CALAMARIEAE. 313 



node and give passage to the traces, will usually leave no knobs behind them 

 on the cast, but that the weak protuberances of the upper internode indicate 

 the lower extremities of its primary rays. In that case the points of emer- 

 gence of the vascular bundles would be in the middle between the two rows 

 of knobs, and this would agree well with the description given on page 303. 



The essential points in all these relations have been correctly recognised 

 and explained by Williamson. But while the whole formation appears to 

 me to rest upon the more or less complete filling up of cavities or depres- 

 sions caused simply by unequal maceration, he inclines to see in them 

 characteristic relations of organisation, the importance of which to the 

 plant has yet to be more fully explained. And though he has since l fully 

 recognised the fact that the lateral branches, the roots and the transverse 

 sections of the trace-bundles appear in the small medullary rays of its 

 upper circle, he still thinks that the canals in the rays of the lower series 

 must have had an important function to perform ; otherwise they would not 

 have remained unchanged throughout the entire thickness of the secondary 

 growth, for this is never the case to the same extent with the primary rays 

 of the internodes. 



All that has hitherto been advanced may serve at least to show how 

 difficult it is even in the case of normal ordinary structure to explain the 

 mutual relations of the wood and casts of our Calamitae, as we have them 

 separated from one another ; and that attempts at similar explanations 

 where the cases are anomalous must be hopeless from the first, so long as 

 we have no greater number of investigations into their anatomy to assist 

 us. But at present I only know of one tangential preparation of the kind, 

 which is preserved in the British Museum and was noticed above on page 

 305 ; my examination of it, though only cursory, led me to the results 

 there indicated. Nothing would be gained by a minute consideration of 

 the constructions which Stur has obtained from the position of the nodal 

 prominences ; it will be sufficient to notice briefly his main results. Further 

 information will be found in his publications 2 . The trace-scheme which he 

 gives for the positions in ordinary Calamitae, in which there is no alternation, 



B B B B 



is A , and in Archaeocalamites radiatus w , but the latter is contested 



w w A W w 



by Rothpletz 3 on the strength of fresh observations and is replaced by A t 



B B 



I have never had opportunity to examine specimens in the high state of 

 preservation necessary for these observations. While then Stur contrasts 

 the course of the strands in Archaeocalamites with that in Equisetum, as 

 he has construed it, he endeavours in a detailed discussion of the subject 4 

 to show the possibility of a gradual transition of the one into the other 



1 Williamson (1), IX. 3 Stur (5), (8), (9). 3 Rothpletz (1), pp. 5, 6. 4 Stur (5), p. 558. 



