180 The Phenomena of Morphogenesis 



pattern, which may be deformed much in the fashion that D'Arcy Thomp- 

 son has demonstrated (p. 424). This can be seen by comparing the dorsi- 

 ventral maple shoot in Fig. 7-10 with one growing vertically. 



SYMMETRY AND FORM 



An analysis like this emphasizes the close relationship that exists be- 

 tween symmetry and organic form in general. Such form results from the 

 symmetrical distribution of material around an axis in a specific pattern. 

 An important part of this pattern lies in its symmetry. As we have seen, 

 certain portions of the pattern (as the lateral leaves of the maple shoot 

 in Fig. 7-10) appear by themselves to be asymmetrical, but they never- 

 theless constitute a part of a larger pattern of symmetry which may be 

 modified in various ways. A second part of the pattern is polar axiation, 

 affecting the lengthenings or shortenings of the axis and the steepness of 

 gradients along it. A third is the tendency toward spirality already em- 

 phasized. Organic form results from the genetic and environmental 

 modification of these three developmental tendencies. 



