196 BOTANY AND PHARMACOGNOSY. 



may consist of a more or less branching net work formed by the 

 anastomosing of a number of cells, as in Taraxacum (Fig. loi, 

 D). 



Special Secretion Cells. In Sanguinaria there occurs a rudi- 

 mentary laticiferous tissue, most of the juice being contained, 

 however, in special parenchymatous cells, which may be more or 

 less isolated, or arranged in irregular longitudinal rows. Cells 

 of this character are known as secretion cells and usually contain 

 oil, resin, tannin, calcium oxalate, mucilage (Figs. 98; loi, B), 

 etc., instead of substances which form an emulsion or milk-juice; 

 these cells are distributed in all parts of the plant, and include the 

 epidermal cells and glandular hairs. The walls usually consist of 

 cellulose but may have lamellae of cutin and suberin, the latter 

 being found particularly in the oil-secretion cells of rhizomes, 

 roots, barks and fruits (Figs. loi, B; 212; 236; 250). 



In some instances mucilage cells containing raphides occur in 

 longitudinal rows resembling the secretion cells of Sanguinaria ; 

 in some of the ferns, the barks of elder and locust, and leaves of 

 the Crassulacese, the tannin-cells are very much elongated, resem- 

 bling the simple laticiferous cells in the Asclepiadacese. 



Oils, resins, mucilage, gum-resins and allied products occur 

 quite frequently in special reservoirs or cavities formed as already 

 described (p. 178). 



INNER STRUCTURE OF MEMBERS OR ORGANS. 



THE STRUCTURE OF THE ROOT. 



Primary Structure. If we make a transverse section of the 

 young portion of a root (Vascular Cryptogam, Gymnosperm or 

 Phenogam), we notice the following tissues (Figs. 109-111). 

 The outermost tissue is epidermis (E), it being generally thin 

 walled and destitute of cuticle; it is as a rule hairy, and these 

 hairs, which are relatively long, but always unicellular, are known 

 as ROOT-HAIRS (Fig. no, FI) ; they ramify but very seldom. In- 

 side the epidermis there is frequently present an exodermis 

 (commonly referred to as hypodermis) composed of a single layer 

 of cells or at the most of but several layers, the cells of which 

 differ in shape and size from those of the epidermis and the ad- 



