RELATION TO ENVIRONMENT 



513 



Edible Seeds and Fruits 



Most seeds contain starch and other reserve-food which makes 

 them suitable for the food of animals. In collecting these for food, 

 and especially when these are stored, some are pretty sure to escape 

 being eaten, and may be carried away and dropped at some distance 

 from where they were gathered. So, also, seeds imbedded in mud 

 may adhere to the feet of birds or animals, and thus be transported. 

 These cases must be considered as more or less accidental, however, 

 and there is no question of special adaptability. 



Very different is the case of fruits in which the edible part is not 

 the seed, but consists of a pulp in which the seeds are imbedded. 

 Such edible fruits are in most cases obviously specially developed to 

 facilitate the distribution of the seeds. The sweet pulp of these is 

 often an important article of food, and the bright colors of such 

 edible fruits may be looked upon, in many cases, as attractive to ani- 

 mals in much the same way that the colors of flowers attract them. 



In some instances the pulp is eaten away and the seeds dropped 

 upon the ground, or, where the seeds 

 are small, and completely imbedded 

 in the pulp, the whole fruit may be 

 swallowed, and the seeds pass through 

 the digestive tract without being in- 

 jured. Birds are especially important 

 in thus distributing seeds. 



Adhesive Fruits and Seeds 



Some seeds e.g. species of Araceae, 

 Mistletoe, various tropical Loranthaceae 

 develop a viscid substance either 

 from the seed itself, or from the fruit, 

 and this causes the seeds to adhere to 

 the bodies of animals, especially birds, 

 which tlms transport them to other 

 trees, to whose branches they may be 

 transferred, and so establish them- 

 selves. Such adhesive seeds usually 

 belong to epiphytic plants. 



Another sort of attachment is effected 

 by the hooks, bristles, and similar 

 organs with which the fruits of many 

 plants are provided. The barbed awns 

 of certain Grasses, the rough spines of Bur-marigold (Bidens), the 

 hooked burs of Clotbur (Xanthium) or Hound' s-tongue (Fig. 479), 

 2 L 



FIG. 479. Adhesive fruits. A, 

 B, Hordeum murinum. C, 

 Medicago denticulata. D, Cyno- 

 glossum offlcinale. 



