144 BOTANICAL MICROTECHNIQUE. 



252. Recently the attempt has been made in several 

 quarters to reach more accurate conclusions concerning the 

 chemical composition of lignified membranes, and especially 

 as to the constitution of lignin. 



Wholly trustworthy results can, of course, only be reached 

 by macrochemical investigations with exact quantitative an- 

 alysis. In this connection should be mentioned the recent 

 researches of Lange (I and II), who has isolated from the 

 woods of the beech, oak, and fir, two compounds of an 

 acid character, " lignic acids," which may, however, possibly 

 come from a single substance. Lange also obtained various 

 by-products concerning whose significance nothing is yet 

 known. 



253. There is also widely distributed in lignified mem- 

 branes a gum-like substance which Thomsen has called wood- 

 gum. It may be extracted with a 5$ solution of caustic soda 

 and then precipitated from this solution with 90$ alcohol. 

 On hydrolysis wood-gum yields either arabinose, C 8 H J8 O 6 ,. 

 or xylose, C & H 10 O 5 . 



Wood-gum and both of its derivatives above mentioned 

 take a cherry-red color on warming with phloroglucin and 

 hydrochloric acid. But Allen (I, 39) has shown that the 

 phloroglucin reaction about to be described is not to be 

 referred to the wood-gum ; for, on one hand, the reaction 

 takes place with lignified membranes in the cold, and, on 

 the other, the colors which appear in the different reactions 

 show very different spectroscopic relations. 



254. Attempts have also been made to determine the 

 chemical constitution of lignified membranes by microchem- 

 ical studies. Especially Singer (I) and, more recently, Heg- 

 ler (I) have tried to prove that coniferin and vanillin always 

 occur in lignified walls. This view is based chiefly on a 

 series of color-reactions which lignified walls give with vari- 

 ous aromatic compounds. I give a compilation of the chief 

 of these reactions with remarks on their application, which 

 should receive notice here because the reactions may be used 

 with good results for the microchemical recognition of lig- 

 nification. 



