CHAP. II. 
LEAVES. 
91 
and the leaves be then broken off, it will be found that a per- 
fectly spiral line will have been formed. Upon this supposition, 
opposite or whorled leaves are to be considered the result of 
a peculiar non-developement of internodes, and the consequent 
confluence of as many nodes as there may be leaves in the 
whorl. Rhododendron ponticum will furnish the student 
with an illustration of this: on many of its branches some 
of the leaves are alternate and others opposite ; and several 
intermediate states between these two will be perceivable. 
In many plants, the leaves of which are usually alternate, 
there is a manifest tendency to the approximation of the nodes, 
and consequently to an opposite arrangement of the leaves, as 
in Solanum nigrum, and many other Solaneae*; while, on the 
other hand, leaves that ai'e usually opposite, separate their 
nodes and become alternate, as in Erica mediterranea : but this 
is more rare. 
The best argument in support of the hypothesis, that all 
whorls arise from the non-developement of internodes and con- 
fluence of nodes, is, however, to be derived from flowers, which 
are several series of whorls, as will be seen hereafter. In 
plants with alternate leaves, the flowers often change into 
young branches, and then the whorls of which they consist 
are broken, the nodes separate, and those parts that were 
before opposite become alternate ; and in monstrous Tulips, 
the whorls of which the flower consists are plainly seen to 
arise from the gradual approximation of leaves, which in their 
unchanged state are alternate. 
A most elaborate memoir has lately been produced by a 
young German named Braun, to prove, mathematically, not 
only that the spiral arrangement is that which is everywhere 
visible in the disposition of the appendages of the axis, but 
that each species is subject to certain fixed laws, under which 
the nature of the spires, and in many cases their number, 
are determined. The original appeared in the Nova Acta of 
the Imperial Academy Naturce Curiosorum ; and a very full 
abstract of it has been given by Martins, in the first volume 
of the Archives de Botanique^ from which we borrow what 
follows : 
* Introduction to the Natural System of Botany, p. 231. 
