176 



BOTANY. 



epidermis (dermatogen) (d), young fibro- vascular cylinder (plerome) 

 (j>Z.), and young ground tissue (periblem) (pb.). The structure of the 

 older portions of such as root is not very easy to study, owing to dif- 

 ficulty in making good cross-sections of so small an object. By using a 

 very sharp razor, and holding perfectly straight between pieces of pith, 

 however, satisfactory sections can be made. The cells contain so much 

 starch as to make them almost opaque, and potash should be used to clear 



FIG. 94. A, cross-section of the stem of the shepherd's-purse, including a 

 fibro-vascular bundle, x 150. ep. epidermis, m, ground tissue, sh. bundle 

 sheath, ph. phloem, v.y. xylem. tr. a vessel. B, a young root seen in 

 optical section, x 150. r, root cap. d, young epidermis, pb. ground. pL 

 young fibro-vascular bundle. C, cross section of a small root, x 150. fb. 

 fibre-vascular bundle. D, epidermis from the lower side of the leaf, x 150. 

 E, a star-shaped hair from the surface of the leaf, x 150. F, cross-section of 

 a leaf, x 150. ep. epidermis, m, ground tissue, fb. section of a vein. 



them. The fibro-vascular bundle is of the radial type, there "being two 

 masses of xylem (xy.) joined in the middle, and separating the two 

 phloem masses (p/t.), some of whose cells are rather thicker walled than 

 the others. The bundle sheath is not so plain here as in the fern. The 

 ground tissue is composed of comparatively large cells with thickish, soft 

 walls, that contain much starch. The epidermis usually dies while the 

 root is still young. In the larger roots the early formation of the cambium 



