150 THE LEAVES. 



leaves of one whorl correspond to the intervals of that underneath, 

 making twice as many vertical ranks as there are leaves in the 

 whorl ; sometimes they wind spirally, so that each leaf of the 

 whorl belongs to as many parallel spirals, analogous to the second- 

 ary spirals in the case of alternate leaves. 



252. The opposition or* alternation of the leaves is generally 

 constant in the same species, and often through the same family ; 

 yet the transition from opposite to alternate leaves upon the same 

 stem is not very rare : it is seen in the common Myrtle, and the 

 Snapdragon. All Exogens, having their cotyledons or embryo 

 leaves opposite, necessarily commence with that mode ; many re- 

 tain it throughout; others change to alternation, either directly in 

 the primordial leaves, or at a later period (231). In Endogens, 

 on the contrary, the first leaves are necessarily alternate (188), 

 and it is very seldom that they afterwards exhibit opposite or 

 whorled leaves. 



253. Only one leaf arises from the same organic point. What 

 are called fascicled or tufted leaves are merely those of an axillary 

 branch, which is so short that the bases of the leaves are in con- 

 tact. This is plainly seen in the Barberry, where, the primary 



leaves hardening into a kind of 

 thorn, the bud in its axil developes 

 into a branch, with very slight elon- 

 gation of the internodes. Of the 

 same nature are the fascicled leaves 

 of the Pine, and, more evidently, 

 of the Larch (Fig. 177), where the 

 whole foliage of such branches is 

 developed without any elongation of the axis. Some of these 

 elongate and grow on through the summer, producing the growth 

 of the season, on which the leaves are distributed so as to show 

 their natural, alternate arrangement. 



254. As regards their position on the stem, leaves are said to be 

 radical, when they are inserted (235) into the stem at or below the 

 surface of the ground, so as apparently to grow from the root, as 

 those of the Plantain, Primrose, and of the acaulescent (139) Vio- 

 lets : those that arise along the main stem are termed cauline ; 

 those of the branches, rameal ; and those which stand upon or at 



FIG. 177. Clustered or fascicled leaves of the Larch. 



