106 THE EVOLUTION OF PLANTS 



tiful, much divided fronds, like those of some 

 finely cut Asplenium or Davallia, but with the 

 main stalk forked, a characteristic feature (see 

 fig. 12). These great fronds were arranged 

 spirally on the stem. Their external features 

 were well known for many years before the stem 

 which bore them was discovered. The little 

 leaflets were rather thick, and curved in at the 

 edges, characters which (together with the in- 

 ternal structure) suggest that the plant grew 

 either in dry places or, as is much more probable, 

 in a salt swamp. The stem gave rise to a number 

 of roots, which seem to have been aerial in their 

 upper part, growing downwards until they reached 

 the soil and began to branch. 



The anatomical structure of all these organs 

 is quite well known, for fragments of all of them 

 occur in abundance and beautifully preserved 

 in the "coal-balls" or calcareous nodules of cer- 

 tain seams of coal hi Lancashire and Yorkshire. 

 We will not dwell on the anatomy here, for it 

 would detain us too long. The structure of the 

 stem when young was remarkably like that of 

 the Royal Fern, Osmunda; with increasing age, 

 however, a broad zone of secondary wood and 

 bast was added by a cambium, the cells of which, 

 delicate as they were, are often quite well pre- 

 served. In the older condition there thus came 

 to be a considerable resemblance to the structure 



