M. WICHURA ON THE WINDING OF LEAVES. 



are composed, in the earliest periods of their formation, of sepa- 

 rate leaves which subsequently become blended together. It 

 will be admitted that if the " aestivatio contorta " depended on 

 an oblique attachment of the leaflets upon the receptacle, this 

 must exist from the moment of the origin of the leaf, and conse- 

 quently in those earliest periods of growth when the individual 

 parts of the gamopetalous corolla were not yet confluent. If 

 then, in the "aestivatio contorta," the oblique position of the 

 leaflets subsequently caused their borders, with the increasing 

 breadth, not to meet together, but to pass over and under one 

 another, this obliquity must, at the time when the confluence of 

 the separate foliaceous elements should commence, hinder their 

 coming into contact and consequently the confluence itself. 

 Hence oblique attachment of the foliaceous elements and gamo- 

 petalous growth seem to exclude each other, and if gamopetalous 

 corollas nevertheless do occur with rolled segments, it follows 

 that the rolled position in the bud cannot be explained by an 

 originally oblique attachment of the leaves. Then there only 

 remains the other alternative, that the foliaceous elements are 

 originally evenly attached, and only after confluence has oc- 

 curred, undergo a twisting of the free points, by which they are 

 brought into the position suited to the formation of the contorted 

 aestivation. 



16. 



I regard this proof as not wholly conclusive, only because it 

 is based upon suppositions which relate to the still somewhat 

 problematical processes of the confluence of the floral organs in 

 the earliest stages of development of the flower. But the twist- 

 ing of the leaflets on which the contorted aestivation depends, 

 was completely demonstrated by an observation which I had an 

 opportunity of making on a plant of Helicteres cultivated in the 

 Berlin Botanical Garden. The long and narrow petals of this 

 plant possess two opposite teeth on the margins, near the lower 

 part. In the bud, the teeth of the adjoining petals cover one 

 another in the manner of the " aestivatio contorta," as do like- 

 wise the upper parts of the little petals, but in an opposite di- 

 rection. While the right tooth of one leaf covers the left tooth 

 of the next leaf, the left margin covers, above, the right margin 



