164 EDWARD C. JEFFREY ON 



appearance. Sucli cavities were considered to l)e definite canals by Williamson (o/;. cit., 

 1871, 1878), and he accordingly called them infranodal canals. He expressed the opinion 

 that the larger series of tubercles described aJjove, as occurring on the pith-casts of Cala- 

 mites ai"e moulds of these canals in stone. Subsequently in collaboration with Scott (Phil, 

 trans, roy. soc, 1894, B., plate 78, fig. 11) he published a figure, which is reproduced in 

 our photograph G (PI. 27, fig. 6), which may be considered as representing a tangential 

 plane of section, somewhere between those of the two former figures, reproduced in our 

 photographs 4 and 5 (Pi. 27, fig. 4, 5). In this figure the traces making their exit in 

 the superior medullary rays, are no longer considered as belonging to branches, but on 

 the contrary to leaves (Phil, trans, roy. soc, 1894, B., p. 876). 



Stur (op. cit.) from the study of the casts of various Calamites and of the stem of 

 their modern representatives, the Equiseta has reached certain conclusions whicli it will 

 not be profitable to consider fully. He states, however, that Williamson's figure, repro- 

 duced in our photograph 4 (PI. 27, fig. 4), is inverted, and that the areas of disintegrated 

 parenchyma, which by the inversion of the figure in question, he places in the upper 

 medullary rays are due to the disappearance of leaf-traces. He enforces this contention 

 by objecting that Williamson's figures make the branches arise above the node and not 

 below it, as he thinks should be the case, from the analogy of Equisetum. He comes 

 to the conclusion that the infranodal canals of Williamson are consequently supranodal 

 indications of leaf-traces, and that the large nodules of calamitean casts, already referred 

 to, are as a result above the node, which hardily follows from his course of argument. It 

 is, moreover, in many cases certain that the larger nodules are below the nodal constric- 

 tions of the casts, for reasons which have been already indicated. 



Weiss (Steinkohlen-Calamarien, Heft 2) has more recently discussed the vexed ques- 

 tion of the tubercles, and after calling attention to Stur's inversion of the casts, expresses 

 his opinion that the disputed nodules, probably represent the points of attachment of 

 either roots or leaves. He realizes that their occurrence below the nodes, and in alterna- 

 tion with the' vascular strands, makes it difficult to regard them as related to the leaves. 

 This would seem to lead to the alternative, that they are the indications of the attach- 

 ments of roots. He does not draw this inference, however, although he records the fact 

 that the nodules are absent entirely, or very imperfectly represented, on parts of Cala- 

 mites which are undoubtedly aerial (oj). cit., \'>.2i) . He leaves the question of their 

 interpretation open, having previously stated that he does not i-egard the nodules as casts 

 of Williamson's infranodal canals. 



Solms-Laubach (Fossil botany, Eng. ed., p. 301-315) discusses at length the organiza- 

 tion of the calamitean stem, and the nature of calamitean casts. As a result of the con- 

 sideration of all the evidence, he comes to the conclusion, that the more conspicuous 



