368 ISLAND LIFE 



Petalophyllum. a small genxis confined to Australia and New Zealand 

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

 have 'also one of the Hepaticte — Mastigojiliora JVoodsii — 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 gTonp of plants as to 

 throw any donbt upon their accuracy. The Atlantic islands 

 present very similar phenomena in the B.liaiwphiclmm 

 pmjmratum, 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 

 of Bogota. 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 

 the southern hemisphere, but always represented by a 

 very few wide-ranging sjDecies except in this one mountain 

 group ! ^ 



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 tliat 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 

 as ferns or Lycopods ; and coupling this antiquity with 

 their great powers of dispersal we may understand how 

 many of the genera have come to occupy a number of 

 detached areas scattered over the whole earth, but 



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



