Fig. 122. Diagram showing the relative distribution of the main groups of plants 

 through the geological eras. The dotted lines connecting the groups and those in the 

 pre-Carboniferous are entirely theoretical, and merely indicate the conclusions reached at 

 present. The size of the surface of each group roughly indicates the part it played in the 

 flora of each period. Those with dotted surface bore seeds, the others spores. 



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