grown on fertile soils have a more compact root system than those grown on poorer soils. 113. Root Tubercles. Plants belonging to the natural order Legumi- -Ool- j- fie Fra. 38. Young clover plant showing MOSH: (le gu-ml-no swe), tubercles on roots (t). (From nature). of which the clover, pea and bean are familiar examples, when grown in ordinary soil have swellings or tubercles on their roots (Fig. 33), These are caused by micro-organisms, probably of the class known as bacteria, and are of special interest, be- cause the organisms producing them render nitrogen of the air available as plant food. Plants have no power to utilize directly the free nitrogen of the air (260). 78 Principles of Plant Culture. SECTION VII. THE STEM 114. As the root develops from the base of the hypocotyl, the plumule, or primary shoot (56), develops from the other end and becomes, at least for a time, the main axis or stem of the plant. 115. The Stem is, generally speaking, the part of the plant that supports the leaves. In excep- tional cases, aS in the potato (Fig.34) and quack grass, a part of the stem grows beneath the ground, on which the leaves usually do not develop (un- derground stems); and ina few plants, as In some cacti, the stem performs the Fig. 34. Potato plant. U. st., under- whole office of ground stems; R, roots. The tubers are the leaves, The stem thickened distal* ends of the underground stems. Much reduced. (After Frank and may be strong Tschirch.) enough to support its own weight, as in trees and shrubs, or it may depend upon other objects for its support, as in vines. 116. Nodes and Internodes. Unlike the root, the stem is developed in successive sections, comparable in part to the stories of a building. Each section or story * See foot note on page 79. The Stem. 79 consists of one or more leaves, attached to the distal* end of a portion of the stem. The part of the stem to which the leaf or leaves are attached is called a node and the part below the node, or in the stem as a whole, the part between the nodes, is called an internode. The nodes are distinctly marked in the younger stems of most plants by a slight enlargement or by leaf- sears, if the leaves have fallen (Fig. 39). The nodes are centers of vital activity and are the points at which lateral growing points (buds (128) ) are normally formed, and whence 9-4 roots usually start first in cuttings and layers (358, 349). 117, The Stem Lengthens by Elon- gation of the Internodes, as well as by the formation of new ones. As the internodes soon attain their ulti- mate length, it follows that the stem lengthens only near its distal end. An internode that has once ceased Fie. 35. Nodes (N); A, of : the box elder, Negundo acer- Clongating does not usually resume pe aia wild grape, it, hence the internodes of peren- nial plants that are only partially elongated at the close of the growing season in general remain undeveloped. When growth is resumed in spring, the formation of a comparatively long internode beyond the very short ones of autumn usually forms a percepti- ble ring about the shoot, which enables us to readily * Distal means farthest from the point of origin, i.e., the point at which growth started. It is opposed to proximal, which means nearest the point of origin. 80 Principles of Plant Oulture. locate the point at which growth started in spring (Fig. 36). Indeed we can often determine the amount of growth that took place during the preceding season or even farther back. 118. The Ultimate Length of the Internodes in any plant, or any part of a plant, depends upon the rate of growth— rapid growth producing long internodes, and vice versa. In the same species, therefore, the average length of the internodes is much greater in vigorous, young plants than in old ones; in the main, central shoot than in the branches, and when growth is well started in spring than dur- ing its decline in autumn. The diameter of young internodes that are not unduly shaded is generally in proportion to their length, hence rapidly-growing shoots are usually thicker than slower-growing ones. We can judge of the com- parative vigor of nursery trees by observing the length and diameter of the internodes, ae *© 119. The Stem Elongates Fastest just behind new and the growing point (67), and at least in young olterwood Slants, just behind the primary or original growing point (56). When we desire to check growth of the stem, therefore, we remove the terminal growing point by pinching (416 a). 120. Pinching Stimulates Branching because removing the terminal growing point stimulates the development of other growing points farther back (105). The Leaves. 81 Section VIII. THE LEAVES We have seen that one or more leaves are normally formed at each node of the stem (116). 121. The Function of Leaves is food preparation (59). Since food is prepared only in the light, the cells of leaves are in most plants so arranged as to best expose them to light, i. e., in thin, more or less horizontal plates, which are strengthened and at the same time suppled with water by a network of vascular bundles (68) con- necting with the stem. They are protected by the epi- dermis (65), but have access to air through the stomata (66). Each leaf, like the stem and root, is developed from one or more growing points (67), one of which forms the terminus of each lobe or division of the leaf. Cell divis- ion in the leaf is confined to the near vicinity of the growing points, hence an injury to the older part of the leaf is not repaired further than by the formation of callus (73) over the wounded parts. 122. The Cultivator Should Provide for Normal Leaf De- velopment. Since the protoplasm of the plant is nour- ished by prepared food (59), and since food preparation in most plants takes place almost wholly in the leaves (121), it is of first importance that the plant be so cared for as to promote normal leaf development. Without this, good crops are impossible. The plants must be grown far enough apart so as not to unduly shade each other; insects and fungi must not be permitted to prey upon them when it is possible to prevent it; and the leaves must not be needlessly removed or injured. 82 Principles of Plant Culture. 123. How Far Apart Should Plants be Grown? When the finest developed plants, or parts of plants, as fruits, flowers, leaves, stems or roots is desired, the plants should not be grown so near together as to interfere with each other’s leaf or root development. But when the largest crop from a given area is of more importance than the development of the individual plant, as with grain crops, the loss from a limited amount of shade and crowding will be more than made up by the increased number of plants. In this case, the amount of crowding that will give the maximum yield will depend much upon the fertility and moisture of the soil, and must generally be determined by experiment. 124. Stem and Root Development Depend on the Number of Leaves. Since the vascular bundles, through the formation of which the stem and root increase in diame- ter, originate in the leaves (68), the size and firmness of the stem and the root depend somewhat upon the num- ber of leaves the: plant bears. The more leaves it has, the more solar energy it can transform into plant tissue. The stem is larger beneath a vigorous leafy branch, and if cut off some distance above a branch, the part thus deprived of its foliage ceases to grow, unless it develops new leaves. Trees growing in the dense forest, where their lower branches continually perish through lack of light, have tall, but very slender trunks, and their wood is soft because it contains comparatively little fibrous tissue, while other trees of the same species, in the full light of the open field, through the large amount of solar energy absorbed by an immense number of leaves, develop massive trunks, of which the wood, being The Leaves. 