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with closely similar climatic conditions. The history of the development leading up to Rarely a native plant shows similar aggres- the conclusion stated and its general adoption, siveness like ragweed in the north and Eupa- was by no means simple. On the agricultural torium capillifolium in the south. Various side the great exponent was Liebig. But one hypotheses have been advanced to explain the can not to-day read Liebig's numerous works aggressiveness of weeds, but they are simply without realizing how much he floundered in hypotheses. Certainly attempts to find a cor- the maze of conflicting facts and theories and relation between weediness and abundance of the many errors into which he was led. In seeds produced has proved a dismal failure. his combatting of the old humus theory of Nor has any better success been achieved plant nutrition he denied any value whatever toward understanding the contrasting phe- to humus except to supply carbon dioxide, but nomenon of dwindling or "petering-out.” in spite of his teachings the German farmers
The distribution of the species of a genus refused to abandon the use of dung and com- let us say the oaks of the United States-is post. Liebig also clung to the idea that an interesting phenomenon. But why is one nitrogen was of no avail as a fertilizer, as the species circumscribed thus and another de- atmosphere furnished abundant supply. One limited so? To say the species have different of the controversies over nitrogen was finally adaptations is merely stating the fact in other solved by Helriegel and Wilfarth, who estabwords. If we are honest, we must admit, I lished the fact that legumes by the aid of think, our complete ignorance. Now these root nodules were able to utilize atmospheric are samples of a great group of phenomena nitrogen. This is one of the striking landthat confront students of cultivated plants. marks of agricultural science, but it is well They must very properly, I think, also be to remember that the practical effect of considered problems of ecological botany. legumes in rotation was well known to the But the ecology of the botanists has not thus Romans and other ancient peoples. In Hartes far developed enough to be an asset to the “Husbandry," published in 1764, is written: plant culturist. The details of pond margins,
All plants that bear leguminous flowers (as lumountain tops, and seashore strand throw no
cerne, sacrifoin, trefoils, vetches, etc.) enrich the light on why maize or potatoes or wheat thrive ground and of this the husbandman has daily exbetter in some situations than in others. perience in the culture of clover. Now we come to soils. Surely chemical
In its final evolution the Liebig theory of and botanical science have here rendered
soil fertility came to mean that the producsignal service to plant culture. Here again it
tivity of a soil was primarily determined by is well to consider primitive plant culture.
the quantity and availability of the nitrogen, Undoubtedly our prehistoric ancestors must have observed the greater luxuriance of plants phosphorus and potash which it contained. on certain soils, about dung droppings and on
Indeed many modern writers identified these landslides. Certain it is that long ago many
three substances as fertility. uncultured tribes had learned to use dung,
Curiously enough, almost any experienced ashes, fish, leaf mold, seaweeds, and other
farmer will express an opinion after examinasubstances to increase yields. One of the
tion as to the quality of a soil. His standards early results achieved by chemists and botan- of measurements are about as follows: Soils ists was to determine the chemical elements decrease in productivity based on correlation necessary to plant life. Eventually from this with texture in about this sequence-clay developed the idea that all of these necessary loams, loams, silt loams, clays, fine sands, elements were amply abundant everywhere coarse sands, gravel; and in color in about except nitrogen, phosphorus and potash. And this order-black, brown, red, yellow, gray; very naturally substances containing these white. His judgment is therefore based in elements were sought out to use as fertilizers. part on texture and in part on color. Crude
