104 VEGETABLE HISTOLOGY. 



cases mere soaking for a shorter or longer time in cold or hot 

 water will suffice to soften the specimen. In other cases weak 

 alkalies are necessary. A very good solution is 2 per cent, am- 

 monia water (24 to 48 hours' immersion). Very hard objects 

 are placed in 5 per cent, caustic potash solution. 



CLEARING REAGENTS. 



To make sections more transparent so that the parts may be 

 better seen various reagents are used. Those most generally 

 used are oil of cloves, creosote, carbolic acid (liquid). These 

 are used before mounting the section permanently in balsam or 

 dammar. Other reagents that are sometimes used are caustic 

 potash (dilute), chloral-hydrate, a mixture of creosote and tur- 

 pentine (1:3), or creosote and alcohol (1:1). Delicate objects 

 are gradually made clear even in glycerin. 



Starch is dissolved in dilute mineral acids, protoplasm in 

 dilute alkalies, oils and resins in alcohol, ether and alkalies. 



Alkalies, acids, alcohol or chloral hydrate solution are used 

 when it is desired to clear out the contents of cells so that the 

 cell-walls alone may be studied without the interference of the 

 contents. 



LABARRAQUE'S SOLUTION (sodium hypochlorite) is also used as 

 a clearing and bleaching agent, especially for cells rich in pro- 

 toplasm, for example, meristem cells. Time of action 5 to 15 

 minutes. It is excellent for bleaching sections, etc., in which 

 the natural plant pigment is too dark to allow a clear view of 

 details. The reagent should not be allowed to act longer than 

 necessary. 



CHLORAL HYDRATE SOLUTION. Chloral hydrate crystals, 5 

 grams, dissolved in 2 cc. of water. It is a very valuable reagent. 

 It causes shrunken cells to expand, and dissolves starch, pro- 

 teids, resin, volatile oils, chlorophyll, etc. When saturated 

 with iodine, by keeping a few crystals of the latter in it, it is 

 employed to detect small starch grains. 



PERMANENT MOUNTING OR ENCLOSING MEDIA. 



CANADA BALSAM. This is a thick solution of the resin in ben- 

 zene, turpentine, chloroform or xylene. If the solution becomes 

 too thick it is diluted with benzene, etc., respectively. The 

 resin is incompletely soluble in absolute alcohol, hence addition 

 of alcohol to the clear solution in benzene, etc., causes a cloudi- 

 ness. The balsam should be kept in glass-capped, wide-mouthed 

 bottles. Before mounting in balsam sections must be soaked in 

 solutions which are miscible with it. Such solutions are clove 

 oil, turpentine, benzene, chloroform, xylene, creosote, carbolic 

 acid. It would not do, for example, to take a section from 



