304 



EXPERIMENTS WITH PLANTS 



pollination does not take place, for the reason that the 

 stigma is not yet mature. In the process of develop- 

 ment it is slowly pushed up, thus gradually expelling 

 the pollen from the tube so that it can be -carried away 

 by bees. When this is accomplished it opens up, as in 

 Fig. 166 (J5), exposing the smooth surface, which is 

 the receptive part: the pollen which is now deposited 



on it comes from another 

 flower. Good examples of 

 this arrangement will be 

 found in the Daisy, Aster, 

 Cosmos, Sunflower, Core- 

 opsis, Zinnia, etc. 



Another method is by 

 placing the anthers and 

 stigma in different posi- 

 tions. This is illustrated 

 by the Iris (Fig. 167) . As 

 the bee enters the flower 

 the stigma scrapes off 

 some of the pollen with 

 which its back is covered: as it goes deeper into the 

 flower its back receives a fresh supply from the an- 

 ther: as it backs out of the flower this pollen is not 

 deposited on the stigma (owing to the manner of its 

 attachment to the style) , but is carried on to the next 

 riower. 



The behavior of the Partridge -berry (also called 



167. Iris flower, showing how the stigma 

 first removes the pollen from the bee, 

 after which the anther deposits a fresh 

 supply, which is carried to another 

 flower. 



