ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
533 
Staining of Vegetable Nuclei.* — The following is the method 
employed by Mr. H. W. T. Wager in staining the nuclei in Peronospora 
parasitica , parasitic on the shepherd’s purse (see p. 491). The sections 
were made by the Cambridge ribbon-section-cutting microtome. The 
fresh infected tissues of the host-plant were cut up into small pieces, 
and placed at once either in absolute alcohol or in chromic acid solution, 
where they were kept until thoroughly penetrated, and were then 
prepared for imbedding in paraffin-wax. The chromic acid specimens 
were thoroughly washed in 70 per cent, alcohol, then transferred to 
methylated alcohol, and finally to absolute alcohol. The pieces of tissue 
may then be stained en bloc , or the separate sections may be stained, 
when cut, on the slide. The latter gave the best results. 
After being thoroughly dehydrated by alcohol, the pieces of tissue 
were transferred to turpentine for about forty-eight hours, and were 
then placed in soft melted paraffin-wax for about twenty-four hours, and 
finally transferred into hard melted paraffin-wax for about two days. 
They were then imbedded in small square blocks of paraffin, and very 
thin sections cut by the microtome. These sections were cemented to 
the slide by a solution of white of egg and glycerin, and the paraffin- wax 
melted by heating the slide on a water-bath, and washed off in turpentine. 
The slide was next placed in absolute alcohol, and afterwards transferred 
to a dilute solution of Kleinenberg’s haematoxylin in water, made by 
adding a few drops of the strong haematoxylin solution to a beaker of 
water, until the whole was decidedly coloured. The sections were left 
in this until they were considerably over-stained, and were then placed 
in a dilute solution of acid alcohol, made by adding a few drops of strong 
hydrochloric acid to a beaker of 70 per cent, alcohol for a short time to 
reduce the stain. They were then washed successively in 70 per 
cent., 90 per cent., and 100 per cent, alcohol, and were next transferred 
for a few minutes to turpentine until quite clear and transparent, and 
were finally mounted in Canada balsam. The preparations thus 
obtained, which were in many cases only about 1/8000 in. in thickness, 
exhibited the structure of the nucleus clearly and distinctly. 
Nessler’s Ammonia Test as a Micro-chemical Reagent for Tannin. t 
— Mr. S. Moore writes : In most cases the presence of tannin is imme- 
diately shown by all the ordinary reagents used by the botanist for its 
discovery. This does not happen sometimes, however, as, for instance, 
in the tannin-cells found in the epidermis on the dorsal side of the 
leaves of some plants. As a good typical example the common prim- 
rose may be cited. Of all the ordinary tests, including iron salts, 
potassium bichromate, Moll’s test (copper acetate and iron acetate), 
ammonium molybdate, and osmic acid in 1 per cent, solution, the 
latter alone acts immediately upon the tannin in the primrose leaf’s 
epidermis. It may hence be worth while recording the discovery of 
a second reagent capable of acting rapidly and effectively; and one 
which is easily made and will keep for some time should be especially 
valuable. Such a reagent is Nessler’s test for ammonia. 
Nessler’s test is made, as all the world knows, by saturating a 
solution of potassium iodide with mercuric iodide, and adding an excess 
Ann. of Bot., iv. (1890) p. 131. 
f Nature, xli. (1890) pp. 585-6. 