83 packed with fibrous tissue, is much stronger than that of the forest tree. 125. The Comparative Size of Leaves on a given plant depends much on the water supply during their forma- tion. The leaves of sap-sprouts (224), that take an undue proportion of water, are usually very large, and in upright-growing plants, the leaves on the more nearly vertical shoots are usually larger than those on the hori- zontal ones. The more vigorous the plant, the larger, as a rule, are its leaves, and the softer is its woody tissue. In plants grown from seed to secure new varieties, large leaves may be, taken as evidence of superior root development, which implies capacity to endure drought and, therefore, hardiness. In the apple, the large-leafed varieties are, as a rule, hardier than others, probably because their vigorous roots supply the needed water during the dry season, thus enabling the tree to mature healthy wood and buds which can pass severe winters unharmed (175). Crops grown for their leaves, as cabbage, lettuce, to- bacco ete., are especially liable to be curtailed by drought, and hence should be given the culture that best promotes soil moisture, as abundant surface tillage and liberal manuring (232). 126. Leaves are usually Short-Lived because they be- come clogged with those mineral matters taken up with the soil water which are not used by the plant (64) and which do not pass off in transpiration (75). In most annual plants (337), the older leaves become useless from this clogging and die before the stem is fully developed, and in most perennials the leaves endure but a single 84 Principles of Plant Culture. ‘season. In the so-called evergreen plants, in which the leaves are usually very thick and are often well protected against evaporation by a very strongly developed cuticle (65), the leaves rarely live more than a few years. 127. The Manurial Value of Leaves, that mature on the plant, is usually small, since the more valuable fertilizing materials they contain pass into the stem before the leaves ripen (171). The mineral matters coutained in largest quantity by leaves are those that are not used by the plant, but have been deposited within them during transpiration (126). SEecTion IX. THE Bubs 128. The Buds. Each tip of the stem (67) is in most plants protected with a covering of rudimentary leaves or leaf-scales, and the tip with its leafy or scaly covering constitutes a bud. A bud forming the apex of a shoot is called a ter- minal bud; one at the junction of a leaf with the stem (axil) is called an axillary or lateral bud (Fig. 35). Each bud generally includes one terminal- and several axillary growing points. Aside from these, which in the stem exist only in the bud, a bud is simply a part of the stem in which the leaves and internodes Fic.37. Buds, are in the embryo stage. tae 3 : ee In most perennial plants, the rudimen- ; tary leaves that form near the terminus of the young shoots at the latter end of the growing season are changed into bud-scales, which serve to protect the growing points within from excessive moisture and sud- The Buds. 85 den changes in temperature. Axillary buds which have not yet formed leaves, are clothed with similar scales. Buds inclosed with scales are often called winter buds. To more effectually shut out water, the scales are coated with a waxy or resinous layer in some plants, as the horse- chestnut and balm of Gilead, and to protect them from too sudden changes of temperature, they are lined in: other plants, as the apple, with a delicate cottony down.* 129. Nature Provides very Early for the Next Year’s Growth in perennial plants. With the expansion of each leaf, a tiny bud begins to form at its axil, destined if need be to become a branch the following year. Some- times, however, especially in very vigorous shoots, the embryo buds at the axils of the earliest formed leaves. remain undeveloped. The more rapid the growth of the shoot, the less developed, as a rule, are the lateral buds. Cions (386) and cuttings (358) should not, therefore, be- taken from excessively vigorous shoots. 130. Branches Develop from Lateral Leaf-Buds (132). In trees and shrubs (woody perennials), the lateral buds. do not usually push into growth until the spring after their formation, unless the terminal bud is injured. Indeed, they may never push into growth. Some lateral leaf-buds, especially those most distant from the terminal. bud, usually remain dormant, through want of light or- nutriment, and are overgrown by the enlarging stem the. following year. Such overgrown buds, stimulated by destruction or injury of the stem above, sometimes push into growth years after their formation. * A vertical section of the onion bulb may be used as a magnified illus-- tration of a bud asit appears in winter, and that of a head of cabbage, of. a bud unfolding in spring. 86 Principles of Plant Culture. We can usually decide if detached dormant shoots of trees and shrubs, as cions and cuttings, are of the preceding year’s growth or older, since, as a rule, only wood formed the preceding year has visible undeveloped buds.* 131. Adventitious (ad-ven-ti’-tious) Buds. Although buds are normally formed only at the nodes of the stem, they may under the stimulus of unusual root pressure (102) be formed without regard to nodes. The trunk of a vigorous elm, willow or horse-chestnut tree, cut off early in the season, often develops a multitude of buds from the thickened cambium (69) at the top of the stump, and a cirele of shoots often spring up about the base of a tree of which the top has been injured by over- pruning or severe cold. Such buds are called adventitious. It is, however, often difficult or impossible to distinguish between adventitious buds and those that have been previously overgrown (130). The roots of many plants, as the plum, choke cherry, raspberry etc., develop adventitious buds freely, especi- ally when injured, a fact often utilized in propagation by root cuttings (376). 132. Leaf-Buds and Flower-Buds. Buds may contain only rudimentary leaves, or they may contain rudimen- tary flowers, with or without leaves. The former are called leaf- or wood-buds, the latter flower- or fruit-buds. Flower-buds are modified leaf-buds. Both originate in the cambium layer (69) and are normally located at the apex of the stem or in the axil of a leaf (128-129). * Exceptions to this rule are not uncommon in unthrifty trees and shrubs. The Buds. 87 133. Flower-Buds are often Readily Distinguished from Leaf-Buds by location and appearance the same season in which they are formed, which enables the fruit grower to anticipate his crop. In the peach and apricot, and in many varieties of plum, a flower-bud is normally formed on each side of the leaf-bud in the young shoots of bear- ing trees (Fig. 38). In the apple and pear, the flower- buds are less definitely located, but are mostly formed on the short, thick, wrinkled and crooked branches from wood three or more years old (fruit spurs, Figs. 42 and 43). In some fruits, as the apple, cherry and peach, the flower-buds are usually thicker and more rounded A Fia. 38. Fie, 39. Fia. 40. Fia. 41. Fic. 38. Flower-buds of Pottawattamie plum, Prunus angustifolia. The central bud of each group is a leaf-bud. Fia. 39. Fruiting branch of European plum, Prunus domestica. B, young wood. A, wood of preceding year. §, fruit spurs. Fie. 40. Fruiting branch of Morello cherry, Prunus cerasus. B, young wood. A, wood of preceding year. F, clusters of fruit-buds. Fia. 41. Leaf-buds of the apple. Fia. 42. Fruit-bud of apple (F). Ail are reduced one-half. (Figs. 39, 40, 41 and 42 are after Barry). 