274 



THE CHEMISTRY OF SOME COMMON PLANTS. 



P. Q. KEEGAN. LL.D., 



Patterdale, Westmorland. 



Lichen {Parmelia parietina), — This flatish and circular 

 org"anism is affixed to farmsteads or stables, or on pales, 

 posterns, rocks, and cold stones. Many an outlying- barn or 

 hay-shed in the heart of the valley away out in the free, pure, 

 unpolluted air is brig-htened by a conspicuous dressing of the 

 yellow thallus and the deep orange apothecia. Physiologically 

 it is a symbiotic association of a green alga and a colourless 

 fungus — living by a kind of mild parasitism — the fungus 

 borrowing from the alga its carbohydrates (or actually feeding 

 on and digesting it, according to some authors), while the alga 

 in return borrows its water, proteids, and salts from the fungus. 

 According to an old chemical analysis this Lichen contains 

 stearin, chlorophyll, carotin, lichenin, sugar, gum, mucilage, 

 traces of volatile oil, resin, wax, and chrysophanic acid. Later 

 researches have shown that the yellow and orange colouring 

 matter is very superficially distributed, and is not chrysophanic 

 acid or vulpinic acid, but a simpler derivative of anthraquinone 

 called chrysophysicin. Still later Hesse found and called it 

 physicon C^^W^'^O'', owing to its quinonic character ; it is brick-red 

 and not yellow, and forms a bluish-violet and purple compound 

 with potass ; the plant also contains two colourless bodies, viz., 

 physcianin C^'^H^'-^O^ coloured bluish-violet by iron salt, and 

 physicol C^H'^O" coloured greenish-black by the same reagent. 

 According to Thompson there is 6*8 per cent, of ash having 

 o'75 per cent, sodium salts, 68 silica, 8*75 carbonate of lime, 

 and 22 to 34 oxide of iron with phosphates of iron and lime. 

 The plant contains a bitter principle which renders it febrifuge ; 

 the hymenium (paraphyses and thecae) and the tissue beneath it 

 are penetrated by a mucilaginous substance (probably a hydro- 

 cellulose) which is blued by iodine, while the walls of the hyphal 

 filaments are extremely thick and enclose fine threadlets of 

 protoplasm. The fact that no lichen is poisonous, while sev^eral 

 fungi are deadly so, points conclusively to a very distinctive 

 difference between these two tribes of plants. Everything tends 

 to prove that the lichen is a higher organism physiologically 

 speaking. Its colouring matters are true products of healthy 

 deassimilation, whereas those of fungi are mere decomposition 

 or degradation waste products of the albumenoids akin to 

 alkaloids. The lichenin of lichens is undoubtedly also a natural 



Naturalist, 



