OF LOWER GREEXSAND PLANTS. 95 



men is really not only undeveloped but truly primitive, for he 

 concludes that " the occurrence of ray-tracheids in this Cre- 

 taceous pine indicates that the development of these structures 

 occurred in the Upper Cretaceous, and not, as has been supposed, 

 in the Tertiary." Reference to the American species will be 

 made in more detail when describing the individual new species. 

 The presence of well-developed ray-tracheids in the new British 

 Aptian fossils carries back this supposed modern feature further 

 than was anticipated. 



With the species of Pityoxylon here described and the Arctic 

 forms described by Gothan (1910A) a comparison would be of 

 interest, but little can be done in this direction because the new 

 Lower Greensand forms all show well-developed ray-tracheids, 

 which are unrepresented in Gothan's species. His Piceoxylon 

 antiquius differs from any of the species now described in 

 having neither ray-tracheids nor tangential pits in the tracheid- 

 walls. This species is supposed by Gothan (p. 21) to be the 

 oldest undoubted wood of abietinean affinity, and is stated 

 to be of Upper Jurassic age. One must, however, note the 

 criticisms of the stratigraphy raised by Burckhardt (1911); 

 see p. 68 of the present work. It seems to be not unlikely 

 that the three Pinus-like members of the genus Pityoxylon 

 described below are the oldest unquestionable wood-remains 

 of truly Finus-like character. 



Pityoxylon Sewardi, sp. nov. 

 [Plates IV & V ; text-figs. 23 & 24.] 



Diagnosis. Secondary wood with the characters of Pity- 

 oxylon, Kraus. The type is part of a trunk not less than 

 18 cm. (and probably more) in diameter. Growth-rings well 

 marked, large. Tracheid-walls rounded at the corners, tracheids 

 up to 25 x 30 fj. in diameter. Bordered pits on radial walls in 

 single rows, border tilling the wall, in most cases each pit 

 isolated from the next one by about the diameter of the border. 

 Parenchyma grouped round resin-canals; cells large, many con- 

 taining resin. Resin-canals vertical and horizontal, isolated all 

 through the wood, and in tangential groups of 2-4 in the outer 

 part of the autumn wood. Single resin-canals up to 170 p in 

 diameter ; epithelium apparently thin-walled. Some canals 



