92 Mr W. Gardiner, On the constitution [Feb. 11, 



acid or Schweitzer's reagent it is quite insoluble. It is deeply stained 

 by most aniline dyes as Russow 1 showed for instance in the case of 

 fuchsin. The two reagents discovered by Wiesner, viz. a solution of 

 phloroglucin 2 or anilin chloride 3 in hydrochloric acid afford very valuable 

 tests for lignified tissue, the former colouring it red or violet, and the 

 latter staining it gold-yellow. With Von Hohnel' s reagent 4 — xylophylin 

 and hydrochloric acid — it also goes violet. 



Mucilage. The reactions as regards mucilage are mostly of a 

 negative character. With Hofmann's blue, (as I shall point out later 

 on,) and with methylene blue 5 it readily assumes a blue colouration. 

 With Hanstein's reagent 6 it stains red, and when well developed 

 Roussin's test 7 (a white precipitate with ferams sulphate, soluble in 

 acetic acid) may be applied. 



Gutin. The cutin of cuticle, like cellulose is insoluble in sulphuric 

 acid, but soluble in caustic potash. With Hanstein's reagent it is 

 coloured blue, and with chlor. zinc. iod. yellow. 



Cork is dissolved by boiling potash, and during the process yellow 

 oily drops (suberin of Yon Hohnel 8 ) escape. Subjected to the action of 

 nitric acid, suberic acid is produced. With Schultze's mixture it is de- 

 composed, yielding an oily, resinous mass, which may be dissolved by 

 subsequent treatment with potash. According to Olivier 9 cork is 

 readily stained by dilute solutions of fuchsin, which persistently coloxir 

 it, even after prolonged action of absolute alcohol. With iodine and 

 chlor. zinc. iod. it merely becomes yellow. When treated for some time 

 with chromic acid it is dissolved. 



An examination of the foregoing list will make it quite ap- 

 parent that with regard to certain of the substances met with in 

 the cell-wall, e.g. cellulose and cutio, there are well-defined 

 chemical tests, which, on the whole, render it probable that the 

 reactions to which they give rise, point to the presence of definite 

 bodies, and are not merely the result of a histological differen- 

 tiation. But as to many other reactions, which have also been 

 regarded as evidences of the existence of other bodies, whose 

 characters are not nearly so well defined, one must, for the present 



1 Eussow, Sitzber. d. Dorpater. Naturf. Gesell. 1880, p. 419. 



2 Wiesner, Sitzber. d. k. Akad. in Wien, lxxvii. 1878. 



3 Wiesner, Sitzber. d. k. Akad. in Wien, lxx. 1874. 



4 Von Hohnel, Sitzber. d. k. ATcad. in Wien, 1877. Wiesner believes that 

 xylophylin is practically the same body as phloroglucin. According to Max Singer, 

 Sitzber. d. k. Akad. in Wien, lxxxv. 1882, both Wiesner's and Von HShnel's 

 reactions are due to the presence of vanillin in lignified tissue. Thus they do not 

 point to the presence of lignin, but rather of lignified tissue. The same is true of 

 the indol advocated by Niggl. See Singer (I. c.). Wiesner's (I. c.) Phenol-Hydro- 

 chloric acid reaction is due to the presence of coniferin. 



5 Gardiner, loc. cit. 



(i Hanstein, Bot. Zeit. 1868. No. 43 et seq. 



7 See Bonnier. Ann. des Sci. Nat. 6th series, vin. 1879, p. 87. 



8 Von Hohnel, loc. cit. 



9 Olivier, Bull. Soc. bot. de France, 1880, t. xxvn. pp. 234, 235. 



