326 



THE APPLE CULTURIST. 



trees, like the yellow locust, have many leaves on each petiole, and are hence called 

 compound leaves. M represents the mid-vein, which is the principal prolongation of 

 the petiole, P. The old name of the mid-vein is mid-rib. The primary branches, 

 V, V, sent off from the mid-vein, are denominated veinlets ; and the secondary 

 branches, issuing from them are called veinulets. The leaves of the apple-tree are 

 serrate, which see. In many apple-leaves the veinlets are opposite ; and in others 

 on the same tree, the veinlets will be alternate. The usual form of apple-leaves is 

 elliptical, ovate, and frequently oblong-ovate. They are often obicular. The apex 

 of an apple-leaf is often acute, or short acuminate. The upper side of apple-leaves 

 is smooth, or glabrous. The under side is pubescent, or tomentose. The leaves 

 of an apple-tree are both the lungs and the organs of digestion. No tree can exist 

 any considerable length of time, during the growing season, without leaves. The 

 mid-vein, veiulets, and veinulets, constitute the frame- work of the leaf, which is 

 covered by the parenchyma, or cellular tissue. They are all conveyers of the vital 

 fluid of a tree, just as the veins of the body of an animal convey the blood away 



Fig. 157. 



A highly-magnified section of a leaf. 



from and back to the heart. The parenchyma of the leaves of an apple-tree is 

 covered with a delicate varnish, which is impervious to water, as we may readily 

 perceive by sprinkling water on the surface. When a tree is growing where there 

 is a large amount of potash and silica in the soil, the leaves will be covered with 

 a much thicker coat of this vegetable varnish than if potash and silica were scarce. 

 Where these ingredients have nearly all been exhausted from the soil, the leaves 

 of a tree will often be sickly, thin, and liable to be attacked by disease, simply be- 

 cause the roots can not find a supply of silica and potash to produce a heavy coat 

 of varnish over the surface of both the leaves and fruit. Hence, when the spores 

 of fungi come floating along in the air, the minute particles readily adhere to the 

 leaves, and soon destroy them. Glass-makers employ silica, sand, and potash 

 to manufacture glass. Apple-trees and other trees need a liberal supply of these 

 materials to form a liquid similar to glass, to spread over the surface of leaves and 

 fruit, to fortify every organ and tissue against the attacks of fungi. Let wood- 

 nshes and sand be scattered round about apple-trees in great abundance, and the 

 leaves will be of a dark-green color, tough like india-rubber, and the fruit will be 



