CHAPTER XII 



BUD INHIBITION 



A. Bud Inhibition as a Correlation Phenomenon 

 It has been known from earliest times that lateral buds, 

 low down on a stem, do not develop in presence of the ter- 

 minal bud. If the terminal branch of a bud or shoot be re- 

 moved, some of the laterals usually grow out at once; this 

 is the basis of all pruning. Sachs' idea of bud-forming sub- 

 stances was abandoned by most workers, largely because 

 the more obvious phenomenon is the inhibition, rather than 

 the promotion, of bud development. However, Errera 

 (1904) ascribed apical dominance and bud inhibition phe- 

 nomena to "internal secretion," or, as we would say now, 

 hormones. Goebel, in his earher works (e.g. 1903) favored 

 Sachs' hypothesis, but later (1908) changed his views, he 

 and his school interpreting bud inhibition as a nutrition 

 phenomenon. Loeb carried out a number of experiments on 

 shoot growth and inhibition in Bryophyllum (1915, 19176, 

 1918a, 1919, 1923, 1924), at the same time as his experiments 

 on tropisms (see X C). He concluded that the growth of 

 shoots was proportional to, and determined by, the amount 

 of nutritive substances available. Thus, if one shoot of a 

 plant is growing rapidly it deflects food substances away 

 from other buds, which are therefore inhibited. However, 

 as with root formation and geotropism, Loeb expressed dif- 

 ferent views at different times, and in 19176 attributed the 

 phenomenon to the influence of special inhibiting substances 

 formed in the leaf and transported basipetally in the stem. 

 His experiments did not, however, pro\dde evidence in favor 

 of either \dew, although his concept of bud-inhibiting sub- 

 stances was shown by Reed and Halma (1919) to explain 

 satisfactorily their experiments on correlations in bud devel- 

 opment. 



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