88 Principles of Plant Culture. than the leaf-buds, especially toward spring. Close and persistent observation will enable the horticulturist to early distinguish the flower-buds in many of his perennial plants. In the apple and pear, the buds on the so-called fruit- spurs are not necessarily flower-buds, but some seasons all are leaf-buds. How early in the life of the bud its character is fixed, or if flower-buds ever change to leaf- buds before expanding, does not appear to be known. The fact that leafy shoots sometimes grow out of the center of flowers, and that petals (143) are sometimes Fig. 44. Fruit spur of the pear. Reduced one-half. (After Barry). Fic. 43. Fruit spurs of Geveloped as leaves, suggest that the apple. A, points at such a change may occur. which apples were detach- ed the preceding year; W, In the grape, flowers appear at wrinkles marking points i + at which fruit and leaves He first two, three or four nodes of were detached in previous the young shoots that grow from oi la seas stems formed the preceding season (canes) and the shoot continues to grow beyond the flowers. The raspberry, blackberry and dewberry bloom like the grape, except that the flowers form the end of shoots. In the strawberry, the terminal bud of the The Buds. 89 preceding year’s growth flowers in early spring. In these plants, therefore, the flower-buds are inclosed by the same bud scales that inclose the leaf-buds, hence it is more difficult to foresee the number of flowers than in the tree fruits. A knowledge of the location of the flower-buds is very important in pruning plants grown for their flowers or fruits (416). 134. The Comparative Vigor of Leaf-Buds on a given shoot depends somewhat upon their location and the length and diameter of the internodes. The terminal bud, when uninjured, is usually the most vigorous one, and the vigor of the buds, as a rule, diminishes as we recede from the terminal bud. On a given plant, the buds are usually less vigorous on shoots having very long and thick internodes, i. e., the shoots that grew very rapidly (118), than on shoots with internodes of average length and thickness (129). The more vigorous buds are often tenderer than the less vigorous ones, since they are usually farther developed the season in which they are formed. Cions (386) or cuttings (358), of dormant wood, should be made from shoots having internodes of average length and thickness and with plump, well-matured buds. In the potato tuber, which is the thickened terminus of an underground stem (Fig. 34), the most vigorous shoot comes from the terminal bud (the so-called seed- end), hence rejecting this part of the tuber in planting, as has often been recommended, is detrimental to the erop. 135. Conditions Affecting the Formation of Flower-Buds. The majority of cultivated plants are grown either for 6 90 Principles of Plant Culture. their flowers or the product of their flowers, i. e., fruit or seed. But the flower is not an essential part of the plant, and instead of contributing to its welfare, as do the leaves and roots, it actually consumes a part of the plant’s reserve food (140). As might be expected, there- fore, perennial plants do not always produce an annual crop of flowers, even when well developed in other direc- tions, hence the grower is often disappointed. Since flowers can only come from flower-buds, a knowledge of the laws that govern the formation of these would often be valuable to the cultivator. Unfortunately, this sub- ject has received less attention than is due to it. Two principles may be cited, however, which if they do not explain all phenomena connected with the formation of flower-buds, are of sufficient general application to have great economic value, viz: A— Plants form flower-buds only when they contain re- serve food (85). B—A water supply insufficient for rapid growth may suf- Jice for abundant food formation (59). In support of the first of these propositions, we men- tion: (a) Rapidly-growing plants rarely form many flower-buds because the food is used up in growth as fast as formed. (b) Checking such rapid growth, by remov- ing the growing points of the stem or root (67), or by withholding water, results in an accumulation of food and is often followed by an abundant formation of flower- buds. (c) Obstructing the rootward current of prepared food (80), as by ‘‘ringing’’ (416g) causes an accumula- tion of food above the obstruction and is often followed by the formation of flower-buds in that part. The Buds. 91 In support of the second proposition we mention: (a) Florists often bring their plants into bloom at a de- sired time by withholding water. (b) The flower-buds of most out-door plants are formed during the drier part of summer,* when a restricted water supply prevents rapid growth, but when abundant sunlight and fully- expanded foliage favor food formation (59). We may infer, therefore, that treatment that favors the accumulation of reserve food promotes the formation of jlower-buds, a proposition that is borne out by the exper- ience of practical cultivators. 136. How can we Promote the Accumulation of Reserve Food? Three general principles may be cited: A — Provide for abundant food formation by giving suf- ficient light and air and by protecting the foliage from attacks of insects and fungi (Chap. III, Section VIT). B— Provide sufficient plant food in the soil to satisfy all requirements of food formation (Chap. III, Section VI). C— Provide for a moderate check to growth after the proper amount of growth has been secured. In the greenhouse where conditions are under control, these principles are readily followed, and the skilled florist rarely fails to secure bloom at the proper time, He gives the desired check to growth by permitting the roots to become densely matted in the pot (pot-bound), by withholding water, or by pinching the tips of the more vigorous shoots. With out-door perennial plants, as fruit trees, the problem is more difficult, since condi- tions are Jess under control than with plants under glass, * Plants that live over winter and bloom in spring, as the apple, straw- berry etc., form their flower-buds the preceding season. 92 Principles of Plant Culture. but the principles just cited should always be kept in mind and carried out so far as possible. We can give sufficient light and air by planting the trees a sufficient distance apart (123) and by proper pruning (Chap. IV, Section IIT). If the soil is properly drained, the natural depletion of soil water about midsummer will usually give the needed check to growth. In wet seasons, the drying of the soil may be promoted by stopping cultivation before midsum- mer and sowing a crop that will increase evaporation from the soil, as oats, clover or buckwheat. 137. Pinching Promotes Flowering (416). In certain cases, aS with seedling trees of which we would early know the quality of the fruit, we may give an abnormal check to growth by pinching the tips of the young shoots or by root pruning (416k). These operations should be performed early in summer, before the period of flower- bud formation, and if the tree is not too young, flowers and fruit may be expected the following season. Frequent transplanting of young trees acts like root pruning, especi- ally if the tap-root is severed. Such harsh measures, however, while they promote early fruiting, doubtless tend to shorten the life of trees. 138. Ringing (416¢) often Causes the Formation of Flower-Buds in otherwise barren trees, by obstructing the rootward current of prepared food. Twisting a small wire about the branch, violently twisting the branch itself, or simple bending and fastening it in an unnatural position, answers the same purpose. But these devices probably weaken the tree and shorten its life by robbing the roots of their normal food supply and are excusable The Flower. 