HOW WATER MOVES THROUGH THE PLANT. 57 



Fig. 48. Fig 49. 



Stoma open. Stoma closed. 



Figures 48, 49. Section through stomata of ivy leaf. 



faces of the leaf and are termed the epidermis. Their walls are 

 quite stout and the outer walls are cuticularized. 



100. Soft tissue of the leaf. The cells which contain the 

 green chlorophyll bodies are arranged in two different ways. 

 Those on the upper side of the leaf are usually long and pris- 

 matic in form and lie 

 closely parallel to 

 each other. Because 

 of this arrangement 

 of these cells they are 

 termed the palisade 

 cells, and form what 

 is called the palisade 

 layer. The other green cells, lying below, vary greatly in size in 

 different plants and to some extent also in the same plant. Here 

 we notice that they are elongated, or oval, or somewhat irregular 

 in form. The most striking peculiarity, however, in their arrange- 

 ment is that they are not usually packed closely together, but each 

 cell touches the other adjacent cells only at certain points. This 

 arrangement of these cells forms quite large spaces between 



them, the 

 intercellular 

 spaces. If 

 w e should 

 examine 

 such a sec- 

 tion of a leaf 

 before it is 

 mounted in 

 water we 



Fig. 50. 



Portion of epidermis of ivy, showing irregular epidermal cells, stoma WOUld S 6 6 

 and guard cells. , ' . 



that the in- 

 tercellular spaces are not filled with water or cell-sap, but are 

 filled with air or some gas. Within the cells, on the other 

 hand, we find the cell-sap and the protoplasm. 



