NOTES ON THE FLORA OF SHETLAND 269 



this habit by gradually accumulated melanic variations. As 

 instances of this nigrescent tendency, take the cases of some of 

 the alpine mosses, Hepaticae and Lichens. One cannot but notice 

 when working in alpine districts the blackness or brownish black- 

 ness of all the species of Andrecea. Many of the alpine species of 

 Grimmia and Bhacomitrium are blackish, such as Bhacomitrium 

 ellipticum, Grimmia atrata, G. elongata, &c. Many other species 

 of Grimmia have their lower portions of a dark colour. The 

 following alpine and subalpine Hepaticae are also black or blackish 

 brown : — Nardia alpina, N. ustulata, N. Funckii, N. adusta, 

 N. emarginata, Herberta adunca, Ptilidium ciliare, Mastigophora 

 Woodsii, Gymnomitrium crenulatum, G. coralloides, G. crassifolium, 

 &c. Lichens often show this tendency, to wit — many species of 

 Gyrophora and Umbilicaria, Parmelia lanata, P. olivacea, P. fuli- 

 ginosa, P. omphalodes, P. triste, Platysma tahhmense, Cetraria 

 aciUeata, &c. Even the black Verrucaria maura and its dark 

 commensals or near neighbours Lichina pygmcEa and L. confinis 

 may have attained their darkness by thus being able to absorb 

 more heat to counteract the coldness produced by the almost con- 

 stant evaporation from their surfaces. Then, again, the black 

 Bacodium rupestre and Ccenogonium always grow in deep shade, 

 and they will also be able to utilize what heat they may get with 

 the light they receive. The species of Ephehe are also alpine and 

 black, and the colour is due to the much greater prevalence of the 

 algal constituent. This genus of algoe (as well as some species of 

 the allied genera), when alpine and autonomous, become blackish 

 brown in colour and probably from the same reason. 



Another tract of the Serpentine in Unst was examined about 

 two miles distant from the last and further from the sea ; it was 

 walled in and used as pasture for the ponies. In some places 

 Calluna only persisted in cushions from 3 to 6 in. high and about 

 12 in. across ; these were markedly mingled with varying propor- 

 tions of Molinia, Carices (barren), Potentilla Tormentilla, Festuca 

 ovina, and with smaller quantities of Scabiosa succisa (only leaves), 

 Thalictrum alpinum, Scilla verna, Statice Armeria, Plantago 

 maritima, and Agrostis tenuis. The plants of the rest of the turf 

 (which had small areas of bareness) surrounding the Calluna- 

 cushions were a mixed formation of Agrostis vulgaris^ Leontodon 

 autumnalis, Luzula campestris, Festuca ovina, BhinantJms, Poten- 

 tilla syluestris, Selaginella, Statice Armeria, Erica cinerea, E. 

 Tetralix, Junc2cs acutiflorus, Cerastium triviale, Plantago maritima, 

 Prunella, Gentiana campestris, Scabiosa succisa, Linum catharti- 

 cum, Siegliiujia, and in the moister places very dwarfed Schocnus 

 nigricans, Sagina nodosa, small patches of barren Nartheciicm, 

 Plantago maritima var. lanata, Euphrasia latifolia (with white 

 flowers), Pinguicula vulgaris, Carexpulicaris, C. dioica, C. cchinata, 

 in barer places C. flava and odd plants of Holcus lanatus. Where 

 rocks abutted slightly Antennaria dioica occurred with Silene 

 acaulis now and then, and on the rocks were Sphoirophorus coral- 

 hides, Cladina sylvatica, C.pungens, Lecanora parella, fragmentary 

 Lecidea atrata (and poor examples of one or two more species of 



