60 VEGETABLE HISTOLOGY. 



it will be found that the cells have the same general appear- 

 ance, showing that they are, in form, essentially like paren- 

 chyma cells, the difference being that the walls are immensely 

 thickened in stone cells, and they no longer take part in the 

 vital processes of the plant, but act as mechanical tissue; in 

 fact, in some cases they are elongated and fusiform, so that it is 

 difficult to distinguish them from prosenchyma fibres. All 

 gradations are found between parenchyma and stone cells and 

 between stone cells and bast fibres. 



Add phloroglucin and hydrochloric acid to a section. The 

 walls are stained red, proving lignified material. 



Stone cells may be studied to better advantage by isolating 

 them by Schulze's maceration solution as directed under this 

 reagent. Stain a section treated thus with methyl-green and 

 mount in water, and tap the cover glass with a teasing needle, 

 when the cells will separate in virtue of the middle lamellas, 

 which unite the cells, being dissolved away by the maceration 

 fluid. 



Examine sections cut in various directions from cocoanut 

 shell. These cells have a natural brownish-yellow color, and 

 their boundaries are more easily seen than in 

 the case of the walnut cells. While many cells 

 are almost circular in outline, others are some- 

 what elongated. This fact indicates that the 

 cells tend towards the fibrous condition and run 

 in different directions, so that in the same sec- 

 tion some are seen in cross-section and appear P of 

 round, while others are seen lengthwise and 

 appear elongated. The cavities are filled with a dark material. 

 In general structure the cells resemble those of the walnut 

 shell. Ground cocoanut shells are used frequently as an adul- 

 terant of ground spices and should, therefore, command close 

 study by the student. 



To study the stone cells as they occur in barks, wrap pieces 

 of the bark of cassia cinnamon and cascara in wet filter paper 

 and keep in a closed bottle until they are soft enough for sec- 

 tioning. Also immerse a piece of viburnum (stem) bark in 

 dilute (1 or 2 per cent.) alkali until soft, and finally wash 

 thoroughly in water. Cut cross-sections between pith or cork 

 and mount in water or chloral solution. Cinnamon has an 

 interrupted chain of colorless stone cells running tangentially 

 about midway of the section. Cascara presents large masses 

 of yellow stone cells at about one-third the width of the section 

 from the outer edge. Viburnum has similar masses of stone 



