314 THE AMERICAN MONTHLY [Oct. 



of the leaf, are charg-ed with a red cell sap of the nature of 

 g-lucosides. The cultivation of Hydrocharis morsusranoe, 

 of Utricularia, and many other land plants, in a weak solu- 

 tion of g"lucose, confirmed his deductions. In each case the 

 leaves assumed a rich reddish-brown tint. 



Chromic Acid. — For g-eneral botanical work the most 

 useful killing- and fixing- agents are solutions containing- 

 chromic acid. Prof. C. J. Chamberlain, g-ives some valu- 

 oble notes on the streng-ths of the solutions used. For 

 spirog-yra, fern prothallia, and similar objects, he sug^g-ests 

 a solution made up of chromic acid, two g-rammes ; acetic 

 acid, one cubic centimetre ; and water, ninety-seven cubic 

 centimetres. If plasmolysis takes place, weaken the chro- 

 mic, or streng-then the acetic, since the chromic has a ten- 

 dency to produce contraction, and the acetic to cause swell- 

 ing-. Too larg-e a proportion of acetic acid, however, may 

 cause distortion, and hence it would be better to weaken 

 the chromic acid. 



Fixing Tissues. — Referring- to the time that should be al- 

 lowed for the fixing- of tissues in chromic solutions. Prof. 

 Chamberlain has found that twenty-four hours should be 

 the minimum even for the most delicate objects. It is now 

 well-known that zoolog-ists allow fixing- ag-ents like Muller's 

 fluid and Erlicke's fluid to act for weeks before the ma- 

 terial is passed on to the next stag^e, and it is therefore 

 questionable whether the time which is usually allowed by 

 microscopistswhenusing-chromicacidsolutionsisnot much 

 too short. Sixteen to twenty-four hours is the time usually 

 allowed ; but Prof. Chamberlain's experiments show that 

 the material is better able to withstand subsequent proces- 

 ses if it has been kept in the fixing- solutions for two or 

 three days. More rapid penetration, and consequently 

 more immediate killing-, can be secured if the reag-ent is 

 kept at a temperature of from thirty deg-rees to forty 

 deg-rees Centig-rade. 



Wickersheim's Preserving Fluid. — This is not com- 

 monly used owing- to the poor preparations that have been 

 put on the market. Animal and veg-etable bodies impreg-- 



