310 M. WICHURA ON THE WINDING OF LEAVES. 



because the usually narrow form opposes the least resistance to 

 the rotating force, perhaps present as in other leaves and only 

 restrained in its effects, is testified by the occurrence of angle- 

 nerved leaves of very long and narrow shape, which, never- 

 theless, do not wind. So far as regards length and breadth of 

 their parts, these stand in exact agreement with parallel-nerved 

 leaves ; indeed the lobes and pinnae into which they frequently 

 divide are sometimes much finer and more delicate than those 

 of winding parallel- nerved leaves. If, therefore, the forces 

 moving the parallel-nerved leaves were active in these, they 

 ought to exhibit the same effect, and it should produce an heli- 

 acal winding of the angle-nerved leaves in a determinate direc- 

 tion. But we do not see this; proof, consequently, that the 

 angle-nerved leaves are devoid of the rotating force, and that 

 the cause of the absence of revolution of the axis from them 

 does not arise from their merely opposing a greater resistance 

 than the parallel-nerved leaves to a rotating force existing in 

 them. Hence latitudinal growth of the leaf and rotation of the 

 axis are really mutually exclusive. When the former is deve- 

 loped, the latter is wanting, and so it seems to follow from this 

 that one and the same force lies at the foundation of both, 

 manifesting itself either in the transversely directed activity of 

 growth, or, when this is absent, in a lateral movement of the 

 leaf. 



132. 



While attention was paid merely to winding stems, it was 

 possible to suppose the object of this motion to be that of ob- 

 taining attachment to outw r ard objects. We are now aware 

 that a great proportion of winding stems, and winding leaves 

 in general, never coil round a support nor contribute to the 

 fixing of a plant. The latter, therefore, appears to be merely 

 an isolated application of the movement of winding in the 

 oeconomy of nature, and we must confess that we are totally 

 ignorant of its peculiar relation to the vital purposes of the in- 

 dividual, or the propagation of the species. This movement is, 

 at the same time, the most frequent of all those detected in the 

 outward organs of plants. The number of plants with winding 

 stems alone, particularly if we include the winding flowering 

 stem of the Monocotyledons and the winding fruit-stalks of the 



