ADDITIONS TO THE FLORA OF THE WILCOX GROUP. 



or narrowed and consisting- of only one or two 

 rows of colls. 



Radial section: Tracheids with one or two 

 rows of mostly well-spaced circular-bordered 

 pits. When in single rows the pits are some- 

 what larger, and when in double rows the pits 

 are almost invariably in pairs, although occa- 

 sionally they may alternate for a short distance, 

 as in the specimen figured; usually well- 

 spaced occasional rows are in contact, as shown 

 in the figure. The rims of Sanio are often 

 prominently shown in the sections of the tan- 

 gential walls. The septate xylem parenchyma 

 is conspicuous in this section, the partitions 

 being at right angles to the walls and from 

 three to four times the diameter or slightly 

 farther apart, usually containing more or less 

 resin. The diameter of the xylem parenchyma 

 is about the same as that of the tracheids but 

 may be slightly greater. It is not excessively 

 abundant, as hi some other species of Cupres- 

 sinoxylon, nor is it generally completely filled 

 with resin. No traumatic or other resin canals 

 are observable. Ray cells uniform in character 

 seem to be radially elongated, with a radial 

 length of li to 2 tracheid fields and a height 

 about one-fourth their length. End walls 

 smooth (without abietinean pitting), mostly 

 transverse and rarely much oblicme; one or 

 more in each ray partly resinif erous ; radial 

 walls with two small oval pits per tracheid 

 field; these pits are relatively large for this 

 genus and appear to have their long axis 

 uniformly inclined about 40° from the vertical. 



Tangential section: The distribution and 

 relative abundance and variation in the rays 

 are well shown in the figure of a large area 

 under low magnification (20 diameters). The 

 rays are uniformly uniseriate, of relatively 

 large, thin-walled, roundish quadrangular cells, 

 one or more of which may be resinif erous ; they 

 range in height from 2 to 17 cells and consist 

 prevailingly of alternations of rays 2 to 4 cells 

 high with those of rays 6 to 8 cells high. There 

 are rarely four rows of tracheids between 

 adjacent rays, the normal number being two. 

 The xylem parenchyma, as in the radial sec- 

 tions, is generally bordered by rays. The 

 tangential walls of the tracheids are marked 

 with circular-bordered pits about one-half the 

 size of the pits on the radial walls. These pits 

 are usually in a single row and well spaced, but 



they may be in juxtaposition for a short dis- 

 tance or hi double rows, either in pairs or 

 alternating for short distances, as shown in the 

 enlarged figure. In this section the rotted and 

 spirally fractured walls of the tracheids are very 

 obvious, and care is necessary to distinguish 

 them when in this condition from normal 

 spirally thickened tracheids, which are not 

 present in this genus. In this section the 

 cross sections of the bordered pits of the radial 

 walls of the tracheids often come out beauti- 

 fully, and they can even be seen in the figure 

 enlarged but 20 times. 



This well-marked species is perfectly dis- 

 tinct from Ciijinssiiiii.il/hni call!, described by 

 Knowlton 8 from material collected in beds of 

 possible Wilcox age in Arkansas. It also 

 appears to be unlike the rather numerous de- 

 scribed species of Cupressinoxylon from other 

 horizons or areas. The incompleteness of 

 large numbers of the descriptions of pre- 

 viously known forms renders detailed com- 

 parisons futile. The distinction between the 

 present species and those forms of fossil wood 

 referred to the genus Podocarpoxylon Gothan, 

 as amended by Stopes 9 to include Gothan's 

 Podocarpoxylon and Phyllocladoxylon, are not 

 especially obvious and rest on the size, form, 

 and number of the pits on the radial walls of 

 the ray cells, which are larger, fewer, and more 

 eccentric in Podocarpoxylon. More recently 

 Seward 10 has proposed the form genus Mest m- 

 brioxylon for these. These differences are all 

 relative and hardly generic in character, as a 

 series of species can be selected which connect 

 the extremes. 



In the present state of our knowledge of wood 

 anatomy, even among the comparatively well 

 known group of conifers, it is not feasible to 

 attempt to point out the most closely allied 

 existing representative of the present species. 



The genera Glyptostrobus and Taxodium are 

 represented by foliage and seeds in the Wilcox, 

 and it may well be that this abundant wood 

 type represents one or the other of these 

 genera. 



Occurrence: Caddo and De Soto parishes, 

 La. Figured specimens, northwest corner sec. 



« Knowlton, F. n., Arkansas State Geologist Ann. Eept. for 1889, 

 vol. 2, p. 254, pi. 9, figs. 3-7, 1891 . 



5 Stopes, M. C, The Cretaceous flora: British Mus. Cat., pt. 2, p. 210, 

 1915. 



10 Seward, A. C, Fossil plants, vol. 4, p. 173, 1919. 



