20 



Growth 



1955 ) . Plants provide examples of all types of growth from that in loosely 

 organized, essentially indeterminate structures to highly organized and 

 sharply determinate ones and therefore are particularly good material 

 for a study of the mechanism by which growth, presumably free and 

 continuous in primitive organisms, becomes controlled and molded into 

 a definite cycle or pattern. Such cyclical, controlled growth is one mani- 

 festation of the general phenomenon of biological organization. 



Growth and Size. The size that an organism attains is often an im- 

 portant factor in determining the character of its development, and size 

 is intimately related to growth. Differences in ultimate size may be due 



Fig. 2-6. Diagram of growth of stipe and pileus of the common mushroom, Agaricus 

 campestris. Homologous points are connected by lines. Growth is most active in the 

 region intermediate between base and apex. (From Bonner, Kane, and Levey.) 



to differences in rate or in duration of growth or in both of these. Little 

 is known in plants as to the relation between growth and size. The in- 

 creased size of heterozygous corn plants is apparently associated with a 

 higher growth rate (Whaley, 1950), and this may be true rather gen- 

 erally for size difference in indeterminate structures. In determinate 

 ones such as the fruit, however, rate may not be important. The great size 

 differences between small-fruited and large-fruited cucurbits of the same 

 species studied by Sinnott (1945b) are due in almost every case to differ- 

 ences in duration of growth, for growth rate is essentially the same in all 

 of them ( Fig. 2-4 ) . This difference in duration applies to all recognizable 



