762 SUMMABY OF CURRENT RESEARCHES RELATING TO 



lignified portions soou assume a deep red colour, which they retain 

 for a long time. 



Wigaii,* Maschki,! and Vogel4 following Poulsen,§ have used 

 the aqueous solution of cochineal mixed with acetic acid or alum, to 

 colour the prosenchymatous cells of the liber. The colouring, which is 

 red, becomes very intense after the tissue has remained for a long 

 time in the solution. 



Cutin; Suherin. — True suberin is a definite compound, not a 

 mixture. When membranes supposed to be suberized or cutinized 

 turn blue under the influence of chloriodide of zinc, after being treated 

 with a boiling acid, it is because they are only lignified. True 

 suberin turns yellow under the action of this reagent, even after im- 

 mersion in boiling acids. The reaction is the same when iodine or 

 sulphuric acid is substituted for chloriodide of zinc. 



The cutin which behaves in this way seems to be identical with 

 suberin. It may be correctly enoiigh represented by the formula 

 C12H22O2. But cuticles in which the treatment by acids still allows 

 the cellulose to be separated and coloured can only be considered as 

 lignified. 



The author has proved that liguin and suberin retain the aniliu 

 colours much more persistently than cellulose. Relying on this 

 observation, he has succeeded, by the use of these colours, in well 

 differentiating in microscopical sections of vegetable tissues, the cellu- 

 lose and non-cellulose portions of the membranes. The sections are 

 put to soak in a solution of fuchsiu, half alcoholic and half aqueous, 

 then immersed in absolute alcohol. After this last treatment the 

 cellulose portions are decolorized, whereas the cutinized or suberized 

 portions retain for a very much longer time the red coluur of the 

 fuchsin. This process would not be iiseful for analysis, but it is 

 very convenient in enabling the sections to be rapidly passed in review, 

 and the most prominent diflterences of their chemical constitution 

 immediately distinguished. 



On these micro-chemical reactions of cellulose, lignin, and suberin 

 is partly founded tlie determination of the nature of the fibres 

 which enter into the manufacture of fabrics. Vetillart |1 has published 

 an important work on this subject, from which the following direc- 

 tions are taken : — 



To isolate the fibres of the tissue to be examined, it is boiled 

 for half an hour in a lye containing 10 per cent, of carbonate of 

 potash or soda. The object of this operation is also to swell the 

 cell-walls, and to render them more pervious to the reagents. In 

 cases where it is insuificiout (which are very rare), H. Beauregard and 

 V. Galippe^ recommend the tissue to be soaked for ten minutes in 



* Bot. Ztg., 1SG2, pp. 129, 139. 



+ Ibid., 1859, p. 22. 



X " Anat. unci Histol. rlcr uuterirdischeu Theile vou Convolvulus arvensi>" 

 SB. Wien. Akad., xiii. (1863). 



§ Loc. cit., p. 42. 



II 'Etudes sur Ics fibivs vegetules textiles einijloyccs dans I'industrie,' 187(5. 



% ' Guide de I'eleve et du praticien pour les travaux pratiques de micrographic,' 

 1880. 



