SILURIAN PERIOD 
And surface cells compressing formed a skin, 
A shield and cover to the cells within : 
And inner cells, in different parts, combined 
Organs to form, each with its work assigned ; 155 
Till root, and stem, and leaf distinct outstood, 
Each with its functions for the whole plant's good. 
Small liverworts perchance here took the lead, 
And slowly graced the mountain and the mead. 
And still a wondrous inner work went on, 1 60 
Till cells compressed to vessel tissue won 
A strength and power for the plant to rise, 
And glory in a greater height and size ; 
And fern-like plants, by fibrous folds upheld, 
Proclaimed the progress of the leafy world. 165 
In due time then the grander growths upstood, 
With fibrous tissue thickened into wood. 
Along Silurian weed-encumbered strands, 
Lake margins, fluvial flats, and boggy lands, 
Some fern-like rhizocarps are now in view, 170 
With whorls of wedge-shaped leaves of sombre hue. 
Club-moss-like growths, like little trees upstand, 
Seeming the chiefs of leafy life on land. 
And reedy growths are also thriving here, 
Whose stems with rings of spiky leaves appear. 175 
And many a wild, that in the past had been 
O'errun with puny weeds, in wealth is seen. 
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