. Introduction to botany. Botany. THE STEM AND THE LEAF 63 groups: one with no continxotis wondi/ eyJiiuler, like the stem of such a climber as the Dutchman's-pipe (fig. 42, A), and one with a continuous wooihj cylinder^ like that of the sunflower (fig. 42, i?). The real difference between the two kinds of stem is that, lUve most climbers, the stem of the Dutchman's-pipe begins the season's growth with a set of separate fibrovascular bundles wliich remain separate, while in the sunflower the bundles are at first sepa- rate but soon join each other. The boundary l)et\\eeu bark and wood is a lay
. Introduction to botany. Botany. THE STEM AND THE LEAF 63 groups: one with no continxotis wondi/ eyJiiuler, like the stem of such a climber as the Dutchman's-pipe (fig. 42, A), and one with a continuous wooihj cylinder^ like that of the sunflower (fig. 42, i?). The real difference between the two kinds of stem is that, lUve most climbers, the stem of the Dutchman's-pipe begins the season's growth with a set of separate fibrovascular bundles wliich remain separate, while in the sunflower the bundles are at first sepa- rate but soon join each other. The boundary l)et\\eeu bark and wood is a layer of thin- walled cells (c, fig. 42, .4), the cambium layer. It is this cambium, its cells filled with mucilaginous proto- plasm, that makes up the slimy layer just outside the wood, from which the bark jDeels so readily in early spring, ^\•hen boys are making whistles or strip- pmg off sheets of slippery- elm bark. It is important to notice that each fibro- vascular bundle consists of an outer portion, o, which belongs to the bark, and an inner portion, u\ which belongs to the wood. A much better idea of the details of structure of the several regions of the stem can be gained from a lengtlnvise section, like that shown in figure 43, than from cross sections, like those of figure xhe uses of some of the parts sho^A'n m figure 43 are briefly stated on the following page. ^ Since the type of stem structure shown in figure 43 is not exactly Yike that of the other two figures, it will not be possible to identify all the kinds of cells shown in figure 43 with those of the other two. Note especially that in figure 43 the cambium is not readily distinguished from the overlying tissues, and that no distinct layer of heavy-walled bast fibers is Fig. 43. Lengthwise section of a young dicotyledonous stem ep, epidermis; cort, cortex; h, bast; «, ves- sels; sh, sheatli surrounding pitli; p, pith; si, sieve cells of the bast. Magnified about 90 diameters. After Bonnier and
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisher, booksubjectbotany
