But, when all due honour is paid to the scientific chemist, it must still be allowed that his problems are different from the real problems of agriculture. To take one set of instances alone. The chemist can analyse a given soil or a given manure, and can even go a long way towards making them, but his analyses do not tell us what conditions are necessary in order that their ingredients may be presented to the roots so as to be absorbed and become built up into the plant. Chemistry told us that carbon was fixed from the air, but physiological experiments determined how this meant the synthesis of certain definite carbohydrates - this, too, in the face of the powerful authority of the chemist Liebig, who supposed that the vegetable acids were the results of the assimilation of carbon. Wolff, De Saussure, and other chemists have done yeoman service in showing that different plants, growing in the same soil, contain different proportions of mineral substances; but it was by means of water-cultures, and other physiological researches, such as those of Pfeffer on osmotic phenomena and of Schwarz and Molisch on root-hairs, that the puzzling question of selective absorption, by means of the living root-hairs, came into the arena of our knowledge.
In every case - and, as already said, I am not undervaluing the work done - the chemist has left us only on the threshold of the real problem. He has stood outside the factory in which the real work we want to know about is being carried on, and has told us of so many tons of this material being carried in at the gates, and of so many tons of that coming out; he has even burnt down the factory, and all its contents and machinery, and has then told us how many tons of the various materials were there at the time; but this is not what we want, valuable as the information is, and still more will be. What we want, and what we expect to obtain, is more information regarding what is done with the materials in the factory: what machinery they are put into, and how they are put in: what stages they go through, and how the stages follow one another: what wear and tear has to be endured, and how we can step in and stop the working of the machine for our own benefit at the best possible time.
The physiologist proceeds empirically, by experimenting with the living machinery. He recognises the parts and their structure, and tries to find out what they are doing: he knows that the laws of physics and chemistry cannot be traversed, but he sees these laws at work under special and very complex and peculiar conditions. He therefore, as the results of his experiments, sets new questions - or old questions under new conditions, if you like - and undoubtedly wants the help of both chemist and physicist; or, if it is preferred, the chemist and physicist may attack the problems, but they must familiarise themselves with the peculiar mechanism of the organism concerned, and cannot hope to attain success without experimenting with it. I confess it seems to me as reasonable to look upon scientific agriculture as a branch chiefly of chemistry as it would be to look upon horse-breeding or pigeon-rearing from the same point of view; and why the professed chemist's advice is regarded as so comforting and final in the one case and not in the other is one of those mysteries which seem inherent in human nature.
The central point in agriculture is the plant: get the most out of it - the energy - winning machine which alone can keep the animals and everything else connected with the farm going - and all the rest follows. The old agriculture has taken a gloomy view of things, and especially on account of a large variable which it blames for many ills, namely, the season or climate. Perhaps the old agriculture has not sufficiently recognised that Nature grows plants in accordance with the fact that variation is not peculiar to the weather: if the seasons vary, so do fruit and other produce and the plants which yield them; and since man cannot hope to control the one variable, possibly relief will be found in doing more, within his limits, towards controlling others.
In any case he cannot hope to succeed without study of the physiology of the plant.
An admirable short account of soil in its relation to root-hairs is given in Sachs' Lectures, XV.; but for a more exhaustive treatment of the subject of soil the reader is referred to King, The Soil (Wisconsin, 1895), or Warrington, Lectures on the Physical Properties of Soil (Oxford, 1900); Larbaletrier, L'Agriculture (Paris, 1888), chapters II. and III. There is also a very good account in Bailey, The Principles of Agriculture (London, 1898), chapters I. - III.
With reference to the organisms in soils and the decompositions they bring about, the student should consult Kramer, Die Bakteriologie in ihren Beziehungen zur Landwirthschaft (Wien, 1890), and Lafar, Technical Mycology (Engl, edition, 1898), sections V., VIII., and IX.