254 PRACTICAL BOTANY 



since it decomposes on keeping ; it will keep some little time if 

 kept in a cool place in the dark, and in completely filled, well- 

 closed bottles (Hoppe-Seyler). 



The solution (b] may be prepared, and kept for adding to (a) 

 freshly prepared when required. 



Before using a kept solution to test for sugar, always boil a 

 little of it by itself to see if any reduction will take place. 



From i c.c. of this solution the copper is completely reduced 

 by o'oc>5 grammes of grape sugar. 



Ferrous Sulphate is used in dilute solution in water, to which 

 a drop of nitric acid has been added, as a test for tannin, 

 v Fuchsin is used in solution in alcohol, for bringing out the 

 structure of thickened cell-walls, and especially the outer walls 

 of the epidermis, and corky walls : the sections should have 

 been previously treated with alcohol. When a section has been 

 stained with fuchsin, and washed in absolute alcohol, the colour- 

 ation is removed from all parts excepting the corky and 

 cuticularized walls. 



Glycerine is the most generally used medium for mounting, 

 as it has the advantages of a high refractive index, and of not 

 being subject to evaporation. It may be applied either pure or 

 diluted : pure glycerine is to be used, after hardening in alcohol, 

 when it is desired to observe the details of the protoplasm, e.g. 

 in the preparation of the contents of the embryo-sac ; dilute 

 glycerine (i part glycerine, I part water), is however, of most 

 general use. 



Glycerine Jelly is a suitable mounting medium for many 

 objects : it may be bought ready for use from dealers in 

 microscopic requisites : or it may be prepared according to 

 Kaiser's receipt, as follows : I part by weight of finest French 

 gelatin is to be soaked for about two hours in 6 parts of distilled 

 water : 7 parts of chemically pure glycerine are added, and to 

 about 100 grammes of this mixture i gramme of carbolic acid 

 is added. The whole mixture is to be warmed and continually 

 stirred for 1015 minutes, till the fluid is clear, and then to be 

 filtered through glass-wool. 



Gold Chloride is sometimes used in a ro per cent, or 0*5 per 

 cent, solution in water as a delicate stain for protoplasm. 



