194 THE MICROSCOPICAL NEWS. 
finds the gum-cells of wheat to be decidedly larger than those of 
rye; the former measuring 3, the latter 1°5-2 ». The thickness 
of the wall of the hairs of wheat he states at 5-8, of rye 3-6 »; 
the diameter of the cavity of the former 1°5—4, of the latter 4-12 p. 
—/. R. M.S. 
MICROSCOPICAL EXAMINATIONS OF 
ARTICLES OF COMMERCGE* 
TOMASCHEK points out the value of microscopical 
e 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 charterized by the beautiful tabular cells 
with thick wavy margins belonging to the palez which are always 
found in the meal in consequence of the close adherence of the 
paleze 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 sub- 
stance 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 o‘o8-o'o1 mm. in length. In 
order to obtain the iodine reaction characteristic of a nitrogenous 
substance, a comparatively 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 gelatinous substance is especially well recog- 
nized 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.—/. 2. AZ. S. 
* Verhandl. Naturf. Ver. Briinn, xix. (1881) p. 15. See Bot. Centralbl., xi. 
(1882) p. 318. 
