YOUNG AND OLD LEAVES. 91 



Screens and coverings of various kinds are an- 

 other form of protection for the tender undeveloped 

 parts of young leaves. This covering is usually 

 formed of stipules, which in Beeches, Lindens, 

 Oaks, Magnolias, and many other plants are mem- 

 branaceous, pale, and almost destitute of chlo- 

 rophyll. They form scales, which envelop the 

 young leaves pressing from the bud, which they 

 often protect from the rays of the sun. When 

 the leaf has outgrown this covering and needs it 

 no longer, the scales wither, detach themselves, 

 and fall to the ground. In Oak and Beech woods 

 as soon as the leaves have reached their normal 

 size, millions of such scales, which are called by 

 botanists " deciduous stipules," may be found. 

 Very deciduous are the stipules of the Tulip-tree 

 (Fig. 18), a kind of Magnolia, native in North 

 America, but now cultivated in every part of 

 Europe. The stipules are large, scaly, and placed 

 together in pairs, so as to form a sort of sack. In 

 this membranaceous, somewhat transparent sack 

 is enclosed the young leaf, whose stalk is bent over 

 upon itself, and whose blade is folded along the 

 midrib, like the leaf of Cherry. The leaf grows 

 there, as if in a little hothouse, till the cells of its 

 skin are so thick that there is no more danger of 



