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 wliich 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 are usually opposite, separate then- 

 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 

 j'oung 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 Naturm 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. 



