204 DESCRIPTIVE CATALOGFE 



spiralaires, surtout quand le bois etait en voie de decomposition 

 avant sa fossilisation." 



The difficulty of distinguishing between the spiral markings 

 and splitting of semi-decayed tracheid- walls, which can be seen 

 in any conifer, and the true tertiary spirals characteristic of 

 the Taxacete, has led to a number of determinations among 

 fossils which cannot be accepted. Schimper & Schenk (1890, 

 p. 849) point out how few of the described species of Taxoxylon 

 can remain in the genus. In Gothan's recent work (1905) he 

 devotes a section to a consideration of the Taxacese, and retains 

 Unger's Taxoxylon, ex parte, for all the forms in which true 

 spiral thickening in the secondary tracheids can be recognised. 



The number of such fossils is small, the " genus " Taxo.ri//H 

 being very much smaller than the other four major genera of 

 coniferous woods (see p. 64). The species on which any 

 reliance can be placed are of Tertiary age, though a few Cn-ta- 

 ceous Taxoxylons have been described, e. g. Taxcxylon cretacexm, 

 linger (1859, p. 281), which was put in tW/VM-y/o/i by Kraus. 

 I do not know of any well-petrified fossil wood of Lower 

 Cretaceous age which can certainly be placed in this genus. 

 Foliage impressions, however (see p. 20!)), have been described 

 which are reliably identified as Taxus, Cephalotaxug, and other 

 Taxaceous genera, proving the family to be well represented 1y 

 Lower Cretaceous times. 



Taxoxylon anglicum, sp. nov. 

 [Plate XIX, figs. 1-3 ; text-fig. 59.J 



Diagnosis. Coniferous wood of regular texture ; resin-canals 

 entirely absent. Annual rings fairly well marked; zone of 

 autumn wood narrow. Tracheids very regularly arranged, up 

 to 40 /z in diameter ; cell-walls, even of spring tracheids, rather 

 thick, and walls rounded off at the corners. Bordered pits 

 round, isolated, in one row, with circular pores ; rims of Sanio 

 evident. Fine spiral thickenings on the walls of tracheids. 

 Resin-containing xylem-parenchyma apparently absent. Medul- 

 lary rays uniseriate; cells apparently all alike, though some 

 have more resinous contents. Walls somewhat thickened, but 

 apparently smooth and without abietinean pitting, end-walls 

 curved or at an angle. In the radial walls are small groups 



