i6o 



PLANT BIOLOGY 



Dense centrifugal clusters are 

 usually flattish on top because of 

 the cessation of growth in the 

 main or central axis. These com- 

 pact flower-clusters are known 

 as cymes. Centrifugal clusters 

 are sometimes said to be cymose 

 in mode. Apples, pears (Fig. 

 220), and elders bear flowers in 

 cymes. Some cyme-forms are 

 like umbels in general appear- 

 ance. A head-like cymose clus- 

 ter is a glomerule ; it blooms from 

 the top downwards rather than 

 from the base upwards. 



Mixed Clusters. Often the 

 cluster is mixed, being determi- 

 nate in one part and indeterminate 

 in another part of the same clus- 

 ter. The main cluster may be indeterminate, but the 

 branches determinate. The cluster has the appearance of 

 a panicle, and is usually so called, but it is really a thyrse. 

 Lilac is a familiar example of a 

 thyrse. In some cases the main 

 cluster is determinate and the 

 branches are indeterminate, as in 

 hydrangea and elder. 



Inflorescence. -- The mode or 

 method of flower arrangement is 

 known as the inflorescence. That 

 is, the inflorescence is cymose, co- 

 rymbose, paniculate, spicate, solitary, determinate, inde- 

 terminate. By custom, however, the word " inflorescence " 



FIG. 219. DETERMINATE OR 

 CYMOSE ARRANGEMENT. 

 Wild geranium. 



FIG. 220. CYME OF PEAR. 

 Often imperfect. 



