M. WICHURA ON THE WINDING OF LEAVES. 



of the next leaf. It is clear that this contrast cannot be explained 

 by an oblique attachment of the young petals, since this can 

 only act in one direction : we are absolutely compelled to the 

 assumption that a curvature must have taken place here, which, 

 as we shall see, in many cases alters its direction within the 

 same leaf. 



17. 



The rolled buds also betray their close relationship with the 

 movement of winding in other respects. A comparatively very 

 large proportion of the plants in which the floral envelopes or 

 segments of the flower twist after the flower has opened, have 

 rolled buds ; for example : Puya ccerulea, Miers (Bromeliaceae), 

 Christya speciosa, Ward and Harv., Strophanthus divergens, 

 Graham (Apocynaceae), Pergularia edulis, E. M., P. accidens, 

 Blume, Diplolepis Menziesii, R. & S., Oxy pet alum riparium, 

 H. B. K. (Asclepiadaceae), Cyclamen europeeum, L., Lysimachia 

 punctata, Wall. We likewise frequently meet with rolled buds 

 which are at the same time twisted in one or other direction, as 

 in jEchmea latifolia, Kth. (Bromeliaceae), Strophanthus dicho- 

 tomus, D.C., Echites longiflora, Desf. (Apocynaceae), Pergularia 

 edulis, E. M., Microloma sagittata, R. Br. (Asclepiadaceae), Gil- 

 lenia trifoliata, Mcench. (Rosaceae), &c. From all these reasons, 

 therefore, I have no hesitation in regarding the " aestivatio con- 

 torta " as an effect of the movement of winding. 



IV. Heliacal shape of Winding Leaves. 



18- 



The characteristic mark of all winding leaves is their heliacal 

 shape, with manifold modifications, however, depending on the 

 variability of the distance of the heliacal line from its axis, the 

 angle of inclination, and the length of the helix. 



19- 



The distance between the heliacal line of the leaf and the axis 

 of the helix may be either great or small. If it is reduced to 

 the smallest possible amount, it coincides with the median line 

 of the leaf itself. The fruit of Ailanthus glandulosus, L., repre- 



