^2 BRITISH LICHENS. 



was found, when applied to the hymenium of certain species, to yield a 

 blue reaction, while in other species it merely yielded a vinous brown 

 colour. The blue colour is attributed to the presence of starch in miinite 

 quantity in the gelatinous matter pervading the hymenium, called by 

 Nylander the gelatina hi/moiia ; or if the colour be produced in the 

 membrane of the ascus and the cell walls of the paraphyses it is 

 attributed to the presence of cellulose in these bodies. Tlie medullary 

 layer of the thallus of some species also gave this blue reaction. At one 

 time this reaction was not only considered of service in separating 

 species, but was even thought to afford a certain criterion by which to 

 distinguish a Lichen from a fungus. Dr. Nylander, however, pointed out 

 in I860 that many fungi belonging to the section Discomycetcs gave a 

 similar reaction. Although it thus proved fallacious for this latter 

 purpose, it has continued to this day to be used as an auxiliary help in 

 determining species. Apart from the reaction iodine occasionally gives, it 

 is found to be a most useful substance as a staining fluid for the purpose of 

 bringing out points of structtxre under the microscope that without some 

 such aid would be invisible. The mode of using it is to place a drop 

 close to the margin of the covering glass under which a section lies on 

 the glass slide, when it will immediately spread by capillary attraction 

 through the whole of the section. Care should be taken, however, 

 that the section has been moistened by pure water only, as any other 

 chemical may interfere with the result. 



In 1866 Dr. Nylander proposed two chemical substances capable of 

 affecting the colouring matter of Lichens, as a test by which to distinguish 

 certain closely- allied species, of far greater value for this purpose than 

 iodine, namely, hydrate of potash and hypochloi-ate of lime. The Rev. 

 W. A. Leighton, and other leading Lichenologists both in this country 

 and on the Continent, at once accepted them as affording most important 

 criteria. Their employment at the present time is all but universal, and 

 hence it is absolutely necessary the student should be put in possession 

 of such information as will enable him to apply them. We will take 

 them in order. 



Hydrate of potash is composed of equal weights of caustic potash 

 and water, and should be kept in a stoppered bottle of green glass. For 

 the sake of brevity, in describing its effects, the symbol K is used to 

 represent it, and this letter should be conspicuously written on the label 

 in addition to the name of the mixture. 



Hypochlorate of lime is formed by mixing chloride of lime — the 

 common bleaching powder of commerce — with water. The water takes 

 up but a very small quantity in solution, the surplus falling as a sediment 

 to the bottom of the bottle. As this solution will lose its effect if kept 

 for many days, it is best to make a fresh solution every week. The symbol 

 for this is C, which, as in the case of the preceding raixture, should be 

 conspicuously written on the bottle containing it. 



For each of these chemicals a separate small brush made of spun 

 glass, procurable at any analytical chemist's, must be used when applying 



