Experiments on growth and inhibition. Part II.-New phenomena of inhibition

If young seedlings of pisum sativum or Vicia faba are decapitated in the epicotyl, the axillary buds of the cotyledons grow out, so that plants are formed with two shoots springing from the same level. If one grows a dated of such plants—" two-shoot plants," as they will be called—one finds that in some of them the shoots are very unequal from the start. In these plants the reader shoot very soon stops growing, often when it is only a few millimetres long, and after some weeds it dies. This is clearly because it is inhibited by the stronger shoot, for If the stronger shoot is removed before the weaker shoot has stopped growing, then the latter goes on growing indefinitely. In other plants in which the shoots are less unequal, the weaker one grows for rather longer before it is stopped by inhibition, and in others again, in which they are very nearly or quite equal, they both grow on indefinitely, or at least for a long time— six weeds or more. (It is stated, indeed, by Mogk (1913) that two such equal shoots sometimes check and finally kill one another. This has not happened in any of the writer's plants, perhaps because they have not been left for a long enough time. At all events, when the shoots. are about equal, it is very much longer before the growth of either is inhibited, If it ever is.) These facts are well known, but none the less they suggest the interesting question bow it is that two equal shoots do not inhibit one another, or at least not completely. It occurred to the writer that if one were to remove from one of them the rapidly developing leaves near the apex, which have been shown to be the inhibiting members (Know, 1929), the balance between them would be upset, and that the results might throw light on the question, Accordingly the following experiment was arranged.