16 LIVING PLANTS 



Chemical sense 



sensitiveness characteristic of each. Some 

 stems, however, like those of the Virginia creep- 

 er, turn away from light, enabling them to 

 cling to dark walls. Roots which are general- 

 ly buried in the soil, rarely exhibit sensitive- 

 ness to light, and when they do, it is usually 

 to turn from it. If light comes to the organ 

 from two directions, it will bend toward the 

 source of the stronger light, and differences 

 which will affect the plant are far more minute 

 than can be detected by the eye. 



As in the case of roots, certain stems place 

 themselves not parallel with the direction of 

 the light, but at some particular angle to it, 

 in accordance with some inherent necessity. 

 Not as large a part of the plant, as a rule, is 

 as sensitive to light as to gravity, but the de- 

 gree of sensitiveness is often greater. 



Plants also possess a chemical sense, a kind 

 of taste, by which they detect certain sub- 

 stances in solution fitted for their nutrition. 

 By this means parasitic fungi starting to 

 grow upon the surface of other plants find 

 their way into the stomata from which the 

 acid juices of the tissues diffuse, and thus gain 

 entrance into the host. Roots exhibit sensi- 

 tiveness to many nutritive substances, al- 

 though not as a rule to the same extent that 

 fungi do. Et enables them to turn and grow 

 in the direction of the best food supply, and 



