112 VIII. THE MONOCOTYLEDONOUS STEM. 



methyl-violet, then so far decolorised in alcohol that the unlignified 

 membranes appear only feebly stained, then transferred to water 

 for a few minutes, and from this into one of the carmine solutions 

 already mentioned, which will stain the unlignified membranes 

 and protein cell-contents. Some control is needed in order to 

 see when the staining has been rightly carried out, and the 

 decolorising is best effected on an object -slide under the low 

 power of the microscope. If the tiny white earthenware saucers 

 sold for paint boxes are used for staining and decolorising, the 

 white background much facilitates the process to the naked eye ; 

 or it is performed even more readily in a watch-glass supported 

 upon a wire ring stand over a piece of mirror which will reflect 

 the light through the staining or decolorising fluid. Very effec- 

 tive double staining can likewise be obtained by first staining 

 with magenta dissolved in 50 per cent, alcohol, and then carefully 

 removing the colour by means of alcohol until it is left only in 

 the lignified and cuticularised membranes ; and afterwards stain- 

 ing with logwood. For a beautiful double stain " Solid green " 

 and Delta purpurin may be recommended ; the vessels are stained 

 deep green, the unlignified tissue red. An instructive double 

 staining is also given by chrysoidin with azurin or purpurin. 



Making. Permanent Preparations. It may be of interest to put 

 up selected cross and longitudinal sections of the stem of Zea 

 Mais as permanent preparations, Neither the colouring due 

 to chlorzinc iodine nor to soda corallin is permanent, and the 

 double stains which we have tried also fade more or less in time, 

 carmine and logwood alone being fairly permanent. Staining with 

 aqueous solution of safranin can, however, be highly recommended, 

 as the colour is quite permanent. As safranin gives beautifully 

 differentiated specimens, the different cell-membranes taking on 

 varied tones of colour according to the degree of their lignification, 

 and the other differences in their constitution (e.g., lignified walls 

 cherry-red, unlignified walls brown-red), the preparations treated 

 in this way are very instructive. A beginner might even with 

 advantage restrict himself to this one method of staining per- 

 manent preparations. 



Magenta (fuchsin) stains are also fairly permanent. The 

 sections are laid for a time in a watery solution of magenta, and then 

 washed with a solution of picric acid (1 part saturated alcoholic solu- 

 tion of picric acid to 2 parts water), and afterwards well washed 

 with alcohol. The lignified cell-walls are stained an intense red. 



