. Nature and development of plants. Botany. NATURE OF PLANTS 37 evergreens, as laurels and rhododendrons, in the needles of cone- bearing trees, and in all plants that are exposed to the hot, dry air of summer or the drying winds of winter. Such leaves may be further protected and strengthened by thick-walled elongated cells, stereome (Fig. 23, st). Coatings of wax, mucilage and lime are also frequently developed upon the cuticle to further reinforce the impermeability of the epidermis. The stomata are also so developed as to meet the conditions under which the plant grows. In dorsiventral lea
. Nature and development of plants. Botany. NATURE OF PLANTS 37 evergreens, as laurels and rhododendrons, in the needles of cone- bearing trees, and in all plants that are exposed to the hot, dry air of summer or the drying winds of winter. Such leaves may be further protected and strengthened by thick-walled elongated cells, stereome (Fig. 23, st). Coatings of wax, mucilage and lime are also frequently developed upon the cuticle to further reinforce the impermeability of the epidermis. The stomata are also so developed as to meet the conditions under which the plant grows. In dorsiventral leaves they are more numerous on the under side of the leaves because they are less liable to be filled with water by rains and with dust which would prevent the interchange of gases. The plugging of the. Fig. 23. Cross-section of the outer cells of a leaf of pine, showing the firm character of the outer cells of the tough leaf: s, stoma; e, epidermis; c, cuticle; st, stereome; m, mesophyll cells. stomata by dust is one of the causes of the sickliness of plants in homes. The arrangement of the stomata on the under side of the leaf is also of especial advantage because the direct light does not fall upon them and cause an excessive loss of water. The stomata of floating leaves, however, are upon the upper surface and their stoppage with water is prevented by waxy coatings, as can be easily demonstrated by dipping a leaf of a water lily or spatter dock in the water. When the leaf is removed the water runs off of the waxed surface without wetting it. Some leaves are more or less erect, as the cattails, rushes and grasses, and these have the stomata developed more or less evenly oriBoth surfaces. Doubtless the intense light of midday is not beneficial to these leaves and the blade of the leaf is consequently placed parallel. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these il
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