

YOUNG AND OLD LEAVES, 89 



a midrib with the veins running out on either side, 

 like the bones on the vertebral column of a fish. 

 The green tissue makes deep folds between these 

 veins, which lie upon each other like the folds of 

 a fan (Fig. 19). The folding is different in the 

 Cherry (Fig. IT' 2 ). Every leaf is folded along the 

 midrib in the bud, and remains so for some time 

 after it has expanded. The two halves lie so close 

 together and cover each other so perfectly, that at 

 first sight they appear to be one. Besides this, 

 they are firmly united by a balsam-like substance. 

 They are also always erect in this stage of their 

 development, which brings us to another contriv- 

 ance which can be observed in young, undeveloped 

 leaves. 



We may affirm that except in the case of a 

 few corrugate forms, the surfaces of young leaves, 

 whether escaping from the earth, the cotyledons, or 

 the bud, are never parallel with the ground. The 

 green, transpiring, tender parts, especially, have 

 always at first a vertical position, and their sur- 

 faces are turned sideways, as in stems which serve 

 the purpose of leaves (pliyllodadia and phyllodia 1 ), 



1 These are stems or petioles which serve as leaves. Myrsiphyllum, 

 known in our greenhouses as Smilax, is an example of a branch acting 

 the part of a leaf, and in Acacia the adult foliage is formed of leaf- 

 stalks. 



