62 THE CONICAL GROWTH OF TREES. 



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 immediately 

 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 inter- 

 vals of stem are formed between them, the axis is reduced 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 pro- 

 portion is there a corresponding amount of increase 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 growths greatly retarded. One such branch now lies before 

 me, whose principal axis is eighteen inches long, and whose side 

 axes have taken a minimum of development. It grew the first 

 three years five inches annually, or altogether fifteen inches ; 

 but in the last four years the growth stagnated, or averaged 



