52 



BOYS AND GIRLS IN BIOLOGY. 



midrib are called the skeleton of the leaf. Over this 

 skeleton or framework is spread the soft part of the 

 leaf, the parenchyma (Fig. 41), which is made of small 

 green cells, very like those which form the protococcus 

 or green mould. These soft, green cells, like the other 

 parts of the plant, are protected by a thin skin (Fig. 41) 

 called epidermis, which means upper skin. If you 



Fig. 42. 



Mouth, or 

 Stomate. 



J Large, Wavy Skin- 



Kerael. Cell. 



A Stkip op the Skin, or Epidermis, of Leaf. 



strip off a piece of this thin outer skin, and put it 

 under the microscope, you will find that the cells con- 

 tain no color-grains, or chlorophyl. They are very 

 large, with wavy edges, which fit with one another 

 (Fig. 42). Here and there in 'the thin outer skin, es- 



