144 



ORGANOGRAPHY. 



arrangement of the leaves has a direct influence upon the forms 

 of the wood, bark, and pith; either upon one of those parts 

 only, or sometimes upon them all; but, although some curious 

 relations have been found to exist between the arrangement of 

 the leaves and the form of certain parts of the stem, yet it is 

 not possible at present to deduce any general laws regulating 

 the relations between them. 



Having now described the general arrangement of leaves 

 when in an expanded state upon the stem or axis, Ave have in the 

 next place to allude to the different modes in which they are 

 disposed while in a rudimentary and unexpanded condition in 

 the bud. To tliese the general name of Vernation or Prrefoliation 

 has been appHed. 



Vernation or Prce foliation. — Under this head we include : — 1 st, 

 The modes in which each of the leaves considered independently 

 of the others is disposed: and 2nd, The relation of the several 

 leaves of the same bud taken as a whole, to each other. In the 

 first place we shall consider the modes in which each of the 

 leaves considered separately is disposed. We arrange these 

 again in two divisions: — 1st, Those in which the leaf is simply 

 bent ov folded ; ?in(\. 2x\([, Those where it is rolled. Of the first 

 modification we have three varieties: — Thus 1st, the upper half 

 of the leaf may be bent upon the lower, so that its apex ap- 

 proaches the base, as in the Tulip-tree {fig. 270); it is then said 



Fig. 271. Fig. 272. Fig. 273. Fig. 274. 



Fig.^ 270 Vertical section of a reclinate leaf. 



Fig. 271. Transverse section of a couduplicate 



leaf. Fig. 272. Transverse section of a plaited 



or plicate leaf. Fig. 27o. Vertical section of a 



circinate leaf. Fig. 274. Transverse section 



of a convolute leaf. Fig. 27.j. Transverse 



section of an involute leaf. Fig. 27fj. Trans- 

 verse section of a revolute leaf. 



to be reclinate ov in flexed; 2nd, the right half may be folded upon 

 the left, the ends and midrib or axis of tlie leaf remaining im- 

 movable {fig. 271), as in the Oak and Magnolia, when it is called 

 conduplicate ; or 3rd, each leaf may be folded up a number of 

 times like a fan, as in the Sycamore, Currant, and Vine (fig. 

 272), when it is plaited or plicate. Of the second inotlification 

 we have four varieties: — 1st, the ajtcx may be roHed uj) on the 

 axis of the leaf towards the base like a crosier, as in the Sundew 

 and Ferns (^f/. 273), when li is circinate; 2nd, the whole leaf may 



