TRANSPIRA TION. 



and should be then mounted in water for microscopic examina- 

 tion.* 



80. Epidermis of the leaf. In this section we see that the 

 green part of the leaf is bordered on what are its upper and 

 lower surfaces by a row of cells which 



possess no green color. The walls of 

 the cells of each row have nearly par- 

 allel sides, and the cross walls are per- 

 pendicular. These cells form a single 

 layer over both surfaces of the leaf and 

 are termed the epidermis. Their walls 

 are quite stout and the outer walls are 

 cuticularized. 



81. Soft tissue of the leaf. The 

 cells which contain the green chloro- 

 phyll bodies are arranged in two dif- , 



Section through ivy leaf showing 

 ferent Ways. Those On the upper side communication between stomate and 



* the large intercellular spaces.of the 



of the leaf are usually long and pris- leaf ; stoma closed. 

 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 th.'.*t 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 we should examine such a section of 

 a leaf before it is mounted in water we would see that the inter- 



Fig. 51. 



Stoma open. 

 Figs. 34, 35. Section through stomata of ivy leaf. 



Fig. 52. 

 Stoma closed. 



* Demonstrations may be made with prepared sections of leaves. 



