. Plant life, considered with special references to form and function. Plant physiology. THE ROOT. 77 and the phloem region, nith the cortex between them, if anything is left of it, constitute a I/ark, which becomes fur- rowed lengthwise, like the bark of the stems of many trees. Such secondary thickening finally produces in the roots a. Fig. qi.âA. diagram of priman' structure. P. C. diagrams shon-ing the results of secondare' thickeniug from the stclar cambium in the two extreme forms c. cortex; e^i. dudodermis : /-, pericycle ; /-h'. primary phloem ; /A", secondary phloem ; .r'* primar
. Plant life, considered with special references to form and function. Plant physiology. THE ROOT. 77 and the phloem region, nith the cortex between them, if anything is left of it, constitute a I/ark, which becomes fur- rowed lengthwise, like the bark of the stems of many trees. Such secondary thickening finally produces in the roots a. Fig. qi.âA. diagram of priman' structure. P. C. diagrams shon-ing the results of secondare' thickeniug from the stclar cambium in the two extreme forms c. cortex; e^i. dudodermis : /-, pericycle ; /-h'. primary phloem ; /A", secondary phloem ; .r'* primary xylem ; .r", secondary xylem ; tY', stelar cambium : r', secandar>' pitli-rays â I", pith.âAfter Wan lieghem. ' Structure which is almost identical with that of stems which ha\'e undergone secondary thickening. (Compare % 133-) 88. (b) Fleshy roots.âBut if thin-walled cells are the predominant products of the stclar cambium, the root often becomes very thick and fleshv, as in the carrot, turnip, radish, sweet potato, beet, dahlia, artichoke, etc. Such roots serve the plant as storehouses of reserve tbod, and are consequently useful to animals as food. The thin-walled cells which are produced in such volume may belong to the phloem region, as in the carrot and parsnip, or to the xylem, as in the radish and turnip. This thickening for storage purposes may affect either the primary or secondary roots, or both. Other plants may develop the cortex (orchids) or the pith (daffodils) to an extraordinary degree, forming fleshy roots which also function as storehouses. 89. (c) Float roots.âIn plants which grow in water or in very wet swamps, roots are sometimes modified to serve as floats. In these cases, the voluminous cortex consists of large. 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 Barne
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