210 PHYSIOLOGY 



Escombe^ analysed the hyphal membranes of Cetraria and found that 

 they consisted mainly of a body called by him lichenin and of a para- 

 galactan. From Peltigera he extracted a substance with physical properties 

 agreeing fairly well with those of chitosan, though analysis did not give 

 percentages reconcilable with that substance; the yield however was very 

 small. No lichenin was detected. 



Van Wisselingh^ examined the hyphae of lichens as well as of fungi and 

 experimented with a considerable number of both types of plants. He 

 succeeded in proving the presence of chitin in the higher fungi (Basidio- 

 mycetes and Ascomycetes) and in lichens with one or two exceptions 

 {Cladonia and Cetraria). Though in some the quantity found was exceed- 

 ingly small, in others, such as Peltigera, the walls of the hyphae were 

 extremely chitinous. More recently Wester^ has gone into the question as 

 regards lichens, and he has practically confirmed all the results previously 

 obtained by Wisselingh. In some species, as for instance in Cladonia rangi- 

 ferina, CI. squamosa, CI. gracilis, Ramalina calicaris, Solorina crocea and 

 others, he found that chitin existed in large quantities, while in Evernia 

 prunastri, Usnea florida, U. articulata, Sticta damaecornis and Parmelia 

 saxatilis very little was present. The variation in the amount present may 

 be very great even in the species of one genus : none for instance has been 

 detected in Cetraria islandica nor in C. nivalis while it is abundant in other 

 Cetrariae. There is also considerable variation in quantity in different 

 individuals of the same species, and even in different parts of the thallus 

 of one lichen. Factors such as habitat, age of the plant, etc., may, however, 

 account to a considerable extent for the differences in the results obtained. 



b. Lichenin and Allied Carbohydrates. It has been proved, as 

 already stated, that chitin is present in the hyphal cell-walls of all the lichens 

 examined except in those of Cetraria islandica (Iceland Moss), C. nivalis 

 and, according to Wester', in those of Bryopogon {Alectoriae). In these 

 lichens another substance of purely carbohydrate nature is the chief consti- 

 tuent of the cell-walls which swell up when soaked in water to a colourless 

 gelatinous substance. 



Berzelius' first drew attention to the peculiar qualities of this lichen 

 product, and, recognizing its resemblance in many respects to ordinary starch, 

 he called it " lichen-starch " or " moss-starch.'' More exact observations were 

 made later by Gu^rin-Varry^ who described its properties and showed by 

 his experiments that it contained no admixture of either starch or gum. He 

 adopted the name lichenin for this organic soluble part of Iceland Moss. 

 An analysis of lichenin was made by Mulder' who detected in addition to 

 lichenin, which coloured yellow with iodine, small quantities of a blue- 



1 Escombe 1896. 2 -wrisselingh 1898 ' Wester 1909. * Berzelius 1813. 



^ Guerin-Varry 1834. 6 Mulder 1838. 



