1026 
Scott. — The Structure of 
arranged tracheides with the smallest elements always on the inner side. 
The whole of the primary wood is composed of spiral or rayed tracheides 
which abut immediately on the pitted elements of the secondary wood. 
Unlike Caenoxylon , Mesopitys Tchihatcheffi has a single bundle constituting 
the leaf-trace, where it passes out through the wood. The medullary rays 
are uniseriate. The genus Mesopitys is established for stems with secondary 
wood of the Dadoxylon type, characterized by the arrangement of the 
feebly developed primary wood in bundles of endarch or even mesarch 
structure, and by the single bundles traversing the secondary wood 
(Zalessky, ’ll 1 , p. 28). The author regards his new genus as forming the 
final term of the group of stems of the Dadoxylon type described by me in 
1902, and considers it to be closely allied to his Eristophyton Beinertianum 
( Calamopitys Beinertiana (Scott)). 
It is interesting to note that Dr. Zalessky is prepared to include stems 
with mesarch as well as those with purely endarch primary xylem in 
the same genus. I have no objection to this in principle, for the one 
structure, no doubt, passed over gradually into the other, nor do I dispute a 
certain degree of affinity between my Calamopitys Beinertiana and Mesopitys 
Tchihatcheffi. At the same time, the presence of very highly developed 
mesarch strands in the former plant (though they become endarch lower 
down in their course) appears to me a more important difference than 
Dr. Zalessky recognizes. I quite agree with the author that his Mesopitys 
Tchihatcheffi requires a new genus. 
Another of Dr. Zalessky’s new genera is Parapitys , founded for the 
reception of Dadoxylon Spenceri (Scott, ’ 02 ). It was inevitable that sooner 
or later this form should acquire generic rank. It is characterized by the 
double leaf-traces, the small mesarch strands of primary xylem, and the 
relatively small pentagonal pith, the wood being of the ordinary Cordaitean 
type. Of all the forms discussed by Dr. Zalessky, Parapitys seems to me 
the nearest to Mesoxylon , from which it only differs (so far as we know 
at present) in the characters of the pith. It seems to be widely separated 
from the species of Calamopitys placed by Dr. Zalessky in Eristophyton by 
the double leaf-traces and the great reduction of the primary mesarch strands. 
Dr. Zalessky devotes a good deal of space to an argument against my 
inclusion of Calamopitys fascicidaris and C. Beinertiana in the genus 
Calamopitys of Unger, founding the new genus Eristophyton for their 
reception (Zalessky, ’ll 1 ). I do not propose to enter fully into the question 
in this paper, because, from my point of view, these plants have very little 
to do with Mesoxylon. It is possible that the various, not very important 
characters, on which Dr. Zalessky lays stress, may in the aggregate justify 
generic separation. The author, however, has not quite realized what the 
characters are which I regard as essential to Calamopitys. As I stated 
(Scott, ’ 02 , p. 360) : e The Calamopitys group is characterized by the 
