. Foundations of botany. dermis ; e, cells of epidermis. MINUTE STRUCTURE OF LEAVES 153 cu In the case of an apple tree, where the epidermis of thelower surface of the leaf contains about 24,000 stomata tothe square inch, or the black walnut, with nearly 300,000to the square inch,the total number Vj]on a tree is incon-ceivably large. 163. Uses of theParts examined. —It will be most con-venient to discussthe uses of theparts of the leaf alittle later, but itwill make matterssimpler to state atonce that the epi-dermis serves as amechanical protec-tion to the partsbeneath and pre-vents excessivee
. Foundations of botany. dermis ; e, cells of epidermis. MINUTE STRUCTURE OF LEAVES 153 cu In the case of an apple tree, where the epidermis of thelower surface of the leaf contains about 24,000 stomata tothe square inch, or the black walnut, with nearly 300,000to the square inch,the total number Vj]on a tree is incon-ceivably large. 163. Uses of theParts examined. —It will be most con-venient to discussthe uses of theparts of the leaf alittle later, but itwill make matterssimpler to state atonce that the epi-dermis serves as amechanical protec-tion to the partsbeneath and pre-vents excessiveevaporation, thatthe palisade-cells(which it may not be easy to make out very clearly in aroughly prepared section) hold large quantities of the greencoloring matter of the leaf in a position where it canreceive enough but not too much sunlight, and the cellsof the spongy parenchyma share the work of the p^isade-cells, besides evaporating much water. The stomataadmit air to the interior of the leaf (where the air spaces. Fig. 118. —A Stoma of Thyme. (Greatly magnified.) A, section at right angles to surface of leaf ; B, sur-face view of stoma, cu, cuticle ; g, guard-cells ;s, stoma ; e, epidermal cells ; a, air chamber ;c, cells of spongy parenchyma with grains ofchlorophyll. 154 FOUNDATIONS OF BOTANY serve to store and to distribute it), they allow oxygenand 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 todiscover 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 alittle of the epidermis from some such soft, pulpy leaf as
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplants, bookyear1901
