THE QUESTION OF ROOT EXCRETIONS 259
Unger, and his pupil, Walser, showed that there had been certain flaw? in the work of Macaire-Prinsep and made objections to his results. Walser believed that, if Macaire's statements were correct, it would be possible to demonstrate the presence of organic material in the soil similar in composition to that existing within the plants which had grown upon it. Braconnot, making the same assumption, attempted to demonstrate the existence of opium-like bodies by washing the soil on which plants of the poppy family had been grown for several years. He obtained a solution of inorganic compounds, and, in addition, only traces of organic compounds, and concluded that " If organic excre- tions really take place in the natural state of the plant, they are, as yet, so obscure and so little known as to justify the assumption that some other explanation must be given for the general system of rota- tion." Working without the proper idea of the difficulties of such a task and without adequate knowledge of the organic compounds in the soil, it is little wonder that they failed to demonstrate the presence of compounds in the soil which might be regarded as excretory matter from plants. They deserve credit, however, for showing that Brug- mans had entirely misinterpreted the death of the root-hairs and the decortication of the growing roots and had assumed that this material was solid excretory matter from the living root.
One of the most scientific attempts to study this question appears to have been made by Alfred Clyde, the results of whose work were published in 1846 in the Transactions of the Highland and Agricul- tural Society of Scotland, and which won for the author a premium of twenty sovereigns. His modus operandi was to raise plants in pots of garden soil, sand, moss or charcoal; to remove them at different times; carefully wash their roots free from all adherent material and place the root systems in vessels of distilled water. After a certain length of time had elapsed, the composition of the water in the various vessels was studied.
Mr. Gyde reported that the roots imparted to the water soluble substances, to be regarded as excretory material, and that these excre- tions seemed to be yielded in greater abundance by plants having coarse roots like beans than by those which had finer roots, like wheat. In some instances the water acquired an odor which was separable on the application of heat and could be distilled over when the water was placed in a retort. Plants like the bean and cabbage imparted an odor to the water similar to that which characterizes their leaves. Plants when in bloom were observed to emit more excretory material than when young or when ripening their seed; but in any case the amount of excretion obtained after evaporating the water was very small. When this small amount of organic matter was reapplied to the soil in which other plants were growing, no harmful effects were