EFFECT OF PARASITIC FUNGI ON THE CELL-WALL. 37 



accompaniment of the attacks of wood-destroying fungi on the 

 woody parts of trees and shrubs. Besides actual perforation 

 of the lignified membranes of their host, the hyphae of many 

 of the Polyporeae and Agaricini exert a solvent effect on the 

 walls, which extends over a considerable area, and is evidently 

 due to the excretion of some ferment. The dissolution of the 

 walls takes place, moreover, in a way so characteristic for each 

 species of fungus that they can be determined by it alone. From 

 this it must be deduced that each wood-destroying fungus 

 excretes a ferment peculiar to itself, which causes a character- 

 istic dissolution of the host. Our present sources of informa- 

 tion on these points are the very valuable investigations of 

 Professor Eobert Hartig of Munich.^ Some of his results will 

 repay our careful consideration, but we must, preface briefly 

 some facts regarding the process of lignification and the forma- 

 tion of heart-wood in our forest-trees. 



The elements of the wood of dicotyledonous trees and woody 

 plants are derived from the cambium ; their walls consist at 

 first of pure cellulose, and when lignification takes place the 

 so-called incrusting substances are laid down in the thickened 

 cellulose wall, particularly coniferin, vanillin, wood-gum, tannin, 

 etc. ; or as they may be collectively called, lignin. The cellulose 

 membrane itself is coloured lilac with chlor-zinc-iodine ; when 

 lignified it no longer shows this reaction, but has others peculiar 

 to itself, the best known being red coloration on treatment 

 with phloroglucin and hydrochloric acid, or yellow coloration 

 with aniline sulphate ; chlor-zinc-iodine colours lignified tissues 

 brownish-yellow. Copper-ammonium-hydrate dissolves cellulose 

 but not wood.^ If the incrusting substances be removed from 

 the lignified membranes by treatment with Schulze's solution, 

 caustic soda, or other solvent, the cellulose remains and reacts 

 as such. In the process of conversion of alburnum into dura- 



' The most important of these works are : 



Die Zersetzungsfrscheinungen d. Hohes d. NadelhOlzer u. d. Eiche. With 21 

 coloured plates. Springer, Berlin, 1878. 



Der echte Hausschwamm, Meruliits lachrymans, 1885. 



Wichtige Kranlcheiten d. Waldbdume, 1874- 



Lehrbttch d. Baumkrankheiten, I. and II. Edition, 1882 and 1889. English 

 translation of II. Edit, by Prof. W. Somerville. 



Lekrbuch d. Anatomie u. Physiologie d. Pflanzen, 1891. 

 " For further reactions see : 



Zimmermann. Die botanische Microtechnik. 1892. 



Strasburger. Das botanische Praktihim, 1887. English Edition, 1889. 



