8o2 BOTANY AND PHARMACOGNOSY. 



tated by moistening both the pith and the razor. In the case of 

 seeds and frnits which are very small and at the same time very 

 hard, as colchicum and mustard, it is best to use a velvet or fine 

 grade of cork for holding the material. The cork is indented by 

 means of forceps and the seed or fruit forced into the cavity. 



In the case of very delicate tissues, where the protoplasmic 

 contents of the cells are to be studied, as in the ovaries of flowers, 

 prothalli of ferns and other parts of the plant, where cell division 

 is going on, the material should be embedded in paraffin or celloi- 

 din, subsequently hardened, and sectioned by means of a finely 

 adjusted microtome. 



Clearing Agents. Most dehydrating agents are also clearing 

 agents, because of the fact that the air and water in the specimen 

 are replaced by a medium having greater refractive properties. 

 Some clearing agents act chemically on the tissues and cell- 

 contents. Among the clearing agents most frequently employed 

 are: Chloral in saturated aqueous solution, and chloral-glycerin 

 solution (a solution of equal parts of glycerin and water sat- 

 urated with chloral). Essential oils, as clove, turpentine, cedar, 

 marjoram, etc., are also useful for this purpose, particularly when 

 the specimen is to be mounted in Canada balsam. 



Staining Agents are those that produce more or less defi- 

 nitelv colored compounds with the cell-contents or walls. They 

 include: (i) the Aniline Dyes and (2) Non-aniline Stains. 



The aniline stains may be used in aqueous solutions, weak alco- 

 holic solutions or strong alcoholic solutions, containing from I to 

 3 per cent, of the dye. The following are the aniline stains most 

 frequently employed: Aniline blue, Bismarck brown, fuchsin, 

 gentian violet, methylene blue, methyl violet and safranin. In 

 addition to these, aniline hydrochloride or sulphate is used in what 

 is known as Wiesner's Reagent, which is a 25 per cent, solution of 

 alcohol containing 5 per cent, of either of these salts, a drop of 

 either hydrochloric or sulphuric acid being used with a drop of the 

 solution, according as the hydrochloride or sulphate has been used. 

 Lceffler's Methylene Blue. This reagent is prepared by 

 adding 30 c.c. of a concentrated alcoholic solution of methylene 

 blue to 100 c.c. of water containing 10 milligrams of potassium 

 hvdrate. 



