1915] BURLINGAME—ARAUCARIANS 19 
It is obvious that forms intermediate in character may be inter- 
preted as araucarians that are being modified in the direction of the 
abietineans (70), or as pines that are about to be transformed into 
araucarians (32, 34, 35). It appears (70) that the older forms are 
more like the araucarians, while the later ones resemble the pines 
more closely. The geological sequence thus appears to be in favor 
of the origin of pinelike conifers from araucarian ancestors. 
Recently evidence (75) has been adduced to show that marginal 
ray tracheids have arisen through a modification of the tracheids 
of the wood, and not by a transformation of parenchymatous cells. 
The oldest known forms with ray tracheids do not antedate the 
Cretaceous. Since the Araucarineae are known with great cer- 
tainty from the Jurassic and probably from earlier strata, the geo- 
logical evidence appears to favor the view that thin-walled unpitted 
ray cells are the primitive type. 
e albuminous cells of the phloem have been considered (13, 
65, 75) homologous with the ray tracheids. Their absence from 
the Araucarineae, accordingly, has been interpreted (70) in the 
same way. 
Annual rings are absent or feebly developed in the Cordaitales 
and in most Araucarineae, though Stopes (64) has recently reported 
a cretaceous Araucarioxylon from New Zealand with very definite 
growth rings. 
Aside from the structure of the seed itself, the ovulate cone of 
Araucaria is nearer to that of the Cordaitales than are those of the 
Abietineae. The essential feature of the cordaitean cone is that 
the single seed is borne on an axis standing in the axil of a bract. 
The seed-bearing axis is not always axillary if one may trust the 
illustrations (16). In some cases the bract appears to be borne 
on the seed stalk. The seed itself is terminal and erect. The cone 
of Araucaria differs in that the bract and axis are much more inti- 
mately associated and in that the ovule is inverted and not terminal. 
There are at least three obvious interpretations of the cordaitean 
cone. First, one may suppose the cone to be simple, consisting 
of an axis covered with branched sporophylls, some of which are 
Sterile and some fertile. Secondly, one may suppose that the cone 
is compound and that the ovule is borne directly on the branch 
