FERNS, FERN ALLIES, AND FOSSILS. 287 



has become of those vanquished floras, which once 

 formed primaeval forests entirely by themselves. 



The series of changes may be compared to successive 

 waves of development, which either ingulfed the former 

 floras, or drove them aside, out of the way, into places 

 not worth colonising. In this respect, they have a 

 certain analogy to waves of human migration. 



We will assume the succession to have been Algae, 

 Lichens, Mosses, Ferns, Lycopods, Tree-Ferns, Horse- 

 tails, Cycads and archaic Conifers, and, finally, the 

 modern Pines, Monocotyledons and Dicotyledons. We 

 now find the Algae confined to water and moist places 

 unfit for any other plants. Lichens and Mosses occur 

 either on bare rocks and vacant places, or on the trunks 

 of trees, and on the ground in woods and other places, 

 where they are occupied in assisting the higher associa- 

 tions of plants. In the latter case, they have been brought 

 under the Forest trees, and become subordinate to the 

 wood flora. Upon rocks and walls, they are still in the 

 sort of country in which their ancestors existed. Pre- 

 cisely the same may be said of the Ferns. The Bracken, 

 Male-Fern, and Lady-Fem are now humble assistants to 

 the forest trees, Pine, Oak, etc. ; but a few, such as the 

 Woodsias, Ceterach, and others, occur at considerable alti- 

 tudes in the Highlands, though they are not able to bear 

 the conditions which suit Alpine mosses and lichens. 

 The CLubmosses have been somewhat unfortunate. Many 

 of the tropical species are found on trees and branches 

 in the jungles. The few British species are only 

 common on the hills, but may sometimes be found near 

 the sea or at comparatively low levels. Equisetuin has 

 been driven to the water, or to very barren ground, 

 where it is able to grow in places that can be colonised 

 by almost no other plant. As soon as it has improved 



