382 



in all cases ina\-, therefore, be traceable to the same cause. This blackening 

 process appears to render certain of the inorganic substances less soluble, because, 

 on again dissoh-ing the dried black gum in water, the dark-coloured constituents 

 could be remo\-ed, and the gum prepared in this way, when precipitated again by 

 alcohol, was practically in a pure condition. The ash of the rinallv purified gum 

 did not contain either manganese or iron, but consisted principally of lime and 

 magnesia, although both manganese and iron were readily detected in the dark- 

 coloured ash of the first precipitated gmii. This blackening can hardly be due to 

 the action of an enz^'me, similar to laccase, because the solution had been boiled 

 for seven hours in order to sepaiate the gum, the volatile acids, and the essential 

 oil. The formation of the various constituents in these oleo-resins may, perhaps, 

 eventually be shown to be largely due to enzyme action, and also that the man- 

 ganese and iron are simply contributing factors towards the final result. It may, 

 perhaps, be shown also, that their action in some plants is more towards the 

 formation of resins, because, in the exudation from Araucaria Bidwilli, manganese 

 was in small amount, and only a trace of resin was present in that material. 



That the manganese pla}'s an important part in the metabolic processes 

 of Agathis robusta, as well as in those of Araucaria Cunninghamii , can hardly be 

 doubted, and this supposition is also supported by the results of recent investi- 

 gations in other directions. Octave Dony-Henault in his " Systematic Investi- 

 gations of the Oxydases," ("Bull. Acad. Roy." Belg., 1907, 537; 1908, 105; and 

 1909, 342), shows that the typical properties of laccase can be reproduced by the 

 catalytic association of manganous and ferric molecules with free alkali, and 

 suggests that laccase does not exist in the latex of the lac tree, but that it is formed 

 during the alcoholic precipitation. He also advances the idea that none of the 

 oxydases are truly enzymic, and assumes that the oxidising action of Bertrand's 

 laccase is fully accounted for by the presence of an organic salt of manganese 

 and the accidental presence of alkali ; it is also asserted that the activity of this 

 substance is practically paralysed in the presence of acids. 



The changes which take place with the alcoholic precipitate from the latex 

 of Araucaria Cunninghamii, also with that from the exudation of Agathis robusta, 

 are almost identical with those given with similar material from the latex of Rhus 

 (See G. Bertrand, "Bull. Soc. Chim.," 1896, and " Compt. rend." 1896); also 

 "Oxydases et les Reductases" by M. Emm. Pozzi-Escot, Paris, igo2, p. 130, &c.). 

 The reason why thess exudations from Agathis and Araucaria remain colourless 

 under ordinary conditions is probably the preventative action of the acids present, 

 and it was not until the volatile acids and the resin acids had been entirely 

 separated, that the blackening of the precipitate tfjok place, which was 

 apparently due to the oxidising influences of the air. It thus appears that the 

 blackening of the gum precipitate from these trees is [)rimaril\- flue to the 

 particular form of manganese comijoiiud present. 



