212 PHYSIOLOGY 



by lichenin, everniin, etc. They are doubtless reserve stores of food material, 

 and they are chiefly located in the cell-walls of the medullary hyphae which 

 are often so thick as almost to obliterate the lumen of the cells. Ulander 

 made no test for chitin in his researches. 



Ulander's results have been confirmed by those obtained by K. Miiller^ 

 In Cladonia rangiferina, Miiller found that the cell-membranes of the hyphae 

 contained, as hemicelluloses, pentosans in small quantities and galactan, but 

 no lichenin and very little chitin. In Evernia prunasirihem\ce\\u\os&s formed 

 the chief constituents of the thallus, and from it he was able to isolate 

 galactan soluble in weak hot acid, and everniin soluble in hot water, the 

 latter with the formula C^ His Og, a result differing from that obtained by 

 Stiide" who has given it as CgHuO,; chitin was also present in small 

 quantities. In Ramalina fraxinea, the soluble part of the thallus (in hot 

 water) differed from everniin and might probably be lichenin. Cetraria 

 islandica was also analysed and yielded various hemicelluloses, chiefly 

 dextran and galactan, with less pentosan. No chitin has ever been found in 

 this lichen. In testing minute quantities of material for chitin, Wisselingh' 

 heated the tissue in potash to i6o°C. The potash was then gradually re- 

 placed by glycerine and distilled water; the precipitate was placed on a slide 

 and the preparation stained under the microscope by potassium-iodide-iodine 

 and weak sulphuric acid. Chitin, if present, would have been changed by 

 the potash to mycosin which gives a violet colour with the staining solution. 



It has been stated by Schellenberg* that these lichen membranes may 

 .become lignified. He obtained a red reaction with phloroglucine test 

 for lignin in Cetraria islandica and Cladonia furcata. Further research is 

 required. 



c. Cellulose. Several workers claim to have found true cellulose in 

 the cell-walls of the hyphal tissues of a few lichens; but the more careful 

 analyses of Escombe' Wisselingh^ and Wester^ have disproved their results. 

 The cell-walls of all the gonidia, however, are formed of cellulose, or according 

 to Escombe of glauco-cellulose, except those of Peltigera in which Wester 

 found neither cellulose nor chitin. Czapek' suggests that the blue reaction 

 with iodine characteristic of the cell-walls in some apothecia, of the asci and 

 of the hyphae in cortex or medulla in a few instances, may be due to the 

 presence of carbohydrates of the nature of galactose. Moreau^ in a recent 

 paper terms the substance that gives a blue reaction with iodine at the tips 

 of the asci " amyloid." In Peltigera the ascus tip is occupied by such a plug 

 of amyloid which at maturity is projected' like a cork from the ascus and 

 may be found on the surface of the hymenium. 



■ Miiller 1905. ^ stiide 1864. ^ Wisselingh 1898. * Schellenberg 1896. 



'■ Escombe 1896. « Wester 1909. ' Czapek 1905, I. p. 515. « Moreau 1916. 



