7” 
228 DR. D. H. SCOTT : 
There are no doubt some points in common with the Pityeæ, notably 
the centrally mesareh primary xylem-strands. In the genus Pitys most of 
the strands are embedded in the pith, as is also the case to a lesser extent 
in C. fascicularis and more rarely in C. Saturni. On the other hand 
Archeopitys, where the xylem-strands are distributed all over the pith +, 
goes much beyond anything that we find in Calamopitys, for there is no 
homology between those independent xylem-strands and the medullary 
metaxylem-tracheides occurring in the protostelic species of Calamopitys 
(Scott & Jeffrey, 1914, pp. 345, 365). The secondary wood of the Pityeæ 
usually has broad medullary rays; it is only in Callizylon (the most 
ancient genus of the family) that uniseriate rays prevail. The xylem- 
strands of Pityeæ are on a small scale compared with those of Calamopitys ; 
the presumption is that the leaves which they supplied were likewise 
relatively small, as Dr. Gordon has now proved (Seward, Fossil PI. iii.). 
The two families are roughly contemporary; there are interesting 
analogies between them, but they can hardly be on the same line of descent. 
The Poroxylese are a much later group (Permo-carboniferous). The 
stem-structure recalls that of Lyginopteris, but the primary xylem-strands 
are exarch, and the two strands of the double leaf-trace pass down at the 
margin of the pith through several internodes before they unite. The 
centripetal xylem dies out below, a point of resemblance to Calamopitys 
Beinertiana, The secondary wood is of the Lyginopteris type. The 
leaves were large and simple, showing a general similarity to those of 
Cordaitez. There is little to connect the family with Calamopitys, though 
a certain affinity, through Lyginopterides, may be presumed. 
The structure of the secondary wood in the more advanced species of 
Calamopitys (Eristophyton) suggests a relation to the family Cordaitem ; we 
now know that certain members of this family retained the centripetal 
wood of the xylem-strands in the stem (Scott & Maslen, 1910; Maslen, 
1911; Scott, 1912, 1918). In Mesowylon no primary centrifugal wood can be 
distinguished ; the strands are exarch, as in Poroaylon. The leaf-trace here 
also is double, the two strands uniting on entering the pith or lower down, 
according to the species. Parapitys Spenceri, which I should also place in 
Cordaitez, is interesting, because here the primary xylem-strands, though 
very small, are distinctly mesarch (Scott, 1902, p. 358). No doubt all 
the Cordaitez are far removed from Calamopitys, but it is not impossible 
that they muy represent an advanced stage of the same, or at least a 
similar, line of descent. 
Zalessky's two genera Canowylon (1911*) and Mesopitys (1911), both 
probably of Permian age, in which there are well-marked endarch strands 
of primary xylem, may also have some affinity with Calamopitys ; as the 
author points out, this is especially probable in the case of Mesopitys, in 
T Dr. Gordon has found a similar arrangement in Pitys, Seward, 1917, p. 288, 
