SCLEROTIC CELLS. 59 



CHAPTER XII. 

 SCLEROTIC CELLS. 



The cells of this tissue are commonly called stone or grit cells. 

 The cells differ from ordinary parenchyma ones in having the 

 walls excessively thickened, so much so frequently that the 

 cavity of the cell is nearly obliterated. Every gradation, how- 

 ever, may be observed between these and ordinary parenchyma. 

 The walls of sclerotic cells are usually lignified and the thicken- 

 ing is deposited in layers, giving the appearance of concentric 

 rings. These are the cells which give the great hardness to the 

 outer coats of seeds and the shells of nuts. They constitute the 

 gritty particles that occur in the flesh of some fruits, as the 

 pear and apple, and are present in many barks, for example, 

 Cinnamon, Oak, Viburnum, Cascara, etc. Stone cells are 

 classed by some with parenchymatous tissues because of their 

 origin and shape, but otherwise they have very little in com- 

 mon with parenchyma. 



SCLEROTIC TISSUE OF WALNUT SHELL. 



Use a piece of shell that has been softened by long soaking in 

 10 per cent, alkali and washed in acidified water. Cut thin 

 sections in various directions, taking care not to let the razor 

 run too deep. Mount in water and examine with low power, 

 picking out the thinnest edge. 



There will be seen a mass of rounded, somewhat polyhedral 

 cells, pressed so closely together that no intercellular spaces 

 are visible. The walls are extremely thickened and contain 

 minute dots, as well as radial lines connecting the small cavity 

 or lumen of the cell with the middle lamella. In this section 

 the cells are almost colorless. 



Put on high power. The radial lines can now be seen to be 

 tubes, and the dots are tubes cut cross-wise, the ends appearing 

 as dots. The tubes are known as pore-canals and are analogous 

 to the pits in ordinary parenchyma cells. They probably serve 

 to help the circulation of nutritive fluids from one cell to 

 another, as is evidenced by the fact that the tubes of neighbor- 

 ing cells end opposite each other. 



With careful examination the walls are seen to be made up 

 of concentric layers. These are made more distinct by adding 

 a drop of chloral-hydrate solution (5 chloral-hydrate to 2 water) 

 and watching closely its swelling action. The lines come out 

 plainly at first, but after a time disappear, owing to continued 

 swelling. 



Examining sections cut in various directions from the shell, 



