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VIII. The chemical composition of the human body is known more than that of any plant; the chemical composition of our medicines is, as a general thing, more accurately known than that of the kinds of manure. If a chemist, knowing both of these compositions equally well, (of the human body and of the medicaments), wished to cure me of any disease, I would take the liberty of asking him whether he bad studied anatomy and physiology; whether he was able to investigate the cause of my sickness, etc. A physician without physiology is, now-a-days, an impossibility. A scientific agriculturist will be just as impossible, after the lapse of some years, without a knowledge of the physiology of plants.
IX. In order to obtain an accurate knowledge of the life of plants, we must divide the process of vegetation into definite periods; we must follow up closely the development of the whole plant, and of every part of it; we must know them thoroughly. By knowing the plant thoroughly, it is not intended to mean that a knowledge of any one plant is to be accepted as a knowledge of all others; on the contrary, every cultivated plant must be submitted for investigation, as if it were an entirely new object, and had no similarity whatever with any other. It is evident that, to be able to understand more exactly, and to judge the sick plants, it is necessary to become fully acquainted with the healthy ones. And now permit us to sketch an outline of the
TASK OF AN AGRICULTURAL PHYSIOLOGIST.
The chief point of investigation of an agricultural physiologist ought to be this:
The Sowing and the Germination.-Seeding is as yet done according to old uninvestigated rules. As every farmer sows one and the same plant but once a year, he has made just as many and no more experiments—even should he be a good observer—as the years of his practice. This subject, if experimented with physiologically, might be very much advanced, even in one year. The following points ought here to be ascertained :
a. How deep is the seed to be sown? We have information on this point in the agricultural works, but they are inaccurate. Exact information can only be had, if seeds of every kind are sown simultaneously at different depths in small parcels on the same soil, the time required for the plants to appear at the surface to be accurately noted, the process of vegetation closely observed and measured, and finally, the crops compared as to their quality and quantity. Shallow 'sowings are, in general, better in wet soil and fast germinating seeds; deeper sowings in soils which dry readily. Seeds with tenacious coverings and weak germ ought to lie deeper than those with thin coverings and strong germ. Deeper planted
seeds of some kind of plants strike more vigorous roots, but they come up late, etc. All these things bear on the strength of the plant and the qual.
ity of crops.
6. How closely should the seeds be planted ? This is a point not yet sufficiently observed by practitioners. There are, even here in this almost every-day matter, not yet any positive laws for every kind of seed, as there is a want of numerous and simultaneously made comparative investigations. There is surely, for every sowing and every kind of crop.plants, a certain density producing the maximum of crops for a given area; but do we exactly know this density for a single species?
c. Which temperature is most favorable to germination? This is practically a very important point; for the rapidity of germination as well as the
power of the future plant depend greatly on the temperature of germination. Too high a temperature renders the plant rank in its very germination, especially in wet weather; too low a temperature renders the germ putrid and weakens the plant in a high degree. Now, there is a best temperature for every species, and we must not believe that the quickest germination is at the same time the best also. The most important principle herein is, that the temperature of germination differs from the best temperature of vegetation. As to the former, it may happen that the entire crop depends upon the circumstance of having sown a few days too early or too late. The best temperature of germination once being known for each ficld, it is then required to observe the degrees of the thermometer from day to day, in order to know the precise moment when the soil (not the air) has reached this best temperature. An accurate knowledge of this point affords many advantages. Seeds may be sown in a loose soil before the appearance of the best temperature of germination in spring; in a compact soil it is better to be done after it. It is better, in a wet soil, to wait for a higher temperature, in order to prevent the germ from rotting as this (rotting) would be an unavoidable consequence of slow germination, in airless and cold soil, etc. If frosts are to be apprehended during the time of coming up, the seeds should be planted deeper; seed which—as barley-strike their roots quickly and strongly, may be sown shallower than such of which the first roots are weak, etc.
d. Humidity. There is nothing that prevents healthy germination to such an extent as a heavy rain-fall, when the earth is dry, after sowing; for the soil will be compact and deprive the germ of air. The roots of the grown plant may prosper even in a soil devoid of air, as the interior parts of the plant will convey air to them; but the germ has no such communication with the atmosphere. Humidity in germination is a point yet to be investigated. If the seed has previously been properly soaked, it can
germinate quickly and healthily in a loose and pretty dry soil. Germinating roots avoid a wet, cold soil much more than old roots, and the injury is permanent in retarding growth, if not as to the quantity of the crop. In sowing, the result of the crops ought always to be borne in mind; if it ripens one day later, it may be injured by rain.
Condition of Air during Germination.-Air stagnates in the soil when there is no wind; a perpendicular circulation of air is caused in the soil, downward, by wind. If, therefore, deep sowing is required, it is better to do it before wind rises; but here there is still a large field open to investigation.
f. Looseness and Fineness of Soil.—There is, besides proper temperature and moisture, nothing that accelerates germination as much as a very loose, airy soil. But very loose soil is subject to great flunctuations of temperature; it requires, therefore, deeper sowing, especially as it readily parts with its moisture, and nothing injures the germ so much as complete dessiccation or drying. A poor crop may always be expected from a poor soil, but, if it is not too sterile or marshy, the failure of germination must be attributed to bad sowing. A fine soil permits a rapid and deep penetration of roots, while hard clods will change the direction of roots and cause a great loss of time to the plant.
