336 



A TEXTBOOK OF BOTANY [Ch. VI, 11 



Fig. 233. — Button Bush, Cephalanthus 

 occidentalis, showing the head of flowers. 

 (From Bailey.) 



largely an arbitrary mat- 

 ter, determined in practice 

 by whether leaves or 

 flowers are more promi- 

 nent in the mass. In 

 many, perhaps most, 

 cases, however, there is no 

 difficulty in distinguishing 

 a cluster, because it ex- 

 hibits a sharp transition to 

 the leafy stem ; and this 

 distinctness constitutes 

 the first step in the indi- 

 viduality of the cluster. 



The simplest clusters 

 are those in which a con- 

 tinuously growing stem 

 produces a flower in the axil of each reduced leaf, the older blos- 

 soms being thus below and the younger above, — and often the 

 lower become fruits while the 

 upper are still buds. Such a 

 cluster, commonest of all 

 kinds, is called a raceme 

 (Fig. 229). In marked mor- 

 phological contrast therewith 

 is the cyme (Fig. 231), in 

 which a terminal flower closes 

 the growth of the stem, and 

 the new flowers appear from 

 buds progressively lower 

 down. The two types, called 

 respectively indeterminate 

 and determinate, corre- 

 spond exactly with the defi- 

 nite and indefinite annual 

 growth of stems, earlier described (page 138) 



Fig. 



234. — Corymb of Cherry. 

 (From Figurier.) 