93 only in special cases, as with seedling trees. It is gener- ally a reproach to the care or knowledge of the cultiva- tor, if his trees of bearing age cannot form flower-buds without such choking. Fruit trees grafted on slightly uncongenial stocks some- times flower and fruit more freely for a time than when growing on their own roots, because the imperfect union of cion and stock (383) forms an obstruction to the root- ward food-current. SEcTION X. THE FLOWER 139. The Flower is the developed and expanded flower- bud (132). Its office is to provide for the formation of new plants of its kind (reproduction, 16). Some plants, as the quack grass,* Canada thistle + and horseradish { multiply freely in nature without the aid of flowers, and nearly all plants may be multiplied in culture by other means, but in most of the higher plants, the flower is the natural organ of reproduction, and the only organ devoted solely to this end. 140. Flowers Tend to Exhaust the Plant, since they are formed from the food prepared by the leaves. But since flower-buds are not usually formed until the needs of growth are provided for (135A), the normal production of flowers does not injure the plant. In certain cases, however, aS in plants weakened by recent transplanting or in cuttings (358), flower-buds should be removed as soon as discovered, to prevent their exhaustive influence. 141. The Parts of the Flower. The complete flower is -composed of four different parts or organs. A knowledge * Agropyrum repens. ft Cnicus arvensis. t Nasturtium Armoracia. 94 Principles of Plant Culture. of these parts is of great importance to the botanist in determining species, and also to the plant breeder who would practice cross-pollination (152, 440), hence we need to consider them in detail. The cherry blossom, of which a vertical section appears in Fig. 45, will serve as our first example. 142. The Calyx (ca/-lyx). Beginning at the bottom, the part marked C in the figure, is called the calyx. This is green in the normal cherry flower. In some plants, as the flax, the calyx is composed of several distinct, more or less leaf- like parts, each of which is called a sepal (se’pal). In the cherry blossom, the sepals are united nearly to the top. The calyx is Fra. 45. Section of cherry blossom. C calyx; usually green, but Cor. corolla; S stamens. in the tulip an d some other flowers it is of another color. In the apple and pear, the calyx becomes a part of the fruit, and its points are visible in the depression opposite the stem. 143. The Corolla (co-rol’-la)._ The more spreading part of the cherry blossom, which is normally white (Cor., Fig. 45) constitutes the corolla. In the cherry, the corolla consists of five distinct parts, only three of which appear in the figure, called petals (pet’-als). In many plants, as the pumpkin and morning glory, the petals are united. In other plants they are united a part of the way to the top. The corolla is usually of some other color than green. The Flower. 95 144, The Stamens (sta’-mens). Inside the corolla is a group of slender organs (S 8, Fig. 45) called stamens. Each stamen consists of three parts, viz., the long and slender portion, connected with the calyx below, called the filament (fil’-a-ment); the swollen part at the top, called the anther (an’-ther); and the yellow dust, found upon or within the anther, called the pollen (pol’-len). Each grain of pollen is a single cell, which if fertile (153) contains living protoplasm. The pollen is set free at maturity. 145. The Pistil (pis’-til). The column-like part in the center of the flower is called the pistil. This also con- sists of three principal parts, viz., the enlarged flattened summit, called the stigma (stig’-ma); the egg-shaped base, called the ovary (o0’-va-ry); and the slender part connecting the two, the style. The ovary contains a smaller, egg-shaped part, called the ovule (o’-vule), which when developed becomes the seed. Many flowers have more than one pistil, and many ovaries contain more than one ovule. Recapitulating, the parts of the flower are, in the or- der we have considered them: a—The calyx; when divided, the parts are called sepals. b—The corolla; when divided, the parts are called petals. c — The stamens; the parts are the filament, anther and pollen. d— The pistil or pistils; the parts are the stigma, ovary and style. The ovary contains the ovule or ovules. 96 Principles of Plant Culture. 146. The Parts of the Flower Vary in Form in different species. In the pea flower (Fig. 46) the five petals, shown separate- ly in Fig. 47, are not only quite unlike the petals of the cherry flower, but, as appears, they are unlike Peer Flower of the pea, Piswm sativum, (After each other. The Fru. 47. The same dissected, showing variation stamens (Fig. 48 in form of the petals. (After Figuier). st. ) and the pis- til (Fig. 49) of the pea are also quite different in form from those of the cherry. The variety of form in the parts of the flowers of different species is almost infinite. 147. Certain Parts of the Flower are often Wanting. The flowers of the maple have no corolla; those of the willow have neither calyx nor corolla; certain flowers of the pump- kin, Indian corn and many other plants have no stamens, while other flowers of the same species have no pistils (154). In many varieties of the American plums* the pis- til is often wanting. 148. Composite (com-pos’- lite) Flowers + are made up of a ae é Fra. 48, Fie. 4, several individual flowers in Fre. 4s. Stamens (st) and pistil the same flower-head. The Of the pea, Piswm sativum. So ‘ Fia. 49. Pistil of same alone. sun-flower (Fig. 50) is a (After Baillon). * Prunus Americana, P. angustifolia, P. hortulana. ¢ The plants having composite flowers form an extensive family in botany, called Composite. The Flower. 97 familiar example of a composite flower. One of the separate flowers is shown in Fig. 51. At the outer edge of the flower-head, is a row of individ- ual flowers, each of which has a long, yellow, petal-like appendage (Fig. SS 52), called a ray. The flowers bearing rays are called ray- flowers. Some com- Fig. 50. Cross-section of flower-head of sun- posite flowers as flower, Helianthus annuus. Reduced. The flor- the tansy* are with- ets appear closely crowded in the center of the head. out ray-flowers. 149. The Flowers of the Grass Family+ to which the cereals belong, as well as corn, sorghum, sugar cane ete., are quite different from those of most other plants. In this family, the flowers are arranged in little groups, each of which is called a spike- let. What we call a head of wheat is made up of a number of spikelets, one of which is shown in Fig. 53. Fig. 54 shows the spikelet dissected. The two scale-like parts at the S \\ hf d ah ; me A CAAT base, g. g., are called glumes. pyre. 51, Fig. 52. The similar pair above tipped Fig. 51. Enlarged floret of sun- M flower. with a bristle (the awn or Fre.52. Ray-flower of same. beard) are called the lower or outer pales or palets (pa’- lets) or flowering glumes —to distinguish them from the * Tanacetum vulgare. + Graminee. 98 Principles of Plant Culture. smaller and more delicate upper or inner palets which are just above and inclosed within the outer palets. Between the outer and inner palets are the stamens and pistils, shown separately in Fig. 55. FIG, 53. Fia. 54. Fig. 55. Fig. 58. Spikelet of wheat; st, stamens. (After La Maout and Decaisne). Fig. 54. The same dissected; x, axis of spikelet; g, glumes; b,, b., outer pales; B,, B,, flowers displaced from the axis of outer pales; ps, inner pales; a, anthers; f, ovary. (After Prantl). Fig. 55. Flower of wheat, enlarged; st, stamens; p, pistil; 0, ovary. (After La Maout and Decaisne). 150. Fecundation (fec’-un-da’-tion) is the union of the male and female cell by which the new plantlet is formed.