266 PROF. W. C. WILLIAMSON ON THE 



form. At tlie same time these are merely fusiform 

 cells, not lignified fibres. The difference between them 

 and what are found in fig. 4, g^\ g" , is merely a morpho- 

 logical one, probably of small physiological import; 

 nevertheless we have here a true Calamite possessing 

 one of the distinctive morphological features supposed by 

 Brongniart to be characteristic of Calamodendron. 



The vessels of the vascular wedge, c, c, are identical in 

 their arrangement, and in the distribution of their secondary 

 medullary rays, /, with what we find in ordinary Calamites. 

 Structurally, however, these vessels present a peculiarity. 

 Instead of their walls being transversely barred round 

 their entire circumference, they are reticulated, and appa- 

 rently only on those sides of each vessel that are parallel 

 to the secondary medullary rays. There is, however, 

 nothing in these reticulations, beyond their positions, to 

 identify them with the true bordered pits of the Gymno- 

 sperms. These reticulated tracheids are very common in 

 other Carboniferous Cryptogams. 



At fig. 5, g" g" , we see traces of special parenchymatous 

 rays passing outwards through the prosenchymatous tissue. 



Turning to fig. 6, where we have a similiar cubic block 

 from the Calamodendron striatum of Autun, we have 

 further peculiar features of resemblance and of differ- 

 entiation. 



As before, the central division of the transverse section, 

 c, is the vascular wedge, made up of numerous radial 

 lamellae consisting of very large vessels separated by very 

 conspicuous secondary medullary rays, /, the latter usually 

 consisting of two rows of cells which frequently separate 

 isolated single vascular lamellse from one another. A 

 little less frequently we have two and occasionally even 

 three such rows of vessels between each two medullary rays. 

 Turning to the longitudinal section, c', we find the vessels 



