62 THE CONICAL GEOWin OF TKEBS. 



curing the symmetrical arrangement of the branches which 

 proceed from the buds in their axillae, and the uniform de- 

 position of the nourishing matter which proceeds from them 

 around the axis. For as the wood is formed by the leaves, 

 when these are placed in regular order over every part of 

 the circumference of the axis, as in the Elm, the Beech, and 

 the Linden, the branches and shoots are cylindrical; for 

 the woody matter formed by the leaves is then distributed 

 equally on all sides. On the contrary, when the leaves on 

 the stem and branches are opposite, the pairs being placed 

 at right-angles to each other, as in the Spindle tree and 

 Maple, the descent of nourishing matter from the leaves 

 is necessarily limited to that portion of the stem imme- 

 diately below them, and consequently the young shoots 

 and branches of these trees are square. 



Not only the form of the single axis, but also the extent 

 to which it is developed, depends on the leaves ; for when 

 their vital activity is enfeebled, no internodes or naked in- 

 tervals of stem are formed between them, the axis is redu- 

 ced to a rudimentary condition, and they become crowded 

 together into little clusters. If the growth of the axis is 

 thus arrested, year after year, it may increase in length 

 slowly ; but there is no increase in its breadth or thickness. 

 A Beech branch now lies on the table before me, and I find 

 that one of its side branches, which is only twelve inches in 

 length, is nevertheless thirty years old, and yet it is not 

 any thicker than one of the young terminal shoots of the 

 same branch, which has grown nearly as much in a single 

 year. 



Hence, it will be found that in proportion as the length 

 of an axis increases or decreases from year to year, in the 

 same proportion is there a corresponding amount of in- 

 crease or decrease in the breadth of the wood-rings visible 

 on the cross-section. In order to verify this truth, it is 

 necessary to select branches, the leaves of whose side axes 

 are annually put forth as leaf-clusters, and which therefore 

 take a minimum of development, and exercise the smallest 

 possible amount of physiological influence on the branch, 

 and where powerful growths are suddenly succeeded by 



