MINUTE STKUCTUEE OP LEAVES 



151 



Take measurements from the last three sketches with a scale and, 

 knowing what -magnifying power was used, answer these questions ^ : 



(a) How thick is the epidermis ? 



(b) What is the length and the breadth of the epidermal cells ? 



(c) What is the average size of the pulp-cells ? 



A stoma is a microscopic pore or slit in the epidermis. 

 It is bounded and opened and shut by guard-cells (Fig. 

 118, g), usually two in number. These are generally 



Fi6. 116. — Vertical Section of the Leaf of the Beet. (Much magnified.) 



c, epidermis ; p, palisade-cells (and similar elongated cells) ; r, cells filled with 

 red cell sap ; i, intercellular spaces ; a, air spaces communicating with the 

 stomata ; si, stomata, or breathing pores. 



1 The teacher may measure the size with the camera lucida. 



