862 



THE DISPEESION OF SPECIES BY MEANS OF FEUITS AND SEEDS. 



serves to fasten it to some place where the conditions requisite for germination are 

 present. For instance, when the seeds of Tillandsia (see 475 ^) come into contact 

 with the boughs of old trees, as they are blown along in a horizontal direction, they 

 fasten on to the bark where they are able to germinate immediately. Thus the 

 pappus to which the seed owes its buoyancy serves subsequently to anchor it to a 

 substratum favourable to its development. 



The modes of dispersion of fruits and seeds through the agency of animals are 



Fig. 475. — Dispersion of fruits and seeds by the wind. 



^ Capsule of Vanda teres, from which the seeds have been transferred to the air by means of hygroscopic hairs, and are being 

 blown away. ^ Open capsule of a TiUandsia ; the seeds are being lifted out by the wind by means of their parachutes. 

 If a-seed is blown against the bark of a tree it is anchored there by the hairs of the parachute. 



almost as varied as the different methods of dissemination by the wind. In many 

 cases such dispersion is brought about by the animals using the fruits and seeds in 

 question for food; the undigested parts are excreted, and any embryos which may 

 have survived the passage through the alimentary canal subsequently germinate. As 

 the fact of this mode of dispersion has been a matter of dispute amongst botanists, 

 and could only be established by experiment, i determined to feed various animals 

 with selected fruits and seeds, and to ascertain first of all whether the embryos 

 preserve their vitality after passing through an animal's intestinal canal. Fruits 

 and seeds belonging to 250 different species of plants were used for the purpose, and 



