K.—BOTANY, 183 
Zalessky’s genus Callizylon, an evident ally of Pitys, is of Upper 
Devonian age. ‘The affinities of the still more ancient Paleopitys 
Milleri have not yet been determined. 
The position of the Pityeze hangs in the balance, at least until 
Dr. Gordon’s new results are fully placed before us. From his 
discovery of the peculiar foliage and leaf-traces as well as from the 
stem-structure it appears that the Pityeee form a very distinct group, 
farther from the other Cordaitales than we once supposed, and not 
much like any of the Pteridosperms either. At any rate, we may 
suppose that the Pityez branched off from the common stock low 
down, while the Poroxylee and Cordaitee may have been of later 
origin. For the present, however, one may be content to regard the 
early Spermophytes as constituting a single main phylum. Since 
these words were written, however, Dr. Margaret Benson has main- 
tained a contrary view, arguing that the Cordaitales, Ginkgoales, and 
Conifers represent a wholly distinct stock, more allied to the Sphenopsida 
than to the Fern-like* races. The independence of this line has also 
been maintained by Prof. Chamberlain® and discussed by Prof. 
Sahni.?° 
On our hypothesis, the Upper Paleozoic phyla, with which we have 
to reckon, are the Pteridosperms (representing the early phase 
of the Seed-plants), the Ferns, the Sphenophylls, the Equisetales, and 
the Lycopods. ‘These five lines were probably all well differentiated 
in the Upper Devonian Flora; the only doubt concerns the Equisetales, 
which seem not to be known with certainty before the Lower Car- 
boniferous, but they were so well developed then that they must have 
existed earlier. 
When we get back to the Middle and Lower Devonian the case 
is completely altered. Not one of the five phyla is here clearly 
represented, unless it be the Spermophyta; for these we have the 
evidence of apparently Gymnosperm-like stems. Thus the field is 
lett absolutely open to speculation. We may imagine, either that the 
various phyla converged in some early vascular stock (illustrated by 
the Psilophytales), or that they ran back in parallel lines to independent 
origins among the transmigrant Alge and, perhaps further still, to 
Separate races of purely marine plants. Both views are represented 
in the publications of recent authors. 
Dr. Arber, in his ‘ Devonian Floras,’ maintained the early 
existence of three distinct lines of descent: the Sphenopsida, 
Pteropsida, and Lycopsida. In agreement with the present writer, 
he included the Equisetales in the Sphenopsida. Each of the three 
lines is described as descended from Thallophytic Algze of a disfinct 
type. Thus Arber’s view was decidedly polyphyletic. It must, how- 
ever, be borne in mind that the supposed ancestral ‘Alge’ were 
plants in which he expected to find ‘some form of primitive vascular 
system, at least as far advanced as in Psilophyton’ (l.c., p. 74). 
8 “The Grouping of Vascular Plants,’ New Phytologist, June 30, 1921. 
®<The Living Cycads and the Phylogeny of Seed Plants.’ American 
Journal of Botany, vol. 7, 1920. 
; 10 B, Sahni, ‘ On the Structure and Affinities of Acmopyle Pancheri.’ Phil, 
Trans. R. Soc., Ser. B., vol. 210, 1920. 
