

* It is an unsettled point amongst vegetable palaeontologists whether 

 the stems of Calamites, in their natural condition, possessed a smooth or 

 a furrowed bark. Some contend that the outer surface of the stem was 

 longitudinally furrowed, others that it was quite smooth, and that the 

 furrows have been imparted by external pressure, or even that the fluted 

 casts, which are of so common occurrence, are merely the internal casts 

 of the hollow stems. But it is generally admitted that when Calamites 

 occur as mere casts or impressions they almost invariably show a fluted 

 exterior. Hence, in dealing with fossils in this condition * (a condition in 

 which all the specimens mentioned in these notes occur), the furrowing 

 of the stem becomes of generic value, whatever structure the outer surface 

 of the stems may have had when growing. 



308 Mr. R. Kidston on the Affinities of the 



than merely indicate its nature to have been that of a Calami- 



taceous plant. 



The characters by which Ave are enabled to show its more 



particular affinity are the leaves, fruit, and stem. 



The foliage is distinctly cliohotomous in its structure, as 



seen in the example from Eskdale. • 



The furrows on the stem are too indistinct to show whether 



or not they alternate at the nodes*. 



The segments composing the fruit must, however, be re- 

 garded as the homologues of the internodes of the stem, so,^ 

 in all likelihood, the longitudinal ridges of the segments of 

 the fruit represent the furrows of the stem. 



In the spike we see that the longitudinal rows of sporangia 

 do not alternate at the nodes, but pass continuously through- 

 out the whole fruit. 



In the genus Bornia, F.A.Rom. (Archceocalamites, Stur), 



the furrows on the stem do not alternate at the nodes as in 

 ordinary Calamites ; and this well-marked character, possessed 

 by no other carboniferous fossil plant, so far as I am aware, 

 gives it an individuality which cannot be mistaken. Like- 

 wise in Pothocites we find that the longitudinal elevations 

 which bear sporangia do not alternate at the nodes, but pass 

 continuously throughout the whole length of the spike ; and 

 these ridges, I believe, are simply a modification of the furrows 

 of the stem. 



In the genus Calamites, where the furrows on the stem 

 alternate at the nodes, we have no reason to suppose that this 

 character would alter, even were they known to produce a 

 Pothocites-iike, cone. But the fruit of the Calamites is well 

 known ; and whatever specific differences there may be in the 

 described genera and species of their fructification, they are 

 always of the Volkmannia type ; hence it is not at all pro- 

 bable that Pothocites belongs to this group of the Calamiteas. 



The dichotomous nature of the foliage is not, however, re- 

 stricted to the genus Bornia. 



