368 ISLAJND LIFE 



The distribution of the non-European genera of 

 HepaticsG is as follows : — 



Chasmatocolia. South America and Ireland. 



AcROBOLBUs. A small genus found only in New Zealand and the 

 adjacent islands, besides Ireland. 



Petalophyllum. a small genus confined to Australia and New Zealand 

 in the southern hemisphere, Algeria, and Ireland in the northern. We 

 have also one of the Hepaticse — 3lastigo2)hora Woodsii — found in Ireland 

 and the Himalayas, but unknown in any part of continental Europe. 

 The genus is most developed in New Zealand. 



These are certainly very interesting facts, but they are 

 by no means so exceptional in this group of plants as 

 to throw any doubt upon their accuracy. The Atlantic 

 islands present very similar phenomena in the Rhamphi- 

 dium purpuratum, whose nearest allies are in the West 

 Indies and South America ; and in three species of 

 Sciaromium, whose only allies are in New Zealand, 

 Tasmania, and the Andes to Patagonia. An analogous 

 and equally curious fact is the occurrence in the Drontheim 

 mountains in Central Norway, of a little group of four or 

 five peculiar species of mosses of the genus Mnium, which 

 are found nowhere else ; although the genus extends 

 over Europe, India, and Japan to the southern hemi- 

 sphere.^ 



Such facts show us the wonderful delicacy of the balance 

 of conditions which determine the existence of particular 

 species in any locality. The spores of mosses and 

 Hepaticse are so minute that they must be continually 

 carried through the air to great distances, and we can 

 hardly doubt that, so far as its powers of diffusion are 

 concerned, any species which fruits freely might soon 

 spread itself over the whole world. That they do 

 not do so must depend on peculiarities of habit and con- 

 stitution, which fit the different species for restricted 

 stations and special climatic conditions ; and according as 

 the adaptation is more general, or the degree of special- 

 isation extreme, species will have wide or restricted ranges. 

 Although their fossil remains have been rarely detected, 

 we can hardly doubt that mosses have as high an antiquity 



^ I am indebted to Mr. Mitten for this curious fact. . 



