OEGAJTS OF NUTRITION". 141 



of the ijiternodes of a branch become non-developed, the leaves 

 become tufted or fascicled {Jiff. 262), as already noticed. As a 

 general rule, however, the relative position of leaves is suffi- 

 ciently constant in the same species as to form one of its 

 characteristic distinctions. 



The arrangement of leaves probably influences, in some degree 

 at least, the form of the stem and branches. Thus, a certain 

 amount of alternation commonly leads to a rounded form of 

 stem, an opposite, or whorled arrangement, to an angular stem ; 

 for instance, the Labiate order of plants, which have opposite 

 and decussate leaves, have square stems ; in the Nerium Oleander, 

 where the leaves on the young branches are placed in whorls of 

 three, the stem has three angles ; and in the Madder order of 

 plants, which have whorled leaves, the stems are always angu- 

 lar. M. Cagnat and others have also endeavoured to show that 

 the arrangement of the leaves has a direct influence upon the 

 forms of the wood, bark, and pith ; either upon one of these 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 

 tlie relations between them. 



3. Arrangement of the Leaves in the Bud or Verna- 

 tion. — Having now described the general arrangement of leaves 

 when in a fully formed and expanded state upon the stem or 

 branch, we have in the next place to allude to the different modes 

 in which they are disposed while in a rudimentary and unex- 

 panded condition in the bud. To these modifications the general 

 name of Vernation or Prcsfoliation has been applied. Under this 

 head we include: — 1st, The modes in which each of the leaves con- 

 sidered independently of the others is disposed : and, 2nd, The 

 relation of the several leaves of the same bud taken as a whole 

 to one another. 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 or folded ; and 2nd, Those where it is rolled . 

 Of the first modification we have three varieties : — Thus, 1st, the 

 upper haK of the leaf may be bent upon the lower, so that the 

 apex approaches the base, as in the Tulip-tree {fig. 268), it is 

 then said to be reclinate or mflexcd ; 2nd, the right half may be 

 folded upon the left, the ends and midrib or axis of the leaf re- 

 maining immovable {fig. 269), 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, Cm^rant, and 

 "Vine {fig. 270), when it is plaited or 'plicate. Of the second 

 modification we have four varieties : — 1st, the apex may be rolled 

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

 the Sundew and Ferns {fig. 271), when it is circinate; 2nd, the 



