108 The Phenomena of Morphogenesis 



main shoot has a variety of effects on the shape of leaves produced later 

 by the terminal bud and on the size and number of their cells (Njoku, 



1956b). 



The various parts of the shoot system also show growth correlations, 

 and these are responsible for the form of the shoot. They are readily 

 observable in coniferous trees where the growth of the terminal shoot, 

 which will form the trunk, is usually greater than that of the branches. 

 This leads to the spire-like form of many of these trees. There are also 

 definite relationships between the members of a branch system. The new 





o 



Hi 



Log. Lamina diam. 



Fig. 5-3. Allometric relation between lamina and petiole in Tropaeolum. I, a series of 

 growing leaves. II, mature leaves in shade. ( From Pearsall. ) 



material added each year is distributed unequally but in regular fashion 

 throughout the tree. 



A somewhat different type of correlation is that between the volume 

 of the shoot system or any part of it and the cross-sectional area of the 

 stem that supports it. Murray ( 1927 ) analyzed this relationship in a 

 number of trees and finds that it is constant and predictable and that as 

 the tree grows larger the cross-sectional area of its trunk becomes rela- 

 tively smaller. It has been shown that where a trunk branches the cross- 

 sectional area of the two branches is larger than that of the united trunk 



