BIOLOGY OF HIGHER SEED PLANTS 



55 



a. Make a general drawing, omitting the cells, to show the 



position of the epidermis, green mesophyll, and veins 



of the section 



which is under 



observation. 

 I. Epidermis. 



(1) Note its color, 



thickness, and 

 extent as a 

 covering of the 

 leaf surface. 

 What is the 

 real form of 

 the en tire epi- 

 dermal layer 

 of the leaf 

 you are study- 

 ing ? Do you 

 find stomata? 

 Stomata may 

 frequently be 



recognized as FIG. 17. Conducting cells (tracheids) of the 

 darker places veins of a leaf 



in flio frocVi u > midvein: 6, lateral veins ; e, termination of 



111 lilt? 1 1 Coll ,, -,, . 



veins ; me, areas occupied by mesophyll cells in 

 epidermis. De- the living leaf. After Sachs 



tails of the 



guard cells cannot be seen in such thick sections. 



(2) What special structural feature of the epidermal 



cells insures against the loss of water? Would 

 the same structural feature serve other protective 

 functions ? Search for sections of the guard cells 

 and of the pores of stomata. Determine the pecul- 

 iar cell character of the guard cells, for example, 



