SEED DISPERSAL 



205 



the ovaries, deposits an egg, then ascends and crowds 

 some pollen on the stigma. The grub, when it hatches 

 from the egg, feeds on the seeds in the ovary, but as there 

 are many seeds in the flower which have been fertilized 

 and the grubs eat only a few of these, the moth has made 

 it possible for the yucca to produce seeds sufficient for its 

 continued propagation, which would be impossible if it 

 were not for the moth. 



These are only a few of the vast number of cases which 

 show the close relationship existing between plants and 

 animals and the dependence of the one upon the other. 



96, Seed Dispersal. Not only must flowers produce fer- 

 tile seeds, if the plants are to continue to exist, but 

 these seeds must be scattered. To do 

 this the seed pods of some plants sud- 

 denly snap open and spread their seeds. 

 The touch-me-not and pea are examples 

 of this. In some plants, like the maple, 

 the seeds are winged (Fig. 100) and float 



for some distance in 

 Others, like the thistle and the 

 dandelion, have light hairlike ap- 

 pendages which enable them to 

 float away. In the case of the 

 tumble-weed (Fig. 101) the plant 

 itself is blown about, scattering 

 the seeds over the fields as it 



air. 



Fig. 101. 



bumps along from place to place. 



Some seeds are provided with hooks or barbs, like the 

 beggar's ticks (Fig. 100), which attach the seeds to 

 animals so that they are carried to a distance. Seeds 

 having an edible fruit cover, such as the cherry, black- 

 berry and plum, are eaten by birds and animals and the 

 undigested seed deposited far away from the place where 



