How Plants Secure Change of Location 



397 



of all living things, some kinds actually occurring in all of the 

 continents. Especially effective is the very sticky "bird-lune," 

 formed by Mistletoe berries and many other parasites ; such seeds 

 adhere to the feet or feathers of birds and thus obtain attachment 

 upon trees, the only positions in which 

 they can grow. Some low-growing 

 herbs Uke the Twin-flower (figure 169), 

 attain the same end by the possession of 

 adhesive glands on the fruit. 



There remains but one other method of 

 utilizing animals in the transport of seeds, 

 and that is the most striking and im- 

 portant of all. It consists in providing 

 the seed with some form of indigestible 

 covering, surrounding the same with a 

 nourishing and appetizing pulp, and giv- 

 ing the whole a bright color which con- 

 spicuously displays its position. Such 

 fruits are then eaten by animals, and the 

 seeds pass through their bodies unin- 

 jured, after an interval that usually en- 

 sures their discharge at a place con- 

 siderably distant from where they were eaten. This without 

 doubt is the explanation of the existence and characteristics of 

 colored and edible fruits in nature ; and so abundant and familiar 

 are they that we need hardly cite any examples. So common, 

 indeed, are edible fruits, and so effective their use, that this 

 method of dissemination must rank very high among the modes 

 of plant transport, and is second, if to any, only to wind waftage. 

 To this method of seed transport, birds are better adapted than 

 other animals, since their smaller size makes it possible to attract 

 them with not too lavish provision of pulp, and their very active 

 habits ensures their movement over considerable spaces. Ac- 

 cordingly, colored fruits are especially abundant on trees, shrubs, 



Fig. 169. ^The glandular-ad- 

 hesive fruits of the Twin- 

 flower. 



