ACCESSORY, AGGREGATE, AND COLLECTIVE FRUITS 83 



cally an aggregate fruit, they are really only a compact 

 head or cluster. Some degree of cohesion is necessary to 

 constitute a cluster of matured ovaries into an aggregate 

 or a multiple fruit. 



116. The Individual Fruits that make up the various 

 kinds just described may belong to any of the classes men- 

 tioned in Sections 73-109; those of the blackberry, for 

 instance, are drupes ; of the strawberry, achenes ; of the 

 sweet gum, capsules. 



117. Use of Fruits to the Plant. — Have you ever asked 

 yourself how it could beneiit a plant to invite birds and 

 beasts to devour its fruit, as so many of the bright berries 

 we find in the woods seem to do .'' 



In order to answer this question we must remember that 

 it is clearly to the advantage of every plant to disperse its 



187-190. — Fruits adapted to wind dispersal: 187, winged pod of pennycress; 

 188, spikelet of broom sedge ; 189, achene of Canada thistle ; 190, head of rolling 

 spinifex grass. 



seeds as widely as possible, both that the seedlings may 

 have plenty of elbow room, and that they may not have 

 to draw their nourishment from soil already exhausted by 

 their parents. The farmer recognizes this principle in 

 the rotation of crops, because he knows that successive 

 growths of the same plant will soon exhaust the soil of 

 substances proper for its nutrition, while they may leave 

 it rich in nourishment suitable for a different crop. Now, 

 Nature, like a good farmer, seeks to provide for a rotation 



