320 Bailey. — A Cretaceous Pity oxy Ion with Marginal Tracheides. 
sporadic occurrence of ray tracheides which has been noted by De Bary, 
Penhallow, and Gothan in certain Taxodineae and Cupressineae leads to 
the same conclusion as does the traumatic occurrence of ray tracheides which 
Jeffrey has described in Cunninghamia sinensis. 
From this we see that a careful consideration of the comparative 
anatomy and phytogeny of living and ancestral Conifers is necessary in 
studying the affinities of the remains of primitive Conifers ; that the 
anatomical features which characterize the genera of Kraus are not of con- 
stant diagnostic value in separating Conifers into natural groups of closely 
related species, and that in many cases a large number of anatomical 
characters must be considered in order to make an accurate identification 
of the remains of primitive forms. 
Before attempting to classify our fossil, therefore, it seems to be 
necessary to point out certain anatomical lines of evolution which are very 
significant and have been made clear by recent researches in the comparative 
anatomy of living Conifers. Primitive Araucarian and Abietineous Conifers, 
which strongly resembled one another, were characterized by the entire 
absence of wood parenchyma except where associated with resin canals, 
and by the presence of resin canals. In these forms the rays were charac- 
terized by the absence of ray tracheides, by thick, usually heavily pitted, ray 
parenchyma walls, and by small lateral ray pits with distinct borders upon 
the tracheide side. The disappearance of resin canals, the development of 
wood parenchyma, the reduction in the thickness of the ray parenchyma 
walls, the development of ‘ Eiporen * or non-piciform lateral ray pits, and the 
development and subsequent loss of ray tracheides are all lines of evolutionary 
modification in the development of modern Conifers. 
Lines of evolution which appear significant in the Araucarian Conifers 
are — the disappearance of resin canals and thick-walled, heavily pitted ray 
parenchyma, and the development of wood parenchyma . 1 In the case of 
the Taxodineae and Cupressineae similar lines of phylogenetic interest 
exist — the disappearance of resin canals, the development of wood paren- 
chyma, and the reduction in thickness of the ray parenchyma walls ; but to 
these must be added the loss of ray tracheides, structures which have never 
been observed in Araucarian Conifers. 
The woody structure of modern Abietineous Conifers has been evolved 
from that of their Mesozoic ancestors by the development of ray tracheides, 
by the development of wood parenchyma, except in Pinus ) and by the 
disappearance in the Abieteae of resin canals. 
In the evolution of modern White and Hard Pines certain highly 
1 In regard to the alternate and flattened bordered pits of modern Araucarians which are strongly 
contrasted to the more Abietineous type of pitting which occurs in Cretaceous genera, it seems to be 
impossible to determine in the light of present investigation whether this type of pitting is really 
homologous or merely analogous to that of the Cordaites. 
