THE LEAVES. 81 



Simplicity in causes and variety in effects mark all the opera- 

 tions of nature ! 



The distribution of leaves about the stem. All who notice 

 plants much have frequently observed the regularity and sym- 

 metry with which leaves are arranged around the stem. Some- 

 times they spring from its sides in pairs, crossing each other at 

 right angles, as in the mint family, or in beautiful whorls, as 

 in the Galium or bedstraw tribe ; and again, they are scattered 

 along the stem on either side, but still with an apparent regu- 

 larity, and certainly not at random. These peculiarities of 

 their distribution are produced by a combination of the two 

 following causes. 



1. The manner in which the stem grows. If the elongation 

 of the stem and the growth of the leaves be simultaneous, the 

 leaves will be scattered on all sides of the stem, and will be 

 few or numerous, according to the greater or less degree of 

 rapidity with which they are developed ; but if the elongation 

 of the stem is periodically checked, and the growth of the 

 leaves at the same time continues, they will necessarily start 

 out from the same point of the stem in pairs or in whorls, 

 according to the length of time taken up before the stem 

 again elongates. This is well seen in Lysimachia quadrifolia, 

 which in ordinary circumstances bears whorls of four and six 

 leaves ; these, when the growth of the stem is rapid, become 

 alternate. We have also instances of the operation of this law 

 in the Coniferae, or pine ' family. The Larch has leaves de- 

 veloped in fascicles or bundles. These leaves are without any 

 lamina or blade, rigid and needle-shaped or linear. They are 

 brought together in consequence of their rapid development 

 and the non-elongation of their axis of growth. That this is 

 really the cause of their fascicled character, is evident on close 



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