XX.] 



BOTANY. 



77 



by pollen brought from other flowers. This operation 

 is called cross-fertilization. 



120. In respect of fertilization flowering plants may 

 be roughly classed under two heads, according as 

 the pollen is carried to the pistil by the wind or by 

 insects. 



Wind-fertilized plants have, as a rule, stamens and 

 pistil in different flowers or individuals. Their flowers 

 are not bright-coloured, are scentless, and have no 

 sugary secretions, and their stigmas are covered with 

 hairs that retain the pollen ; in some the anthers hang 

 out of the flower (plantain, poplar, willow, oak); their 

 pollen is abundant, dry, and powdery (birch, alder, 

 pine). 



121. Insect-fertilized plants, on the other hand, pre- 

 sent innumerable contrivances to ensure the fertiliza- 

 tion of the pistil by pollen from another flower or 

 plant, of which the following examples must suffice- 



FIG. 56. Vertical section of corolla of, a, long-styled, and b, short-styled 

 primrose. 



122. The primrose has two sorts of flowers, which 

 never occur on the same plant ; one has the stamens 



