90 OCCASIONAL PAPERS. 



some of the pollen, and upon entering another is 

 pretty certain to leave some of it behind. It is now 

 a well-known fact that this process, which is called 

 cross-fertilization, is the rule and not the exception ; 

 the exceptions He on the other side, the case of a 

 flower fertilizing itself by its own pollen, being rare 

 even in flowers like the short-styled primroses. And 

 when such self-fertilization takes place the seed 

 deteriorates. 



But then you will say in a case like this the short- 

 styled Primrose how is it possible to prevent self- 

 fertilization? Now we make use of another or two of 

 Mr. Darwin's discoveries in the physiology of plants. 

 He discovered that when a stigma is covered with 

 two or three kinds of pollen, species or varieties, 

 one only takes effect to the exclusion of all others ; 

 also that the pollen from a long-styled Primrose is 

 more powerful on the stigma of a short- sty led 

 specimen than its own, and vice versa : hence if the 

 stigma in a rose centre gets sprinkled with pollen, 

 both from its own anthers and from those of a pin 

 centre, the latter will be most probably the effectual 

 agent ; and if the stigma in a pin centre receives 

 pollen by any means from its own anthers (which is 

 unlikely) and from a rose centre, the latter only will 

 take effect. Hence a cross fertilization goes on, and 

 this you see by the agency of insects. It may not have 

 struck you, could not in fact, unless some of these 

 facts were known to you, that insects and flowers 

 are mutually necessary to each other, and neither 

 could exist without the other. I remember being 

 much struck with this remark when I heard it from 

 the lips of Mr. Bates, the traveller of the Amazons, 