All the conditions of germination just mentioned ought to be submitted to thorough experiments before a rational prescription can be given for sowing. The experiments—to be marked in diaries—ought partly to be made in the fields, partly in pots, partly in glass vessels (in order to see the roots), and continued to the time of ripening. Here is a work of years for a physiologist.
The Crop.—The safety of the crop depends sometimes on a day, on hours; a slowly.gathering, general rain may render a late crop valueless. In such cases, if it could be harvested a few days sooner, all would be right. But the exact moment of ripening is not known! It might sometimes be very important not to wait for that moment, if it was known for a certainty whether the grains are in a state to be equivalent to a crop, and whether they are capable of germinating!
Treatment during Vegetation.—Very little, comparatively, in a practical sense, can be said of treatment with regard to the several species of grains ; more, however, is known in relation to forage plants, Indian corn, etc. The effects of plucking off the leaves, of earthing, ventilating the soil, etc., are as yet too problematical, and will remain so, as long as good experiments do not give more light on the subject.
The most important studies of an agricultural physiologist are experiments: demonstrative experiments as to the functious of the various organs,
especially in different plants. What is known upon this subject? What purpose do leaves, roots, and stem serve? General or very trivial principles only are known about them. But what is desirable or important to know, is the functions of each organ in each plant. This must be discovo ered partly by experiments and partly by their anatomical structure.
Functions of the Roots. All that is known for certain about this is that they absorb fluids by endosmose, and with these fluids dissolve salts and absorb gases. The following practically important questions are here to be examined:
a. What part of the root absorbs fluids ? The views on this subject are very contradictory. Men of great reputation believe that the ends of the roots are the main organs of absorption, while others with equal assurance assert that the simplest physiological knowledge has established that the very ends of the roots have nothing at all to do with this absorption.
b. How does time influence the activity of roots ? It is concluded from the changed anatomical structure of the old roots, that they operate entirely different from what they did when they were young and tender. This would account for the difference in the absorbtion of nutritious matter during the different periods of age.
c. What is the relation of roots to gases and vapors ? The roots find water only at certain times in a good soil obtained by draining; the soil at other times contains vapors, but the plants, nevertheless do not wither. Do the roots absorb carbonic acid ?
d. What external influences cause the rise and prolongation of secondary roots ? Does the power of vegetation depend on the number and size of roots ?
e. Do the roots grow at the expense of the parts above earth ? Can they continue growing after the latter have been cut away? How do the roots of marsh plants differ from those on dry land ?
f. What substances are peculiar to the root? What ones do not exist in it?
g. How are the absorbed fluids conducted upward by means of the roots? Do the roots force the sap in an upward direction? Do the roots secrete any substances? How many and what ones?
h. How may a shallow or deep striking of roots be produced ? In what cases will a shallow striking of roots operate more favorably ?
i. How is the striking of roots connected with the leaf-quantity and stem-formation? How do the roots operate in penetrating through various strata of soil ?
j. At what time is the formation of new roots still desirable for the crop ?
Any new formation-also the one of roots—directly diminishes the crop; which diminution must be exceeded by subsequent operations of the roots. The period of hoeing or stirring and ventilating the soil depends upon that point. The respective experiments have yielded negative results, probably because it was done too late. The non-physiologists have, as a general thing, an incorrect idea of the plant's process of development: the mere development is confounded with the new formations; the time in which the organ exhausts the plant by its origin is confounded with that in which this organ is useful to the plant by its function.
Functions of the Stem. a. How is the sap conducted in the stem-from above downward, or from below upward? What function does the bark, the core, and vessels perform ? How is a solid vigorous stem obtained ?
b. Is it better to promote side-shoots under equal circumstances? Can side-shoots increase the crop of grain when they do not bear ears? At what time is the origin of side-shoots useful; when does it weaken the plant?
c. The potatoes are stem formations, and must be treated as such in rational agriculture. Is it better to increase their number at the cost of their size, or their size at the cost of their number?
d. Do the subterranean stem-parts depend upon those above earth, in the same manner as the roots ?
Functions of the Leaves. It must be remembered that the leaves absorb no vapors (water), and no running water. A great number of facts which were accounted for in this manner according to old prejudice, must now be otherwise explained.
a. Do the leaves absorb gases, as for instance, ammonia ?
6. How do the leaves of grasses differ from those of the fruit plants in their functions ? Their inner structure is very different.
c. The evaporation of the vegetation water is one of the most important functions of the leaf, as it supports the motion in the plant. It is necessary to learn exactly, by means of accurate experiments, the amount of evaporation from the leaves of each cultivated plant, especially during various periods of vegetation. The old statements of Ilales are absolutely unavailable.
d. The very general opinion that a rapid evaporation from the leaves, with the simultaneous absorption of water by the roots, was a favorable relation of vegetation is utterly false. Too strong a circulation of water in the plant, occasioned by rapid evaporation, hinders the quiet assimilation within the cells, and brings too many inorganic salts into the plant.
e. The evaporation from leaves is decreased when the plants stand too close, therefore the proper distance of plants apart ought to be known.
f, What relation does the development of leaves bear to the formation