as this basis of measurement may be, it cer- is therefore still almost wholly empirical. tainly has some correlation with productivity. The extension and clarification of this knowlIndeed it may be said that chemical methods edge is, it seems, most likely to be obtained of soil examination resulted in a great neglect by a much more intimate knowledge of the of the study of the more obvious character- plant reactions to each of the soil factors that istics. Unquestionably the best index of the can be controlled and the different combinaquality of a soil is its productivity in crops. tions of these factors. An exceedingly interAnalyses of soil from good spots and from esting recent contribution is that of Bottompoor spots in the same field have sometimes ley, who presents strong experimental evidence revealed no differences. This fact and others to show that highly organized green plants led to the concept that productivity might be must have dead organic matter as part of lessened not only by the absence of a nec- their food. essary element but the presence of a deleter- The effects of one crop upon another often ious agent, and that fertilizers were in some very marked, sometimes beneficial, more often cases at least substances that inhabited the injurious. The nature of these effects is very injurious factor. It is a long story to con- obscure, but it now seems clear that it can not sider this subject, but viewed purely as a be wholly related to the quantitative supply of theory it can explain some things not clarified plant food. These phenomena have been used by the plant food theory. It is well to re- to lend support to the theory that yields are member that many investigators who con- often greatly reduced by the presence of sidered the effects of nitrogen, phosphorus and deleterious substances, in this case supposed potash as due solely to additional plant food, to be excreted by the preceding crop. The nevertheless regarded the effects of lime as theory is attractive in its simplicity and there partly at least due to overcoming an is some evidence in its favor, but there is favorable factor, and the action of still other no clear proof that plants do excrete repellant materials as stimulants, without clearly de- substances. The curious way in which certain fining what they meant by stimulants. The wild plants occupy areas to the complete or available facts were simply the addition of nearly complete exclusion of other species the substance and the end reaction of the might well be due to such a factor. The plant. The different rôles postulated are in effect of one plant upon another is an old the main hypotheses, and the existing body of observation in plant culture, and appears in facts certainly is insufficient to prove any one botanical literature as early as Von Mohl. It of the simple theories. A broader view now is only in recent years that the actuality of coming to be widely held is that the soil is a the fact is established beyond doubt. An complex of very numerous factors, good, bad, understanding of its basic causes is manifestly or indifferent so far as a particular plant is a matter of great importance. At the Rhode concerned, and the end result measured in Island Experiment Stations, onions varied in yield is the balance of the conflicting factors. yield from 13 bushels to 412 bushels per acre To stato it in another way productivity is in a long series of plots, the differences being probably quite as much influenced by qualiti- due solely to the effects of the preceding tative soil differences as by quantitative diver- crops. sities-but the theory that has generally been The subject of tillage is likewise one much accepted is purely quantitative. Such a view involved. The simplest plant culture requires of “ soil fertility” which it must be admitted some disturbance of the soil, even if only to can now be measured only in terms of yield, remove stones or roots. But different methmeans that it is comparable in scope to ods or different degrees of stirring the soil, “weather as applied to the seasonal complex show marked effects on subsequent yields. So of climatic factors. The actual knowledge that great are these differences that the famous we have of soil productivity and of fertilizers Jethro Tull proclaimed the slogan "Tillage is manure," meaning that the same end results The nature of plant diseases and the methcould thus be obtained. Why? There is a ods discovered for their control is a contribubewildering array of hypotheses as to why tion to plant culture for which the botanists tillage tends to increase yields, including of the schools may rightly claim large credit. better mechanical conditions; improved aera- This is clear in spite of the fact that farmers tion; increased nitrification; additional car- and gardeners had before the day of plant bon dioxide; mixing of the soil; elimination pathologists found out the efficacy of blueof weeds; and in dry regions particularly con- stone for wheat smut and sulphur for milservation of moisture. There may be and dew; and against other diseases had developed probably is some truth in all of these ex- resistant or immune varieties. The developplanations but exact data on any of them ment of phytopathology is an index, I believe, are far from abundant. The really definite of what might well happen in other fields of knowledge is empirical, namely, that tillage plant culture, if trained botanical workers will methods do tend to increase yields.
