258 PRACTICAL BOTANY 



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 (zooglcea), 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 

 short time, and be then washed with water, it will be found that 

 the cell-walls have become swollen and transparent, that the 

 protoplasm has become deeply stained, and that the sieve-plates 

 are very well brought out. Lignified tissues treated with this 

 fluid assume a yellow colour, as they do when treated with 

 aniline sulphate. 



Moist Chamber (see Water) . 



Nitric Acid colours cuticularized cell-walls and proteids 

 yellow ; it also causes swelling up of cellulose and of lignified 

 cell-walls. When diluted with water it is useful for dissolving 

 the crystals of calcium oxalate which are frequently present in 

 the cells. It is used with ammonia as a test for proteids 

 (xanthoproteic reaction) ; with potassium chlorate as a test for 

 r suberin, and as Schulze's macerating fluid. 



Olive Oil is used as a medium for mounting aleurone-grains, 

 so as to see them unaltered. 



Orcin. A solution in alcohol is used as a test for inulin. 

 Sections are to be soaked in the solution and subsequently 

 warmed with strong hydrochloric acid : an orange-red colour 

 shows the presence of inulin. 



