DISTRIBUTION OF SPHAGNUM AND CAREX 358 



majority of species belong to the subsection Subsecunda, which 

 possesses no world-ranging species. But this is not only a closed 

 subsection for Africa, it is the same for Australia and New Zealand. 

 Although it holds one-fourth of the Australian and New Zealand 

 species, they are all confined to the region, the species connecting 

 it with the outside world belonging to other subsections. 



The Behaviour of Sphagnum and Carex and the Theory of 

 Differentiation. — If I were to endeavour to show how the be- 

 haviour of the Carices and the Peat-mosses, as discussed in this, 

 chapter, fits in with the general theory of differentiation adopted in 

 the two preceding chapters, it would be, as briefly expressed, some- 

 what to this effect. The Carices represent one of the results of the 

 differentiation of a generalised cyperaceous type originally spread 

 over the globe; whilst the Cyperi represent another result. These 

 two genera largely compose the family, the second being as character- 

 istic of warm latitudes as the first is of the cool regions of the north. 

 Whilst the distribution of Carex has been mainly determined by the 

 divergence of the land-masses from the north and by the secular 

 changes of climate, that of Cyperus has been affected to a much less 

 degree by these influences. While the tide of the Carices has ebbed 

 and flowed in the north, the Cyperi could have reached the common 

 focus of dispersal in the Arctic polar area only when exceptionally 

 warm conditions reigned at the pole. Cyperus ought to represent 

 to some extent the attitude of relative passivity adopted by typical 

 plant-groups in the tropics. Its efforts to penetrate the cooler 

 regions of the globe have not been very successful ; whilst its sister 

 genus, Carex, has only been able to reach the temperate regions of 

 the south by halting on the tops of the mountains during its traverse 

 of the tropics. 



It is the same with Sphagnum, since it is at home in the moors 

 of the north and occurs at high altitudes on the mountains of the 

 tropics. But there is evidence, as we learn from Ule as quoted by 

 Warnstorf (p. 33), that these plants are adapting themselves to a 

 low-level station in the tropics in the coast-plains of South Brazil* 

 We seem to know but little of the evolutionary history of a genus 

 which was raised by the elder Schimper to the rank of a separate 

 family; and it would be useless to evoke a differentiating process 

 that would involve the common origin from a generalised type of 

 the Peat-mosses, the Mosses proper, and the Liverworts. 



One great lesson supplied by the striking parallelism of two plant- 

 types so widely divergent as Carex and Sphagnum is that time has 

 long since discounted any especial advantage which the one might 

 possess over the other as regards facilities for dispersal. In both 

 cases their distribution has been largely determined by the arrange- 

 ment of the land-masses and by the alternations of climate. Yet 

 such a parallelism would acquire but little importance, if it was 

 merely concerned with these two plant-groups. It indicates a 

 principle enunciated by Dyer as affecting a host of other plants of 

 the north, plants that are often strangely contrasted in almost every- 

 thing but their response to the principle of distribution so well 

 illustrated in the behaviour of Carex and Sphagnum. 



