308 FILICALES [CH. 



carried by the wind at least 25 to 30 miles. It is not surprising, 

 therefore, to find that many ferns have an almost world-wide 

 distribution; and, it may be added, in view of their efficient 

 means of dispersal, wide range by no means implies great 

 antiquity. Prof Campbell^ has recently called attention to the 

 significance of the wide distribution of Hepaticae in its bearing on 

 their antiquity; the spores are incapable of retaining vitality for 

 more than a short period, and it is argued that a world-wide 

 distribution can have been acquired only after an enormous 

 lapse of time. If we apply this reasoning to the Osmundaceae 

 among ferns, it may be legitimate to assume that their short- 

 lived green spores render them much less efficient colonisers 

 than the great majority of ferns; if this is granted, the wide 

 distribution of Osmundacequs ferns in the Mesozoic era carries 

 their history back to a still more remote past, a conclusion 

 which receives support from the records of the rocks. 



The Bracken fern which we regard as characteristically 

 British is a cosmopolitan type; it was found by Treub among 

 the pioneers, of the New Flora of Krakatau ; in British Central 

 Africa, it greets one at every turn " like a messenger from the 

 homeland 2"; it grows on the Swiss Alps, on the mountains of 

 Abyssinia, in Tasmania, and on the slopes of the Himalayas. 

 The two genera Matonia (fig. 228) and Dipteris, which grow 

 side by side on Mount Ophir in the Malay Peninsula, are examples 

 of restricted geographical range and carry us back to the Jurassic 

 period when closely allied types flourished abundantly in north- 

 ern latitudes. Similarly Thyrsopteris elegans, confined to Juan 

 Fernandez, exhibits a remarkable likeness to Jurassic species 

 from England and the Arctic regions. 



The proportion of ferns to flowering plants in recent floras is 

 a question of some interest from a palaeobotanical point of view ; 

 but we must bear in mind the fact that the evolution of 

 angiosperms, effected at a late stage in the history of the earth, 

 seriously disturbed the balance of power among competitors for 

 earth and air. The abundance of ferns in a particular region is, 

 however, an unsafe guide to geographical or climatic conditions. 

 Many ferns are essentially social plants ; the wide stretches of 

 1 Campbell (07). = Davy (07) p. 263. 



