of the stem;

_Whorled_ or _Verticillate_ (Fig. 183) when there are more than two
leaves on a node, in which 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.

[Illustration: Fig. 183. Whorled leaves of Galium.]

183. In both modes and in all their modifications, the arrangement is
such as to distribute the leaves systematically and in a way to give
them a good exposure to the light.

[Illustration: Fig. 184. A piece of stem of Larch with two clusters
(fascicles) of numerous leaves.]

[Illustration: Fig. 185. Piece of a branch of Pitch Pine, with three
leaves in a fascicle or bundle, in the axil of a thin scale which
answers to a primary leaf. The bundle is surrounded at the base by a
short sheath, formed of the delicate scales of the axillary bud.]

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 in the Larch (Fig. 184), in which
examination shows each cluster to be made up of numerous 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 scattered
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 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.

185. =Phyllotaxy of Alternate Leaves.= Alternate leaves are distributed
along the stem in an order which is uniform for each species. The
arrangement in all its modifications is said to be _spiral_, because, if
we draw a line from the _insertion_ (i. e. the point of attachment) of
one leaf to that of the next, and so on, this