1906] JEFFREY & CHRYSLER—CRETACEOUS PITYOXYLA 7 
bordered pits in the tracheids of the hard pines are an ancestral 
feature. It is accordingly not surprising to find them more com- 
monly present in older types of hard pines than those now living. 
CONWENTZ in his admirably accurate and thorough account of the 
wood of Pinus succinifera notes their invariable presence in this 
species, which on account of its denticulate marginal ray-tracheids 
must be considered to belong to the hard pines. As has already been 
pointed out, the structure of the associated leaf fascicles and cone 
scales leads to the conclusion that the Cretaceous Pityoxylon under 
discussion belongs also to a hard pine. The mode of occurrence of 
the resin canals in the medullary crown, which is illustrated in jig. 
2, is also that which is characteristic of the hard pines. 
The most reliable feature of difference separating histologically 
the hard pines from the soft pines is the occurrence of denticulate 
marginal tracheids in the former group. In the soft pines the mar- 
ginal tracheids are entirely without denticulations. In our Pity- 
oxylon, as has been shown above, marginal tracheids of any kind 
are quite absent; so that it is not possible on this feature to diagnose 
the affinity of our material with either of the two main groups of 
pines still living. It is of interest to note that the Cretaceous Pity- 
oxylon under discussion has the general structure of the rays found 
in Abies or Pseudolarix, with the wood structure found in Tertiary 
and modern species of Pinus. There can be little doubt that in the 
peculiar structure of the rays we have to do with an ancestral feature; 
for if we take for example a modern species of Pinus, in which the 
marginal tracheids are well developed even in the first annual ring, 
such as P. palustris, we find the marginal tracheary cells entirely 
absent in most of the rays of the two annual rings of the female 
cone. It is well known that in many of the modern species of Pinus 
the marginal tracheary ray-cells do not appear until the branch 
is from one to several years old. The same feature, if one may 
judge from CoNweENtTz’ description, was also present to an even 
more marked degree in the Baltic amber pines, which are considered 
by CoNnWENTz to belong to the early Oligocene or late Eocene. 
Another feature of striking resemblance presented by the wood 
of the cones only of existing species of Pinus, to the vegetative woods 
of Cretaceous Pityoxyla which we have investigated, is the highly 
