. Essentials of biology presented in problems. Biology. Section across tt young twig of box elder, sbtnviug the four stem regions : c, epidermis, represented by the heavy bounding line; c, cortex; w, wood; p, pith. (From Coulter, Plant Relatiotis.) distinct regions. The center is oeeupied by the spongy, soft pith; surrounding this is found the rather tough wood, while the outer- most area is called cortex or bark. More careful study of the bark reveals the presence of three la>'ers — an outer layer, a middle green layer, and an inner fibrous la>'er, the latter usualh' brown in color. Thi
. Essentials of biology presented in problems. Biology. Section across tt young twig of box elder, sbtnviug the four stem regions : c, epidermis, represented by the heavy bounding line; c, cortex; w, wood; p, pith. (From Coulter, Plant Relatiotis.) distinct regions. The center is oeeupied by the spongy, soft pith; surrounding this is found the rather tough wood, while the outer- most area is called cortex or bark. More careful study of the bark reveals the presence of three la>'ers — an outer layer, a middle green layer, and an inner fibrous la>'er, the latter usualh' brown in color. This layer is made up largely of tough fiberlike cells known as bast fibers. The most important parts of this inner bark, so f:ir as the plant is con- cerned, are manj^ tubelike struc- tures known as sie\(' tubes. These are long rows of living cells, having perforated sievelike ends. Through these colls food materials pass downwai'd from the upper part of the plant, where they are manufactured. ,C In the wood will be noticed (see Figure) a number of lines radiating outward from the pith toward the cortex. These are the so-called medullary rays, thin plates of pith which separate the wood into a num- ber of wcnlfic-shaped masses. These masses of wood are composed of nuin>' elongated cells, which, placed end to end, form thousands of little tulles connecting the leaves with the roots. In addition to these are man>' thick-walled ('(>lls, which give strength to the mass of wood. In sec- tions of wood which have. Section across u twig of l)ox elder three j'cars old, show-ing three annual growth rings in the vascular c.\linder. The ra- diating lines (m), which cross the wood (w), represent the pith raj-s, the prin- cipal ones extending from the pith to the cortex (c). (From Coulter, Plant Jiila- tions.). 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
Size: 1622px × 1540px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
