CALAMARIEAE. 311 



There is no sufficient ground therefore for Stur's l assertion, that the presence 

 of this character on an otherwise questionable specimen is quite sufficient 

 to place it with perfect certainty in the class of Equisetaceae. Even if we 

 accept Stur's conception of the protuberances, since according to Janczewski's 

 researches branch and root spring from a common primordium, there would 

 not be three, but only two alternating rows of small knobs on the cast of the 



b b 

 pith in our genus. We should have not Stur's scheme for Equisetae a, 



but , a w >. . But there is another point to be considered. Since the leaf-scars 



must be the most conspicuous objects on the nodes of leafy stems, Stur 

 endeavours to show that the most prominent row of knobs belongs to the 

 leaves ; and this row must be the uppermost if the comparison with Equi- 

 setum is to be maintained. This is the reason why Stur, in opposition to 

 the current view, which rests, as has been shown above, on weighty argu- 

 ments, inclines to determine the direction of the stems in Calamitae in such 

 a manner that the most conspicuous, often the only recognisable, line of 

 knobs comes uppermost. But, as Weiss 2 rightly urges, this would mean 

 the insertion of the leaves on the base of the internode lying next above 

 the node. There is no need to give further proof that such an insertion is 

 not probable. But the other mode of conceiving the direction of the stems 

 results in the same improbability ; for in that case, since the commissure of 

 the bundles must be situated in the node itself, the foliar bundles must 

 originate beneath it and in a very strange position, and the comparison with 

 Equisetum, in which each trace is the continuation of an ascending strand 

 of the lower internode, could scarcely be maintained. But I have satisfied 

 myself from the radial section in the British Museum mentioned on p. 303, 

 that the leaf-trace does in fact pass outwards exactly at the level of the node. 

 Further, the examination of Equisetum supplies no reason for assuming 

 so considerable differences in height between the points of departure of the 

 traces. For these appear first on the surface of the stem in consequence of 

 the diverging course of the members ; their points of origin, alternating with 

 one another, are nearly at the same height, so that they can be encountered 

 in one and the same transverse section. Hence the points corresponding 

 to the points of departure of the traces would probably be found on a cast 

 of the pith of Equisetum in a single circle only. Lastly, Weiss 3 has brought 

 forward yet another weighty consideration. This is founded on the ex- 

 amination of the mould of a Calamites from the Museum at Halle, which 

 will have to be noticed again presently, in which the ribbing of the wood 

 and the surface with the leaves can be seen together. In this specimen from 

 six to seven leaves have dropped off at regular distances from one another on 

 the nodal line over a breadth of twenty millimetres, but there are also fourteen 



1 Stur (5), p. 1 12. 2 Weiss (5). 3 Weiss (5), pp. 28 and 65, t. i, f. i. 



