498 Plant Physiology 



seed in a moist chamber pinned in a horizontal posi- 

 tion will respond to the stimulus of gravity by growth 



curvatures in the same manner. 



frtj. 



[ Secondary roots and branches take 

 up plagiotropic positions, but in the 

 ' ti s remote branches of the root little geo- 



IIILZZZIZ If tropic response is manifest. Shoots 



from a fallen trunk assume the ver- 



,, ^ tical position. If the terminal shoot 



J ^Z" o f spruce is cut off, one or more lateral 



"* 



shoots of the first whorl may be 

 T L raised into the vertical position. 



The erection of the jointed stems of 

 grasses is effected by curvatures in 

 the nodes, and these stems are par- 

 ticularly interesting for study. 



FIG. 142. Geotropic ~ 



curvature of root of Geotropic response is not a ques- 



Vicia Faba ; horizontal tion of weight, and this is shown by 



position (I), after? hrs. ,1 v , f ,\ 



(ID, and after 23 hrs. the diverse reactions of the mam 

 (ill). [After Sachs and axis and branches. Furthermore, 



there is no geotropic response when 



gravity is eliminated, as by revolving seedlings in a ver- 

 tical plane on a klinostat geared to make one revolution 

 in about fifteen minutes. On a klinostat rotated hori- 

 zontally at a low rate of speed the usual stimulus of 

 gravity is N felt ; but when rotated at a higher rate of 

 speed the root grows outward and toward the horizontal, 

 and the shoot inward and toward the horizontal, de- 

 pending upon the rate of rotation. 



In the case of the root the perceptive region is usually 

 confined to about one millimeter, or less, at the very tip, 



