. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. DICOTYLEDONOUS STEM 77 from that of the root in having strongly thickened outer walls. It forms a continuous layer except where interrupted by the presence of stomata ^ or lenticels (p. 139). Its function is to protect the more dehcate internal tissues, and in correspondence with this it does not mther at an early stage like the piliferous layer. Occasional cells grow out into hairs (Fig. 34, h.), but these are quite different in character from the root-hairs. Immediately within the epidermis are several laye
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. DICOTYLEDONOUS STEM 77 from that of the root in having strongly thickened outer walls. It forms a continuous layer except where interrupted by the presence of stomata ^ or lenticels (p. 139). Its function is to protect the more dehcate internal tissues, and in correspondence with this it does not mther at an early stage like the piliferous layer. Occasional cells grow out into hairs (Fig. 34, h.), but these are quite different in character from the root-hairs. Immediately within the epidermis are several layers of collenchymatous cells (Fig. 34, s.), thickened mainly on the. Fig. 34.—Photomicrograph of a transverse section of the young stem of the Sunflower (Helianihiis). c, cortex; /;., hair; p., pith; ph., phloem; r, raj'S ; s, collenchyma ; xy., xylem. tangential walls, whilst between the cells of the inner layers are relatively large intercellular spaces. Such spaces are also abun- dant in the remainder of the ground tissue, and form small tri- angular cavities between the polygonal cells of the pith. At the inner limit of the cortex there is a single layer of cells distinguished b}' the frequent presence of large starch-grains (Fig. 36, sh.), which can be rendered more prominent by staining vnt\i iodine. The layer in question bends outwards around each 1 For a detailed consideration of epidermis and stomata, see the next 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 Fritsch, Felix Eugene, 1879-; Salisbury, E. J. (Edward James), Sir, b. 1886. London, G. Bell and sons ltd.
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