wholeheartedly engage in its problems and The breeding of plants has been a most avoid being attracted more to the purely potent factor in securing larger and better scientific problems than to those of cultural yields. Our knowledge of genetic phenomena import. has been enormously increased in recent The climatic complex of factors is difficult years from the activity incited by the redis- to evaluate. Numerous attempts have been covery of Mendel's law. The effect of this made to correlate growth and yield with the greatly increased knowledge of genetics has curves of temperature and of moisture preinspired many immoderate statements as to cipitation and even specifically to outline the its effect on agriculture. Thus one writer limits of the future extension of wheat culsays “ Through scientific work in the study of ture northward. Thus far these attempts heredity, we have learned to multiply the have not thrown any great light on the probraces of our useful plants so that they may
lems of climatic adaptations. fit in more exactly to the variable conditions I must not omit, however, the recent illumiin which plants must be grown," and that nating contribution of Garner and Allard, Mendel's law " is the basis of most of our who have discovered the remarkable reactions work in the study of heredity and this in of plants to the length of daily illumination. turn has made agriculture scientific.” It is Any one who has cultivated plants has come pleasing to learn that a bit of leaven like to realize the extraordinary way in which they this is able to uplift all agriculture into the behave under different conditions, one might condition called scientific, while presumably say the vagaries which they exhibit. One of it was before something different. As these is the manner in which most plants matter of fact, the practical value of Men- speed up their maturing in fall. The farmer delian knowledge to plant breeding is dis- says the plant is hurrying to get ripe before appointingly small. Witness the innumerable frost. Several vague theories were current improved varieties in all our cultivated plants among plant culturists as to the cause of this long antedating Mendel. Consider the lilies, phenomenon, one that the stimulating factor the roses, the chrysanthemums, the carnations, was the increasing difference between day and the tulips, indeed, any plant much cultivated, night temperatures, another that it was due to and ponder upon the infinite amount of work the increased temperature of the soil. It is that led to their development—all without the remarkable to how high a degree the temperaguidance of any scientific theory. This ad- ture factor was assumed in every periodic mission does not discount the tremendous phenomenon. Garner and Allard have acvalue of the new knowledge of genetics which cumulated a mass of experimental data that gives us so great an insight into the factors leave no room for doubt that the stimulating involved in plant variations.
factor is associated with the daily length of
illumination. Indeed it may be hazarded that hand, Wood was able to increase yields it is this stimulus which normally controls materially by determining the optimum all recurrent periodic phenomena in plants spacing distance. Incidentally this greatly and animals. Just how it is to be correlated reduced the amount of seed necessary which with certain other phenomena which form the in a country where the daily wage is eight basis of Kleb's salts-carbohydrate theory is not cents was a considerable economic factor. yet clear. It is quite possible that entirely Such empirical data as these are highly imdifferent stimuli affect the control of vege- portant in plant culture—and it seems not tative and reproductive phenomena so as to unlikely that they always will have to be give similar end reactions. The Garner- determined by test and not by some matheAllard factor certainly provides a new method matical equation. of approach to study the internal factors that In America, crops are mostly planted as control the plant's activities. It is probably pure culture, in India usually as mixed culnot a wild guess that these internal factors tures, one of the plants commonly a legume. are as numerous as the genetic factors con- Mixed cultures usually outyield pure cultures cerned in the plant's heredity mechanism. As --but except where the crops are garnered by it happens, the approach to this problem and hand, the increased cost of harvesting becomes the progress made in its solution was purely an important economic factor. Why mixed from the agronomic viewpoint and with the cultures, even of the small grains, outyield object of solving an agronomic puzzle. This pure cultures is an interesting phenomenon, is worthy of mention as an illustration of the and one can easily theorize to his heart's confact that the plant culturist gets a different tent. In nature plants are usually, but not contract with plant phenomena from the always, in mixed cultures. Actually we know botanist of the laboratory.
practically nothing of these phenomena except The plant culturist has long been familiar the observed or experimental facts. with the phenomena illuminated by Garner Perhaps no one will contend that a graduand Allard. It is this factor which in the ate of the best botanical courses in America case of field crops led to date of seeding trials is thereby fitted to undertake the cultivation -by which in a purely empirical way the best of any crop, let alone such as require special date of seeding, or planting for each locality knowledge and skill. It is remarkable to how was determined. Any one who has seen plots great a degree that success in growing a crop of millet, for example, planted at succeeding is based on the slowly accumulated results of dates will appreciate how much this factor experience. During the war you will rememalone can affect yields.
