Inorganic plant poisons and stimulants / by Winifred E. Brenchley.

  • Brenchley, Winifred Elsie, 1883-
Date:
1914
Catalogue details

Licence: In copyright

Credit: Inorganic plant poisons and stimulants / by Winifred E. Brenchley. Source: Wellcome Collection.

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    whole subject leads one to conclude that in general both favourable and unfavourable conditions of nutrition are present side by side, and only when a balance is struck in favour of the good conditions can satis- factory growth take place. As indicated above, experiments have shown that the very substances that are essential for plant food may be, in reality, poisonous in their action, exercising a decidedly depressing or toxic influence on the plant when they are presented singly to the roots. This toxic action of food salts is decreased when they are mixed together, so that the addition of one toxic food solution to another produces a mixture which is less toxic than either of its constituents. Consequently a balanced solution can be made in which the toxic effects of the various foods for a particular plant are reduced to a minimum, enabling optimum growth to take place. Such a mixture of plant foods occurs in the soil, the composition of course varying with the soil. While the earliest observations set forth the poisonous action of various substances upon plants, it was not long before investigators found that under certain conditions these very substances seemed to exert a beneficial rather than an injurious action. The poisons were therefore said to act as “ stimulants ” when they were presented to the plant in sufficiently great dilution. This stimulation was noticed with various plants and with several poisons, and a hypothesis was brought forward that attempted to reconcile the new facts with the old con- ceptions. Any poison, it was suggested, might act as a stimulant, if given in sufficiently small doses. It will be seen in the following pages that this is not universally true, such substances as copper, zinc, and arsenic failing to stimulate certain plants even in the most minute quantities so far tested. Of recent years investigators in animal physiology have brought into prominence the striking effect of minute quantities of certain substances in animal nutrition, as for example iodine in the thyroid gland (see E. Baumann, 1895). This and other work has rendered it imperative to re-examine the parallel problems in plant physiology. The words “ stimulant ” and “ stimulation ” themselves need more precise definition. As a matter of fact the “stimulation” noticed by one observer is not necessarily held to be such by another. Stimulation may express itself in various ways—the green weight and the general appearance of the fresh plant may be improved, the dry weight may be increased, the transpiration current may be hurried up, entailing increased absorption of water and food substances by the roots, assimilation processes may be encouraged. But these benefits are
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