ON CALIFORNIAN MOSSES. 23 



tirely dry in summer. Hence, they periodically disappear, being apparently renewed each 

 year from their thallus, and never reaching their entire development. They bear simple 

 short stems, scarcely branching, and have never been found in fruit. It is evident that 

 their presence, if not their form, is due to peculiar and local circumstances. 



In the Pliascaceoe, we have in Eastern North America five exclusively indigenous species 

 of Bruchia. A single species of this genus has been found once only in the Vosges 

 Mountains of Europe, at an altitude corresponding with that of the summit of Mount 

 Marcy (about 6000 feet), on the decomposed dung of cows. Our Brucliia flexuosa Schw., 

 whose habitat I had opportunity to closely examine, is found in the spring in large round 

 patches, apparently on the naked clay ground, but really at such places which were for- 

 merly covered by the dung of animals feeding in the meadows. The southern species 

 have probably a habitat of the same kind, being found along the canals on the sand of 

 the tow-paths. If this is the case, the distribution of these mosses is according to the 

 general rule. The dung in various climatic conditions is the local habitation of different 

 species of mosses. Our only true American Splachnea, Tetraplodon Atistmlis Sul. & 

 Lesq., lives in the Southern swamps on the dung of mules. 



The Fontinales are always found in water. The number of true American species, either 

 on the east or on the west side of the continent, is pretty large, most of the species being 

 truly arboreous. Indeed, they attach themselves to branches and roots of trees plunging 

 in water, and occasionally only to stone. The few species which may be called rock 

 species, generally attached to stones, like Fontinalis Dalecarlica Bryol. Ear., are found both 

 in Europe and in Eastern North America. 



The genus Dicranum shows apparently another kind of anomaly of distribution, that is, 

 identity of forms and variety of habitat. Twenty-seven of our Eastern North American 

 species are the same as in Europe, though some of them are truly arboreous. All the 

 arboreous ones live on rotten or decayed wood in the spruce region. The other species 

 are mostly inhabiting the stones or the ground in the subalpine region, or the bogs. Their 

 distribution is thus according to the common rule. 



The affinity and also the modifications of forms following the influence of habitat, are 

 better marked perhaps in the distribution of the genus Orthotrichum than in any other. 

 The species living on rocks, Orlhotrichum Sturmii Hpp., 0. anomalum ffedw., 0. cupula- 

 tum Hoff., 0. Hutschinsice Grev., and also the subalpiue arboreous species living on the 

 bark of the spruce and the beech, Orthotrichum Roijeri Briil., 0. speciosum Nees., 0. leio- 

 carpum Br. & Schp., 0. Ludwigii Schw., 0. crispulum Hrsch., are identical in Europe 

 and Eastern North America. On the contrary, the true arboreous species of the plain or 

 of the temperate zone, Orthotrichum exiguum Sul., 0. Texanum Sul., 0. stmngulatum 

 -Beauv., 0. Canadense Br. & Schp., are exclusively indigenous. One of our Orthotricha- 



