C. J. Hylander — Mid-Devonian Callixylon. 317 



This Cordaite is not likely to be as old as the Paleopitys 

 Milleri of the Old Red of Scotland; 2 and, incidentally, even 

 the wood-cuts of the latter given by Hugh Miller in the 'Testi- 

 mony of the Rocks,' fig. 3, permit fair judgment of the main 

 features. It is seen that the pitting is of the Dadoxylon type 

 (2 to 3-seriate), and the rays thin (uniseriate), as Miller 

 discerned. 



'The fossil botanist on taking leave of the lower Carboniferous 

 beds, quits the dry land and puts out to sea. ' So wrote the stylist 

 of Cromarty over seventy years ago ; and while not intended in 

 the very severest literal sense, the epigram was long justified. But 

 new methods of study and new discoveries have broadened the 

 paleobotanic horizon, and helped to give material once thought 

 inadequate, high value as evidence of structure, or distribution, 

 or both. Perhaps no further answer is needed to any question 

 why the fossil tree type here described was not earlier taken up." 



Structure. 



The tracheids of the sections cited are mostly rectangu- 

 lar in cross-section, and vary much in size. The average 

 is thirty-five to forty-five microns across, in this respect 

 differing sharply from the larger tracheids of Callixylon 

 Oweni (3), which run from forty-five to sixty microns 

 across. The walls appear thick, from three to five 

 microns. In radial longitudinal section, the tracheids 

 show the chief characteristic of the genus — the bordered 

 pits of the radial walls, aligned in discontinuous groups. 

 As in Callixylon Oweni (3), the pits are circular or 

 irregularly elliptical in outline, and occur in a varying 

 number of vertical rows, from one to three (in rare 

 instances, four). These vertical rows of pits are rather 

 closely set, without compression to marked hexagonal 

 form, in the groups as aligned in radial bands that corre- 

 spond to the bands of pit groups on the neighboring 

 tracheid. Only in a few places in the Eighteen Mile 

 Creek material is the grouping of the pits fully visible 

 over any great area; the best area of preservation is 

 shown in fig. 2. These features can of course only appear 

 to advantage where there is little compression and the 

 section cuts closely to the true radial wood lines. 



2 McNab, W. E. : On the Structure of a Lignite from the Old Bed Sand- 

 stone; Trans. Bot. Soc. of Edinburgh, vol. 10, p. 312. 



Am. Jour. Sci.— Fifth Series, Vol. IV, No. 22.— October, 1922. 

 21 



