362 DR. W. NTLAXDER ON TWO liKW CRITERIA 



laevigata* and revoluta, wliich have "been so often confounded. 

 The revoluta is given in Sdner. L. H. 612, Zw. Exs. 181 bis B, 

 Hcppe, riecht. Eur. 581, Arn. Exs. 137, Anzi, Langob. 49 & 256 

 (angustifolia, analogous to tlie var. dissecta of P. Iccvigatd)^ most 

 frequently named by these authors " P. siiiiiosa,'''' but distinct 

 from Icevigata at^ well as from sinuosa (which is only a variety of 

 it) by the evident erytlirinic reaction, whilst the Icevigata and 

 sinuosa do not present the least trace of this reaction. The 

 revoluta is also distributed in Lechl. PL Chil. 855. 



By these examples, which may be verified with the greatest 

 ease, I believe that I have sufficiently established the invaluable 

 assista^nce which the hypochlorite of lime affords us in the study 

 of Lichens. The least frustule of the thallus is sufficient for the 

 verification, without the microscope, of the beautiful chemical 

 character which distinguishes, even in the very youngest indi- 

 vidual 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 re- 

 actions obtained with iodine as characters of Lichens), that we 

 are guided by the differences manifested through the reaction to 

 search with more attention for orcfanic characters: and, as a 

 general rule, we shall not fail to find themf. 



w 



II. HrnRATE OF Potash . 

 A solution of hydrate of potash is of equal practical utility by 



To l^vi(]ata (Sm,) belongs the P. sinuosa, var. virescem, of Kplib. Licli. 

 Bay. p. 131, according to a specimen sent by M. von Krcmpelhubcr himself. 



t Most of tiie species of the genus Umbilicaf^a exhibit an erythrinic reaction 

 visible in the medulla, but generally very pale by reason of the small quantity 

 of colourable matter which is to be found in them. The Z7. alroprtnnosa^ siifi' 

 iata, cylindrical Belisei, rngifera, corriigaia^ erosa^ scIerophi/Uai do not 

 exhibit any trace of this reaction. The U. reticulata, Duf, has an erythriuic 

 medulla; and for this same reason its varieties, cinerascens, micropTitflla^ b.w 

 pallens (var. nuda, Sehser. Enum. p. 27), ought to be separated from it. 

 Sometimes in the UtnbiUcarice the reaction (of a pale red) is observed on the 

 surface of the thallus— for example, in U.^aprina and lecano-carpoides. In 

 certain eases, as in U. hyperhorea, in some specimens, the colourable matter is 

 in so small a quantity that we can scarcely test its presence, whilst in other 

 specimens, and this most generally in this species, we see the erythrinic reaction, 

 although pale, without difnculty. It is useful for observations in this genus, to 

 "have iu the lierbarium not only well- developed and aged specimens, but also 

 young specimens, which will exhibit the characteristic chemical signs whenerer 

 .the reaction is feeble or less distinguishable. 



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