OTHER METHODS OF PROPAGATION 167 



usually profitable for seed. Farmers have known these 

 facts for a long time, but only recently have they known 

 that the difference between the two crops is due to the 

 habits of the bumblebee. In the spring, when the first 

 crop is in blossom, bumblebees are rarely seen; and the 

 few that have survived the winter can cross-pollinate only 

 a small proportion of the flowers. But by the time the 

 second crop is in blossom, the colonies of bumblebees 

 have multiplied, and many more of the flowers are cross- 

 pollinated. 



The honeybee has a tongue too short to reach the 

 nectar of the red clover, but for multitudes of other 

 flowers it is a most efficient pollen carrier. Butterflies, 

 some moths, and humming birds help in a like way. 

 Usually a study of any one of these creatures and of the 

 flowers it visits most will show some striking way in which 

 the blossom and its helpful visitor are suited to each other, 

 as bumblebee and clover are. 



117. Other Methods of Propagation. Many plants propa- 

 gate themselves in other ways besides by seed. This used 

 to seem very strange. Some years ago, however, August 

 Weismann, a famous German scientist, advanced the 

 theory that all life comes from a certain form of proto- 

 plasm which he called germ plasm. In the higher animals 

 this germ plasm is found only in the organs of reproduc- 

 tion; but in plants it is more or less distributed through all 

 their live tissue. This is why we can propagate some 

 plants from shoots or by grafting and budding. 



Many plants, to be sure, have little germ plasm except 

 in the flower. Such plants can be propagated to advantage 

 only from their seed. In other plants, the germ plasm 

 permeates the entire structure, or at least various parts 

 besides the flower. Many plants reproduce themselves 

 underground by tubers, like the potato, or by new shoots 



