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, 

 Compositce, that is, plants with compound flowers. In such 



FIG. 143. Catkins of willow 

 A, staminate flowers ; B, pistillate flowers 



