Experiments on growth and inhibition. I.—The increase of inhibition with distance

Experiments were recently reported showing that, in young seedlings ofPisum sativum , the complete inhibiting effect which the shoot exerts upon its axillary buds comes entirely or almost entirely from three or four of its developing leave acting together (6). A single developing leaf was found usually to inhibit only partially—that is to say, sufficiently to delay the growth of an axillary bud below it, but not to check it completely. The strength of this partial inhibiting effect was measured by the retardation of the outgrowth of the axillary buds of the first or lowest leaf, as compared with their growth in completely defoliated controls. Comparisons were further made of the inhibiting effects of single young leaves of equal sizes near the apex in seedlings of different ages and heights, and it was found that in very young short seedlings the inhibiting effect was very slight or inappreciable, although in seedlings of a height of about 30 mm. or more (but still possessing well filled cotyledons) the effect was strong.