154 FOUNDATIONS OF BOTANY 
serve to store and to distribute it), they allow oxygen 
and carbonic acid gas to escape, and, above all, they regu- 
late the evaporation of water from the plant. 
164. Leaf of ‘India-Rubber Plant.’”?!— Study with the micro- 
scope, as the lily leaf was studied, make the same set of sketches, 
note the differences in structure between the two leaves, and try to 
discover their meaning. 
How does the epidermis of the two leaves compare ? 
Which has the larger stomata? 
Which would better withstand great heat and long drought ? 
165. Chlorophyll as found in the Leaf. — Slice off a 
little of the epidermis from some such soft, pulpy leaf as 
Fic. 119.— Section through Lower Epidermis of Leaf of India-Rubber Plant 
(Ficus elastica). (Magnified 330 diameters.) 
0, opening of pit; p, pit leading to stoma; s, stoma, with two guard-cells ; w, 
water-storage cells of epidermis ; a, an air space; around and above the air 
spaces are cells of the spongy parenchyma. 
that of the common field sorrel,? live-for-ever, or spinach ; 
scrape from the exposed portion a very little of the green 
pulp ; examine with the highest power attainable with 
your microscope, and sketch several cells. 
1 Ficus elastica, a kind of fig tree. 
2 Rumex Acetosella. 
