NOTES ON CALAMOPITYS. 295 
any tendency to endarch structure in the xylem-strands of Calmopitys proper; 
where there is any departure from central mesarchy it is in the exarch 
direction. This seems to me an important difference; it marks a distinct 
step, in the case of the ristophyton species, towards the ultimate disappearance 
of the centripetal xylem, which finds its realization in the Coniferous type. 
of stem. If the species in question are to be placed in a separate genus, T 
should be inclined to rest the distinction rather on the primary characters 
just diseussed, than on the difference in the structure of the secondary wood. 
The latter hardly affords a constant criterion, unless the case of the Halle 
specimen, referred to Calamopitys annularis, with its narrow medullary rays, 
can be explained away. I have no objection to generic separation, though 
I do not, at the moment, adopt it myself. In my first paper I pointed out 
that the reference of the two species C. fascicularis and C. Beinertiana to 
Calamopitys must be regarded as provisional until the structure of their 
cortex and leaf-bases was known (Scott, 1902, pp. 345, 361). ‘This, unfor- 
tunately, is not yet the case, and the question is thus still open. If these 
plants should turn out to have Kalymma structure in the leaf-base they 
should, I think, remain in Calamopitys ; otherwise their separation will 
undoubtedly be necessary. 
But, on the broader question of the near affinity between the two groups, 
I think the evidence is very strong. So far as the larger (i.e. the outgoing) 
xylem-strands are concerned the structure of C. Beinertiana and C. fas- 
cicularis is identical with that of C. Saturni (compare for example Phot. 22 
with Phots. 24 & 25, or with Scott, 1902, Pl. 1. fig. 2). I have seen no 
xylem-strands of this type, large, circular and centrally mesarch, in any other 
group of plants. The agreement with C. annularis and C. americana is 
less close, for in these species the xylem-strands are as a rule somewhat 
eccentrically mesareh with the protoxylem nearer the outer side. In 
fact the species form a kind of series, as shown in the synopsis on p. 221 ; 
C. annularis and C. americana retain much of the protostelic structure, 
with an almost continuous primary xylem-ring and medullary tracheides *. 
The xylem-strands are usually eccentrically mesarch. In C. Saturni, so 
far as I have observed, there is no continuous primary ring, the xylem- 
strands being isolated; medullary tracheides are either quite absent or 
extremely reduced; the strands are centrally mesarch. In these respects 
C. fascicularis agrees with C. Saturni, but there is the important difference 
that in the former the xylem-strands, in the lower part of their course, tend 
towards an endarch structure and diminish in size, while the secondary 
wood assumes a more Cordaitean character. Lastly, in C. Beinertiana the 
change has gone further, for while the outgoing xylem-strands are identical 
with those of C. fascicularis and C. Saturni, they attain, as they pass 
downwards in the pith, a completely endarch structure, the centripetal 
xylem here dying out. 
* Certainly in C. americana, probably in C. annularis. 
