68 



LEAVES. 



[SECTION 7. 



Opposite (Fig. 182), when there is a pair to each node, the two leaves in 

 this case being always on opposite sides of the stem ; 



Wkorled or Verticillate (fig. 183) when there are more than two leaves 

 on a node, in whica. case they divide the circle 

 equally between them, forming a Verticel or whorl. 

 When there are three leaves in the whorl, the 

 leaves are one third of the circumference apart ; 

 when four, one quarter, and so on. So the plan of 

 opposite leaves, which is very common, is merely 

 that of whorled leaves, with the fewest leaves to the 

 whorl, namely, two. 



183. In both modes and in all their modifica- 

 tions, the arrangement is such as to distribute the 

 leaves systematically and in a way to give them a 

 good exposure to the light. 



184. No two or more leaves ever grow from the same point. The so- 

 called Fascicled or Clustered leaves are 

 the leaves of a branch the nodes of 

 which are very close, just as they are 

 in the bud, so keeping the leaves in a 

 cluster. This is evident hi the Larch 

 (Fig. 184), in which examination shows 

 each cluster to be made up of nume- 

 rous leaves crowded on a spur or short 

 axis. In spring there are only such 

 clusters ; but in summer some of them 

 lengthen into ordinary shoots with scat- 

 tered alternate leaves. So, likewise, 

 each cluster of two or three needle- 

 shaped leaves in Pitch Pines (as in Pig. 185), or of five leaves 

 in White Pine, answers to a similar extremely short branch, 

 springing from the axil of a thin and slender scale, which 

 represents a leaf of the main shoot. Por Pines produce two 

 kinds of leaves, 1. primary, the proper leaves of the shoots, 

 not as foliage, but in the shape of delicate scales in spring, 

 which soon fall away ; and 2. secondary, the fascicled leaves, 

 from buds in the axils of the former, and these form the 

 actual foliage. 



Fig. 183. Whorled leaves of Galium. 



Fid. 184. A piece of stem of Larch with two clusters (fascicles) of numerous 

 leaves. 



Fid. 185. Piece of a branch of Pitch Pine, with three leaves in a fascicle or bun- 

 dle, in the axil of a thin scale which answers to a primary leaf. The bundle is sur- 

 rounded at the base by a short sheath, formed of the delicate scales of the axillary 

 bud. 



