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 offensiveness 
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 
