MINUTE STRUCTURE OF 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 
o 
on” 
2309 
° 
6 
(TS) 
6 
() 
ee 
Fig. 116. — Vertical Section of the Leaf of the Beet. (Much magnified.) 
e, 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; st, stomata, or breathing pores. 
1 The teacher may measure the size with the camera lucida. 