ber there was urgent need for a large supply Another important factor affecting yield is of castor beans. It is doubtful if in the whole the spacing of the plants whether secured by history of American agriculture there was rate of seeding or by planting at measured ever a more dismal failure than the attempt distances. It is easy to understand why too to produce these beans. There was an abunsparse seeding will reduce yields and also to dance of theoretical data based on the culture comprehend that crowding may result un- in other countries, but in attempting to grow favorably—but it is doubtful if any other the crop in the United States the handicaps method than actual trials will ever enable us of unadapted varieties and unexpected diffito ascertain the optimum rate of spacing for culties proved disastrous. Perhaps in no other any particular crop at any specific place. industry is the advice "Make haste slowly” Curiously enough as Mooers has shown, more applicable than in agriculture. varieties of maize not markedly unlike have I have endeavored to point out by a few exvery different optima as regards spacing. amples of plant cultural problems how difIn southern India where rice culture is very ferent they are from those considered in the ancient, and the seedlings are transplanted by conventional botany of the schools. The methods of research developed in the labora- who goes about with a tin box over his shoulder tories hardly apply at all to the problems of collecting plants. Perhaps this had something plant culturist, a fact that the laboratory men to do with the loss of caste of taxonomy among have scarcely appreciated, and which has led botanists. It may be questioned, however, if them into a mental attitude disparaging toward the whittling of paraffine sections, or the use the methods of the agronomist and horticul- of strange apparatus in the woods and marshes, turist. It is not insignificant that the discov- or the growing of fungi in test tubes will lead eries of Mendel, of Helriegel and Wilfarth. to a profoundly different evaluation of botany. of Garner and Allard were made possible by I trust that any frankness of expression that problems revealed in the culture of plants and I have indulged in will not be interpreted as all were solved by the simplest of methods. ill-will, but that it will be regarded as an effort Koelreuter's work in hybridization was largely to clear away the mist and to bring about inspired by his knowledge of garden plants, better understanding. Much that has been and was promptly utilized by honticulturists written on the general subject seems to carry though ignored by botanists. One may well the impression that plant culturists have a doubt whether laboratory botanists could ever stolidity that partakes of the ox, and do not have detected the meaning of the dance of the wince at the reflections that come from the chromosomes; though I am not unaware that pens of botanists. It may be well to dispel there were dim guesses as to what they might any such assumption, which in my judgment signify even before the revelations of modern has done incalculable harm to botany. Mendelism.
The points of my thesis are virtually three: One of the phrases too often seen in print is (1) that our knowledge of plant culture is to “revolution in agriculture.” The expression
a very large extent still almost purely empiris almost purely rhetorical and not a state- ical; (2) that there has been a lamentable ment of fact or even of approximation. In
tendency to consider plant culture and its most cases large changes in agriculture have
methods of study as something apart from been due to very simple things, usually the in
botany and not worthy of so high respect; and troduction of a new crop or the sudden expan
(3) that there has been proneness to claim for sion of an old one. Witness alfalfa in the
botany as well as for chemistry an undue west, sorghums in the southwest, rubber in
amount of merit for what they have contribMalaya, the sugar beet in Europe, the increase
uted to agriculture. of cotton in the south following the invention
I have, I believe, as much faith as any one of the cotton gin. I can recall nothing of
in the services that plant science can render to comparable effect on agriculture resultant from a discovery in a botanical laboratory. It may
mankind, and that not by furnishing bread be argued, truly enough, that the knowledge
alone. There is need, however, of broadening of bacteria has revolutionized modern medi
our vision and ideals, of freeing ourselves cine; but the credit for this advance can
from any caste feeling, of recognizing that the scarcely be claimed by botanists. Botany
human race is at least as much interested in seems truly to have neglected its splendid op
food and food production as it is in the fate portunities in its adherence to the fetich of of the synergids, the origin of the angiosperms, pure science.
or the genes of Capsella. For the good of all It may be well to caution that in any at
of us there is every reason to bring about a tempt to unify botany and plant culture, the
closer union of the societies interested in word botany will exercise no hypnotic influ- plants and their culture. Such a union will ence. Rightly or wrongly the word does not
without doubt lead to better mutual underconvey to the public mind something highly standing and reciprocal sympathy. At least desirable and useful. To the ordinary man a
we shall learn that most conventional botanbotanist is a more or less queer individual ists as well as plant culturists are, after all, to