348 



THE POPULAR SCIENCE MONTHLY. 



In the beech, the general plane of the leaves is again that of the 

 branch (Fig. 2), but the leaves themselves are ovate in form, and 

 smaller, being only from two to three inches in length. On the other 

 hand, the distance between the internodes is also smaller, being, say, 

 one and a quarter inch against something less than two inches. The 

 diminution in length of the internode is not, indeed, exactly in propor- 

 tion to that of the leaf, but, on the other hand, the leaf does not make 

 so wide an angle with the stem. To this position is probably due the 

 difference of form. The outline of the basal half of the leaf fits neatly 

 to the branch, that of the upper half follows the edge of the leaf be- 

 yond, and the form of the inner edge being thus determined decides 

 the outer one also. 



In the nut ( Corylus), the internodes are longer and the leaves cor- 

 respondingly broader. In the elm (Ulmns, Fig. 3), the ordinary 

 branches have leaves resembling, though rather larger than, those of 

 the beech ; but in vigorous shoots the internodes become longer and 

 the leaves correspondingly broader and larger, so that they come 

 nearly to resemble those of the nut. 



But it may be said the Spanish chestnut ( Castanea vulgaris, Fig. 4) 

 also has alternate leaves in a plane parallel to that of the branch, and 



Fig. 3. 



Fio. 4. 



Fio. 5. 



with internodes of very nearly the same length as the beech. That is 

 true ; but, on the other hand, the terminal branches of the Spanish 

 chestnut are stouter in proportion. Thus, immediately below the 

 sixth leaf, the chestnut-stalk may be '15 of an inch in thickness, that 

 of the beech not much more than half as much. Consequently, the 

 chestnut could, of course supposing the strength of the wood to be 

 equal, bear a greater weight of leaf ; but, the width of the leaf being 

 determined by the distance between the internodes, the leaf is, so to 



