G YRA TION OF PLANTS. 1 5 1 



to the opposite side, not, however, returning along the 

 same Hne."^ That plants did exhibit motion during 

 growth had been observed, but it was left to more 

 recent times to demonstrate how general this kind of 

 growing movement was, and the direction it assumes. 

 Heliotropism, geotropism, sleep of plants, and cir- 

 cumnutation are expressions for forms of the same 

 phenomena of revolving motion in growing plants. 



In the volume which Mr. Darwin has written on 

 the movements of plants, he has distinctly expressed 

 his opinion that apparently every growing part of 

 every plant is continually rotating, though often 

 on a small scale. This movement may be traced 

 in seedlings before they have broken through the 

 ground, and in the extremities of their young roots ; 

 in the stems of some climbing plants, and in the 

 tendrils of others ; in leaves and leaflets, and in all 

 the growing points. 



When seeds commence to germinate they thrust 

 out a small radicle, or rudiment of a root, which at 

 once bends downwards and endeavours to enter the 

 ground. The young rootlet is clad with delicate 

 hairs, which, by the softening of the outer surface and 

 its subsequent hardening helps to attach the plant 

 to the soil. As soon as it emerges from the coat of 

 the seed the young rootlet begins to rotate, and thus 



* Darwin, " On the Movements of Plants," p. i. 



