Contributions to the Anatomy of Mesozoic Conifers. 
No. I. Jurassic Coniferous Woods from Yorkshire . 1 
BY 
RUTH HOLDEN, 
Wilby Prize Student of Radcliffe College . 
With Plates XXXIX and XL. 
URING the last few years, a large number of Cretaceous woods have 
been investigated anatomically, and found to throw considerable light 
on the inter-relationships of the various families of Conifers. Structurally 
preserved material from the Jurassic is comparatively rarer and less known, 
but seems to be of even greater value than the Cretaceous from this 
standpoint. Especially interesting are those specimens described by 
Professor Seward from Yorkshire, England (1), by Gothan from King 
Karl’s Land (2) and the island of Spitzbergen (3), and by Lignier from 
Normandy (4). The woods to be described in this article are all from the 
Jurassic of Yorkshire. They are in two conditions of preservation — petri- 
fied and lignitic. With a few exceptions, the petrified material was sent 
by Mr. James Lomax to Professor Jeffrey, to whom the writer is indebted 
for an opportunity to study it. All the lignite, on the other hand, and 
a small number of petrified specimens, were obtained by the writer from 
various localities on the Yorkshire coast. All the sections from Mr. Lomax, 
and representative ones of the lignitic material, are now at the University 
Museum, Harvard College, Cambridge, Massachusetts. 
Before entering on the descriptive part, it will be apposite to consider 
briefly those features which have been found to be of greatest significance in 
diagnosing woods, especially in differentiating between the two great groups 
of Conifers — Araucarian and non-Araucarian, or Abietineous. The earliest 
classification, that of Kraus (5), was based entirely on the character of the 
radial pitting of the tracheides — the pits being alternating and compressed 
in the Araucarineae, and opposite and separated in the Abietineae and 
other tribes. This is the criterion used by both Seward and Lignier. 
Jeffrey (6), however, has shown that in the Cretaceous there were woods 
which combined the Araucarian type of pitting with that characteristic of 
1 Contributions from the Phanerogamic Laboratories of Harvard University, No. 6i. 
[Annals of Botany, Vol. XXVII. No. CVII. July, 1913.] 
O O 2 
