Elkins and Wieland — On Devonian Wood. 71 



the normal wood tracheid where, presumably owing to termina- 

 tion of a ray cell, two of the largest single groups coalesce ; 

 they may be crowded or lie well apart. Several examples like 

 the following have been noted : two distinct radial bands 

 gradually approach each other, coalesce for the distance of 

 several tracheids, then part, resuming their separate identities. 

 Along the line of coalescence occur the large or double groups 

 of pits. In the main, however, the radial grouping of the pits 

 is the most striking feature of the wood, appearing with great 

 regularity over large areas of the radial section. The pit groups 

 are normally separated by about the width of a ray cell, and 

 the radial surface of the tracheids between the groups is finely 

 but characteristically rugose. Furthermore, the dominance of 

 the group system of pits is conditioned by induration and 

 thickening of the appressed tracheid walls between the groups, 

 with presence of intercellular spaces. This feature is quite 

 apparent under even low powers, and so definite that it may 

 be studied to advantage with a 1/12 oil immersion and 

 ocular 5. In the tangential section a spindle-shaped interspace 

 may mark the point of tracheid wall thickening between the 

 pit groups. 



The bordered pits are circular or elliptical in outline, occa- 

 sionally irregularly flattened. The hexagonal form, which is 

 reputed to be a constant feature of Cordaitean bordered pits, 

 appears to be wanting here. Even when the pits are very 

 close together they maintain their circular outline (figure 4 and 

 5, photomicrograph 4). Occasionally pits occur which might 

 be considered hexagonal, though such are not a striking fea- 

 ture (photomicrograph 4). The oblique slit-like opening extends 

 nearly the full diameter of the pit and lies at right angles to 

 the corresponding orifice in the wall of the adjacent tracheid, 

 thus presenting a cross-like arrangement to the eye. And in 

 the sections where the slits cross there is formed a rhombic 

 perforation of the paired pits across which one looks through 



Fig. 6. Detail of transverse section. Note the- bordered pits, b, and the 

 middle lamella, I. x 240. 



Fig. 7. Tangential section of wood, x 30 ± . [Another area is shown 

 x 105 by Wieland as fig. 43 of his American Fossil Cycads.] 



Fig. 8. Detail of tangential section showing two medullary rays and por- 

 tions of tracheids with the actual distribution of the bordered and semi- 

 bordered pits. 6, bordered pits ; &', semi-bordered pits connecting tracheid 

 and ray cell. The middle lamella is not distinct in this section, x 120. 



Fig. 9. Outlines of ray cells and tracheids showing their arrangement, 

 x 30. 



Fig. 10. Eadial section of wood, Detail of ray cells showing the semi- 

 bordered pits, also indicated in fig. 8. The vertical dotted lines indicate 

 tracheid walls, x 240. 



Fig. 11. Radial section detail showing ray three cells in height cross- 

 ing pitted tracheids. Lower ray cells thicker walled with considerable inter- 

 cellular space next the tracheids ; middle ray cells squarish, and containing 

 tyloses. Other ray cells with much vacuolated resin attached to cell walls. 

 Resin vacuoles of upper ray cell all on cell wall, not in interior. 



