368 PLANT LIFE. 



they may not be subject to further disturbance. Such an- 

 chorage is sometimes secured by the transformation of the 

 outer layer of cells into mucilage, so that the seed, upon be- 

 coming wet, is stuck fast to the soil ; or by the tufts of hair 

 which, once wetted, cling to the surface of the earth ; or by 

 barbed bristles and hygroscopic awns which, having become 

 entangled among the grass, work a pointed seed body deeper 

 by every change of moisture (fig. 406). 



Study of plants in relation to their surroundings, therefore, 

 yields the conclusion that these organisms are wonderfully • 

 plastic, responding either temporarily or permanently to 

 every change in conditions. It is greatly to be desired that 

 the too common thought of plants as only things to he clas- 

 sified may be replaced by the conception of them as beings at 

 work, to be studied alive. 



