FLO WER-CLUSTERS 



159 



the top is convex or flat, it is a corymb (Fig. 217). The 

 outermost flowers open first. Centripetal flower-clusters 

 are sometimes said to be corymbose in mode. 



When the branches of an indeterminate cluster arise from 

 a common point, like the frame of an umbrella, the cluster 

 is an umbel (Fig. 218). Typical umbels occur in carrot, 

 parsnip, caraway, and other plants of the parsley family : 

 the family is known as the Umbelliferae, or umbel-bearing 



Fig. 218. —Remains of a Last Year's Umbel of Wn.n Carrot. 



family. In the carrot and many other Umbelliferae, there 

 are small or secondary umbels, called umbellets, at the end 

 of each of the main branches. (In the centre of the wild 

 carrot umbel one often finds a single, blackish, often 

 aborted flower, comprising a i-flowered umbellet.) 



Centrifugal or Determinate Clusters. — When the ter- 

 minal or central flower opens first, the cluster is said to be 

 centrifugal. The growth of the shoot or cluster is deter- 

 minate, since the length is definitely determined or stopped 

 by the terminal flower. Fig. 219 shows a determinate or 

 centrifugal mode of flower bearing. 



