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 ot 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 be clas- 

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

 work, to be studied alive. 



