Leaves and Their Structures 15 



find that there is a skin covering it above and below. The 

 skin is readily stripped off, leaving the interior of the leaf 



FIG. 9. Divided and compound leaves: A, buckeye; B, oxalis; C, avens; 

 D, celandine ; E, cliff fern ; F, dandelion. 



as a green, granular mass of cells with veins running through 

 it in all directions. The skin is called the epidermis, or 

 epidermal tissue (Greek: epi, upon, and derma, skin). The 

 green part is the mesophyll tissue (Greek : meso, middle, and 

 phyll, leaf). The veins consist of three tissues, the water- 

 conducting, food-conducting, and mechanical tissues. The 

 blade therefore commonly contains five tissues : the epidermis 

 and mesophyll, and the three tissues of the veins.. 



Cells. When any one of the tissues of a leaf or other living 

 part of a plant is magnified under a microscope, it is seen to 

 be composed of small parts built together in much the same 

 way as the little chambers in a honeycomb. These small 

 parts are the plant cells (Fig. 1 1) . Each cell consists of a small 

 mass of jellylike living matter, the protoplasm, which is inclosed 

 by a firm, transparent wall. The protoplasm is divided into 

 a denser round or oval body, the nucleus, and a more liquid 

 portion, the cytoplasm. The nucleus is of great importance ; 



