228 



THE FLOWER 



viduals. Examples of dimorphic flowers are the pretty 



little bluets (Honsfonia ccerulea), the partridge berry ( Mit- 



chella repens}, the swamp loosestrife (Lythrum lineare}, 



and the English 

 cowslip. Of tri- 

 morphic flowers 

 we have exam- 

 ples in the wood 

 sorrel, and the 

 spiked loosestrife 

 (Lythrum salica- 

 ria) of the gar- 

 dens. These 

 flowers were a 

 great puzzle to 



botanists until the celebrated naturalist, Charles Darwin, 



proved by a series of careful experiments that the seed pro- 



duced by pollinating a dimorphous flower with its own pollen, 



or with pollen from a 



flower of similar form, are 



of very inferior quality to 



those produced by im- 



pregnating a long-styled 



flower with pollen from 



a short-styled one, and 



vice versa. 



449-451. Three forms of Lythrum salicaria. 



332. Wind Pollination. 

 But the problem is 

 only half solved when a 

 plant has been rendered 

 incapable of impreg- 

 nating itself. Cross- 

 pollination, that is, the 

 transfer of pollen from a 

 separate flower or plant, 

 has been rendered necessary, and provision must now be 

 made for the transportation. In many cases, of which the 



452. Feathery stigmas of a grass adapted 

 to wind pollination. 



