ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 761 



Therefore the plan should be adopted of washing them well (either in 

 water, alcohol, ether, or chloroform) before subjecting them to the 

 action of the reagents. 



The author employs four or five different preparations of chlor- 

 iodide of zinc, and when one does not give any result recourse is had 

 to another. The chloriodide is prepared by adding to an aqueous 

 solution of very concentrated chloride of zinc a variable quantity of 

 iodide of potassium. Sometimes a small quantity of iodine may be 

 added. 



By modifying the proportions and by adding or not adding water 

 to the mixtures, a series of four, five, or six is obtained, of which at 

 least one may be useful when the others are not. 



Poulsen * recommends the successive use of potash and sulphate 

 of copper to colour the old cellulose membranes deep blue. 



Carmine in alum solution colours cellulose membranes deep red. 

 Tanglj prepares the reagent in the following manner. He saturates 

 distilled water with alum, adds to it a small quantity of carmine, 

 allows it to boil for ten minutes and when clear filters it. The 

 solution has the advantage of not colouring either the lignin or 

 suberin. 



Lignin or Lignose. — Under the influence of chloriodide of zinc 

 employed alone, or of iodine and sulphuric acid employed simul- 

 taneously the lignified membranes turn yellow. They turn blue 

 when the action of these substances has been preceded by the 

 immersion of the tissues in an acid, particularly sulphuric, chromic, 

 and nitric acids. These reactions being common to the walls of the 

 ligneous cells, the lignified fibres, and the old vessels, we are justified 

 in concluding that they are composed of the same ligneous substance. 



The lignification consists in an impregnation of the primitive 

 cellulose ; that is, the polymeric molecule (Cg Hjo Og)^ is decom- 

 posed into a lower polymere which becomes coloured and im- 

 pregnates the other part of the polymere remaining in the state of 

 cellulose. According to Bergmann, the formula of lignose is 

 Ci8 H26 On which for comparison with that of cellulose may be 

 approximately written C12 Hjg O7. The substance which impregnates 

 cellulose is therefore less oxygenated than this latter substance. The 

 action of the acids consists in eliminating the membranes. 



Van Tieghem made known in 1863 a reaction of the lignified 

 membranes, on which has since been founded a means of characterizing 

 them. This means consists in the production of a substance which is 

 formed in the presence of acids in the lignified membranes. It origi- 

 nated with Wiesner. J Poulsen § operates in the following manner. 

 An aqueous, or better still an alcoholic solution of phloroglucine is 

 made, and a drop is placed on the slide on which is the vegetable 

 tissue, this having been previously immersed in acetic acid ; the 



* Loc. cit., p. 59. 



t "Ueber offene Communication zwischen den Zellen des Endosperms," 

 Pringsh. Jahrb., sii. (1880). See this Journal, 1. (1881) p. 70. 

 X SB. "Wien. Akad., Ixxvii., 1 Abth. 

 § Loc. cit., p. 40. 



