MANUAIv OF NATURK STUDY. 153 



take the form of a raceme ? Of a corymb ? Of an 

 umbel ? 



Shorten the axis of the plantain until the sessile 

 flowers arise from about the same point and the 

 flower cluster would be called a Head. The button- 

 wood or sycamore ball is a head. How is a head 

 different from an umbel? A spike different from 

 a raceme ? The spadtx, as in Indian turnip, the 

 catkin, as in birch, willow or alder are simply dif- 

 ferent modifications of the spike. 



Broaden the receptacle of the head and surround 

 it with a set of bracts called involucre and you have 

 a composite flower. Examine the dandelion, iron 

 weed, ox-eyed daisy, dog fennel and sun flower. 

 In what respect are these flowers difierent from a 

 clover blossom, or button- wood ball? 



The teacher may be able to trace the determinate 

 inflorescence to the compositae in the same way as 

 with the indeterminate. 



The cyme of the determinate corresponds with 

 the raceme of the indeterminate. In the determin- 

 ate inflorescence the flowering is centrifugal, that 

 is, the oldest flower* is in the center and the order 

 of flowering is outward. In the indeterminate 

 inflorescence the mode of flowering is centripetal, 

 that is, beginning on the outside and flowering 

 toward the center. 



