[pENHAixow] îs^OTES ON TERTIARY PLANTS 61 



Tertiary. In the Gccond place, it shows that the extension! of the 

 species into the Cretaceous is not to be interpreted as a factor of 

 secondary value, but rather that it was, during that time, at its highest 

 development, and that its occurrence in the Eocene represents a period 

 of decline. Tliis relation is also indicated with respect to the genus 

 as a whole, though the data are not so pronoun!ced as to permit of more 

 than a provisional conclusion. Thus, for fifteen species of North 

 American Cupressus, the geological age of which is definitely known, 

 seven species are from the Tertiary, while nine are from the Cretaceous 

 — one species being comanon to the two formations. 



Thuya, sp. 



Laramie series (Lignite Tertiary) of Assiiiiboia. 



'The material representing this genus is much too incomplete to 

 admit of definite determination, though there can be no doubt as to 

 its being the wood of a Thuya. It represents a remisant of the collec- 

 tions from the Laramie formation, made by the British North American 

 Boundary Commission in 1874. . No definite locality is given, but it 

 is undoubtedly from the Lignite Tertiary, and probably from either 

 the Porcupine Creek or Great Valley deposits. The diagnosis, as far 

 as obtainable, is as follows: — 



Transverse. — Growth rings rather broad. The summer wood very thin, of 3-6 

 rows of tracheids, rather open; the transition from the spring wood 

 gradual. Spring tracheids large, round-hexagonal, rather uniform, 

 in regular rows, the walls thickish. Resin passages wholly wanting. 

 Resin cells numerous, large, resinous and scattering throughout the 

 growth ring. Medullary rays rather numerous, narrow, distant 2-7 

 rows of tracheids. 



Radial. — Structure of the rays too far obliterated to make the details avail- 

 able. Bordered pits not recognizable. Resin cells numerous, 40// 

 wide, 298// lon^. 



Tangential. — Rays numerous, narrow, uniseriate; the cells very uniform and 

 equal, oblong, narrow. 



Eeference to the geological distribution of the genus Thuya shows 

 that of ten species at present occurring within the limits of North 

 America, eight belong to the Tertiary and only two to tlie Crctiiceous, 

 which seems to indicate very strongly that it is essentially a Tertiary 

 type, and therefore of more recent date than Cupressus. 



During the winter of 1903-3, Dr. F. H. Knowlton, of the United 

 States National Museum, placed in my hands two specimens of wood, 

 with the request that I should determine them and ascertain, if 

 possible, the age of the horizon in which they were found. The fir. t 



