AS A SPECIFIC CHAUACTER IN LICHENS. 37 



tlic study of Licliens, The least frustule of the thallua is suffi- 

 cient for the verification, without the microscope, of the beautiful 

 chemical character which distinguishes, even in the very youngest 

 individual specimens, the species in which other differences are 

 scarcely visible. The chemical characters have also this advantage 

 (as I have noticed elsewhere in speaking of the utility of the 

 different reactions obtained with iodine as characters of Lichens), 

 that we are guided by the differences manifested through the 

 reaction to search with more attention for organic characters ; 

 and, as a general rule, we shall not fail to find them '* [!] (p. 362). 

 " It is very easy to convince ourselves of the importance of this 

 distinctive sign [reaction with hydrate of potash], according to its 

 existence or non-existence in the Lichens which we are studying 

 or determining'' (p. 363). " By the presence or absence of this 

 yellow reaction, we can equally distinguish many species in a 

 manner far easier and more certain than by the ordinary characters 

 hitherto affixed to them " (p. 364). 



The veteran Rev. Mr. Leighton, of Shrewsbury, immediately 

 supported all Nylander's assertions, adding a further means of dia- 

 gnosing the species of Gladonia by the double reaction of hypochlo- 

 rite of calcium and hydrate of potash, his language of recommenda- 

 tion failing in no respect in enthusiasm or confidence*. Thus 

 he writes, " Dr. Nylander has recently discovered two new chemical 

 tests or criteria w^hich are likely to prove oi great value in the 

 study of Lichens, not only in the discrimination of many difficult 

 and closely allied species, but also in associating varieties with 

 their proper species, and in some instances in defining the affinities 

 of genera Their usefulness is at once demonstrated and en- 

 hanced by the fact that the very smallest frustule is sufficient to 

 determine the lichen submitted to them, and that whetlier in the 

 sterile or fertile state, and even in the youngest condition '* 

 (p. 169) f. Chemical tests are "most useful and indispensable 

 aids as affording confirmatory characters and in discriminating 

 doubtful or externally allied species " (p. 440) %. 



* « 



tf 



On the Examination and Hearrangement of the Cladoniei aa tested by 

 Hydrate of Potasli," Ann. Nat. Hist. 1866, vol. xviii., and " On the Cladonid in 

 the Hookerian Herbarium at Kew [tested by hypochlorite of lime after potash], 



Ann. I^at. Hist. 1867, vol. xix. 



t '-Notulse Lichcnologiae, No. IX./' Annals of Nat. History, 18GG, vol. 



ivm. 

 X "Not. Lich. No. XVIII.," Ann. Nat. Hist. 1867. vol. \x. 



