312 CALAMARIEAE. 



ribs with their knobs. Since the regularity of the arrangement appears to 

 exclude the supposition that half the leaves have dropped off, Weiss con- 

 cludes that there was only one leaf to every two ribs. But in that case the 

 leaf-traces would b,e twice as many as the leaves. This would necessarily 

 imply that the course of the strands was more complicated than we are in 

 the habit of supposing ; and this may prove to have been the case in certain 

 groups of Calamitae, for the specimen in question belongs to the Calamitinae 

 which we shall shortly have to consider. 



In contrast to all these difficulties the prominences under discussion 

 become readily intelligible, if with Williamson we see in them the traces of 

 the small medullary rays of the node, and also the substance filling the so- 

 called infranodal canals mentioned above, which, as that author has shown, 

 remain parenchymatous all through the life of the plant, and are never 

 traversed by interfascicular strands of later formation, as is the case with 

 the primary rays of the internodes. The differences also in the mode of 

 development of the prominences can on this view be sufficiently explained. 

 For if only a small portion of tissue has disappeared on their inner border, 

 then they present only flat swellings ; if more is gone and the matter filling 

 the canals is fine enough to follow such narrow passages, then the small 

 sharply defined cylinders are produced, to which Weiss has called attention. 

 Lastly, the case of most complete filling is exemplified in specimens such 

 as those figured by Williamson 1 , in connection with which Weiss' 2 remarks 

 should be consulted. A cylindrical cavity contains the narrowed conical 

 extremity of a cast of Calamites, from which thin rods of stone arranged 

 in a whorl, and spreading like the spokes of a wheel, stretch to the outer 

 wall which bounds the cavity. These rods answer to the substance which 

 filled the canals and exactly occupy their place ; there is no reason for 

 regarding them with Stur as roots. The surrounding mass of wood was 

 converted into coal, which has for the most part disappeared, though traces 

 of it are still attached to the wall of the cavity. Since the entire cavity is 

 inside a cast which is striated like a Calamites, we can only suppose that 

 the base of the particular branch was deposited in the medullary tube of a 

 broader portion of a Calamites, and in this position was inclosed in the mass 

 of mineral matter with which the latter became filled. If this supposition 

 is correct, it confirms also Williamson's view as to the direction of the 

 pieces of wood of Calamitae, which coincides with that which Weiss main- 

 tains in respect to the casts. For the disappearance of much tissue in the 

 infranodal canals will necessarily cause the formation of the more prominent 

 row of knobs ; weaker prominences on the cast will answer to the upper 

 medullary rays of the nodes filled with a less delicate parenchyma. I 

 should even conjecture that the rays which lie exactly on the level of the 



1 Williamson (1), ix, t. ai, f. 31 and (7), t. I, f. i. * Weiss (5), p. 105. 



