323 
Two Palaeozoic Stems from India . 
renders any real comparison impossible, but the grouping of the radial 
tracheary pits recalls certain Devonian stems now referred to the genus 
Callixylon. In 1909 Zalessky 1 described a new stem of the Pitys type under 
the name of Dadoxylon TrifilievL\ in 19 11 2 he published further observations 
on this stem and decided that its structure was sufficiently distinctive to 
warrant the inception of the new genus Callixylon , for, in addition to the 
numerous bundles of primary tissue surrounding the pith, the secondary 
xylem is distinguished by the peculiar distribution of the radial pits. They 
are of the normal Dadoxylon type, — closely compressed and flattened to 
a hexagonal outline, but instead of being scattered uniformly over the cell- 
wall, they are localized in groups of six to thirteen or more. The groups of 
one tracheide are on the same horizontal line as those of the next, and give 
a characteristic radially banded appearance to the wood. In this respect 
Zalessky’s stem closely resembles one described by Newberry from the 
Upper Devonian of the State of Ohio, U.S.A., since named by Penhallow 3 
Cordaites NewberryL In 1914 Elkins and Wieland 4 discovered another 
beautifully preserved specimen of the same general type from the Upper 
Devonian of Indiana and, on the basis of the pitting, included both stems 
in the genus Callixylon. If we accepted their view that bordered pits are 
sufficient to define the limits of a genus the Indian fossil should also be 
referred to Callixylon . To facilitate comparison the following table may 
be of value : 
Callixylon (secondary wood). 
C. Newberryi . 
C. Oweni. 
C. Trifilievi. 
Indian stem. 
Annual rings 
- 
+ ; 6 in 1 5 mm. 
? 
+ ; 10-12 mm. wide 
Rays 
1-3 seriate 
1-2 seriate 
1 seriate 
1 seriate 
1-20 cells high 
1-40 cells high 
1-13 cells high 
1-20 cells high 
3-6 pits to each 
cross-field 
6-8 pits to each 
cross-field 
1-5 pits to each 
cross-field 
2-7 pits to each 
cross-field 
Tangential pits 
of tracheides 
? 
? 
+ 
— 
Radial pits of 
tracheides 
Pit circular, 9 a 4 in 
diam. ; pore dia- 
gonal 
Pit circular ellipti- 
cal or irregularly 
flattened, 10-n ft 
in diam. ; pore 
diagonal 
Pit flattened or 
hexagonal, 12-13 
fj. in diam. ; pore 
diagonal 
Pit flattened or 
hexagonal, 4 ^ in 
diam.; pore dia- 
gonal 
2-3 seriate groups 
of 6-13 groups 
banded radially 
1-4 seriate groups 
of 3-40 groups 
banded radially 
2-3 seriate groups 
of 6-13 groups 
banded radially 
1-4 seriate groups 
of 2-5 groups not 
banded radially 
It seems to the writer, however, that to combine these into one genus 
is to take an exaggerated view of the importance of radial pitting. While 
unquestionably constant, its value as a test for affinities is doubtful. Thus 
1 Zalessky ( 1909 ). 
8 Penhallow ( 1907 ). 
2 Zalessky ( 1911 ). 
4 Elkins and Wieland ( 1914 ). 
