10 PRACTICAL BOTANY. 



distilled water ; the whole is then boiled, and evaporated to 

 400 c.c. : when it is cool a trace of carbolic acid is to be added, 

 and then the liquid is passed two or three times through a filter. 

 A dirty -red substance remains on the filter, and the filtrate is a 

 clear fluid, thin layers of which appear red and thicker layers 

 violet. This fluid will keep well for some months, but every now 

 and again a trace of carbolic acid must be added to it, and it 

 must be filtered. 



Both these preparations give good results, the differentiation 

 being very marked. In using the alcoholic solution, the sections 

 must be first soaked in 70 per cent, alcohol before they are placed 

 in the staining liquid : it is also necessary, when sections are to 

 be stained, to dilute the solution considerably with 70 per cent, 

 alcohol. The watery solution acts very rapidly, staining fresh 

 or alcohol material in a few minutes (3 5). 



The solution of cochineal in water stains especially the bast- 

 fibres of vascular bundles. In some cases the whole of the wood 

 stains, but if the section be treated with dilute hydrochloric or 

 sulphuric acid, the colour will be removed from all the cell-walls 

 except those of the bast-fibres. 



Gold-chloride, in 0'5 per cent, solution in water, has 

 been employed for staining Fungi. They must remain 

 in it from one to six hours, and be mounted in dilute 

 glycerine. 



Aniline colouring-matters.; A large number of 

 these have been employed, only the more important 

 are mentioned here ; they all stain rapidly. 



1. Safranin. This is used in solution in absolute alcohol. 

 It is especially adapted for staining sections which have been 

 previously hardened with chromic or picric acid ; it is not quite 

 so good for those which have been treated with osmic acid. The 

 sections must be well washed in distilled water, and then placed 

 in a small quantity (1 c.c.) of the saturated alcoholic solution 

 mixed with an equal volume of distilled water ; they require to 

 be left for several hours in the staining fluid. They must then 



