NO. 2 MOSSES OF AFRICAN EXPEDITION — DIXON 5 



this view is considerably strengthened by the mosses of the present 

 collection. To begin with, it may be postulated with practical cer- 

 tainty that the species I have noted above were not transmitted in 

 the spore state, but in the gametophytic stage. For of the four 

 species newly recorded as common to both regions, Callicrgon sar- 

 mcntosum and Aulacomnium turgidum are dioicous and extremely 

 rare fruiters in the palasarctic region, while Neckera complanata 

 also is dioicous and infrequent in fruit, though not so rare as the 

 above two. For Aulacomnium turgidum Limpricht (2) cites only 

 three fruiting localities in Central Europe, Hagen states that it is only 

 found sterile in northern Norway, and the same is the case in Great 

 Britain, while in North America the fruit is described as " rare," 

 and I have seen no localities given. Callicrgon saru:cntosum is also, 

 except in the most northerly arctic regions, extremely rare in fruit. 



And these four species do not exhaust the contribution of the 

 present collection to the common flora. For of the new species 

 described, Hygroamblystegium proccrum, while striking and distinct 

 in habit, is structurally identical with the pakearctic H. Hlicinum 

 and would without doubt, I think, if it had been found within the 

 recognized range of that species, have been described as a variety 

 or subspecies at most. And Callicrgon Keniae, while scarcely, I 

 think, to be placed under C. sariuentosum, is undoubtedly nearest to 

 and a derivative from either that plant or C. stramineum (Dicks. ) ; 

 and the small genus to which these belong is one of the most 

 markedly alpine-arctic types, reaching the southern part of the 

 north temperate zone only under extreme alpine conditions, with a 

 similar but still more restricted distribution in the southern hemi- 

 sphere, and having no representative in the African flora. And 

 again, Philonotis speirophylla sp. nov., while a clearly marked 

 species, is undoubtedly near to and almost certainly a derivative 

 from the northern, alpine-arctic P. seriata Mitt. These three re- 

 lated species are also dioicous, fruiting extremely rarely, H. Hlicinum 

 indeed probably never fruiting in any form such as is at all likely 

 to have given off the plant in question. 



Here again, therefore, we are confronted with the problem as 

 to why, under the theory of a fortuitous transport, north to south, 

 from like conditions to like, a counter-exchange from south to 

 north should not have occurred, and we do not find isolated species 

 of African alpine genera among the alpine mosses of Europe ; while 

 in addition the further question arises as to why, postulating aerial 

 transport by wind or by bird carriers, and failing a land connection, 



