282 SUMMARY OF CURRENT RESEARCHES RELATING TO 



most permanent dye, while the latter imparts a brighter colour than 

 iodine green. 



Staining of Cell Contents. — While some aniline dyes act specially 

 on the thickened walls of cells, others are extremely useful for 

 demonstrating the structure of protoplasm. Heliocin and naphthaline 

 in this respect are valuable ; and eosin, though not an aniline dye, 

 is equally so. For epidermis cells and ordinary parenchyma the 

 latter is preferable. It is best prepared by dissolving 1 part in 1200 

 of alcohol. The specimens are allowed to lie for 5 minutes in the 

 stain, and are then washed in water and mounted in a cell with 

 acetic acid, or Goadby's solution. The cells of Spirogyra, however, 

 have their minute structure beautifully revealed by treatment with 

 heliocin. The following is the best method to adopt : — Decolorize the 

 filaments by placing them in a 1 per cent, solution of chromic acid for 

 two days ; add then to the solution 1 part in 2000 of the dye, and 

 shake slightly, so that it may dissolve equally. In an hour the 

 filaments will be ready for examination or permanent preparation." 



Indol as a reagent for Lignified Cell-membrane.* — Max Niggl 

 gives a resume of the observations of previous observers on the use of 

 indol as a reagent for testing the lignified condition of the cell -wall, 

 supplemented with additional observations of his own. 



If a section of a branch is treated with dilute hydrochloric acid, 

 and an alcoholic solution of indol added, the lignified cells acquire a 

 beautiful cherry-red colour, while the non-lignified cells of the cam- 

 bium, cortex, and epidermis remain uncoloured. The use of hydro- 

 chloric acid is, however, for several reasons inconvenient, and the 

 author prefers the use of dilute sulphuric acid of sp. gr. 1*2 (1 vol. 

 English sulphuric acid with 4 vols, watei-). The best mode of pro- 

 cedure is as follows : — Pure indol is dissolved in warm water. The 

 section is moistened with a drop of this solution, and covered with 

 a cover-glass. The indol is then removed by blotting-paper, and a 

 drop or two of the dilute sulphuric acid run in. Wherever this 

 comes into contact with the indol which i:)ermeates the section, the 

 lignified cell-walls take a beautiful cherry-red, the sclerenchymatous 

 cells even a purple colour, which is retained by the preparation for a 

 considerable time. If the acid used is too concentrated, or the excess 

 not removed, the colour passes, after some weeks, to brownish red. 



Among Thallophytes, Niggl found, by the use of this reagent, no 

 trace of lignification in algte, or in the majority of fungi ; it was only 

 present in the cortical and medullary layers of a few lichens. 



In vascular plants the cuticle is as a rule uncoloured by indol. 

 In many plants (contrary to the statement of other observers), the 

 walls of the guard-cells of stomata appear to be strongly coloured. 

 This is also the case with cork, except that in older cork-cells the 

 middle lamella gives indications of lignification. With very few 

 exceptions collenchyma also shows no colouring with indol. The 

 author enters into considerable detail with regard to the colouring of 

 the various elements of parenchyma, and of sclerenchyma. A charac- 



* Flora, Ixiv. (1881) pp. 545-.59, 561-8. 



