ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 603 



projecting from the corner of the larger group is well displayed. 

 Where the view of the compound eyes is a full-face one, the darker 

 pigment is seen so strongly that its true position is concealed. A 

 profile view shows the little lenses to be clear, like glass, and the 

 pigment to be behind them. 



Microscopical Examinatioiis of Articles of Commerce.* — A. 

 Tomaschek points out the value of microscopical examination in the 

 determination of the purity of many articles of commerce, and gives 

 the following illustrations : — 



Tea-leaves are readily recognized by their peculiar idioblasts. 



Barley-meal is very well characterized by the beautiful tabular 

 cells with thick wavy margins belonging to the pale^ which are 

 always found in the meal in consequence of the close adherence of the 

 paleae to the fruit. The following method is recommended for their 

 detection : — A drop of concentrated hydrochloric acid is thrown on to 

 the meal and rolled in it. A piece of the dough thus obtained is 

 placed on the slide, and another drop of hydrochloric acid run on to 

 it before covering with the cover-glass, and the cover-glass then 

 pushed lightly backwards and forwards. The tabular cells are not 

 only not attacked by the acid, but are coloured by it a bright sulphur- 

 yellow colour. They may be detected even after the baking of the 

 barley-meal. 



The microscopical appearance of wheat-meal is distinguished by 

 the peculiar properties of the paste, which can be best demonstrated 

 in the following way : — A thin layer of meal is placed on the slide, 

 carefully covered with a cover-glass, and then moistened by a drop of 

 water placed on its margin. The cover-glass is then lightly pressed, 

 and pushed backwards and forwards, the gelatinous substance being 

 thus separated from the starch-grains, and appearing in the form of 

 dense clouds. If glycerin is used it solidifies into bluntly angular 

 granules, averaging 0*08-0 '01 mm. in length. In order to obtain 

 the iodine reaction characteristic of a nitrogenous substance, a com- 

 paratively large quantity of the reagent must be used, as the golden- 

 yellow reaction of the proteinaceous substance does not appear until 

 the starch-grains have absorbed what iodine they require. This gela- 

 tinous substance is especially well recognized by its reaction with 

 cochineal. If cochineal-powder is scattered over the wheat-meal, and 

 moistened merely by breathing on it, the proteinaceous masses at once 

 take a beautiful carmine-red colour, the starch-grains remaining quite 

 colourless. 



Microscopical Separation of Wheat- and Rye-Meal. f — L. Witt- 

 mack records the following observations on the microscopical distinc- 

 tions between wheat-meal and rye-meal. The amount of starch gives 

 no certain character, and the size of the starch-grains is not in itself 

 sufficient ; the maximum size of the starch-grains of rye is 42-52 {x ; 



* Verhandl. Naturf. Ver. Briinn, xix. (1881) p. 15. See Bot. Centralbl., xi. 



(1882) p. 318. 



t SB. Bot. Ver. Prov. Brandenburg, xxiv. (1882). See Bot. Centralbl., xili, 



(1883) p. 91. 



