. Botany for high schools. Botany. » LEAVES: STRUCTURE 85 the epidermal cells. These outgrowths are in the form of hairs (long slender cells or rows of cells), glands (special cells for excret- ing various substances) and scales (as in Shepherdia), The hairs are simple or branched (in the mullein), some of the latter being star-shaped (as in some oaks). These hairs and scales aid the leaf in retaining moisture since evaporation of moisture from the surface is hindered. 144. Structure of the leaf in cross section.—The epider- mis and guard cells as seen in a cross section of a leaf have been de
. Botany for high schools. Botany. » LEAVES: STRUCTURE 85 the epidermal cells. These outgrowths are in the form of hairs (long slender cells or rows of cells), glands (special cells for excret- ing various substances) and scales (as in Shepherdia), The hairs are simple or branched (in the mullein), some of the latter being star-shaped (as in some oaks). These hairs and scales aid the leaf in retaining moisture since evaporation of moisture from the surface is hindered. 144. Structure of the leaf in cross section.—The epider- mis and guard cells as seen in a cross section of a leaf have been described above. The interior portion of the leaf consists of the mesophyll and the fihro-vascidar bundles. These may be studied in cross and longitudinal section according to the way the veins run in the portion of the leaf sectioned; and the parts in general, the wood portion with its vessels and wood fibers, and the bast portion with its bast, can be made out by consulting paragraphs 94-98. The mesophyll usually consists of t^o kinds of paren- chyma cells,—the palisade layer of cells and the loose, spongy tissue. The pali- sade layer of cells is found usually just beneath the upper epidermis. It consists of elongated cells lying closely side by side and perpendicular to the epidermis. Sometimes there are two layers of pali- ^ . Section of iv>' leaf, palisade cells Sade cells; in the compass plants, one above, loose parenchyma, with ^ ^ large intercellular spaces in center, layer on each side of the leaf. The Epidermal cells on either edge. with no chlorophyll bodies. remaining part of the mesophyll is the loose parenchyma, so-called because the intercellular spaces are large, thus giving the cells a loose arrangement. These inter- cellular spaces connect throughout the leaf and also with the stomates. They thus provide for aeration of the leaf, for the entrance and escape of gases in photosynthesis and respiration, and for the escape of moisture. 145. The chlorophyll b
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
