404 Mr Vernon, On the occurrence of Sckizoneura pa^^adoxa, 



grooves, which, in the best preserved specimens, appear to be 

 continuous at the node. The specimens vary greatly in size, in 

 the coarseness and fineness of the ribbing, and in the character 

 of the ribs, which are generally broad and nearly flat-topped. 

 Reversed casts also occur in which the ridges are represented by 

 grooves, causing the true grooves to stand out as narrow ridges, 

 whilst the nodal constriction is now represented by an upstanding 

 ridge. These specimens are undoubtedly Equisetaceous pith 

 casts, which, by themselves, cannot be generically identified. 



Branching. Certain specimens of the {d) type appear to be 

 casts of the pith cavity of large branches. They are gradually 

 contracted towards the base of the branch, just as is the case 

 with the medullary casts of Calamites. Large scars which occur 

 on the nodes of other casts of the {d) type may thus be inter- 

 preted as branch scars. 



Nodal Diaphragms. Some interesting examples of nodal 

 diaphragms have been collected. One specimen of the exterior 

 portion of a stem with a node shows a diaphragm displaced by 

 crushing, somewhat in the manner so often found in Equisetites 

 lateralis. Other specimens have a smooth, central concave portion, 

 bearing at the node a number of long, stout, narrow, spoke-like 

 structures which appear to be branches. 



Many of the diaphragms, apparently belonging to the under- 

 ground stem, are still in the position of growth and appear to 

 have suffered hardly any distortion. Radiating from the edge 

 of the node are four, five, sometimes six, roots which at first 

 are confined to one plane; they bear numerous branching 

 rootlets which ramify in all directions. One specimen of a small 

 diaphragm, only 12 mm. in diameter, has, attached to the node, 

 four roots which bear numerous rootlets. Another broader, thicker, 

 more woody looking structure with a smooth surface is also borne 

 at the node ; this appendage is quite different from, and very 

 much larger than the associated roots ; it appears to be a portion 

 of a stem. 



Roots. In addition to the roots described above which are 

 found still attached to the node, there are numerous examples 

 of detached fragmentary roots and rootlets, which show the same 

 characters. All possess a smooth, irregularly wrinkled, or finely 

 reticulated, external surface. Occupying the central axis of the 

 root in several specimens is a stout central structure which 

 probably represents the stele, its surface bears the imprint of 

 longitudinal and transverse lines giving an appearance strikingly 

 suggestive of cell structure. 



The rootlets differ from the roots merely in size ; the angle 

 they make with the root is sometimes 60° but usually 90°. 



