28 COMMERCIAL SICILIAN SUMAC. 



to use. It is well to make several slides from the specimen, so as to 

 get a good idea of its character. 



Another method of procedure which some may prefer, and which 

 lends itself readily to the examination of finely powdered samples, is 

 the following: Place in a test tube a portion of the sample equal in 

 size to a hazelnut, add a few cubic centimeters of the chloral hydrate 

 solution and boil slowly for two or three minutes, allow to stand until 

 the larger pieces have settled to the bottom and then remove a part 

 of them with a pipette and mount on a slide in the usual manner. 



Such treatment is all that is necessary in the preparation of samples 

 for immediate examination. It is often desirable, however, to pre- 

 pare specimens for future reference. For this purpose the specimen 

 is cleared with chloral hydrate as described, the excess liquid is 

 removed by a piece of filter paper, and then mounted in glycerin or 

 glycerin jelly. To mount in glycerin, add to the moist fragments a 

 small drop of the 50 per cent glycerin and after covering seal with a 

 good microscopical cement. In order to mount in glycerin jelly, the 

 sample is cleared and the excess chloral hydrate solution removed as 

 previously directed, a tiny drop of 50 per cent glycerin is mixed with 

 the moist fragments, and then a small piece of glycerin jelly (about a 

 quarter of the size of a pea) is placed on the slide. The whole is gently 

 heated until the jelly melts, and the fragments are mixed with the 

 jelly by means of a teasing-needle or scalpel, care being exercised not 

 to make bubbles in the mass, as they are difficult to remove. Care 

 should also be taken not to heat the glycerin jelly on the slide enough 

 to produce bubbles. 



Permanent samples can be made, after clearing in chloral hydrate, 

 by dehydrating in alcohol, clearing in xylol, and mounting in xylol 

 Canada balsam. This method is not satisfactory, however, unless the 

 sample is stained; and with many small fragments, as is usual in a 

 powdered sumac, this step is somewhat difficult and tedious. 



SOME HISTOLOGICAL FEATURES. 



A short description of the most characteristic histological features 

 of sumac and the most important of its adulterants may be of value. 

 Although written descriptions and photographs aid greatly, in begin- 

 ning such investigations the microscopist should, of course, first 

 work on samples of known purity, then on known mixtures, and finally 

 on mixtures of a content unknown to him but prepared from authen- 

 tic samples. 



SICILIAN SUMAC (Rhus coriaria). 



The upper epidermis of Rhus coriaria (PI. I, fig.l) is made up of 

 cells about 35yu in diameter (varying from 20/* to 50>0 . They appear 

 in the surface view to be bounded by walls with fairly straight sides 



117 



