512 PRACTICAL BOTANY 



cellulose blue (p. 36), a reaction similar to that with chlor-zinc- 

 iodine (p. 37). 



Methylene Blue is used in solution in water : it stains the 

 cell-wall, but not the protoplasm. 



Methyl-green, A tolerably strong alcoholic solution of this 

 is used. The sections of the object, which must have been 

 previously kept in absolute alcohol, are to be treated with the 

 staining- fluid for from 5-25 minutes, then quickly washed with 

 distilled water, and mounted in glycerine. The nucleus stains 

 of a green or bluish-green colour, the protoplasm remaining 

 uncoloured. It is especially good for staining nuclei which are 

 dividing, and for bringing out the nuclei in the cells of Fungi, 

 and of the Siphonese, for which purpose Strasburger recommends 

 the following method : The fresh object or section is mounted 

 in 2 per cent, acetic acid, to which a little methyl-green has 

 been previously added : the nuclei are fixed almost instantaneously 

 and at the same time stained. These preparations may then be 

 washed in 1 per cent, acetic acid, and be mounted in weak 

 glycerine and acetic acid. Objects stained with methyl-green 

 fade very rapidly. 



Methyl-violet. This is used in concentrated alcoholic solu- 

 tion. It is especially useful for staining Bacteria. A few drops 

 of the solution are added to 15-20 c.c. of distilled water, and a 

 drop or two of the mixture should then be placed on the Bac- 

 teria-membrane (zoogloea), and be allowed to remain there for a 

 short time until the membrane appears to be coloured : if the 

 solution used be too strong, the substance between the Bacteria 

 will become stained. The colouring matter is then washed off 

 with distilled water, or better with a 10 per cent, solution of 

 acetate of potash. The preparation may then either be allowed 

 to dry in the air and be then mounted in Canada balsam, or it 

 may be mounted in a 50 per cent, solution of potassium acetate 

 in water. 



A useful preparation of methyl-violet is the following : 

 Some of that substance is dissolved in strong sulphuric acid, 

 forming a brownish-green solution : on the gradual addition of 

 water the violet colour reappears. This is especially useful 

 for sieve tubes. If a section be treated with this fluid for a 



