M. WICHURA ON THE WINDING OF LEAVES. 263 



made partly in the field, partly in the Botanical Gardens of 

 Breslau and Berlin, and lastly, partly in the General Herbarium 

 at Berlin, have revealed to me so great a number of similar 

 phaenomena, that I venture to found upon them an attempt at a 

 general description of the phaenomenon. 



I. Form and outward condition of Winding Leaves, 



§1. 



Although examples of winding leaves may be pointed out in 

 all metamorphoses of the leaf, in the most diverse families of 

 the vegetable kingdom, and in all the local floras of the globe, 

 much agreement in structure is exhibited by them in spite of 

 this wide diffusion. They are all of longish, mostly linear- 

 lanceolate shape, have smooth entire margins, and in regard to 

 the distribution of their vascular bundles, either belong to the 

 parallel-nerved system, as developed most clearly in the stem- 

 leaves of Monocotyledons, or they are totally devoid of vessels, 

 as in the leaves of the Mosses and Liver-worts. The angular- 

 nerved leaves of the Dicotyledons, as for instance of our fruit- 

 trees, of the Poplar, Lime, &c., appear never to admit this 

 winding movement. In the Dicotyledons only those leaves 

 wind which imitate, either perfectly or at least approximatively, 

 the parallel-nerved system of the Monocotyledons. 



§2. 



If we attempt to bring the properties of winding leaves, men- 

 tioned in the preceding section, under a common point of view, 

 we must say that the longitudinal growth is developed at the 

 cost of the transverse growth in winding leaves. For, if the 

 angular-nerved distribution of the veins in which strong branches 

 turn off toward both sides from the midst of the leaf, and, sud- 

 denly leaving the longitudinal direction, pass into the transverse, 

 is to be considered, no less than the lateral subdivision of the 

 leaf into teeth, pinnae, &c., as the expression of an active growth 

 in the direction of the breadth, — it follows that the essential 

 feature of leaves which neither have an angular venation, 

 nor are toothed or pinnate, but are parallel-veined, smooth- 

 edged and very narrow in proportion to their length, must be a 



