SELF-FERTILISED FLOWERS 175 



of the tall leafy green orchis, are so organised as 

 completely to prohibit self -fertilisation. 



The complicated mechanism of the milkweed 

 rigidly exacts cross-fertilisation; and we know that 

 the clover is as firm in the matter as was proved 

 by the experience of the farmers of Australia, who 

 could get no clover to make seed till bumblebees 

 were imported. 



The jewel- weed, iris, trumpet-vine, and monkey- 

 flower should be crossed off, since their mechanisms 

 also forbid self-fertilisation. Then, the many flow- 

 ers whose stamens shed pollen and wither before 

 the stigma is ripe, of which the wild geranium is a 

 type, are practically secure against self-fertilisa- 

 tion ; for, to all intents and purposes, they are stam- 

 inate flowers at one stage and pistillate at another. 



The flowers belonging to the classes so far men- 

 tioned are perpetuated through cross-fertilisation 

 only. 



After them come many flowers which are less 

 strict in their habits, and which permit or even ar- 

 range for self-fertilisation, as a last resort, to avoid 

 extermination. 



In the mountain laurel flower it might easily hap- 

 pen that a few grains of pollen should be thrown 

 upon the stigma, though as a rule the body of the 

 moth visiting the flower is likely to form a shield 



