ENDODERMIS. 



63 



In many cases it can be shown 

 thickened walls, as shown in 

 Fig. 41.1 



212. Certain modified pa- 

 renchyma cells are often united 

 to form sheaths around flbro- 

 vascnlav bundles. These cells 

 are prismatic, and in close 

 apposition. Their walls are 

 thin, except at their faces of 

 mutual contact, where they are 

 conspicuously thickened, and 

 often plicate, and nearly all 

 parts of the membrane are 

 more or less cutinized. 



that canals run thronwh these 



213. These cells con- 

 stitute the endodermis. 

 The}- generally contain a 

 large amount of starch. 



214. Parenchyma cells 

 may undergo the mu- 

 cilaginous modification 

 (see 147), as in the con- 

 ductive tissue of the 

 stjle of man}' flowers 

 and the albumen of many 

 seeds. This change is 

 common also in the lower 

 plants. 



215. An appearance 

 closely resembling in 

 some points that pro- 

 duced by the mucilagi- 

 nous modification is pre- 



1 A second kind of sclerotic iiavenchyma sometimes accompanies the longer 

 sclerotic cells in a few •ferns and son)e monocotyledons. Its cells appear as if 

 segments of a jointed fibre, somewhat flattened on the side next the long cells, 

 and decidedly convex on the other. Such flattened cells are unequally thick- 

 eiied on the two sides, and the walls are somewhat siliciHcd. But the most 

 striking feature in many cases is the deposition within the cavity of the cell 

 of a mass of silicic acid ; this is well seen in the hard cells which accompany 

 the fihro-vascular threads in the leaves of some palms. 



Fig. 41. A sclerotic cell from the nutshell of Juglans regia. (Reinke.) 

 Fig. 42. Section tlirough the central cylimier of a binary root of a vascular crypto- 

 gam (Cyathea meUullaris). p, r, r = endodermis. (Van Tiegliem.) 



