3o6 FLOWERS 



is believed to be one of the causes of rose cold and hay- 

 fever. With the wind blowing it and many kinds of in- 

 sects carrying it, pollen may frequently be caught by other 

 stigmas than those of its own kind. Since in such cases 

 the pollen usually does not germinate, it is believed that 

 stigmas generally stimulate their own kind of pollen to 

 germinate and do not so stimulate the pollen of other 



Fig. 127. — A common meadow grass (Festuca). A, the end of a spike showing 

 the bracts from whose axils the flowers arise. B, a single flower and bract much 

 magnified ; note the prominent swaying stamens and the feathery expanded stig- 

 mas. — After Strasburger. 



species. This power of the stigma is probably due to 

 varying properties of the secretions which are found upon 

 its surface. It has been found that on some stigmas pollen 

 from the same flower will not germinate, while pollen from 

 other flowers of the same kind will germinate. This is 

 true of buckwheat and of the day-Kly. This fact evidently 

 prevents close-polKnation in such plants. Much more 

 common, however, are cases in which pollen does germinate 

 upon its own stigma, but not so well as it does on other 

 stigmas. Thus if pollen from the same flower and poUen 



