15G SUMMARY OF CURRENT RESEARCHES RELATING TO 



stain the cell-nuclei and the investing membrane of the bordered pit only. 

 The preparation is then washed in water, dehydrated in alcohol, and 

 cleared up in oil of cloves. Clearing up acts very beneficially, because 

 the optical effect produced by the curvature of the pit is diminished. 



The reaction of the bordered pit membrane to dyes undoubtedly 

 shows that it differs in its chemical and physical relation from the rest of 

 the membrane substance. The circumstance that membranes of the 

 cambium cells and the membranes consisting chiefly of pure cellulose 

 stain deeply with hematoxylin might lead to the conclusion that in the 

 pit membrane we have to deal with a pure cellulose. This, however, is 

 contradicted by the fact that it stains deep red with phloroglucin and 

 hydrochloric acid. 



Staining Diatoms.* — Prof. 0. Drude discusses the method of staining 

 diatoms as a suitable means for obtaining proper microscopical prep liga- 

 tions. The methods which merely preserve the siliceous valves, and 

 which at one time was the only object aimed at, have since Ptitzcr's 

 systematic classification (ef. Hanstein's 'Beitrage' and Schenk's ' Hand- 

 buch der Botanik,' ii. p. 403) have been recognized and adopted, no 

 longer suffice, and must give way to a method which clearly shows and 

 permanently retains in the microscopical preparation, the cell-nucleus 

 and the endochrome-plates. 



Such a method was communicated by Pfitzer four years ago,f and has 

 been employed by the author with great advantage. It consists in 

 staining the fresh material with picronigrosin : to a saturated watery 

 solution of picric acid is added as much of a saturated watery solution 

 of nigrosin as causes the mixture to assume a deep olive-green hue. 

 This solution is poured over the fresh Bacillarias, or the rotting leaves, 

 stems, &c, of water plants on which they are found are placed in test- 

 tubes filled with the picronigrosin solution. The first kills and fixes, 

 the latter stains, the nucleus most strongly, less so the endochrome- 

 plates, and very faintly the thin layer of protoplasm. 



The stained valves are best mounted in balsam, after having been 

 thoroughly washed with spirit, then dehydrated with absolute alcohol, 

 and cleared up in oil of cloves. Thus are obtained very useful prepara- 

 tions which show beautifully the nucleus and nuclear fission, and also 

 the endochrome plates which formerly soon lost colour or altered in 

 form and position. Glycerin may be also used for mounting. 



Stained Yeast - preparations.^ — Dr. P- Lindner states that the 

 behaviour of yeast-cells to dyes is the same as occurs in Bacteria. If 

 yeast-cells dried on cover-glasses be placed in solutions of methylen- 

 blue, gentian-violet, fuchsin, Bismarck-brown, &c, they greedily pick 

 up the dye. If the preparation be over-stained the mistake is easily 

 obviated either by prolonged washing with distilled water, or by the 

 application of spirituous or slightly acidulated water. The spores too 

 behave in a manner similar to the resting spores of Bacteria. They are 

 stained with difficulty ; if this, however, take place, it is extremely per- 

 manent. For example, if they be stained with fuchsin, they may be 

 washed for a long time, without being decolorized, while everything 

 except the spores quickly loses its colour. In order to stain the mother 

 and the sporeless cells e.g. blue, it is merely needful to immerse the 



* SB. u. Abb. Naturwiss. Gesell. Isis, 1887, pp. 8-9. 



t See this Journal, 1883, p. 445. % Wocbenschr. f. Braueroi, 18S7, p. 773. 



