72 BOTANICAL MICROTECHNIQUE. 



same reaction. The staining with alcannin may be much 

 hastened by warming. This is especially to be recommended 

 when one has to deal with fats which are solid at ordinary 

 temperatures, as in the cocoa-bean. If cross-sections of 

 this seed are heated to the boiling point in a considerable 

 quantity of the above solution, the crystals of cocoa-butter 

 melt and fuse into drops, which become colored deep red at 

 once. 



110. Ranvier has used (I, 97) cyanin (identical with 

 chinolin blue, bleu de quinoleine) for the recognition of 

 fats. This coloring matter is pretty easily soluble in alco- 

 Tiol, but practically insoluble in water, especially in cold 

 water. On the dilution of alcoholic solutions with water, 

 precipitates are readily formed, and I have found it most 

 convenient to dissolve the dye in 50$ alcohol and to use 

 this solution directly for staining. Fresh material or such 

 as has been fixed in any aqueous fixing fluid (an aqueous 

 solution of corrosive sublimate or of picric acid, for exam- 

 ple) may be used. It is usually sufficient for the staining 

 to leave the objects in the above solution about half an 

 hour. Over-stained sections may be washed out with gly- 

 cerine or concentrated caustic potash solution. The per- 

 manent preservation of these preparations in glycerine- 

 gelatine does not appear to be possible ; at least, after a few 

 months such a preparation was completely decolorized. 



I can recommend as suitable objects for study old leaves 

 of Agave americana, which contain large oil-drops (cf. 364) 

 in the leucoplasts of their epidermal cells. These are 

 deeply colored in preparations made in the way above 

 described, while the nuclei and chromatophores remain 

 unstained. The only disadvantage of the method consists 

 in the fact that the lignified and suberized membranes are 

 also pretty deeply stained by it. 



111. Osmic acid, commonly used in a \% aqueous solution, 

 colors most fats deep brown or quite black. But this reac- 

 tion, which depends on a reduction, may always be checked 

 in a short time by means of hydrogen peroxide. According 

 to Flemming (II), the same thing may be accomplished with 

 oil of turpentine, xylol, ether, or creosote, but it requires 



