268 M. WICHURA ON THE WINDING OF LEAVES. 



comparatively much more frequently in these two regions than 

 in the other parts of the globe. 



III. Single and associated Winding Leaves, 



§11. 



The phaenomenon of winding is not confined to the single 

 leaves of plants, but appears also in structures arising from the 

 confluence of several leaves. Longish shape and parallel course 

 of the vascular bundles are also conditions here. For example, 

 the tubes of the corollas of several Stylideae, which may be called 

 rather long in proportion to their diameter, those of Trifolium 

 resupinatum, L., and certain species of Peristrophe and Hypo'estes 

 of the family of Acanthaceae. So, moreover, the elongated 

 buds of the Convolvulaceae and of Thevetia neriifolia, Juss. 

 (Apocynaceae), originally composed of five separate and very 

 narrow segments, are folded toward one side like a closed um- 

 brella and curved spirally toward the other, &c. If the view, 

 now continually gaining ground, that the stem is not an inde- 

 pendent organ, but originates from the confluence of the 

 sheathing portions of the leaves fitted into each other, could be 

 regarded as completely demonstrated, the winding stem also 

 would have to be included here. 



§ 12. 

 After these examples of winding of several confluent leaves, 

 we may come to those which certainly wind separately, but are 

 situated so close together that they come in contact in the move- 

 ment of winding, and in this way enter into certain combina- 

 tions, which, from the regularity of the movement on which 

 they depend, assume a regular shape. 



§ 13. 



Here belong : the entwined cotyledons of the Gyrocarpeas ; the 

 awns of the panicles of Streblochate nutans, Hochst., and Andro- 

 pogon Allionii, D.C., which are twisted together into a cord-like 

 body ; the floral envelopes of many species of Iris and all the 

 species of Aristea (Iridaceae) known to me, which wind round 



