ON LEAVES. 



349 



say, compelled to draw itself out. In Fig. 5 I have endeavored to 

 illustrate this by placing a spray of beech over one of Spanish chest- 

 nut. Moreover, not only do the leaves on a single twig thus admirably 

 fit in with one another, but they are also adapted to the ramification 

 of the twigs themselves. Fig. 6 shows a bough of beech seen from 

 above, and it w 7 ill be observed that the form of the leaves is such that, 

 while but little space is lost, there is scarcely any overlapping. Each 

 fits in perfectly with the rest. 



The leaves of the yew (Fig. 7) belong to a type very different 

 from those which we have hitherto been considering. They are long, 

 narrow, and arranged all round the stem, but spread right and left, 



Fia. 6. 



Fia. 7. 



Fig. 8> 



so that they lie in one plane, parallel to the direction of the branchlet, 

 and their width bears just such a relation to their distance apart that 

 when so spread out their edges almost touch. Fig. 8 represents a 

 sprig of box. It w T ill be observed that the increase of width in the 

 leaves corresponds closely with the greater distance between the 

 points of attachment. 



The leaves of the Scotch pine (JPinus sylvestris) are needle-like, 

 one and a half inch in length and one twentieth in diameter. They 

 are arranged in pairs, each pair inclosed at the base in a sheath. One 

 inch of stem bears about fifteen pairs of leaves. Given this number 

 of leaves in such a space, they must evidently be long and narrow. 

 If I am asked why they are longer than those of the yew, I would 

 suggest that the stem, being thicker, is able to support more weight. 

 In confirmation of this, we may take for comparison the Weymouth 

 pine, in which the leaves are much longer and the stalk thicker. 



When we pass from the species hitherto considered to the maples 

 (Fig. 11), sycamores, and horse-chestnuts (Figs. 9 and 10), we come to 

 a totally different type of arrangement. The leaves are placed at right 