* The ovule produces within itself a female cell which may be fecundated by the male cell produced by the pollen (144). This fecundated cell then grows to form a young plant—the embryo (56), and the parts of the ovule develop about it, the whole forming the perfect seed. Unless the ovule is fecundated, the seed very rarely develops. A flower that contains no pistil and hence no ovule, can of course produce no seed. 151. Pollination (pol-lin-a’-tion), is the access of pollen (144) to the stigma (145) —the first step in the process * The term fertilization (fer-til-i-za’-tion), that has been commonly used for this process, tends to confusion, because this term is also applied to the addition of plant food to the soil. The Flower. 99 of fecundation. During a certain period, the surface of the stigma is moistioned by the secretion of a viscid liquid, to which the pollen grains readily adhere. Fer- tile pollen grains,* alighting on the stigma of sufficiently near-related plants during this period, undergo a process comparable to germination, in which a slender projection from the pollen cell penetrates the stigma, passes length- wise through the center of the style and enters the ovule, where fecundation occurs. Pollination is not necessarily followed by fecundation. In young plants, and in older plants that are lacking in vigor (9), flowers often fail to produce seed or fruit, even when pistil and stamens appear to be normally devel- oped, and pollination occurs. In some flowers, as in the pea, the stigma is brought into direct contact with the pollen by the elongation of the style, but in most plants the pollen must be trans- ferred to the stigma by some outside influence, as by in- sects, the wind, or gravity. Most flowers which have a showy corolla or calyx, or secrete nectar, or yield a fra- grant perfume, depend largely upon the visits of pollen- loving or nectar-loving insects for pollination. The showy parts and the perfume serve as signboards to direct the wandering insects to the flowers. Pollination is favored by a warm, dry atmosphere. 152. Cross-Pollination occurs when the stigma receives pollen from a different plant, especially from a plant of a different variety or species (21). The fecundation resulting constitutes a cross or hybrid, as the case may be * Fertile pollen is pollen that is capable of fecundating female cells of its own species. 100 Principles of Plant Culture. (23). Cross-pollination is often performed artificially (440). Close- or self-pollination occurs when the stigma receives pollen from its own flower or plant. 153. Cross-Pollination is Advantageous in plants, as Darwin’s careful experiments have shown. The seeds formed are usually more numerous and larger and make more vigorous plants than with close-pollination. Es- pecially is this true when the parent plants have been subjected to different growth conditions in previous gen- erations. Nature favors cross-pollination in perfect- flowered plants by numerous adaptations tending to pre- vent self-pollination, as maturing the pollen either before or after the receptive stage of the stigma, or so locating the stamens that the pollen is not readily deposited on the stigma of the same flower.* In some cases, pollen is infertile on a stigma of the same flower or plant that is abundantly fertile on stigmas of other plants of the same species (155). 154. Perfect, Moncecious (mo-nce’-cious) and Dicecious -(di-ce’-cious) Flowers. Flowers containing both stamens and pistils (or pistil), as in the apple, tomato, cabbage etc., are called perfect or hermaphrodite (her-maph’-ro- dite); those containing but one of these organs, as in the melon, Indian corn ete., are called imperfect or unisexual (u'-ni-sex’-u-al).¢ Flowers of the latter class are called monecious when the stamen-bearing (staminate (stam’-i- * Darwin’s work “On the Various Contrivances by which Orchids are Fertilized by Insects’? describes many most interesting adaptations of this sort. t+ The terms hermaphrodite, unisexual and bisexual, though often ap- plied to flowers, are inaccurate. The Fruit and the Seed. 101 nate) ) and pistil-bearing ( pistillate (pis’-til-late ) ) flowers are both produced on the same plant, and diwcious when produced on different plants only, as in the hop and date. In a few plants, as the strawberry (155) and asparagus, some individuals produce perfect, and some imperfect flowers. 155. Planting with Reference to Pollination is important. in certain plants. All dicecious plants (154) intended for seed or fruit must have staminate and pistillate plants growing near together or they will not be productive. The hop plant and date palm are of this class. The flowers of many of our most productive varieties of strawberry yield little or no pollen and are unproductive, unless growing near pollen-bearing sorts Fie. 56. FIG. 57. Fre. 56. Imperfect flower of the straw- (Figs. 56,57). In many bee varieties of American Fic. 57. Perfect flower of same. The 1 aor ini numerous pistils appear in a circular Pp ums an in certani mass at the center, around which the varieties of the pear, stamens are seen in Fig. 57. the pollen, even though produced freely, is infertile on stigmas of the same variety. To insure fecundation, it is wise to mingle varie- ties in fruit plantations rather than to plant large blocks of a single variety. SEcTION XI. THE FRUIT AND THE SEED 156. The Fruit, as the term is used in botany, is the mature ovary with its contents and adherent parts; it may be hard and dry, as in the wheat and bean, or soft. 102 Principles of Plant Culture. and pulpy, as in the apple and melon. But in common language the term fruit is limited to the pulpy and juicy part of certain plants that normally contains or supports the seed or seeds. To avoid explaining botanical terms, we use the word in the latter sense. In this sense, the fruit serves the plant by attracting animals that can assist in disseminating the seed. The seed, as we have seen, is the fecundated and ma- ture ovule (145), and its normal office is reproduction (16). 157. The Fruit Rarely Develops Without Fecundation of the germ cell of the ovule (150). Varieties of the apple and pear have appeared, however, in which the pulp develops without seeds. The fruit of the banana is almost invariably seedless. The cucumber, grape, orange and fig sometimes develop their fruit without fecundation of the germ cell. These instances are all exceptions to the general rule. 158. Seed Production Exhausts the Plant far more than other plant processes. The seed prepares little or no food, while it removes from other parts of the plant a comparatively large amount of prepared food, which it stores up in a concentrated form as a food supply for the embryo (55). Many plants (all annuals and biennials) are killed the first time they are permitted to seed freely, and perennials are often weakened by excessive seeding.* 159. Prevention of Seeding Prolongs the Life of Plants. Many annual flowering plants, as sweet peas, dianthus etc., that soon perish when permitted to mature their * Double-flowered varieties of the annual larkspur (Delphinium), that bear no seed, have become perennial. The Fruit and the Seed. 103 seed, continue to bloom throughout the summer if the flowers are persistently picked.* The yield of cucum- bers, peas, beans and other garden crops, of which the product is gathered immature, may be considerably in- creased by preventing the ripening of seed. 160. Overbearing Should be Prevented. Certain varie- ties of some of our cultivated fruits, as the apple, plum and peach, tend to devote an undue amount of their reserve food to fruit and seed production in favorable seasons, which if permitted, results in enfeeblement or premature death. The wise cultivator guards against this tendency by thinning the fruit before it has made much growth, thus saving the tree from undue exhaus- tion and improving the quality of the fruit allowed to mature. Thinning should be done as early as the fruits can be properly assorted, and the more imperfect ones should always be removed. The proper amount of thinning will depend upon many conditions, as age and vigor of tree, abundance of crop, fertility of soil, water supply etc. It must be determined by judgment and experience. 