INFLORKSCENCE. 



71 



disk florets. (Fig. 110.) The ray and disk florets often differ 

 in respect to the organs they contain. Sometimes they are 

 both perfect — that is, both containing stamens and pistils — 

 when they are said to be homogamous ; at other times, the ray 

 florets may be destitute of either stamens or pistils, or contain 



Fig. 111.— Umbel. 



a. Universal umbel, h. Partial umbe.. 



pistils only, and the disk contain only stamens; in any of 

 these cases, the capitulum is said to be heterogamous. 



Umbel (Fig. Ill) is formed when the secondary axes origi- 

 nate from the same point on the stem, and rise to nearly the 

 same height. The whole is 

 called a universal umbel. If ^'^* ^^~ 



the secondary axes develop ter- 

 tiary ones in the same manner, 

 each is called 2l partial umbel. 



115. The preceding varieties 

 follow the centripetal order of 

 flowering — that is, the flowers 

 farthest from the center expand 

 first. 



But there are others of the 

 determinate form which follow 

 the centrifugal order — that is, 

 the central or upper ones ex- 

 pand first, and the external or Cyme. 

 lower ones last. 



What are disk florets ? When homo2:amous ? When heteroffamons ! 

 What is an umbel? A universal umber? A partial umbel?— 115. What 

 is the centripetal order of inflorescence ? The centrifugal ? 



