228 PHYSIOLOGY 



lichens ; solorinic acid (C16H14O6) occurs in orange-red crystals on the hyphae 

 of the pith and under surface of Solorina crocea; nephromin (CiaHijOe) is 

 found in the yellow medulla of Nephromium lusitanicum; rhodocladonic acid 

 (CiaHgOe or C14H10O7) is the red substance in the apothecia of the red-fruited 

 Cladoniae. 



There are, in addition, a short series of coloured substances which are of 

 uncertain position. They are imperfectly known and are of rare occurrence. 

 An acid containing nitrogen has been extracted from Roccella fuciformis, 

 and named picroroccellin' (C27H29N3O5). It crystallizes in comparatively large 

 prisms, has an exceedingly bitter taste, and is very sparingly soluble. It is 

 the only lichen-acid in which nitrogen has been detected. 



One acid at least, belonging to the Fat series, vulpinic acid, which gives the 

 greenish-yellow colour to Letharia vulpina, has been prepared synthetically 

 by Volkard^ 



F. Chemical Reagents as Tests for Lichens 



The employment of chemical reagents as colour tests in the determination 

 of lichen species was recommended by Nylander* in a paper published by 

 him in 1866. Many acids had already been extracted and examined, and 

 as they were proved to be constant in the different species where they 

 occurred, he perceived their systematic importance. As an example of the 

 new tests, he cited the use of hypochlorite of lime, a solution of which, 

 applied directly to the thallus of species of Roccella, produced a bright-red 

 "erythrinic'' reaction. Caustic potash was also found to be of service in 

 demonstrating the presence of parietin in lichens by a beautiful purple 

 stain. Many lichenologists eagerly adopted the new method, as a sure and 

 ready means of distinguishing doubtful species ; but others have rejected 

 the tests as unnecessary and not always to be relied on, seeing that the 

 acids are not always produced in sufficient abundance to give the desired 

 reaction, and that they tend to alter in time. , 



The reagents most commonly in use are caustic potash, generally indi- 

 cated by K ; hypochlorite of calcium or bleaching powder by CaCl ; and 

 a solution of iodine by I. The sign -|- signifies a. colour reaction, while — 

 indicates that no change has followed the application of the test solution. 

 Double signs % or any similar variation indicate the upper or lower parts of 

 the thallus affected by the reagent. In some instances the reaction only 

 follows after the employment of two reagents represented thus: K (CaCl) +. 

 In such a case the potash breaks up the particular acid and compounds are 

 formed which become red, orange, etc., on the subsequent application of 

 hypochlorite of lime. 



' Stenhouse and Groves 1877. 2 Volkard 1894. 3 Nylander 1866. 



