92 A SJiort Talk on Lichens. [Sess. 



mination. The next and third important aid in their deter- 

 mination, as in other lichens, is the use of chemical reagents, 

 those now used being first pointed out by Dr Nylander of 

 Paris in 1866. These reagents do not of themselves con- 

 stitute a special specific, but only an additional and confirma- 

 tory, character. They are — 1. Hydrate of potash, shortly 

 denoted by K, and composed of equal weights of caustic 

 potash and water. 2. Hypochlorite of lime, denoted by C or 

 CaCl, composed of chloride of lime and water. 3. A solu- 

 tion of iodine, which is scarcely ever used with the Cladonite, 

 whose spores are all simple and similar, and among the smallest 

 of lichen spores. Iodine tinges the thecse of Cladonise blue. 

 Full directions for using the reagents are given in any good 

 text-book of lichens, as those of Leighton and Crombie. 

 K giving a yellow reaction is K -}- , and giving no reaction is 

 K — , and so with C. Formulae are also used when these two 

 reagents are applied immediately after each other, as K -f- C -|- , 

 or K — C — , &c. A more or less fuscous colour by K or C is 

 disregarded and considered negative. The reaction is always 

 the same for the same species, if the plants are young, healthy, 

 and growing, and are more vivid on the young and growing 

 parts of the lichen. The reaction must be immediate and not 

 tardy. These thalline reactions depend upon the presence in 

 the thallus of certain colourable materials in the form of acids, 

 as erythrinic, chrysophanic, and lecanoric acids. Take a few 

 examples and see how they apply. Cladonia pungens and 

 C. furcata are outwardly like each other and have no scyphi, 

 but the reactions distinguish them, C. pungens having K -|- C -H , 

 and C. furcata K — C — . C. squamosa and C. subsquamosa 

 are like each other, but C. subsquamosa gives at once a 

 brilliant yellow turning crimson with K, while C. squamosa 

 gives no reaction. C. digitata and its varieties growing at the 

 decaying roots of trees give K -|- a vivid yellow, and has red 

 apothecia ; while the cosmopolitan C. pyxidata, with flesh- 

 coloured apothecia, gives no reaction K — C — . C, cervicornis 

 has K -|- C -f- , and C. alcicornis, like it, has K — C -f- . The 

 majority of Cladoniee have no reaction K — C — . Of course, 

 other points, in fact every point, has to be taken into account 

 in the determination of species. The description of any 

 Cladonia in such a text-book as Leighton's ' Lichen Flora of 



