The Response of Plants 



sponse, functional response, if you prefer, is just as 

 definite, just as intimate as in the case of their congeners 

 of the animal world. 



Volumes might not suffice to set forth or illustrate the 

 variety of the plant response. Let us for the present 

 note as we may a few cases simply, which may establish 

 the general fact. It will not be possible to discuss even 

 these with any fulness, but we may at least see the out- 

 lines of the argument. 



In the first place, then, plants respond to the force of 

 gravity. Every one of the higher plants is to greater or 

 less extent, in the axis of its growth, a simple extension 

 of the radius of the earth. The fern, the blade of grass 

 quite as much as the birch, the oak, the pine, the taper- 

 ing spruce upon the mountain shelf each and all are 

 subjects of that eternal power that holds alike in place 

 the planet and the grain of sand. The mountain spruce 

 unvexed by storms, erect, two hundred feet in height 

 drawn sunward by the light, held downward by its 

 Weight as by a thousand equal silken cords, shines in a 

 spire of conic symmetry the very dream of architectural 

 elegance and grace. The very posture and form of 

 every plant you see is the outcome, first, of what we call 

 'its nature, its heredity accumulated responses of all 

 its ancestors plus the resultant of gravity in conjunc- 

 tion night and day with meteoric forces from "a' the 

 airts the wind can blaw." The fact is that we are so 

 familiar with the response of plants to gravitation that 

 we have ceased to think the case remarkable. 



I have mentioned in that other sentence "heredity" 

 as a dominant factor in the plant's behavior; but hered- 



