KNOWLTON, ] JURASSIC WOOD FROM THE BLACK HILLS. 421 
bordered pits, usually only one to the width of a spring cell of the 
wood, although not rarely there are two in a similar width. They are 
always in only one row on the ray cells. They are also shown in the 
figures. ; 
Tangential section: The medullary rays are naturally the most promi- 
nent feature in this section. They are always ina single superimposed 
series. They number from i to rarely 30 cells, an average number 
being from 5 to 12 cells high. None of the rays in sections examined 
are of the fusiform type, or that in which resin passages are included. 
The wood cells, as far as can be made out, are without pits or markings 
of any kind on their walls. 
I am not a little in doubt as to the proper disposition that should be 
made of this interesting wood. It is so beautifully preserved, and the 
histological elements are so plainly discernible, that it seemed at first an 
easy matter satisfactorily to place it, but a somewhat prolonged exam- 
ination has failed to settle it. Before it could be examined microscop- 
ically, and basing the conclusion upon its supposed geological position, 
it was presumed to belong to Araucarioxylon, but a glance at the 
structure serves to show that this can not be so. This genus is with- 
out resin passages, and, moreover, is well characterized by having the 
bordered pits more or less distinctly hexagonal. This hexagonal form 
of the pits, of which the living Araucaria may be taken as the type, 
appears to have had its origin in the Lower Paleozoic in the forms 
known as Cordaites and Dadoxylon. It is sufficient to say in the present 
connection that all of these distinctive features are absent from the wood 
under consideration. 
From a number of other types of living wood this is separated by 
characters of importance. Thus from Sequoia it differs in having 
very broad instead of narrow growth rings and distinct resin passages, 
these being either entirely absent or very imperfectly found in both the 
living Sequoias, and finally the absence of resin cells. 
In an exhaustive paper on the Generic Characters of the North 
American Taxacesx and Conifere,' Prof. D. P. Penhallow presents the 
distinguishing characters of the living genera. They are readily divis- 
ible into two groups, as follows: Resin passages and fusiform rays 
present, including Pseudotsuga, Larix, Picea, Pinus, Seguova semper- 
wirens, and several species of Abies, and those in which these features 
are wholly wanting, including Taxodium, Sequoia, Libocedrus, Juni- 
perus, Thuja, Cupressus, Tsuga, and most of Abies. The fossil wood 
under consideration is excluded from the last of these two groups, for 
it has very pronounced resin passages, and it must therefore be 
included in the first division in spite of the fact that there are seeming 
contradictions. This first division is again divisible into three sub- 
groups on characters taken from the presence or absence of the fusi- 
1 Trans. Roy. Soc. Canada, 2d series, Vol. II, Section IV, 1896, pp. 33-57, pls. i-vi. 
