34 SOUTH AFRICAN FLOWERING PLANTS. 



in unfavourable seasons, when such bees are scarce, 

 much clover fails to produce seed. 



When it was first introduced into our Colonies in 

 the Southern Hemisphere, complaints arose of its 

 failure, so the English humble-bee was imported. This 

 was said to overcome the difficulty. But it appears 

 to have failed only in some places ; 

 for in others reports were received 

 that there was no difficulty in 

 getting seed, but whether by 

 native bees or by acquired self- 

 fertilization was not stated. 



It may be mentioned that it 

 was thought at one time that self- 

 fertilization was injurious, and that 

 plants habitually setting seed by 

 their own pollen grew weaker and 

 weaker, and finally died out. This was due to an 

 error of observation. They are mostly insignificant 

 flowers ; but for health, vigour, and abundance of good 

 seed, the plants are not to be surpassed. Moreover, 

 self-fertilizing " weeds " are far more widely dispersed 

 over the globe than the plants which display brighter 

 and larger flowers, but are dependent upon the 

 capricious visits of insects for fertilization. 



Mr. Darwin made a large number of experiments 

 in " crossing " some and " self-fertilizing " others, arti- 

 ficially, of the same kinds of plants. He then compared 



Fig. 18.— Clover. 



