38 Rev. W. A. Leighton on new Characters in 



value in recognizing and determining the species or varieties 

 in which thej occur. More especially are they serviceable in 

 those genera in Avhich the spores, from their general simila- 

 rity, are only partially available. In the preparation of my 

 * Lichen-Flora of Great Britain,' now drawing towards com- 

 pletion, these secondary characters have been frequently no- 

 ticed in many genera ; and I have accordingly pressed them 

 into service. By accident my attention has been veiy re- 

 cently drawn to the genera Nephroma and Nephromium^ the 

 species of which have been hitherto involved in very con- 

 siderable confusion, especially those of the latter genus, by 

 reason of the several species and varieties being frequently 

 found growing in the same locality, and often in inter- 

 mixture. 



The new characters which I have detected here are the 

 chemical reaction of the thallus, the colour of the medullary 

 stratum and its chemical reaction, and the sti'ucture of the 

 back of the receptacle of the apothecia. Having gone through 

 the goodly store of specimens in my own herbarium with 

 satisfactory results, I was naturally anxious to extend my 

 researches through the Hookerian Herbarium at Kew. Dr. 

 Hooker, with that generous liberality so characteristic both 

 of himself and of his father, the lamented Sir W. J. Hooker, 

 ever ready and desirous to aid and promote scientific in- 

 quiry, at once opened these collections to me. The examina- 

 tion has enabled me to effect a double service — to test and 

 establish the certainty and constancy of these characters, and 

 to rearrange in a more complete manner these genera in that 

 herbarium. 



The genus Nephroma is distinguished by the gonidial stra- 

 tum being of a pale yellow-green colour and comjiosed of 

 simple gonidia ; whilst Nephromium has that layer of a dark 

 blue or verdigris-green, and composed of granular gonima. 

 The thallus in Nephroma is, moreover, by reason of its pale 

 ochroleucous colour, capable of exhibiting certain chemical 

 reactions with hydrate of potash and hypochlorite of lime, 

 which serve also to separate it from Nephromium, in which 

 the fuscescent or darker colour of the thallus renders any such 

 reaction imperceptible. Practically, of course, it is of little 

 real consequence whether we regard these as sections of one 

 genus or as separate genera, so long as we can readily distin- 

 guish them by fixed characters. For readier comparison I 

 have tabulated the characters to which I would call attention 

 in the following way. 



