Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 108 BOTANY Transverse section of a stem of burdock, showing fibrovascular bundles not com- pletely united into a ring. Young Monocotyledonous Stem. — Almost the entire stem of a very young, green monocotyledon is composed of soft, thin-walled cells. These are the cells making up the paren- chyma (parent tissue.) Later in the life of the stem their contents are used up by the plant, and we find them empty and dry in the sec- tion
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 108 BOTANY Transverse section of a stem of burdock, showing fibrovascular bundles not com- pletely united into a ring. Young Monocotyledonous Stem. — Almost the entire stem of a very young, green monocotyledon is composed of soft, thin-walled cells. These are the cells making up the paren- chyma (parent tissue.) Later in the life of the stem their contents are used up by the plant, and we find them empty and dry in the sec- tion of cornstalk. In some mono- J til^^ :J^^fe I cotyledonous stems their walls '^: •^SSL *'-**^.*v*. \ become hard, while in other cases, as in the bamboo, they entirely dis- appear. Structure op a Young Dicoty- ledonous Stem. — In the stem of a young dicotyledon the pith is found to occupy relatively a small space in the middle of the section. This pith is composed of the paren- chyma cells such as we found in the cornstalk. Surrounding the pith is the wood. The wood consists (in the cross section) of the ends of many tubes and the woody walls of supporting cells which occupy that area. If the section is several years old, we shall find a definite ring in the wood for each year's growth. Medullary Rays. — Radiat- ing from the center of the stem outward are found a number of tiny lines. These are more promi- nent in stems of older growth. The medullary rays, as they are called, are seen to begin at the pith and pass out to the bark. They are, indeed, formed of the pith. They are part of the original parenchyma which at first formed a large part of the whole stem. As the stem grew in size, fibrovascular bundles appeared. These bundles were not scattered through the
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