DISTRIBUTION OF SPHAGNUM AND CAREX 335 



The general principle that the farther the continents recede from 

 the north the fewer are the species common to the east and the west 

 is strengthened by including in the table South America as repre- 

 sentative of the west hemisphere and Africa and Australia with New 

 Zealand as representatives of the east. But numerous other con- 

 siderations arise; and in fact the subsequent discussion is mainly 

 occupied with the distribution of Sphagnum and Carex in the southern 

 hemisphere. Here, since the source of these floras is one of the 

 principal points dealt with, the islands are often permitted to tell 

 their story. 



Comparison of the East and West Hemispheres in the North. 

 — It is legitimate, in a sense, to compare the endemism of the large 

 land-masses of the southern hemisphere, South America, Africa, 

 and Australia, since they are widely separated and independently 

 situated; but it would be worse than useless to contrast the great 

 land-masses of the north in their entirety, diverging as they do from 

 a common centre in the polar area. I will take the case of Sphagnum. 

 In the combined area of the North American and Eurasian land- 

 masses there are, excluding the islands, 110 species, of which fifty- 

 three are found in both hemispheres. A little consideration will 

 show that the mere statement that 48 per cent, of the North 

 American and Eurasian species are held in common, however true 

 it may be, becomes pointless after an analysis of the details of distri- 

 bution. Thus, of the fifty-three species held in common, forty-six are 

 Arctic and Subarctic species, and twenty-two are practically circum- 

 polar. Since, therefore, the species held in common between 

 Eurasia and North America mostly congregate in the north, we 

 would expect that the species held separately by these two great 

 land-masses would gather in the south. This is indeed the case. 

 Of thirty-nine species confined to North America, only two are found 

 in Subarctic latitudes. The rest belong to the south, being especially 

 numerous in the Southern United States. Warnstorf, who had no 

 theory to support, is emphatic on this point. Whilst, as he says 

 (p. 38), there is great agreement between the species of the Arctic, 

 Subarctic, Atlantic, and Pacific regions of North America and 

 Europe, in the Southern States of the Union and in tropical America 

 endemism prevails. The rule in North America that the species 

 it holds in common with Eurasia belong to the north, whilst those 

 peculiarly its own belong to the south, is also illustrated in Eurasia. 

 Of the seventeen species restricted to that continent only one is 

 found in the cold latitudes of the north. 



It would be equally futile in the case of the Carices to employ any 

 common value when contrasting the endemism of Eurasia and North 

 America. This is sufficiently illustrated in the fact that the number 

 of species which North America shares with Eurasia gradually 

 decreases from 93 per cent, in the Arctic latitudes to as little as 

 11 per cent, in the Southern United States and in Mexico. 



The Connections of the South American Sphagnum and Carex 

 Floras. — The parallelism between Sphagnum and Carex is strikingly 

 illustrated in the case of the connections of South America with the 

 rest of the globe. In both genera the predominance of North 



