. Adventures with animals and plants. Biology. Side view of stoma ein fconducf- ing cells of leaf) Lower epidermis Chlorophyll bodies Fig. 164 Lookhjg into a leaf. Which two layers lie between upper and lower epideriuis? What is in the "empty" spaces between the spongy cells? In most plants the two cells enclosing the stoma, called guard cells, ordinarily take the shape of a half doughnut during the daytime, making the opening larger. At night they straighten out, making the stoma smaller. The opening is never shut completely. The stomata are extremely numerous. A medium-sized cabbag
. Adventures with animals and plants. Biology. Side view of stoma ein fconducf- ing cells of leaf) Lower epidermis Chlorophyll bodies Fig. 164 Lookhjg into a leaf. Which two layers lie between upper and lower epideriuis? What is in the "empty" spaces between the spongy cells? In most plants the two cells enclosing the stoma, called guard cells, ordinarily take the shape of a half doughnut during the daytime, making the opening larger. At night they straighten out, making the stoma smaller. The opening is never shut completely. The stomata are extremely numerous. A medium-sized cabbage leaf probably has about 11,000,000 stomata, and a sunflower leaf may have up to about 13,000,000. In most land plants the stomata are more numerous on the lower side; in floating leaves they are more numerous on the upper side; none occur on leaves that grow submerged in water. To determine the number of stomata, do Exercise 2. What makes the leaf green? As you study a fresh section of a leaf under the microscope, what strikes you most is the bright green color, particularly of the palisade cells. There is usually less green color in the spongy cells and the epidermis has faint traces of green in the guard cells only. This color is caused by the presence of the tiny green bodies. Stoma Guard cell Epidermal cell Fig. 165 A tiny piece of lower epidermis. How many stomata do yon see? Are they open or closed? What are the cells on each side of a sterna called? within the cytoplasm, the chloroplasts. They are often oval in shape. They are made of protoplasm containing several coloring matters, one of which is bright green in color. This is the chlorophyll. Chloroplasts are found not only in leaf cells but in all parts of the plant which look green. Fruits are green before they ripen and stems always have chlorophyll when they are young; sometimes they keep their green color throughout the life of the plant. You probably saw chloroplasts in Elodea cells when study- ing the precedin
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