CHAPTER II 



CERTAIN GENERAL CHARACTERISTICS OF 

 DEVELOPMENTAL PATTERNS 



THE various forms of agamic development, reconstitution from 

 experimentally isolated pieces of individuals, and development 

 from the egg have different starting-points and follow more or less 

 different courses. The question of their physiological resemblances and 

 differences is of great interest and importance, since it is a question wheth- 

 er the same organism may arise in fundamentally different ways or wheth- 

 er the different forms of development are physiologically more or less sim- 

 ilar in pattern. Observation of different forms of development under nat- 

 ural conditions and of experimentally induced development shows certain 

 features which indicate or suggest that underlying physiological factors 

 may be more or less similar. Certain of these characteristics of patterns 

 which are directly evident are briefly pointed out in the present chapter. 

 Attention has been called to some of them in earlier publications.' 



BUD PATTERNS 



In both plants and animals new axes which become new individuals, 

 branches, zooids, organ systems, or organs such as leaves, roots, tentacles, 



A B C 



Fig. I. — Diagrammatic sectional outlines of stages of bud growth; arrows indicate direc- 

 tions of gradients. 



appendages of various sorts, develop from what we call "buds." In its 

 early stages a bud is a locus, usually at or near an external or internal sur- 

 face of the parent body, in which the conditions which determine its de- 

 velopment operate in decreasing degree from a physiological center which 

 may or may not be the geometrical center. These conditions apparently 



' Child, 1915c, pp. 65-87; 19246, pp. 74-100; i928</. 



16 



