244- POSITION OF LEAVES, [BOOK i. 



Pear, the Willow, the Oak, will also be found to indicate the 

 same arrangement, which is only less manifest because of the 

 distance between the leaves, and the irregularity of their 

 direction. If, in the Apple-tree for instance, a line be drawn 

 from the base of one leaf to the base of another, and the 

 leaves be then broken off, it will be found that a perfectly 

 spiral line will have been formed. Upon this supposition, 

 opposite or whorled leaves are to be considered the result of a 

 peculiar non-development 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 Nightshades ; 

 while, on the other hand, leaves which are usually opposite, 

 separate their nodes and become alternate, as in Erica medi- 

 terranea : but this is more rare. 



The best argument in support of the hypothesis that all 

 whorls arise from the non-development of internodes and 

 confluence 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 been written by a German 

 naturalist 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, 



