YOUNG AND OLD LEAVES. 93 



The coats of resin that often appear on young 

 leaves also preserve them from too great evapora- 

 tion, and when the leaf is fully expanded and the 

 skin has become thickened, they finally disappear. 

 It is a great protection for the leaves just escaped 

 from the bud to be clothed with hairs. In a great 

 many plants the leaves are only hairy in the begin- 

 ning of their development. The Silver Poplar, the 

 Pear, and the Mountain Ash are examples of this. 

 The leaves of the Horsechestnut are thickly cov- 

 ered with wool when they push forth from the 

 brown scales which they have forced apart, but 

 they lose this wool in the coarse of the spring so 

 completely, that in the full-grown leaves its former 

 presence could only be guessed by a few shreds 

 which hang here and there upon them. In the 

 Beech (Facjus sylvatica, Fig. 19) the garment of 

 the young leaves is formed of silky hairs, and 

 their position and action are so peculiar that it is 

 worth the trouble to examine the leaf more closely. 

 At the first glance the young Beech leaf appears 

 to be entirely clothed with silk on its under side, 

 but on looking more closely, the silky hairs are 

 to be found only on the margin and the side ribs, 

 while the green tissue of the leaf is not hairy, 

 but in fact perfectly bare. But as the green tissue 



