106 Dr. Greville on some new species of Sargassum. 



above the subalpine zone ; and there are a few other Pyrenaean 

 mosses wanting to the Alps*. 



Two Jungermannia exceedingly common in Britain, Lophocolea 

 bidentata and heterophylla, are all but absent from the Pyrenees ; 

 and two others, Jungermannia barbata and Ptilidium ciliare, 

 great ornaments of our mountainous districts, are altogether 

 wanting. The latter attains its southern limit in the north of 

 Italy; it is distributed throughout middle and northern Europe, 

 but grows in greatest luxuriance within the Arctic circle. (Conf. 

 Wahlenberg and the accounts of our Northern voyagers.) 



According to Wahlenberg, there are in Lapland, as in the 

 Pyrenees, extensive forests of Pinus Abies and P. sylvestrisy and 

 both descend into the plain ; the former cease at the altitude of 

 800 feet and the latter at 1200 feet, indicating respectively the 

 upper limits of the " regio sylvatica '' and the '' regio subsylva- 

 tica.^^ But in the Pyrenees these trees ascend proportionally far 

 higher than in Lapland ; and that they do not occupy the same 

 climatal zones we shall see by comparing the positions of a few 

 mosses common to both countries. In the Pyrenees, Tortula tor- 

 tuosa, Bryum crudumf Didymodon capillaceus and Dicranum virens 

 are found in the region of coniferous trees, and are rarely seen 

 above it ; but these are precisely species mentioned by W ahlen- 

 berg as characteristic of his " Alpes inferiores,^^ which are above 

 the region even of the birch ('^ regio subalpina, Wahl.^'), and are 

 characterized by the presence of Betula nana^ Diapenzia lappo- 

 nica and Silene acaulis. Yet the comparative altitudes attained 

 by the mosses in the Pyrenees and in Lapland accord very nearly, 

 and the species which ascend highest in the one for the most part 

 do the same also in the other. Hence the zone occupied by a 

 moss common to both has probably in both the same average 

 cestival temperature. 



[To be continued.] 



XI. — Alg£B Orientales : — Descriptions of new Species belonging to 

 the genus Sargassum. By R. K. Greville, LL.D. &c.t 



[Continued from vol. ii. p. 434.] 



[With a Plate.] 



WiGHTIANiE. 



10. Sargassum porosum (nob.) ; caule cylindraceo, brevissimo, mu- 

 ricato, ramis planis ; foliis ovato-oblongis, subundulatis, inciso- 



* The number of species which I have found in the Pyrenees new to the 

 flora of France is considerable ; but I cannot give a correct list of them, as I 

 have not the dates of several species discovered in the Alps and Jura and 

 nearly contemporaneously in the Pyrenees. 



f Read before the Botanical Society of Edinburgh 14th Dec. 1848. 



