238 BOTANICAL GAZETTE [makh 



radiator. In a few days the evaporation will leave the fluid thick. Once 

 the preparation is in thick glycerin the color will not change, if the formalin 

 has been completely removed. 



The potassium-copper-acetate solution will not keep the natural color 

 of diatoms. It has the property of removing the diatomin or yellow color- 

 ing matter from the diatoms and leaving the plants perfectly green. The 

 solution can thus be used in demonstrating the presence of chlorophyll in 



these plants. The diatomin is removed or absorbed in a few minutes after 

 application. 



As I have found some difficulty in keeping the microscopic mounts 

 made in the potassium-copper-acetate solution because of drying, I have 

 evolved a modification of the glycerin method in combination with it. The 

 mounts made by this method are perfectly durable, and when carefully 

 prepared are superior to ordinary glycerin mounts, as all green algae treated 

 with it keep their natural colors indefinitely. Glycerin jelly can also be 

 used at the end to make the mount even more durable than the ordinary 

 glycerin mount would be. The procedure is as follows. 



The algae to be used are fixed in the potassium-copper-acetate 2 per 

 cent, solution. After they have been killed and fixed in this fluid (the 

 time varying according to the specimen treated), add to the above solution 

 an equal part of 10 per cent, glycerin solution and allow to concentrate 

 by evaporation in a warm dry place protected from dust. The algae must 

 be thoroughly separated from dirt and soil or the concentrated solution 

 will precipitate a reddish-brown cloud of reduced copper. In nearly all 

 cases the preparation when thickened will be covered with a film of acetates, 

 which can be removed from the top of the fluid without injury to the mate- 

 rial. The concentrated solution should be perfectly clear, of a light green 

 color, and the chromatophores of the algae as perfect a green as in lite. 

 I have often been asked by students, and in fact by those well acquainted 

 with algae, whether the plants thus given them for examination were no 

 really alive. The advantage of having plant material, especially for ee- 

 mentary students, in a condition as near as possible to the five state, obvia * 

 explanations about stains. I have found it very undesirable to give begin- 

 ners any material other than alive or such as looks like the live stage 

 plant studied.— J. A. Nieuwland, University of Notre Dam, Ind. 



