276 M. WICHURA ON THE WINDING OF LEAVES. 



VII. Direction of the Movement of Curvature. 



31. 



The leaf may be curved, toward either the upper or lower 

 face. It follows from the nature of the mixed movement pro- 

 duced by a combination of curvature and revolution around the 

 axis, that the concave side of the curve is directed towards the 

 inside of the heliacal winding, the convex looking outward. 

 Wound leaves which are at the same time curved, are conse- 

 quently divisible into those with the upper and those with the 

 lower face turned to the inside of the winding. 



32. 



Examples of both kinds of winding leaves occur in nature. 

 To the first category belong, for instance, the stem- leaves of 

 most of our Gramineae and Liliaceae, to the latter the acicular 

 leaves of Pinus sylvestris, L., and the anthers of Erythraa Cen- 

 taurium, L. An individuality of a peculiar kind occurred on an 

 Allium transplanted from the Halle Botanical Garden to that of 

 Berlin, which was cultivated in the latter in the years 1848-49 

 under the name of A. simplex, and perhaps still exists there. 

 The two alternating series of opposite leaves of this plant were 

 curved to one side in the earliest condition, in such a manner 

 that in one series the upper and in the other the lower sides of 

 the leaves formed the curved surface. If revolution around the 

 axis is subsequently added to this, we get in one series leaves 

 with the lower faces, and in the other leaves with the upper 

 faces turned toward the interior of the helix. The two kinds of 

 wound leaves elsewhere only found, in the same leaf-metamor- 

 phosis, on different species, were here combined in the same 

 individual. 



VIII. Direction of the Revolution around the Axis. 

 Terminology. 



33. 



In the revolution round the axis likewise only two different 

 directions are conceivable. They receive names from an oppo- 



