302 PLANT-LIFE 



called " pollination." We shall see how water, wind, 

 insects, and even birds, are drawn into the service of 

 plants in this regard. 



A remarkable feature of Flowering plants is the 

 number and variety of ingenious devices that have been 

 elaborated to ensure cross-fertilization that is, that the 

 male element of one flower shall only fertilize the egg 

 cell of another flower. The different flowers may occur 

 on the same plant, but for obvious reasons cross-fer- 

 tilization, if it has advantages, is calculated to produce 

 them to the fullest extent only when the union is secured 

 between the sexual cells of totally distinct plants. So 

 notable are the devices that ensure cross-fertilization in 

 many Flowering plants that students of the phenomena 

 at one time rushed to the conclusion that self-fertiliza- 

 tion was an actual evil. But that notion is now under- 

 going revision. That cross-fertilization has its own 

 advantages will not be denied, but they are not easy to 

 define. On the other hand, it is not demonstrable that 

 self-fertilization in flowers, where it occurs, has any 

 harmful effect on their posterity; indeed, some of the 

 most widespread and vigorous weeds, including such 

 well-known species as the Shepherd 's-Purse (Capsella 

 Bursa-pastoris), the Groundsel (Senecio vulgaris), and 

 Chickweed (Stettaria media), are self- fertilized. It is 

 obvious that self-fertilization can take place only in 

 hermaphrodite flowers that is, in those which include 

 in the same flower both male and female organs. The 

 great Linnaeus tumbled to the conclusion that her- 

 maphrodite flowers were invariably self -fertilized. He 

 evidently had not time to observe the varied devices in 

 such flowers for the avoidance of self-fertilization. We 



