392 



LIFE ON THE EARTH 



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 re- 

 lationship existing between 

 plants and animals and 

 the dependence of the one 

 upon the other. 



Seed Dispersal. Not 



only must flowers produce 

 fertile seeds, if the plants 

 are to continue to exist, 

 but these seeds must be 

 scattered. To do this the 

 seed pods of some plants 

 suddenly 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 (Figure 126) and 



float for some distance in the air. Others, like the thistle 



and the dandelion, have light, hairlike 



appendages which enable them to float 



away. In the case of the tumbleweed 



(Figure 127) the plant itself is blown 



about, scattering the seeds over the fields 



as it bumps along from place to place. 

 Some seeds are provided with hooks or barbs, like the 



beggar 's-ticks (Figure 126), which attach the seeds to animals 



so that they are carried to a distance. Seeds having an 



YUCCA OK SPANISH BAYONET 



FIGURE 126 



