THE BRYOPHYTA OF ICELAND 619 



In the following pages some examples of the Bryophyte vege- 

 tation of lava-clefts will be described. 



Thing vail a lira un. The lava-clefts (Icelandic Gja) there, are 

 peculiar on account of their unusual depth (as much as 20 30 

 metres). Several of those situated nearest to the lake of Thingvellir 

 have deep water at the bottom. 



The Bryophyte carpet at the bottom of the clefts is composed 

 of Hylocomhun loreum, H. proliferum, H. parietinum, H. sqimrrosum, 

 Hypniim uncinatum, H. callichroum, H. stramineum, H. molluscum, 

 Eurhynchium piliferum, Antitrichia curtipendula, Polytrichum alpinum, 

 Rhacomitriiim hypnoides, R. canescens, Dicranum Blyttii, D. Starckei, 

 D. mollc, Sphagnum teres, S. Girgensohnii, Lophozia uentricosa, L. 

 quinquedentata, L. Knnzeana, L. alpestris, Ptilidium ciliare and Sca- 

 pania irrigua. On the sides of the clefts there grew especially An- 

 cectangium compactum, Grimmia torquata, G. funalis, Gymnostomum 

 rupestre, Amphidium Mougeottii and A. lapponicum. Intermixed with 

 these, and in cushions on the ledges, in the crevices and among 

 the blocks there grew: Hypniim cupressiforme, Isoihediim tenuinerve, 

 Ptagiothecium pulchellum, P. denticulatum, P. silvaticum, Amblystegium 

 Sprucei, Neckera complanata, Schistidium gracile, Rhacomitriiim sude- 

 ticum, Scelania ccesia, Ditrichum flexicaule, Tortella tortuosa, Fissidens 

 osmundoides, F. bryoides (rare), Pohlia cruda, P. commutata, Bartramia 

 ityphylla, Conostomum boreale, Philonotis tomentella, Mnium orthor- 

 rhynchum, Bryum pallens, Plagiobryum Zierii, Distichium montanum. 

 Diplophylhun albicans (in abundance), Lophozia heterocolpos, Lejennea 

 cavifolia, Blepharostoma trichophyllum, Alicularia scalaris, A. geo- 

 scypha, Anthelia Juratzkana, Scapania subalpina, Pleuroclada albescens 

 var. islandica, Cephalozia bicuspidata, Eucalyx siibcllipticus, Gymno- 

 mitrium concinnatum, Metzgeria furcata, Radula complanata, Aneura 

 pingnis and Preissia commutata. 



The above list is very long, but is nevertheless hardly complete, 

 since some of the common chomophytes are not enumerated in it r 

 and, at any rale, several of them were undoubtedly forgotten, while 

 the list was being made on the spot, but it gives a good idea of 

 the exceedingly great number of species which are found in these 

 localities. 



H afn a r fj arda rhraun. Almost the same species are found 

 there as in Thingvaiiahraun, but the situation close to the sea-side 

 makes its influence felt. Rhacomitriiim heterostichum and R. fasci- 

 culare are exceedingly common, and in several places Ulota maritima 



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