142 



ORGANOGRAPHY. 



Fig. 269. Fig. 270. Fig. 271. Fig. 272. 



Fig. 273. Fig. 274. 



Ftgf. 268. Vertical section of areclinate leaf. < 



Fig. 269. Transverse section of a conduplicate 



leaf. Fig. 270. Transverse section of a 



plaited or plicate leaf. Fig. 271. Vertical 



section of a circinate leaf. Fig. 272. Trans- 

 verse section of a convolute leaf. Fig. 273. 



Transverse section of a revolute leaf. Fig. 



274. Transverse section of an involute leaf. 



whole leaf may be rolled up from one margin into a single coil, 

 with the other margin exterior, as in the Apricot and Banana, 

 in which case it is convolute {fig. 272) ; 3rd, the two margins of 

 the leaf may both be rolled inwards towards the midrib, which 

 remains immovable, as in the Violet and Water-Lily {fig. 274), 

 when it is involute; or, 4th, the two margins may be rolled out- 

 wards or towards the lower surface of the leaf, as in the Dock 

 and Azalea {fig. 273), in which case it is revolute. 



"We pass now to consider, secondly, the relation of the several 

 leaves of the same bud taken as a whole to one another. Of 

 this we have several varieties which may be also treated of 

 in two divisions: — 1st, Those in which the component leaves 

 are 'plane or slightly convex ; and 2nd, Where they are hent or 

 rolled. Of the first division we shall describe three varieties : — 

 1st, that in which the leaves are placed nearly in a circle or at 

 the same level, and in contact by their margins only, without 

 overlapping one another {fig. 283), when they are valvate; 2nd, 

 that in which the leaves are placed at different levels, and the 

 outer successively overlap the inner to a greater or less extent 

 by their margins, as in the Lilac, and in the outer scales of the 

 Sycamore {fig. 276), when they are said to be imbricate ; and 

 3rd, if when leaves are placed, as in imbricate vernation, the 

 margin of one leaf overlaps that of another, while it, in its turn, 

 is overlapped by a third {fig. 277), the vernation is twisted or 

 spiral. Of the second division, viz. where the component leaves 

 of the bud are bent or rolled, we shall describe four varieties : — 

 1st, When involute leaves are applied together in a circle with- 

 out overlapping, they are said to be induplicate {fig. 278) ; 2nd, 

 If the leaves are conduplicate, and the outer successively embrace 

 and sit astride of those next within them as if on a saddle, as 

 in Privet, and the leaves of the Iris at the base {fig. 279), they 

 are equitant ; 3rd, If the half of one conduplicate leaf receives 

 in its fold the half of another folded in the same manner, as in. 



