. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. A cross section through a taproot (a parsnip); C, cortex; W, wood. Notice in the right-hand specimen, which has been dipped in iodine, that the core of wood continues out into the rootlets which leave the main root. Where is most starchy food stored in a parsnip ? a little first-hand evidence as to its internal structure. If you cut open a parsnip or carrot so as to make a cross section of the root, you find two distinct areas, an outer portion, the cortex, and an inner part, the central cy
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. A cross section through a taproot (a parsnip); C, cortex; W, wood. Notice in the right-hand specimen, which has been dipped in iodine, that the core of wood continues out into the rootlets which leave the main root. Where is most starchy food stored in a parsnip ? a little first-hand evidence as to its internal structure. If you cut open a parsnip or carrot so as to make a cross section of the root, you find two distinct areas, an outer portion, the cortex, and an inner part, the central cylinder. If you cut another parsnip in lengthwise section, these struc- tures show still more plainly. An additional fact is seen; namely, that all the smaller roots leaving the main or primary root have a core of wood which bores its wav out through the cortex wherever the small rootlets are given off. Make a drawing that will show these points. Fine Structure of a Root. — If we could now examine a much smaller and more delicate root in thin longi- tudinal section under the compound microscope, we should find the follow- ing structure: (Cross sections and longitudinal sections of Tradescantia roots are excellent for demonstration of these structures.) The entire root is seen to be made up of cells, the walls of which are uniformly rather thin. The cells of this part of the root are more or less regular in size and shape. The central cylinder can easily be dis- tinguished from the surrounding cortex. The cells of the former have somewhat thicker walls. In a longitudinal sec- tion a series of tubelike structures may be found within the central cylinder. These structures are, in fact, cells which have grown together at the small end, the long axis of the cells running the length of the main root. In their de- velopment the cells mentioned have grown together in such a manner as to lose their small ends, and now form continuous hollow tubes with rather strong walls. Other cells h
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