OTHER ORGANIC COMPOUNDS. 4/ 



viz. the phloroglucin test, for lignin. An aqueous 

 solution or, better, an alcoholic tincture of the 

 reagent is employed, and even in excessively small 

 quantity induces the reaction. 1 The section to be 

 studied is treated with hydrochloric acid, and then 

 placed in a drop of phloroglucin on the slide. The 

 parts containing lignin assume a beautiful and in- 

 tense rose-red color with a rapidity depending upon 

 the concentration of the solution. The prepara- 

 tions may be kept for a considerable time. If 

 difficulty is experienced in getting the reagent and 

 at present it is quite expensive and hard to obtain 

 an extract of cherry wood diluted with water may 

 replace it. This contains the substance in question 

 among others, but gives a more violet reaction than 

 the pure reagent. 2 



ROSOLIC ACID 



Is recommended by Janczewski 3 as " the best of the 

 reagents which color the callosities of sieve tubes." 

 A little ammonia or sodic carbonate should be 

 added to it. 



1 Wiesner: Sitzungsber. der wiener Akad, Bd. LXXVIL, Abth. i., 

 Januarheft. 



2 This has been called the xylofilin reaction by its discoverer, Hohnel. 

 Sitzungsanzeiger d. wiener Akad., 1877, No. 23, pp. 228, 229. 



3 Etudes comparees sur les tubes cribreux. Mem. de la Soc. das Sc. 

 nat. de Cherbourg, 1881, XXIII., p. 350. The discovery is due to 

 Szyszyloviez. 



