DIV. 



MORPHOLOGY 



57 



(1) The Cutis Tissue is a primary permanent tissue and arises by 

 the early suberisation of cells of the epidermis or of thinner or 

 thicker layers of parenchyma from which intercellular spaces are 

 frequently absent. A tissue of the latter kind not uncommonly 

 sheathes the outside of older parts of the plant (e.g. roots, Fig. 159 ex) 

 or delimits strands of tissue within the plant from the surrounding 



tissue. The cells of this cutis tissue 

 usually retain their living contents. 



In place of suberisation the introduction 

 of cutin or other substances that are imper- 

 fectly known chemically may render the mem- 

 branes less permeable to water. 



(2) Endodermis. This tissue is 

 formed of the endodermal cells ( 43 ). 

 It very frequently encloses and bounds, 



FIG. 55. Stinging hair of Urtica 

 dioica, with a portion of the epi- 

 dermis, and, to the right, a small 

 bristle, (x 60. After STRASBURGER.) 



FIG. 56. Glandular colleter from a stipule of 

 Viola tricolor, showing also to the left a uni- 

 cellular hair, (x 240. After STRASBURGER.) 



as a sheath, a single layer of cells in thickness, living tissues within 

 the plant, but it may also form a limiting layer on the outside. Its 

 origin is sometimes primary and sometimes secondary. The elongated 

 prismatic living cells of the endodermis have no intercellular spaces 

 between them. When young the walls are not suberised, but a narrow 

 strip of the membrane, in the form of a band running completely 

 round the cell, has undergone a peculiar change by the introduction 

 of an imperfectly known (1 cork -like) substance (Caspary's band, 