161. The Maturing of Seed Injures Fodder Crops. The food value of straw, from which the ripe grain has been threshed, is comparatively small, and that of grass and other crops intended for coarse fodder is much reduced by permitting the seed to ripen before cutting. 162. The Ripening of Fruits. Green fruits assist the leaves in food preparation to some extent, but as they begin to ripen, the process is reversed. Carbonic acid and water are then given off, while oxygen is absorbed. * See foot note on page 102. 104 Principles of Plant Culture. Fruits first become sour from the production of acids which disappear in part at a later stage, while sugar is notably increased. Ripening is favored by warmth and in some fruits by light. Some fruits, as the strawberry and peach, increase rapidly in size during the ripening period, provided the water supply is sufficient. Color is not always an index of maturity. Blackberries, currants, and certain other fruits improve in edible quality for some time after assuming their mature color. Most fruits that have attained nearly normal size, ripen to a degree when detached from the parent plant. Pears are usually improved in quality if picked before maturity and ripened in-doors. The grape, however, fails to. develop its sugar if prematurely picked. After a certain stage of maturity is reached, all vital processes in the pulpy part of the fruit cease, and disor- ganization (decay ) begins, unless prevented by a preserv- ative process. SEcTION XII. THE GATHERING AND STORING OF SEEDS 163. The Stage of Maturity at which Seeds will Germi- nate varies greatly in different plants and bears no direct relation to the time at which the seeds are set free from the parent plant. Seeds of the tomato will germinate when the fruit is little more than half grown, and those ot the pea will germinate when fit for table use. Seeds of the lemon sometimes germinate within the fruit. On the other hand, seeds of the thorn * and juniper rarely germinate until the second spring after their production. * Crataegus. The Gathering and Storing of Seeds. 105, Seeds of many annual and biennial plants, as the cereals, cabbage etc., may germinate as soon as set free by the parent plant, but those of many annual weeds and of most trees and shrubs will not germinate until some months afterward. Seeds necessarily gathered immature will often ripen sufficiently for germination if a considerable part of the plant is plucked and cured with them. Gernunating seeds in which the germination process is stopped by undue drying are not always destroyed. Germination may be resumed on access to water. Seeds of different species differ widely in this respect. Those of the parsnip and carrot cannot endure much drying during germination, while those of the cereals may be repeatedly dried at ordinary temperatures without de- stroying their vitality. 164. Immature versus Ripe Seeds. Seeds not fully grown lack a part of their normal food supply, and their embryo is probably imperfectly developed. If capable of germination, they rarely, if ever, produce vigorous plants. As a rule, the most vigorous plants come from Sully-matured seeds. Tmmature seeds, persistently used, may tend to reduced vigor, early maturity, dwarfness and shortened life. In some over-vigorous plants, as the tomato, slightly immature seed may tend to increased fruitfulness. Slightly immature seeds usually germinate sooner than fully matured ones. 165. The Vitality of all Seeds is Limited by Age, but the duration of the vital period varies greatly in different species. Seeds of the chervil rarely germinate if much 7 106 Principles of Plant Culture. more than one year old, while those of the gourd family, the tomato and celery often germinate well when ten years old. Asa rule, oily seeds, as of Indian corn, rape and sunflower, are shorter lived than starchy seeds, as wheat and rice. The following table gives the average period during which the seeds named are reliable for germination, when properly cared for: * 5 9 Spinach — 5 9 Squash... 10 Strawberry. 10 Tomato... 10 Turnip Cress — Common Ga Cress — Water Cucumber — Eggplant Endive.. a Duration of Duration of Germinating Power. Germinating Power. Average. Extreme. Av. Ext'm. Years. Years. Yrs. Yrs, Artichoke .. 6 10 Gumbo or Okra 5 10 Asparagus 5 x “4 4 Bean ..... 6 10 5 10 Bean —h 3.8 3. 9 Bean—Soy. 2 6 4 9 Beetisccsstesx 6 10 5 9 Borecole or 5 10 Maize or I 2 7 Broccoli .. 5 10 Melon — Musk,. 5 10 Cabbage .. 5 10 Melon— Water . 6 10 Cardoon ve 9 oo Ah 9 Carrot...... 5 10 2 ve Cauliflowe x Oo 10 y 4 Celery. a. & 10 9 Chervi or 3 6 8 Chervi scented, ..... 1 1 10 Chervil — Turnip-rooted ...... 1 1 8 Corn Salad waa “10: Salsafy.. 8 Cress — American 3 Sea-Kale... 7 7 0 6 OUR OS DOT OOD DOD OO 166. Conditions Affecting the Duration of Seed Vitality. A uniform degree of humidity and temperature tends to prolong the vital period of seeds, by causing little drain upon the life of the living cells. Seeds deeply buried in the ground are often capable of germination at a great age, and kidney beans at least one hundred years old, taken from an herbariuin, are said to have germinated. In these cases, the seeds were subjected to few variations in humidity and temperature. * From “ The Vegetable Garden,” Vilmorin, Andrieux & Cie, Paris. The Gathering and Storing of Seeds. 107 Seeds usually retain vitality longer when not removed from their natural covering, probably because they are thus exposed to fewer changes of humidity and temper- ature. Timothy seeds, that become hulled in threshing, lose vitality sooner than those that escape hulling, even when the two sorts have been kept in the same bag. In- dian corn is said to retain vitality longer on the cob than shelled, and longer when the ear is unhusked than if husked. 167. Moisture is an Enemy to Stored Seeds, except for the class that requires stratification (170). A _ little moisture in stored seeds is very liable to cause the devel- opment of fungi (moulds) that may destroy the embryo. Damp seeds are also liable to be destroyed by freezing. It is important that seeds be dried promptly after gathering, for if mould once starts, subsequent drying may not de- stroy the fungus; the latter may resume growth as soon as the seed is planted, thus enfeebling or destroying the embryo before it has time to germinate. Drying by moderate artificial heat (not higher than 100° F. ) is wise with seeds gathered in cold or damp weather. Oily seeds, as of Indian corn, sunflower, and the cab- bage family (cabbage, cauliflower, kohl-rabi, Brussels sprouts, ruta-baga, rape, turnip, mustard) cannot safely be stored in bulk in large quantities, except in cool weather. Seeds are shorter-lived in warm than in cooler climates. The most satisfactory method of preserving seeds in quantity is to inclose them in bags of rather loose texture and of moderate size, and to store these in a cool, dry and airy place. 10s Principles of Plant Culture. 