44 NUTRITION'. 



surface (that which is exposed to the air) being 

 alone furnished with stomata. In like manner, 

 leaves which are constantly immersed have no 

 stomata. The nervures of the superior surface 

 are supposed to be the channels by which the 

 juices are conveyed from the stem to the limb ; 

 those of the lower surface conduct them back to 

 the bark. If we attempt to twist a leaf so that 

 the naturally superior surface shall be undermost, 

 it endeavours to regain its original situation; 

 and if the force used prevent it from doing so, 

 the leaf quickly perishes. 



34. Stipules. This name has been given to 

 small leafy organs, whose only essential character 

 is their lateral position at the base of the leaf. 

 They are occasionally changed into true leaves, 

 and one of them is sometimes wanting; they 

 vary exceedingly in appearance. 



35. Leaf Buds are those vital points, sur- 

 rounded by scales, which are usually found in 

 the axils of the leaves, and from whose growth 

 a branch is formed.* The scales, as the vege- 



* " Leaf-buds are always formed from the cellular 

 portion of the stem or brandies, on which the function 

 of extending the growth of the individual seems espe- 

 cially imposed. They may be distinctly traced, in young 

 branches, to the pith ; and where this has dried up, they 

 may be seen to arise from the medullary rays." (Car- 

 penter's Veg. Phy. p. 197.) 



