ENDODERMIS. 



63 



In many cases it can be shown 

 thickened walls, as shown in 

 Fig. 41. ' 



212. Certain modified pa- 

 renchyma cells arc often united 



/ 



to form sheaths around fibro- 

 vascular bundles. These cells 

 are prismatic, and in close 

 apposition. Their walls are 

 thin, except at their laces of 

 mutual contact, where they are 



B> 



conspicuously thickened, and 

 often plicate, and nearly all 

 parts of the membrane are 

 more or less cutinized. 



\ 



that canals run through these 



41 



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 

 st}-le of many 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 parenchyma sometimes accompanies the longer 

 sclerotic cells in a few ferns and some 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- 

 ened on the two sides, and the walls are somewhat silicified. 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 fil>ro- vascular threads in the leaves of some palms. 



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

 FIG. 42. Section through the central cylinder of a binary root of a vascular crypto- 

 gam (Cyathea medullaris). j), r, r endodermis. (Van Tieghem.) 



