226 DR. D. H. SCOTT : 
So far as the primary structure is concerned, the relationship throughout 
the series appears perfectly clear. It would of course be desirable to put it 
on a broader basis, in particular as regards the course of the leaf-traces, but 
data are almost lacking in the case of the ** /Zristophyton" species. All we 
know is that in C. fascicularis, at any rate, the protoxylem of the leaf-trace 
divided into two in passing through the zone of thickening, just as in 
C. Saturni, an indication of the subsequent division of the trace itself. 
But corticated specimens are needed before the affinities can be fully 
cleared up. 
In the meantime, on the evidence already available, it seems to me clear 
that the species placed by Dr. Zalessky in Zristophyton are more nearly allied 
to the Calamopitys of Unger than to any other known plants, and that the 
affinity is closest between C. fascicularis and C. Saturni, while C. annularis 
and americana show a more primitive type of structure ; C. Beinertiana, on 
the other hand, is the most advanced of all the five species. 
Affinities of the Genus. 
Assuming that the five species which I have included under Calamopitys 
form a natural series of nearly allied plants, we may now consider the 
affinities of the group to other families. We have to compare our plants on 
the one hand with the Cycadofilices and on the other with the Paleozoic 
Gymnosperms. 
Among the Cycadofilices * the nearest affinity would appear to be with the 
Lyginopterideæ. The comparison has hitherto been made with Lyginopteris, 
which, in its ring of mesarch xylem-strands and in the first division of 
the leaf-trace, presents considerable analogies with Calamopitys Saturni. 
The discovery that certain species of Calamopitys (C. americana and probably 
C. annularis) were protostelic suggests a relation to Heterangium, while the 
recent observation that several species of //eterangium contained a number of 
vascular bundles in the petiole (Scott, 1917) strengthens the analogy, and 
tends to remove the most obvious discrepancy between the structure of 
Calamopitys and that of Lyginopteridem. At the same time it is clear that 
no direct filiation of the two groups is admissible; Calamopitys is at least as 
ancient as the Heterangiums, and much more ancient than the polydesmic 
species: there is at no point any evidence of a transition from one group to 
the other; they form parallel series, which, however, may well have had a 
common origin. The Medullosex are more remote, recalling Calamopitys 
only in their highly polydesmic petioles ; they show, however, a certain 
relation to Lyginopteridee through //eterangium, and all three groups may 
probably have sprung from a common source. 
* [ use this name in a wide sense, to cover all plants which appear to be intermediate 
between Ferns and Cycadophyta whether their fructilication is known or not. 