168. Age of Seed as Affecting the resulting Crop. Seeds grown the same or the preceding season produce, as a rule, more vigorous plants than older seeds. They may not, however, in all cases produce plants that are most productive of fruit or seed, for excessive vigor is gener- ally opposed to reproduction, Cucumber and melon plants grown from seed three or four years old are often more fruitful than those from fresh seeds. In crops grown for parts other than fruit or seed, fresh seeds are undoubtedly preferable, but in crops grown for seed or fruit. fresh seed may not always give as large returns as seed of some age, This subject needs further investiga- tion. 169. How Drying Affects the Vitality of Seeds. The vigor of seeds is probably never increased by drying them, but the seeds of most annual and biennial plants may become air-dry without material loss of vitality. The seeds of many shrubs and trees, however, lose vital- ity rapidly by such drying and those of some species are destroyed by it. In nature, seeds of the latter class are usually dropped from the parent plant before becoming dry and are soon covered by leaves or other litter that keeps them moist. Nurserymen either plant such seeds as soon as they are ripe, or if of species that do not ger- minate as soon as ripe, they imitate nature by the process known as 170. Stratification of Seeds. This consists in mixing the freshly-gathered seeds with sand, taking care that the sand is kept moist until the time for sowing arrives. Large quantities of seeds may be stratified in boxes, by placing the moist sand and seeds in alternate layers, or Decline of Growth and the Rest Period. 109 the layers may be built up in a pile on the ground. The sand should be coarse enough to admit some passage of air between the particles and to give perfect drainage. The layers should not much exceed an inch in thickness, ex- cept for the larger seeds, and the number of layers should not be so large as to prevent proper aeration of the mass. Small quantities of seeds may be mixed with sand or porous loam in flower-pots. Moisture may be maintained in the boxes or pots by burying them a foot or more deep in the soil in a well-drained place, or by storing them in a moist cellar. Care is necessary to keep mice and other vermin from stratified seeds. It is well to cover pots in which valuable seeds are stratified, with a sheet of tin or zinc; metal labels are best for distinguishing different sorts of seed. The seeds should remain stratified until sowing time, when they may be sifted out of the sand or sown with it, as is more convenient. Seeds that do not germinate well until the second spring after maturity (163) are commonly left in stratification until that time. Section NII. THe DECLINE OF GROWTH AND THE ReEsr PERIOD 171. Annual plants usually perish soon after maturing their seed. In other plants, a certain period of vital activity is followed by one in which growth gradually declines until it almost or entirely ceases. In woody plants, the cells become thickened and a part of the rudi- mentary leaves change to bud-scales, which inclose the growing point (128). In deciduous (de-cid’-u-ous)* trees and shrubs, the chlorophyll and starch, with most of the * Deciduous trees and shrubs are those of which the leaves perish at the beginning of the rest period. 110 Principles of Plant Culture. potash and phosphorie acid contained in the leaves, are withdrawn into the woody parts (127), while the leaves themselves are detached and fall. The root-hairs also die in many, if not all plants. The leaves of many trees and shrubs assume striking colors as they approach ma- turity. In perennial herbs, the nutritive matters in the foliage and stem are withdrawn to the underground parts. A period of almost complete repose ensues, during which the plant owing to the dormant condition of its protoplasm is able to endure, without harm, ex- tremes of temperature or dryness that would be fatal in its active state. Growth ceases in many trees and shrubs earlier than is often supposed. Most orchard and forest trees of mature age grow little, if any, after midsummer in the temper- ate zones. Cultivation, mulching and manuring tend to prolong the growth period (200). 172. The Rest Period is Not Peculiar to the Temperate Zones, but occurs in the tropics as well. It can be as- cribed in part to the change of seasons, as a few familiar examples will indicate. Tubers of the earlier varieties of the potato, that ripen in northern countries by the be- ginning of August, do not sprout if left in the ground till October, but if stored in a cellar during winter at a temperature little above freezing, they often begin to sprout in March. Bulbs of the crocus, tulip, narcissus, crown imperial ete., that form in spring, lie dormant in the warm soil during summer and early autumn, but start vigorously in the colder soil of the late autumn or the succeeding spring. The buds of many trees, that form in summer for the next year’s foliage and flowers, remain dormant during the hot weather of August and Septem- Decline of Growth and the Rest Period. 111 ber, to push vigorously in the first warm days of spring. The rest period is to be regarded as a normal, if not a necessary factor of plant life. 173. Most Plants Under Glass Require Rest from time to time, or they do not thrive. The rest is provided either by keeping them at a lower temperature than is favorable to growth, or by submitting them to a degree of dryness that prevents growth. The latter is preferable for plants native in the tropics, where they naturally lie dormant during the dry season. 174. The Time of Leaf Fall is an Index of Wood Maturity in healthy deciduous trees and shrubs. In these, the coloring and fall of the leaves in autumn is not necessarily due to frost, but results from the dormant condition that accompanies maturity. As a rule, the more mature leaves are precipitated by the first autumn frosts. Those less mature usually remain until the more severe frosts. In trees with well-ripened wood, the leaves at the tip of the shoots usually fall before, or not later than, those on the older parts of the tree. With poorly-matured wood the reverse is the case. Ina few deciduous trees, as the beech and some oaks, many of the mature leaves remain on through the winter. 175. Hardiness Depends upon the Degree to which the Dormant State is Assumed. Since the most severe cli- matic extreines come during the natural rest period of plants, the ability of the plant to endure these extremes depends upon the extent to which the protoplasm be- comes dormant during the decline of growth. Asa rule, a given plant is hardy (10) in a locality in which the duration and the warmth of the growing season are suf- 112 Principles of Plant Culture. ficient to complete and fully mature its normal amount of growth. Varieties of the apple and other trees, that so far complete their growth in any given locality that their leaves fall before hard frosts. are rarely injured in winter, while those that continue growth until their foliage is destroyed by freezing suffer in severe winters. Deciduous trees are liable to destruction in severe win- ters in a climate where none of the leaves fall before hard frosts, as is the case with the peach, apricot and nectarine in northern United States. 176. Individual Plants Cannot Adjust Themselves to a New Environment, except to a shght extent. The power to complete the annual growth processes and become sufficiently dormant to endure the rigor of the rest period in any given locality is inherited, and not acquired. We are, therefore, able to do very little toward inuring or aeclinatizing (ac-cli-ma-tiz-ing) individual plants to an environment to which they were not adapted by nature. We anay, however, through the variations of offspring (18), secure varieties in some eases that can endure an environment which the parents could not endure. 177. Plant Processes during the Rest Period may not entirely cease. Although food preparation is wholly suspended, root growth and the callusing (73) of injured root surfaces proceed to some extent during the winter in unfrozen layers of soil; and in sufficiently mild weather, the reserve food in the stem gradually moves in the diree- tion of the terminal buds. 178. Cuttings (355 ) of Woody Plants are Preferably Made in Autumn in climates of severe winters and buried in the ground below the limit of hard freezing, in order that Decline of Growth and the Rest Period. 