C8 



LEAVES. 



[SECTION 



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

 this case being always on opposite sides of the stem ; 



Whorled or Verlicillale (Fig. 1S3) when tliere are more than two leaves 

 on a node, in which case they divide tlie circle 

 equally between them, forming a Vcrticel or whorl. 

 Wiien there are three leav.,-s 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 iu all their modifica- 

 tions, the arrangement is such as to distri})ute the 

 leaves systematically and in a way to give them a 

 gocd exposure to the light. 

 184. No (wo or more leaves ever grow from the same point. Tlie so- 

 called Fascicled or Clustered leaves are 

 the leaves of a brancli the nodes of 

 which are very close, just as they are 

 in the bud, so keeping the leaves in a 

 cluster. This is evident in 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 iu 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 Fig. 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. For 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 spriug, 

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

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

 actual foliage. 185 



Fig. 183. Whorled leaves of Galium. 



Fig. 184. A piece of stem of Larcli with two clusters (fascicles) of numerous 

 leaves. 



Fig. 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 tlie base by a short sheath, formed of the delicate scales of the axillary 

 bud. 



