134 



INFLORESCENCE 



FIG. 142. Spike of plantain and 

 head of red clover 



the plantain (Fig. 142). The willow, alder, birch, 

 poplar, and many other common trees bear a short, 

 flexible, rather scaly spike (Fig. 143), which is called 

 a catkin. 



The axis of the inflorescence is often so much short- 

 ened as to bring the flowers into a somewhat globular 

 mass. This is called a head (Fig. 142). Around the 



base of the head usually occurs 

 a circle of bracts known as the 

 involucre. The same name is 

 given to a set of bracts which 

 often surround the bases of the 

 pedicels in an umbel. 



165. The composite head. The 

 plants of one large group - - of 

 which the dandelion, the daisy, 

 the thistle, and the sunflower 

 are well-known members - - bear 

 their flowers in close involucrate heads on a common recep- 

 tacle. The whole cluster looks so much like a single flower 

 that it is usually taken for ^ 



one by non-botanical people. 

 In many of the largest and 

 most showy heads, like that 

 of the sunflower and the 

 daisy, there are two kinds 

 of flowers, --the ray flowers, 

 around the margin, and the 

 tubular disk flowers of the in- 

 terior of the head (Fig. 144). 

 The early botanists supposed 

 the whole flower cluster to 

 be a single compound flower. 

 This belief gave rise to the name of one family of plants, 

 Composite, - - that is, plants with compound flowers. In such 



FIG. 143. Catkins of willow 

 A, stamiuate flowers ; B, pistillate flowers 



