178 



Introduction to Botany. 



and sailing qualities. The pistillate inflorescence is in 

 the form of a cone (Fig. 93, a) whose scales are broadly 

 expanded and collect the pollen as it settles down upon 



them, directing it downward 

 to their axils, where it comes 

 in close proximity to the 

 micropyles of the naked 

 ovules (see Fig. 94). 



The staminate catkins of 

 the poplars are shaken and 

 emptied by the wind, while 

 the branched and widely 

 spreading stigmas of the 

 pistillate flowers, occurring 

 on a different tree, catch 

 and hold the pollen which 

 is wafted to them. 



It is characteristic of 

 flowers which depend on 

 the wind that they are either 

 monoecious or dioecious. It 

 is plain that this mode of 

 pollen transference is ex- 



FIG. 93. 



Pistillate inflorescence of the pine. At a, 

 young cone of the current spring ready 

 to receive pollen ;, cone which the pre- pensive, SHICC ITiOSt of the 

 vious spring was like a; c, cone one 



year older than b ; here the scales have pollen must be lost in tran- 

 spread apart and the seeds have dropped 

 out. 



sit. There is some com- 

 pensation, however, in the 

 fact that allurements for insects in the form of brightly 

 colored corollas, nectar, and fragrant odors are not neces- 

 sary, and are accordingly not produced. 



128. Cross Pollination by Water. In the case of flower- 

 ing plants which are entirely submerged in water, the pollen 

 frequently has the same specific gravity as the water, and 



