HOLDEN. — CRETACEOUS PITYOXYL.\.. G13 



It is of interest to compare tliis type with other fossil pines. The 

 only ones described up to now with ray tracheides are Puius scituaten- 

 siformis, Bailey (5) and P. succinifcra, Conw. (4). First let us con- 

 sider the former, since it is of the same geological age as our specimen. 

 Both have a sclerified pith, large short shoots, and tyloses in the resin 

 canals. P. situatensiforviis differs from the lignite described in this 

 article in numerous features, — the ray tracheides are smooth walled, 

 the rays and abundant epithelium of the vertical canals are highly 

 resinous, the lateral pits of the rays are small and in\ariably one per 

 crossfieUl, the summer tracheides are pitted on their tangential walls, 

 and the short shoot has no axillating leaf trace. While our specimen 

 is a typical hard pine, that described by Mr. Bailey unites the char- 

 acteristics of both groups,— it has the tangential pitting and smooth 

 ray tracheides of a soft pine, with the sclerified pith of a hard. It 

 seems to be a more generalized type, perhaps representing an ancestral 

 condition before the two groups had become sharply separated. 



With P. succinifera of the early Tertiary, our lignite has more in 

 common. Both have sculptured ray tracheides in marginal and inter- 

 spersed positions; thin-walled, non-resinous ray parenchyma; septate 

 tracheides around the resin ducts, which are surrounded by thin-walled 

 heavily pitted epithelium and filled with tyloses. On the other hand, 

 as opposed to our specimen, P. succinifera has but a single row of resin 

 ducts in the first annual ring; tangential pits; tyloses in the tra- 

 cheides; ray cells with sometimes four small piciform pits to each cross- 

 field, sometimes one large fusion pit; resin canals embedded in the 

 pith, and no stone cells. Further, ray tracheides in P. succinifera 

 do not occur normally in the first few years' growth, while in our form 

 they are present in the first annual ring. 



From this comparison of P. yroiosclerointys with other similar 

 Pityoxyla it is evident that the former represents a higher and more 

 specialized type than either of the others. It has all the features of a 

 living hard pine, while the others present different combinations of the 

 features of both hard and soft. The occurrence of a completely differ- 

 entiated hard pine as far back as the Middle Cretaceous substantiates 

 the conclusion reached by Jeffrey (9) from a study of the leaves that 

 the two groups had already become separate by the Middle Creta- 

 ceous. Zeiller's description of cones of both groups from the Jurassic 

 renders it probable that the separation goes back to that epoch. An 

 interesting corollary to the presence of such a modern type of wood in 

 the Cretaceous is afforded by the modern character of the leaves of 

 Upper Cretaceous pines described by Stopes and Kershaw (10). 



