194 BAILEY AND TUPPER. 



Size of tracheary Elements in vascular Cryptogams and 



OLDER GyMNOSPERMS. 



The tracheids in the vascular cryptooams appear to have been of 

 such unusual length as to attract the attention of many paleontolo- 

 gists. The great length of the secondary tracheids in Calamites led 

 Williamson (1871) to describe them as vessels — -compound structures 

 — in one of his earlier papers. Williamson and Scott (1S94) described 

 the tracheary elements of Sphenophyllum as follows: "If they were 

 tracheids they must have been of great length, for they can often be 

 traced all through a section without finding any terminal wall." In 

 another paper, these writers (1895) stated that in Lyginodendron the 

 secondary "tracheids are of great length" and that in Heterangium 

 " their length must have been great as terminations are by no means 

 frequently seen." Williamson (1873) had previously stated in regard 

 to the tracheary elements of Dictyoxi/lon Oldhamium: "It is very 

 difficult to measure their length, because, owing to its amount which 

 is considerable, and to their interlacing freely within their respective 

 bundles, it is almost impossible to see the extremities of each fiber; 

 it is, however, sufficiently great to give them an almost vascular 

 character." Similar descriptions have been recorded by other paleon- 

 tologists. 



Through the courtesy of Drs. G. R. Wieland and E. W. Berry, the 

 writers secured the opportunity of examining sections of well preserved 

 fossil stems of various representatives of the Calamariales, Spheno- 

 phyllales, Lepidophytineae and Cycadofilices, and of verifying the 

 statements of preA'ious investigators. The tracheary elements of the 

 secondary xylem in such forms as Calamites, Sphenophyllum, Lepi- 

 dodendron, Sigillaria, Lyginodendron, Heterangium and other 

 Cycadofilices were undoubtedly very long, averaging usually several 

 millimeters. The first formed secondary tracheids appear to have been 

 as long if not longer than the primary tracheids, but the tracheids of ^ 

 nodal wood — at least in the Calamariales — were apparently some- 

 what shorter than those of the internodal wood. 



The secondary tracheary elements in li^•ing representati^■es of the 

 Cycadales, and in fossil stems of Bennettitales and Cordaitales, re- 

 semble in length the tracheids of the vascular cryptogams mentioned 

 above. Although the later formed secondary tracheids may be some- 

 what longer than those formed by the first activity of the cambium, 

 the latter — in contrast to similar elements of Ginkgo, the Coniferae 



