88 MANUAL OF BOTANY 



of growth ; or if the whole of the internodes of a branch become 

 non-developed, the leaves may become tufted or fascicled 

 (fig. 163), as already noticed. Generally, however, the relative 

 position of leaves is so constant in the same species that it forms 

 one of its characteristic distinctions. 



A certain order of arrangement may often be noticed between 

 the leaves of a stem and those of the branches springing from 

 their axils. Thus in Dicotyledons which have opposite leaves, 

 the pair of leaves first produced upon a branch usually decussate 

 with the leaf at its base. In Monocotyledons the first leaf is 

 placed upon the side of the branch nearest to the stem, sub- 

 tending thus the leaf from whose axil it arises. 



3. AEEANGEMENT OF THE LEAVES IN THE BUD. 



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 

 unexpanded condition in the bud. We may consider, Ist, The 

 modes in which each of the leaves considered independently of 

 the others is disposed ; and 2nd, Th6 relation of the several 

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

 may be spoken of as vernation and prafo Kation respectively. The 

 modes of vernation may be arrange'd again in two divisions : — 

 1st, Those in which the leaf is simply bent or folded ; and 2nd, 

 those in which it is rolled. Of the first modification we have 

 three varieties : — 1st, the upper half of the leaf may be bent 

 upon the lower, so that the apex approaches the base (fig. 

 169), as in the Tulip-tree ; it is then said to be recUnate or 

 inflexed ; 2nd, the right half may be folded upon the left, the ends 

 and midrib or axis of the leaf remaining immovable (fig. 170), 

 as in the Oak and Magnolia, when it is called condupUcate ; 

 3rd, each leaf may be folded up a number of times like a fan 

 ( fig. 171), as in the Sycamore, Ourrant, and Vine, 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 (fig. 172), as in the Sundew 

 and Ferns, when it is circinate ; 2nd, the whole leaf may be 

 rolled up from one margin into a single coil, with the other 

 margin exterior (fig. 173), as in the Apricot and Banana, in 

 which case it is convolute ; 3rd, the two margins of the leaf may 

 both be rolled inwards on the upper surface of the leaf towards 

 the midrib, which remains immovable (fig. 175), as in the 



