POLLINATION 



227 



It was recognized by the older botanists that this transfer 

 was necessary to the production of fruit, but they were 

 puzzled for nearly two hundred years by the fact that 

 many flowers seem to be constructed as if on purpose to 

 defeat this object. In our examination of the iris, for 

 instance, it was seen that the anthers lie under the broad 



445 446 



445, 446. — Flower of fireweed {Epilobium angustifolium) (Gray) : 445, with 

 mature stamens and immature pistil ; 446, tlie same a few days older, with expanded 

 pistil after the anthers have shed their pollen. 



divisions of the style in such a manner that the pollen 

 from them can not possibly reach the stigma without ex- 

 ternal agency ; and in all monoecious and dioecious plants, 

 self-pollination is clearly impossible. In other cases, of 

 which the cone flower {Rudbeckid) and the common sage 

 furnish examples, the anthers and stigma in the same 

 flower do not matpre together, thus producing the same 

 effect as if they were unisexual. 



331. Dimorphism is an expression for denoting a con- 

 dition in which the stamens and pistils are of different 

 relative lengths in different 

 flowers of the same species, 

 the stamens being long and 

 the pistils short in some, the 

 pistils long and the stamens 

 short in others. Flowers of 

 this sort are said to be dimor- 

 phous, or dimorphic, that is, 

 of two forms ; and some 

 species are even trimorphic, having the two sets of organs 

 long, short, and medium, respectively, in different indi- 



- Flower of pulmonaria: 

 447, long styled ; 448, short styled. 



