6oo 
jfeffrey , — Traumatic Ray-Tracheids in 
Still another fact must be kept in mind in this discussion, viz. that the 
wood of early Cretaceous Pines had not yet acquired the marginal tracheids 
which are found in those of late Cretaceous and later epochs (E. C. Jeffrey 
and M. A. Chrysler, On Cretaceous Pityoxyla, Bot. Gazette, vol. xlii, 
pp. 1-14). This conclusion follows not only from the study of the wood- 
structure of Lower Cretaceous Pityoxyla, but also from a consideration of 
the anatomy of the first year’s growth of vegetative branches and of that 
of the cone-axis of living Pines, where their marginal ray-tracheids are late 
in appearing (vegetative branches) or are almost entirely unrepresented 
(cone-axes). It is further significant in this connexion to note that Conwentz 
has described the very much retarded appearance of the marginal tracheids 
in the amber-containing Pityoxyla (Late Eocene or Early Oligocene) of the 
Baltic amber deposits. This author states that the marginal tracheids are 
quite absent in the earlier annual rings of the branches and only appear at 
a late stage of growth (Monographic d. Baltischen Bernsteinbaume, p. 53). 
The primitive absence of marginal ray-tracheids in the genus Pinas makes 
it still more difficult to accept the hypothesis of Penhallow (Anatomy of 
North American Gymnosperms, Am. Naturalist, vol. xxxviii, pp. 696-708. 
Manual of N. A. Gymnosperms, pp. 122-71, Boston, 1907), that this 
genus and its allied genera have come from Cupressineous or Taxodineous 
ancestors, which have developed ray-tracheids and resin-canals as well. 
Moreover Pinas , or a closely-allied genus, according to the observations 
of Goeppert (Revision meiner Arbeiten, Bot. Centralblatt, vol. V, p. 405, 
1881) and of Professor Penhallow himself (North American Species of 
Dadoxylon, Trans. Roy. Soc. Canada, ser. 2, vol. vi, 1900), already possessed 
ligneous resin-canals in the Palaeozoic. 
We can in fact only conclude from all the evidence at our disposal, that 
Pinas and its nearer allies are among the oldest of living Conifers, and that 
its ancestors possessed ligneous resin-canals already in the Upper Palaeozoic 
and Lower Mesozoic. Further it acquired marginal tracheids in the later 
Cretaceous long before the true Sequoias or their allies had come into 
existence. Since the Taxodineae and Cupressineae, according to our most 
accurate and recent information, appeared long after the Abietineae, it 
is neither necessary nor logical to consider any sporadic Abietineous 
features which they may present, such as the normal and traumatic resin- 
canals of the living species of Sequoia or the marginal ray-tracheids of 
Sciadopitys, Sequoia , Cunninghamia , Cupressus , Juniper us, and Thuya as 
indicating that the Abietineae have been derived from either of these 
groups. On the contrary, the rational explanation of these peculiar 
features of structure in the Taxodineae and Cupressineae appears to be 
that they are vestigial or reversionary structures, indicating that these 
tribes have had an Abietineous ancestry. It is clear from the palaeonto- 
logical evidence that if the two tribes in question came from the Abietineae, 
