M. WICHURA ON THE WINDING OF LEAVES. 269 



spirally as the flower withers ; and lastly, what is called the 

 " contorted aestivation." The latter deserves a separate discus- 

 sion, because its connection with the winding movement is not 

 at first sight clear. 



The " aestivatio contorta " is a structure which makes its ap- 

 pearance at a comparatively late stage of the growth of the bud. 

 When examined in their earliest conditions the rolled buds ex- 

 hibit leaflets standing singly, so narrow that their margins do 

 not touch. They become broader at a later stage, and the posi- 

 tion of the leaves, peculiar to the twisted aestivation, arises 

 from the mutual over- and inter-growth of their margins. 



Fig. 1, PL IX. represents two horizontal sections of oppositely 

 rolled buds. By an examination of these it is readily ascertained 

 that the surfaces of the leaves are obliquely inclined to the centre 

 of the flower, and in the same direction in all the leaves of the 

 same flower. Either the leaves have been attached obliquely on 

 the receptacle from the first ; and then the twisted aestivation is 

 not the effect of a subsequent twisting of the separate leaflets, 

 and does not belong here ; or the leaflets are not originally 

 attached obliquely ; and then they can only be brought into the 

 oblique position subsequently evident, by a slight twisting. 

 Which of these two alternatives is the correct one, I could not 

 ascertain by direct observations, since the oblique position of 

 the leaflets only becomes perceptible by its effect, the growth of 

 the borders over and between each other. It is so slight, and 

 the curvature, if such occurs, is so lost in the earliest stages of 

 the bud, that it sinks to a microscopical magnitude, from the 

 transparency and delicacy of all the parts no longer recognizable 

 by the sight. On the other hand, conclusions may be drawn 

 from other perceptible facts, which give very reliable testimony 

 that the twisted aestivation owes its origin to a winding of the 

 individual leaflets. 



15. 



In the first place, an approximative testimony is furnished by 

 the occurrence of the twisted aestivation in gamopetalous corol- 

 las. The history of development of these, teaches us that they 



