250 



STRUCTURAL BOTANY 



Next below the epidermis comes the liypoderma, a 

 layer of cells which are elongated parallel to the axis 

 of the leaf. They have extremely thick walls, and 

 help much in giving rigidity to the whole organ. 

 The hypodermal layer is interrupted below the 

 stomata, while at the corners of the leaf it may be 

 more than one cell thick. 



FIG. 102. External tissues of leaf from the same section as Fig. 

 101 ; enlarged to show details, g, guard-cells of stoma ; 

 a.c, air-chamber; , epidermis; h, hypoderma ; p, 

 assimilating parenchyma. Magnified 330. (R. S.) 



Within the hypoderma we find the most important 

 part of the leaf-tissue, namely, the assimilating 

 parenchyma, containing chlorophyll granules. This 

 forms a thick layer, and indeed makes up the greater 

 part of the substance of the leaf. Its cells are thin- 

 walled and rather irregular in shape, and their cell- 

 walls are often somewhat folded. The cells contain in- 



