THE GENUS EQU FSKTUM. 



17!) 



position. It can be only in one of two ways: they innsf puss up on either the inside or 

 the outside of the nodal wood. But before considering either of these possibilities, one of 

 their figures (op. cit., pi. 78, fig. 7) shows the leaf-trace running directly outwards from 

 die protoxylem of the lower vascular strand and consequently below the node. Tin's is a 



difficulty in connect ion with either of the above Suggestions. Let us suppose thiit it, does 



not exist, however, and imagine the Leaf-trace to pass upwards inside the nodal wood. 

 But this would involve the presence of ringed and spiral woody elements on the inside 

 of the nodal wood, since the leaf-trace consists largely of these elements. They state, 

 however (op. dt., p. 872 and 877), that protoxylem is absent from the inside of the 

 nodal wood of the Calamites just as it is in Equisetum. These difficulties make us turn to 

 the other alternative, that the leaf-traces pass to their supranodal position on the outside 

 of the nodal wood. Photograph 4 (PI. 27, fig. 4) is a reproduction of a figure from one 

 of Williamson's memoirs (Phil, trans, roy. soc, 1871, pi. 2G, fig. 22). The section which 

 it represents is so profoundly tangential that the carina! canals of the protoxylem are laid 

 open. The so-called leaf-traces are nevertheless already in their supranodal position, and 

 consequently cannot have passed up external to the node. If, in spite of all these difficulties, 

 the leaf-traces are still maintained to start outwards in the lower ends of the supranodal 

 medullary rays, other difficulties make their appearance. All figures which indicate the 

 internal relations of calamitean branches represent their vascular strands as running in the 

 medullary rays and at the same time above the nodal wood. Since, according to William- 

 son's and Scott's statement (op, cit., 1894, B., pi. 78, fig. 11), the leaf-traces also run in 

 the same rays and in the same relation to the nodes, the branches must originate in the 

 axils of the leaves, which is not only contrary to the arrangement in Equisetum, where the 

 branches originate between the leaf-traces, but also to the statements of Williamson and 

 Scott themselves (op. cit., p. 864, 868, 890) that a similar state of affairs obtained in the 

 Calamites. There is, in fact (Williamson, oj). cit., 1871, pi. 28, fig. 38), a figure of a 

 branch in this anomalous position in one of Williamson's older memoirs, but the joint 

 authors of the later memoir already referred to (op. cit., 1894, B., p. 890) tell us that 

 this represents an arrangement which was exceptional. It is not easy to see, however, 

 why it should not have been present whenever the strands alternated at the node, as they 

 inform us they generally did (op. cit., p. 868, 876, 877), since in such cases the leaf-traces 

 and the branch-traces would both run, according to their descriptions, in the superior 

 medullary rays. If we return to Williamson's original statements (op. cit., 1871 and 

 1878) that the strands running in the upper medullary rays belonged to branches, the 

 difficulties are just as great ; for here, too, since the strands of the lower internode gener- 

 ally alternated with those of the upper, the branch falling in the interval between the two 

 upper strands would be exactly over a lower strand, but from the lower strand the leaf- 



