CROSS-WJEBTILIZA TION 



235 



times of maturing of the organs of the same 



flower (150ffl). Certain simple movements or habits 



of the pistils or stamens are often associated with 



dichogamy. Fig. 226 is a flower 



of one of the wUd phloxes. The 



stigmas are seen to be three, but 



these are closed until the stig- 



matic surfaces are receptive, which 



commonly occurs after the pollen 



is discharged. A similar behavior 



may be detected in the blue -bells 



in Fig. 176. In the middle flower 



the style is merely club-shaped ; in 



the lowest flower, the style has 



opened to three branches, but the pig. 226. 



anthers are shrivelled. Inasmuch nichogamous flower of 



as the period of blooming of any 



plant usually extends over several days at least, 



the dichogamous flower is likely to receive pollen 



from various flowers which are borne either upon 



the same or another plant. 



270a. Pistils of dichogamous flowers may accidentally receive 

 pollen from the same flower; but Darwin and others have found 

 that pollen is often impotent, or sterile, upon the associated stigmas. 

 That is, if pollen from the same and from another flower were 

 to fall upon a stigma, the foreign pollen is the more likely to be 

 fecund. Foreign pollen is commonly prepotent. If, however, no 

 pollen is received from another flower, the stigma may accept the 

 pollen from the associated anthers. 



