. Elements of botany. Plants. STllUCTURE OF THE STEM. 61 83. Stem of Conifers. ^ — Sketch the end of a cut-off billet of hard pine or red cedar. Study the cut surface with a magnifying glass and decide whether any of the parts readily found in the wood of the coarser- grained hard-woods are absent from coniferous wood. Under a power of 100 or more diameters it is easy to see what it is that marks off one annual ring from another. Study the section, compare it with Fig. 50, and state the difference between spring wood and fall wood. Sketch the whole cross - section, moderately magnified Examine
. Elements of botany. Plants. STllUCTURE OF THE STEM. 61 83. Stem of Conifers. ^ — Sketch the end of a cut-off billet of hard pine or red cedar. Study the cut surface with a magnifying glass and decide whether any of the parts readily found in the wood of the coarser- grained hard-woods are absent from coniferous wood. Under a power of 100 or more diameters it is easy to see what it is that marks off one annual ring from another. Study the section, compare it with Fig. 50, and state the difference between spring wood and fall wood. Sketch the whole cross - section, moderately magnified Examine longitudinal sections, both radial and tangential, of pine, spruce, fir, or red cedar. 2 Sketch a radial section and a tangen- tial one, labeling the medullary rays and the cells of the wood, with their circular markings, as shown in Fig. 51. 84. The Early History of the Stem. — In the earliest stages of tlie growth of the stem it consists entirely of thin-walled and rapidly dividing cells. Soon, however, the various kinds of tissue which are found in the full-grown stem begin to appear. In Fig. 52 the process is shown as it occurs in the castor bean. At m, in B, is the central column of pith, surrounded by eight fibro- vascular bundles, fv, each of which contains a number of ducts arranged in a pretty regular manner and sur of the true Fig. 52.— Transverse Section through the Caulicle of the Castor- Oil Plant at Various Stages. A, after the root has just appeared outside the testa of the seed; B, after the caulicle is nearly an inch long; C, at the end of germina- tion ; r, cortex (undeveloped bark); vi, pith; st, medullary rays ; fv, fibro-vascular bundles ; cb, layer of tissue which is to develop into cambium. (Consider- ably magnified.) rounded by the forerunners 1 That is, of the cone-bearing trees (mostly evergreens), such as the pines, spruces, cedars, larches, and so on. 2 Pine shows the large circular pits very plainly, while red cedar shows the med
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1896
