ON CALIFORNIAN MOSSES. 21 



has explored some parts, and he makes the same remarks ahout the scarcity of mosses. 

 On Mount Diahlo he found Grimmia montana and Bmunia on dry rocks, and one or two 

 species only at the bottom of deep canons. 



Now looking to the part of Europe to which the Bryologia of California is essentially 

 related, viz., to the countries around the Mediterranean Sea, and inquiring into their 

 climatic conditions as related to the vegetation of the mosses, we find them remarkably 

 identical. 



W. P. Schimper, the greatest of all past and present bryologists, went to Spain some 

 years ago for the purpose of exploring and collecting the mosses of the mountains of that 

 country, especially of the Sierra Nevada. He hoped to find there remarkable and new 

 species, and expected a rich scientific result of his researches. He came back disappointed. 

 The Sierra Nevada of Spain had scarcely any mosses ; only those common species found 

 everywhere on dry ground and dry rocks. The high summits of these mountains, covered 

 part of the year by dense fogs, or drenched by diluvial rains, are in the summer entirely 

 dry and barren. Everywhere, says the celebrated professor of Strasbourg, the naked rocks 

 are exposed to view without any trace of those green carpets of Sphagnum, Aiidrcea, 

 Gymnostomum, Weiaia, Dicranum, &c., &c., which cover the constantly-watered declivities 

 of the Swiss Alps, of the Pyrenean, and especially of the Dovrefield Mountains of Norway. 

 The same absence of mosses, due to the same climatic conditions, has been remarked 

 also in the Caucasus by Mr. Dubois de Montperreux, and in Algeria by French botanists. 

 All these countries are about on the latitude of California, and evidently we can trace to 

 a similarity of mere climatic circumstances, the first cause of the extraordinary relation 

 of the bryological vegetation. 



The climate of Eastern North America has a greater degree of similarity with that of 

 North and Middle Europe, and we find the same degree of relation in our mosses. We 

 have especially in common the subalpine species, inhabiting the mountains of New York, 

 of Massachusetts, even the summits of the Alleghany Mountains, and the plain near the 

 northern lakes, exactly following the geographical distribution of the Abies. If this flora 

 of ours is not quite as rich as that of Europe, the reasons are easily found, 1st. In the ab- 

 sence of a higher group of Alpine mountains, Avhose influence tends to enrich the vegeta- 

 tion of mountains of second order. 2d. In the predominance of forests in this country, 

 where they cover the subalpine mountains nearly to their highest summits, preventing 

 therefore the differences caused by a variety of habitat and of station. 3d. In the frequent 

 conflagration of these forests, which tends to destroy in part the vegetation of the mosses, 

 and of course to render it more uniform. 



But there is still another cause of distribution of the mosses, by which we can explain, 

 not only the relation of forms, but also the differences which characterize the Bryologia of 



