46 THE HUMAN SIDE OF PLANTS 



fields, and so the original purpose of the parent 

 plant is accomplished. 



The sourness and bitterness of unripe fruits are 

 due to the temporary secretion of acids in order 

 to keep off attacking animals and birds until the 

 seeds are ripe and ready for distribution. This 

 sourness is merely a defensive move ; once the seeds 

 are ready, the plant softens and sweetens its fruits 

 in order to attract to itself with its sweetness the 

 unintentional seed-carrier. 



Odours form a strong protective force in use by 

 many kinds of plants. These by their off ensiveness 

 ward off the attacks of depredatious animals and 

 insects which otherwise would destroy them. There 

 are many familiar examples of this means of de- 

 fence: the skunk-cabbage, the Datura, snakeroot, 

 tobacco, and many other plants employ it; one of 

 the St. John's-worts has an odour like that of a 

 goat. 



In the world of humans there are always a num- 

 ber who "fight with their heels," who run from 

 danger to the shelter and protection of some 

 stronger person or force. The plants which seek 

 safety in flight are not so numerous as are the 

 humans, but there are several types of grasses and 

 plants which do so. In southern Texas and north- 

 ern Mexico there is a well-known grass, much 



