CHAPTER XIII. — THE FRUIT AND SEED. 



107 



feathery, and serves to waft away the ripened fruit ; in the Straw- 

 berry the receptacle becomes thick and succulent, and consti- 

 tutes the edible portion of the fruit, and in the Dandelion and 

 Thistle the modified Calyx-limb, or pappus, renders the fruit 

 buoyant and easily wafted by the wind. 



Doubtless the reason why fruits often have conspicuous colors 

 is to render them attractive to birds and other animals that can 

 aid in their dispersion. As the seeds of edible fruits are usually 

 indigestible, or difficultly digestible, the fact that the fruits are 

 pleasing to the taste aids the dispersion of their seeds, and 

 secures their deposit under conditions favorable to germination. 

 The hooks and spines which are found on many fruits, or 

 attached to accessory organs, are also means by which plants 

 utilize animals for the dispersion of their seeds. 



Dispersion. —The agencies made use of by nature for the 

 dispersion of fruits and seeds may be classified as follows : 



(1) The Wind, as when they acquire thin and flattened forms, 

 or are provided with membranous expansions called wings, or 

 have a feathery, hairy or parachute-like pappus, or are other- 

 wise rendered light and buoyant. 



(2) Water Waves or Currents, as in the case of the Cocoa-nut, 

 which, by its structure, is rendered buoyant, and by reason of its 

 possessing a fibrous husk, and a thick, 

 hard shell, is enabled to resist for a 

 long time the action of salt water. 



(3) Hygroscopism. This consists in 

 the property possessed by some fruits, 

 by which one part either absorbs water 

 more rapidly than another, or parts 

 with it more readily, thus in some cases 

 causing a strain upon and at last a 

 sudden rupture of the pericarp, scatter- tree ' Hura cre P ltans - 

 ing the seeds, or else giving rise to movements of a different 

 character which are serviceable in placing the fruit or seed in 

 conditions favorable to germination. To hygroscopism is attrib- 

 utable the violent bursting of the large capsules of the tropical 

 Sandbox tree, Hura crepitans, Fig. 307. When the fruit is 

 thoroughly ripe the segments suddenly separate with a loud 

 report resembling that of a pistol, and the seeds are thrown out 



Fig. 307. — Capsule of Sandbox 



