PEACH AND THE PEAR. 2O9 



of the slow growers, as Beurre Bosc, come in late. 

 The leaves are made up of the veins, the ribs, and the 

 leaf-stalk ; thus giving the frame work and vessels for 

 the flowing of the sap. and the leaf is completed. Then 

 we have the green pulp which fills the intervals of the 

 frame work, and the whole covered by skin. These 

 leaves are made up of cells crowded together on the 

 upper side of the leaf, and on the lower side not so 

 closely crowded. Hence the leaf is of a darker green on 

 the upper side than on the lower side. On the lower 

 side are mostly situated the pores for breathing, and in 

 the pear, number thirty thousand to the square inch. 

 The pear is exogenous ; that is, grows by additions to the 

 outside of the wood ; and the process of growing of 

 such trees is as follows, as described by physiological 

 botanists, and for the main parts of which description, as 

 for the foregoing, I am indebted to the admirable work 

 of Thomas, on Fruit Culture. The roots absorb water, 

 which, in them, changes slightly by matter from the 

 root cells being added, and is then sap. The sap passes 

 from cell to cell, up through the sap-wood until it reaches 

 the leaves. Now the sap having reached the leaf 

 emerges from the dark cells through which it has been 

 traveling and is spread out to sun-light. Now it is 

 largely evaporated through the breathing pores of the 

 leaf we just now spoke of, and it is thickened. The 

 carbonic acid of the air, and that previously contained 

 14 



