208 PHYTOHORMONES 



A detailed study of bud inhibition was made by Dostal 

 (1926). He placed isolated internodes of Scrophularia nodosa 

 in water and found that if one of the pair of opposite leaves 

 were removed, the bud in its axil began to develop, while the 

 one in the opposite axil, with its leaf present, did not. The 

 leaf, therefore, inhibits the bud in its own axil. A growing 

 bud, however, he found to exert a greater inhibiting influ- 

 ence than a leaf, the effect of the leaf being merely to upset 

 the balance between the pair of buds, so that one could get 

 ahead of the other. Once ahead, this growing bud inhibited 

 the other strongly. Dostal therefore made it clear that the 

 balance between inhibition and growth is rather delicately 

 poised. Like his predecessors, however, he interpreted his 

 results in terms of nutrition and water relations, and his 

 experiments were therefore not designed to throw any light 

 on the role of special substances. 



Evidence for a special inhibiting substance was first 

 brought by Snow (1925a), whose results were apparently 

 not known to Dostal. Snow's essential experiment was to 

 split the epicotyl of a Phaseolus seedling longitudinally 

 from the roots up to 2 cm. above the cotyledons; another 

 cut at an angle to the first then divided the plant into two 

 parts, one of which, with one cotyledon, was completely 

 isolated from the upper part, while the other, with the other 

 cotyledon, was connected through the split stem with the 

 upper part of the plant. The two halves were bound tightly 

 together, and the growth of the buds in the axils of the 

 cotyledons measured. The bud on the decapitated half was 

 then found to grow out somewhat more slowly than that 

 on a control decapitated and isolated split half. An inhibit- 

 ing factor must therefore have come from the buds and 

 leaves on the other half and crossed the cut surface. In 

 later work (1929) he showed that the principal inhibiting 

 effect was exerted by the very young leaves. A similar re- 

 sult was obtained by Weiskopf (1927). 



As to the path of movement of the inhibiting influence, 

 Harvey (1920) found that if a stretch of the stem of Phaseolus 



