INFLORESCENCES 



299 



have pedicels, since many of them arise from the top of a 

 sitigle stem. A flower stem of that kind, or one which sub- 

 divides into a number of pedicels, is called a peduncle. 



a. Indeterminate Inflorescences. — Of 

 these the following are the most com- 

 mon: — 



The spike. (See Figures loi and ug.) 

 This kind of inflorescence is illustrated by 

 the common plantain, at least when the 

 flowering stems are not kept cut off by 

 a lawn mower. A much more dense kind 

 of spike is that of the cat-tail. In spikes 

 the flowers are sessile, that is, they have 

 no pedicels. They arise directly from 

 the main flowering stem and they usually 

 grow close together. 



The catkin. (See Figures 94, 104, and 

 105.) Catkins are spikes whose flowers 

 are borne in the axils of structures called 

 scales. Scales are like leaves in origin. 

 Catkins are commonly flexible and swing 

 freely, like tassels, in the wind. As is 

 almost equally true of spikes, the plants 

 which bear them are wind-pollinated. 



The raceme. (See Figures log and 

 118) This type is well illustrated by 

 the graceful, drooping inflorescence of 

 lily-of-the-valley. It may be described 

 as a spike in which the flowers have 

 pedicels. The inflorescences of pepper- 

 grass and shepherd's-purse, already referred to, are also 

 racemes. It is a common type. 



Fig. iig. — The upper 

 part of a spike 

 of plantain. Note 

 that the stigmas, g, 

 ripen befofe the 

 anthers, u. This 

 plant is wind-pol- 

 linated, and, like 

 other wind-polli- 

 nated plants, its stig- 

 mas are prominent. 

 They have the ap- 

 pearance of small 

 white plumes. The 

 fact that they ripen 

 before the anthers 

 of the same flower 

 prevents close-polli- 

 nation; the pollen 

 which is received 

 must come from a 

 different flower. 

 The ripening of stig- 

 mas and anthers at 

 different times is 

 called dichogamy. 



