100 The Phenomena of Morphogenesis 



total growth is much the same, reduction in one structure being compen- 

 sated by increase in the other. 



Stimulatory Correlations. Many correlations, however, do not depend 

 upon the distribution of building materials but upon the operation of 

 other factors which affect development, particularly the stimulatory and 

 inhibitory action of auxin and other growth substances. 



The stimulatory effect is well shown in the control of root growth. 

 Van der Lek (1925) and others have found that in many cases cuttings 



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Leaf Position 



Fig. 5-1. Compensatory correlation in Coleus. Increase in leaf length in 27 days after 

 removal of axillary buds and branches, as compared with controls. Leaves at left of 

 vertical line had not unfolded from apical bud. ( From Jacobs and Bullwinkel. ) 



on which buds are present will root much better than those without buds. 

 This evidently is due to a root-stimulating substance produced by buds 

 which passes down to the base of the cutting. The character of the buds 

 may also be important, for O'Rourke (1942) has shown that blueberry 

 cuttings root better if the buds on them are leaf buds than if they are 

 flower buds. 



The relation between a leaf and the development of a bud in its axil 

 is a complex one. Felber (1948) observed that in apple the size of a 



