476 THE STORY OF PLANT LIFE 



Take enough of the medium to fill the space between the 

 cover-glass and slide to extend to the margin, any excess 

 being absorbed by blotting-paper. Let the cover-slide fall 

 obliquely, one edge resting on the medium, and lower it 

 carefully on the slice so that the medium is evenly spread 

 out and no air bubbles are present, using a forceps or 

 needle, alcohol being used to prevent air bubbles beforehand. 

 If any air bubbles are present, heat gently over a spirit lamp 

 or expel them with an air pump. 



To apply reagents, the specimen is irrigated. The fluid 

 used is run on to the slide so that it may soak into the 

 medium by capillary attraction along the edges of the cover- 

 slip. Iodine, aniline sulphate, chlor-zinc-iodine are often 

 used. If necessary, the cover-glass may be raised to allow 

 quicker penetration. 



In order to render the section clearer, certain reagents 

 for temporary mounts may be used such as those mentioned, 

 potash causing swelling of contents and rendering objects 

 transparent. When this has been applied, the section should 

 be washed in distilled water, and, after being treated with 

 alcoholic solution, in dilute alcohol ; then it may be 

 permanently mounted in glycerine after thorough washing. 

 Glycerine itself is a good clearing reagent. If eau de Javelle 

 is used, it should be warmed, the section washed in water 

 and acetic acid, then mounted in glycerine. For embryos 

 chloral hydrate is used, the specimen being soaked in it for 

 several hours, or heated. Calcium chloride is used for the 

 growing points, specimens being placed in a drop of water, 

 the slide covered with the dry powder warmed, and the 

 water evaporated; then a drop of water is placed on the 

 specimen and the section mounted in glycerine. Leaves 

 from which chlorophyll has been extracted in alcohol may 

 be cleared by phenol, or 3 parts turpentine, i part phenol. 



Staining media are hsematoxylin, eosin, safranin, aniline 



