. Elements of botany. Botany; Botany. STETJCTimE OF THE STEM. 65 Study the bundles in various portions of the section and notice particu- larly whether the relative amount of surface in each covered by ducts and by thick-walled wood-cells or sclerenchyma cells is everywhere the same. On the whole the structure of monocotyledonous stems is much simpler than that of dicotyledonous, stems. The bun- dles which they contain are somewhat similar to those which the exogenous or outside-growing stems of dicotyledons form at a very early period of their growth. But while in exogens these bundles soon u
. Elements of botany. Botany; Botany. STETJCTimE OF THE STEM. 65 Study the bundles in various portions of the section and notice particu- larly whether the relative amount of surface in each covered by ducts and by thick-walled wood-cells or sclerenchyma cells is everywhere the same. On the whole the structure of monocotyledonous stems is much simpler than that of dicotyledonous, stems. The bun- dles which they contain are somewhat similar to those which the exogenous or outside-growing stems of dicotyledons form at a very early period of their growth. But while in exogens these bundles soon unite into a ring of woody tissue, with a cambium layer outside, capable of continual growth inward and outward, in the endogenous or inside-growing stems of monocotyledons this is not the case. True cambium is not formed, but the procaTm- biiim which precedes the mature bark-ceUs and wood- cells is all transformed into cells of bark or of wood, which attain their full size and are then incapable of giving rise to new cells of any kind. Therefore, the stems of such perennials as palms remain unchanged in diameter year after year. Monocotyledonous stems which do increase in diameter from year to year do so by the introduction of new bundles among the old ones. This growth by interposition of new bundles affords some justification for the name endogenous, often given to the monocotyledonous stem. 88. Disirihution of Material in Monocotyledonoiis Stems.— The well-known strength and lightness of the straw of our. Fig. 54. — Cross-Section of Stem of Indian Corn. c I', fibro-vascular bundles; g c, pithy ma- terial between Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bergen, Joseph Y. (Joseph Young), 1851-1917. Boston, Ginn
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