58 EVOLUTIOH 



The order of development, and especially the manner of 

 it, are by no means established. It is usual to speak of 

 the Bryophyta (mosses and liverworts) as developed 

 from the Algae, and leading on in turn to the ferns and 

 other Pteridophyta ; but they may be divergent de- 

 scendants of a common Alga-ancestor. In some as yet 

 unopened tomb in the geological strata we may in time 

 find the connecting links. At present we have a rapid 

 and sudden appearance of one type of plant after another. 

 The marine Algae continue in the Devonian period, and 

 the land is now overrun with giant ferns, club-mosses, 

 and horse-tails (to use the names of their small modern 

 representatives). Coniferous trees of the pine and yew 

 order appear apparently in the drier uplands as the 

 period passes into the Carboniferous, or the age of the 

 great coal forests. Then the low-lying swampy lands 

 that have emerged during the Devonian period take on a 

 mantle of the most luxuriant vegetation, and the plant 

 climbs to higher types on the rising ground beyond. 



Those sombre and fantastic forests of the Coal-age 

 have been so often described and depicted that we need 

 not dwell on them. The nearest picture we have on the 

 earth to-day is probably in the New Zealand forests of 

 araucarias and tree-ferns, but even these convey an im- 

 perfect idea. No bird as yet enlivened the stillness with 

 its song or brightened the scene with its plumage; no 

 flower relieved the dull monotony of the vegetation ; no 

 grass covered the soil; and little sunlight pierced through 

 the carbon-laden atmosphere. Ferns of all sizes, some 

 sending up their fronds to a height of twenty feet, 

 formed the great bulk of the vegetation. Lepidodendra 

 reared their huge stems, clothed in scale-like leaves and 

 ending in a massive club (giant club-mosses), to a height 

 of forty to sixty feet. Sigillaria, the giants of the 

 forests, sent up their gaunt stems to a height of seventy 



