284 M. WICHURA ON THE WINDING OF LEAVES. 



XI. Regular Succession of the two Opposite Directions. 



§48. 

 The examples of leaves which wind toward opposite sides, 

 mentioned in § 12, all agree in the circumstance that the direc- 

 tion to the left invariably precedes the subsequently occurring 

 winding towards the right. The leaves with their points and 

 bases wound in opposite directions exhibit a similar condition. 

 With the single exception of Alstroemeria pelegrina, the upper 

 part of the leaf always winds to the left, the lower part to the 

 right. Here therefore the winding to the left likewise precedes 

 the winding to the right, since the upper portion of the convo^ 

 luted organs is always older than the lower. 



§49. 

 The application of the same law may further be shown in 

 organs wound only in one direction, insofar as they are to be re- 

 garded, either wholly or in the winding part, as metamorphosed 

 summits or bases of leaves. The summits of leaves, consequently 

 the style, stigmas, anthers, and, above all, the petals in contorted 

 aestivations, which wind at a period when the point only of the 

 leaf has been protruded from the receptacle, — follow the direc- 

 tion toward the left in a vast majority of cases. The blade of 

 the stem-leaves, as a superior region, is most generally, although 

 not quite so frequently, w^ound to the left, while the sepals and 

 carpels, as metamorphosed forms of the sheathing portion of the 

 leaf, are predominantly w^ound to the right. 



§ 50. 

 From this it follows that the two directions to the right and 

 left stand in a fixed relation to the different periods of the age 

 of the leaf, which at the same time have their material expres- 

 sion in the upper and lower parts of these organs. The winding 

 to the left belongs to the earlier period of growth, and occurs 

 chiefly in the upper parts of the leaf. The winding to the right 

 follows at a later period, and is connected principally with the 

 upper parts of the leaf. Since the stem, considered in relation 

 to the leaf, represents a structure standmg underneath, it is 

 completely in consonance with this law, that, as we find, the 



