24 



PRACTICAL COURSE IN BOTANY 



adhesive weed pests, are no doubt very unwilling carriers of 

 those disagreeable burdens. 



21. Tempting the appetite. — This is the most important 

 adaptation to dispersal by animals. Have you ever asked 

 yourself how it could profit a plant to tempt birds and beasts 

 to devour its fruit, as so many of the bright berries we find in 

 the autumn woods seem to do? To answer this question, 

 examine the edible fruits of your neighborhood and you will 

 find that almost without exception the seeds are hard and 



bony, and either too 

 small to be destroyed 

 by chewing, and thus 

 capable of passing 

 uninjured through 

 the digestive system 

 of an animal ; or, if 

 too large to be swal- 

 lowed whole, com- 

 pelling the animal, 

 by their hardness or 

 disagreeable flavor, 

 to reject them. In 

 cases where the seeds 

 themselves are ed- 

 ible and attractive, 

 the fruits are usually 

 armed during the 

 growing season with 

 protective coverings, 

 like the bur of the chestnut and the astringent hulls of the hick- 

 ory nut and walnut. The acidity or other disagreeable quali- 

 ties of most unripe fruits serves a similar purpose, while their 

 green color, by making them inconspicuous among the foliage 

 leaves, tends still further to insure them against molestation. 



22. Voluntary agency. — The cultivated fruits and grains 

 owe their distribution and survival almost entirely to the 



Figs. 40-42. — Adhesive fruits : 40, fruit of hound's- 

 tongue ; 41, akene of bur marigold ; 42, fruit of bur 

 grass (cenchrus). 



