24 THE GEOLOGICAL fflSTOEY OF PLANTS. 



1 ginning of the Silurian age and to have finally disap- 

 j peared in the early Brian, are altogether distinct from 

 any form of vegetation hitherto known, and are possibly 

 ! survivors of that prototypal flora to which I have already 

 jreferred. They are trees of large size, with a coaly bark 

 and large spreading roots, having the surface of the stem 

 smooth or irregularly ribbed, but with a nodose or Jointed 

 appearance. Internally, they show a tissue of long, cylin- 

 drical tubes, traversed by a complex network of horizontal 

 tubes thinner walled and of smaller size. The tubes are 

 arranged in concentric zones, which, if annual rings, would 

 in some specimens indicate an age of one hundred and 

 fifty years. There are also radiating spaces, which I was 

 at first disposed to regard as true medullary rays, or which 

 at least indicate a radiating arrangement of the tissue. 

 They now seem to be spaces extending from the centre 

 towards the circumference of the stem, and to have con- 

 tained bundles of tubes gathered from the general tissue 

 and extending outward perhaps to organs or appendages 

 on the surface. Carruthers has suggested a resemblance 

 to Algae, and has even proposed to change the name to 

 Nematophycus, or "thread -sea- weed"; but the resem- 

 blance is by no means clear, and it would be quite as rea- 

 sonable to compare the tissue to that of some Pungi or Li- 

 chens, or even to suppose that a plant composed of cylin- 

 drical tubes has been penetrated by the mycelium or spawn 

 of a dry-rot fungus. But the tissues are too constant and 

 too manifestly connected with each other to justify this 

 last supposition. That the plant grew on land I cannot 

 doubt, from its mode of occurrence ; that it was of dura- 

 ble and resisting character is shown by its state of preser- 

 vation ; and the structure of the seeds called Pachytheca, 

 with their constant association with these trees, give coun- 

 tenance to the belief that they are the fruit of Nema- 

 tophyton. Of the foliage or fronds of these strange 

 plants we unfortunately know nothing. They seem, how- 



