252 PRACTICAL BOTANY 



Chloroform is used as a solvent for various substances, e.g. 

 oils, coagulum of latex, &c. 



chior-zinc-iodine (Schulze's Solution) is the best differen- 

 tiating reagent, and the one most generally used, but the chief 

 objection to it is that, as in the case of other preparations 

 of iodine, the stain is not permanent. There are. various ways 

 of preparing it, but the best is as follows : 



1. Dissolve no grammes of zinc in 300 c.c. of pure hydro- 

 chloric acid, and evaporate to 150 c.c. (sp. gr. r8). 



2. Dissolve 12 grains of potassium iodide in as little water as 

 possible, and add 0-15 grammes of crystals of iodine. 



3. Mix (i) and (2). 



This reagent may however be obtained ready prepared from 

 dealers in microscopic requisites. It may be used either for 

 fresh material, or after treatment with picric acid, or alcohol : 

 the colouring of cellulose walls is intensified if the objects have 

 been previously treated with potash, arid the alkali thoroughly 

 washed out. 



Under this reagent cellulose walls turn blue, or violet, lignified 

 walls yellow, or various shades to a sherry brown, corky walls 

 yellow or brown, protoplasm brown, while starch-grains swell 

 and turn blue. 



Chromic Acid. A strong aqueous solution of this acid, 10 per 

 cent., dissolves lignified and cellulose cell-walls : cuticularized 

 cell-walls resist its action ; but they become very transparent, 

 and may be easily overlooked. A dilute solution brings out the 

 stratification of cell-walls very clearly. A one per cent, solu- 

 tion may be used in the preparation of Seaweeds. 



Clove. oil is used as a clearing agent before mounting speci- 

 mens which have been treated with alcohol in Canada balsam. 



Copper Sulphate is used in the preparation of Fehling's fluid 

 (see below), and the preparation of ammoniacal solution of 

 cupric hydrate (see below). 



Corallin (Rosolic Acid). A solution of corallin in a 30 per 

 cent, solution of sodium carbonate colours lignified tissue, the 

 callus of sieve-tubes and starch-grains pink. 



Creosote is used together with turpentine as a clearing agent 

 before mounting in Canada balsam : i part of creosote and 4 



