106 LEAF-ARRANGEMENT. 



merits, would have also to be taken into considera j 

 tion ; but still it seems clear that there is a corre- 

 spondence between thickness of stem and size of 

 leaf. This ratio, moreover, when taken in rela- 

 tion with the other conditions of the problem, has, 

 as we shall see, a considerable bearing not only on 

 the size, but also on the form, of the leaf. . . . 



Perhaps it will be said that in some trees the 

 leaves are much more uniform in size than in 

 others. This is true. The Sycamore, for instance, 

 varies greatly. In the specimen tabulated its stem 

 was .13 in diameter, and the area of the six upper 

 leaves was 60 square inches. In another the six 

 upper leaves had an area of rather over a hundred 

 inches, and in this case the diameter of the stem 

 was .18. 



Another point is the length of the internode. 

 In such trees as the Beech, Elm, Hornbeam, etc., 

 the distance from bud to bud varies comparatively 

 little, and bears a tolerably close relation to the 

 size of the leaf. In the Sycamore, Maple, etc., on 

 the contrary, the length varies greatly. 



Now, if, instead of looking merely at a single 

 leaf, we consider the whole bough of any tree, we 

 shall, I think, see the reason of their differences 

 of form. 