113 callusing (73) and the transfer of food may make some progress before the final planting. 179. The “ Turn of the Year.’? Toward the close of the dormant season, vegetation, as if benefited by the rest, is prepared to start with renewed vigor, even at moderate temperatures. Buds, that remained dormant during the latter part of the previous summer, push into growth with the first warm days of spring, and many seeds, that could not be induced to germinate the preceding autumn, start with vigor as soon as the soil is sufficiently warm. The cause for this energetic resumption of plant growth after the rest period is not well understood, but exposure to cold, in the case of temperate plants, and to prolonged dryness in that of tropical ones, doubtless explains it in part, for it is well known that potato tubers may be in- duced to start their buds soon after maturity by exposing them to the sun a few days, or by placing them for a like time in a refrigerator containing ice. By these means, farmers of Tennessee grow a second crop of potatoes in the latter part of summer and during autumn. Plants under glass usually thrive better after mid- winter than before, and the most favorable time to plant seeds of greenhouse plants is toward the close of the natural rest period. 180. The Round of Plant Life has now been traced, from the first swelling of the planted seed, through the de- velopment of the embryo into the plantlet, the penetra- tion of the root into the dark and damp soil cavities, the absorption and conduction of water with its food mate- rials in solution, co-operating with the sunlight and car- bonic acid in the mysterious laboratory of the leaf, in 114 Principles of Plant Culture. building up the plant body into node and internode, leaf, bud, branch, flower, fruit and seed; through growth de- cline, leaf fall and winter sleep, to the renewed vigor of another springtime. In our study of the round of plant life, we have assumed the environment to be favorable. But in the practical culture of plants, we are constantly meeting with adverse conditions of environment. Talent for plant culture les in the ability to discern these adverse conditions by the appearance of the plant, and in know- ing how to correct them. We will, therefore, next con- sider the plant as affected by unfavorable conditions of environment. The following books are recommended for reading in connection with the preceding chapter: How plants Grow, Gray: Lessons in Botany. Gray; Botanical Text- Book, Gray; A Treatise on the Physiology of Plants, Sorauer; The Soil, King; The Fertility of the Land, Roberts. CHAPTER III THE PLANT AS AFFECTED BY UNFAVORABLE ENVIRONMENT IS!. Factors of Environment. The plant environment is mostly comprehended under the terms, climate, soil, animals and other plants. But as these are more or less complex influences, it is well to analyze them and to con- sider separately the component factors of each. SEcTion I. THE PLANT AS AFFECTED BY UNFAVOR- ABLE TEMPERATURE A—THE PLANT AS AFFECTED BY EXCESSIVE HEAT 182. Transpiration Increases with the Degree of Heat. The most common effect of heat upon plants is the droop- ing of the foliage, due to excessive transpiration (75). With insufficient water, this may occur at a temperature that is normal for the plant. But with a water supply that is sufficient at ordinary temperatures, transpiration may be so much increased by an overheated atmosphere that the roots are unable to supply the plant with sufficient water, and as the result, the cells become partially emptied and the foliage droops. Herbaceous plants in an overheated greenhouse or hotbed are sometimes so prostrated from excessive loss of water as to appear dead, but unless the heat has been sufficient to destroy their protoplasm, or the heated period has been protracted, they will recover when normal temperature and water supply are restored. (115) 116 Principles of Plant Culture. 183. Evergreen Trees are sometimes Destroyed by Un- timely Warm Weather in spring. With a soil so cool that the roots are inactive, a sudden rise of atmospheric tem- perature, especially if accompanied by a drying wind, may so far reduce the water in the leaves of evergreen trees as to cause death of the foliage and even of the trees themselves. This most frequently happens in the seed-bed, in compact nursery plantations, or with recently - transplanted evergreen trees. It is most disastrous on poorly-drained clay soils that have a sunny exposure, and at times when the ground is deeply frozen. The preventives to be observed are, «, means that will prevent the tardy thawing of the ground, as thorough drainage and not too close planting; 0, means that will prevent, in a measure, exposure to the sun, as planting on a northern slope or shading the trees (414); ¢, means that tend to prevent the deep freezing of the soil, as pro- viding wind breaks which tend to retain the snow (204). 184. A Temperature of 122° F. is Fatal to the Protoplasm of most land plants. Aquatic plants and the more watery parts of land plants perish at a somewhat lower temperature. Watery fruits, as tomatoes and gooseber- ries, and the younger leaves of deciduous trees, are some- times destroyed by full exposure to the sun’s rays in very warm weather. An occasional sprinkling of the plants and of the soil about them will usually prevent this result. {85. Plants Under Glass should Not be Sprinkled in Bright Sunshine. Drops of water upon the leaves of plants often act as lenses in converging the rays of the sun, and in a closed greenhouse or hotbed may cause a Plants as Affected by Heat. 117 heat that is fatal to the foliage beneath them. This may explain the brown spots so often observed upon the leaves of indoor plants that have been sprinkled in bright sunlight. Sometimes, but rarely, this trouble occurs in the open air. 186. Sun-scald is the term ap- plied to an affection of the trunk and larger branches of certain not quite hardy trees, usually upon the south or south- west side, in which the bark and cambium layer (69) are more or less injured (Fig. 58). In severe cases, the cambium is totally destroyed, and the loosened bark splits longitudin- ally or becomes detached. The effect is apparently the same as when a tree is exposed to the heat of a fire. Sun-scald is most common in young trees and appears to be due, in some cases, to the superheating of the cambium in summer—in others to a return of severe freezing weather after a period suf- ficiently warm to excite the jie Ss: Shewingenectscren” cambitum cells to activity. A silver maple tree, Acer dasycar- preventive is to shade the ee trunk and larger branches by inclosing them with straw or similar material, or with a lath screen (Fig. 59). ie Sk eed ee Ss 118 Principles of Plant Culture. 187. Potato Foliage is often Injured by Sun Heat in sum- mer, as is shown by the browning of the leaves from the 4 tip and edges toward the center, or ‘ ff on the border of holes made by insects. This affection, known as ¥ tip-burn, is due to the destruction of protoplasm in the cells and is often Xl 774 mistaken for the work of fungus. It {if is most serious in dry seasons. No remedy for it is known, but it may be in part avoided by selecting varieties least subject to it. B—THE PLANT AS AFFECTED BY EX- CESSIVE COLD 188. The Immediate Effect of Cooling the Plant is to check the activity of its vital processes. When a certain degree of cold is reached, the proto- plasm loses its power to imbibe water (63); hence the plant tissues become less turgid, and the foliage droops somewhat. With a sufficient reduc- tion of temperature, ice crystals form