line will wind spirally
around the stem as it rises, and in the same species will always bear
the same number of leaves for each turn round the stem. That is, any two
successive leaves will always be separated from each other by an equal
portion of the circumference of the stem. The distance in _height_
between any two leaves may vary greatly, even on the same shoot, for
that depends upon the length of the _internodes_, or spaces between the
leaves; but the distance as measured around the circumference (in other
words, the _Angular Divergence_, or angle formed by any two successive
leaves) is uniformly the same.

186. =Two-ranked.= The greatest possible divergence is, of course, where
the second leaf stands on exactly the opposite side of the stem from the
first, the third on the side opposite the second, and therefore over the
first, and the fourth over the second. This brings all the leaves into
two ranks, one on one side of the stem and one on the other, and is
therefore called the _Two-ranked_ arrangement. It occurs in all
Grasses,--in Indian Corn, for instance; also, in the Basswood (Fig.
181). This is the simplest of all arrangements, and the one which most
widely distributes successive leaves, but which therefore gives the
fewest vertical ranks. Next is the

187. =Three-ranked= arrangement,--that of all Sedges, and of White
Hellebore. Here the second leaf is placed one third of the way round the
stem, the third leaf two thirds of the way round, the fourth leaf
accordingly directly over the first, the fifth over the second, and so
on. That is, three leaves occur in each turn round the stem, and they
are separated from each other by one third of the circumference. (Fig.
186, 187.)

[Illustration: Fig. 186. Two-ranked arrangement, shown in a piece of the
stalk of a Sedge, with the leaves cut off above their bases; the leaves
are numbered in order, from 1 to 6. 187. Diagram or cross-section of the
same, in one plane; the leaves similarly numbered; showing two cycles of
three.]

188. =Five-ranked= is the next in the series, and the most common. It is
seen in the Apple (Fig. 188), Cherry, Poplar, and the greater number of
trees and shrubs. In this case the line traced from leaf to leaf will
pass twice round the stem before it reaches a leaf situated directly
over any below (Fig. 189). Here the sixth leaf is over the first; the
leaves stand in five perpendicular ranks, with equal angular distance
from each other;