INFLORESCENCE 



189 



Corymb of plum 

 blossoms. 



268. The Corymb. Imagine the lower pedicels of a 

 raceme to be elongated so as to place their flowers on a 

 level with those of the upper nodes, 



making a convex, or more or less flat- 

 topped cluster, as in the wall-flower and 

 hawthorn, and we have a modification 

 of the raceme called a corymb. In such 

 a cluster the outer blossoms, or those 

 on the circumference, proceed from the 

 lower axils and are, consequently, the 

 oldest ; hence, the order of flowering 351 

 is centripetal, that is, from the circum- 

 ference to the center. This, an inspection of Figure 351 

 will show, is only another way of saying that it is of the 

 indefinite or indeterminate order. 



269. The Umbel is a still further modification of the 

 raceme. The pedicels with their bracts are all gathered 



at the top of the peduncle, from 

 which they spread in every direc- 

 tion like the rays of an umbrella, 

 as the name implies. This, though 

 confined to no one group, is the 

 prevalent type of flower cluster in 

 the parsley family, which takes its 

 botanical name, Umbellifcrce, from 

 its characteristic form of inflo- 

 rescence. The 



352. -Umbel of milkweed. pe di C els of an ^ 



umbel are generally called rays and the 

 circle of bracts at the base of the cluster 

 is an involucre. 



270. Compound Clusters. All these 

 forms of inflorescence may be com- 

 pound. Most of the parsley family 

 have compound umbels. The lilac, 

 grape, catalpa, and many grasses fur- 

 nish familiar examples of the panicle, 353. panicieofagrass. 



