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 sunlight. Fig. 114 shows the structure. There are two guard-cells at the mouth of each stomate, which may in most cases open or close the passage as the conditions of the atmosphere may require. The guard-cells contain chlorophyll. In Fig. 115 is shown a case in which there are compound guard-cells, that of ivy. On the margins of certain leaves, as of fuchsia, impatiens, cabbage, are openings known as water-pores.

(Osterhout).

, showing compound guard-cells.

Stomates are very numerous, as will be seen from the numbers showing the pores to each square inch of leaf surface:

Lower surface Upper surface Peony                   13,790       None Holly                   63,600       None Lilac                  160,000       None Mistletoe                  200        200 Tradescantia             2,000      2,000 Garden Flag (iris)      11,572     11,572

The arrangement of stomates on the leaf differs with each kind of plant. Fig. 116 shows stomates and also the outlines of contiguous epidermal cells.

The function or work of the stomates is to regulate the passage of gases into and out of the plant. The directly active organs or parts are guard-cells, on either side the opening. One method of opening is as follows: The