262 M. WICHURA ON THE WINDING OF LEAVES. 



Article IX. 

 On the Winding of Leaves, By M. Wichura. 



[From the * Flora,' January and February 1852.] 



1 HE leaves of plants possess in the flexibility of their tissue 

 full capability of twisting, and it has long been known that this 

 property must often serve to assist the efforts of plants to ap- 

 proach towards the light. Twisting movements of this kind are 

 readily recognizable from the circumstance that all the characters 

 of the movement may be brought into agreement with their pur- 

 pose, to direct the upper face of the leaf towards the light. The 

 twisting begins directly anything turns the upper face of the 

 leaf away from the light, and continues until that face is again 

 directed to the full rays of the incident light. It turns indif- 

 ferently either to the right or left, according to which path will 

 lead quickest to its object. Its extreme degree never exceeds 

 a half-revolution, since this suffices to turn the leaf completely 

 over, and therefore to return the upper side again towards the 

 light, when it has been wholly turned away from it. 



But there are plants the winding leaves of which present ex- 

 actly the opposite character in all these things, and, in particu- 

 lar, exhibit the same regularity in their lateral direction as we 

 detect in winding stems. 



The winding movements of the second kind cannot be re- 

 garded as an effect of the irritability of vegetable tissue excited 

 by light. They are immediate expressions of the vital force ac- 

 tive in the interior of the plant, and nearly aUied to the winding 

 of tlie stem and tendrils. While, however, the latter have long 

 occupied the attention of botanists, the windings of leaves have 

 remained almost unknown, and all that we possess are a few 

 scattered and mostly very meagre notices thereon. I myself 

 gained my first knowledge of them through perceiving the 

 heliacal winding of the leaves and strict regularity displayed in 

 their direction, in some Oat and Barley plants germinating in- 

 doors. Further researches, to which I was thereby attracted. 



