THE ANATOMY AND AFFINITY OF STROMATOPTERIS MONILIFORMIS, METT. 153 
antithesis to the typically horizontal position of the axis and the continued axial 
growth shown by the Gleichenias, with which Stromatopteris has been habitually 
and closely grouped. 
The anatomical evidence shows that the branching in Stromatopteris is funda- 
mentally dichotomous, but the branches of the dichotomy may not develop equally, 
and indeed one branch may be partially or almost completely suppressed, and may 
survive only as an apparent nodule at the base of the petiole of the leaf which it has 
produced. Professor Bower has drawn my attention to the fact that this condition is 
of interest in connection with a question raised by Dr Scott ( Studies in Fossil Botany, 
pt. i, p. 318), and discussed also by Schoute ( Uber verdstelte Baumfarne und die 
Verdstelung der Pteropsida in allgemeinen, 1914, pp. 94, 95). It will be well to 
quote the passage from Dr Scott’s book. In discussing the morphology of Zygopteris, 
and the interpretation to be put upon it by the comparative morphologist, he makes 
the following statements : — 
“ The great peculiarity of Zygopteris corrugata as compared with the other 
three species in which the stem is known, consists in its mode of branching, which 
is not axillary, but rather of the nature of a dichotomy, the stem forking into two 
nearly equal branches without obvious relation to the leaf-insertion. This fact 
raises the question whether, as has been suggested, the apparent axillary branching 
of other species and of recent Hymenophyllacese may not be a modified dichotomy, 
in which case the £ undivided leaf-trace ’ would really be the stele of the smaller 
branch, and the ‘ subtending ’ leaf would belong to this branch and not to the main 
axis. The data are insufficient to settle the question, but for the present it seems 
better to keep up the distinction between the two kinds of branching.” 
From a wide study of branching Schoute has concluded that the evidence is 
strongly in favour of the belief that dichotomous branching is primitive, and that 
axillary branching is secondary and has commonly arisen by the modification of 
a dichotomy. This process is indeed held to have had a wide application in the higher 
plants. Now it is apparent that if, in the specimens of Stromatopteris described in 
this memoir, the suppressed apex had been arrested slightly earlier, it would actually 
have a position axillary to the leaf. In ferns generally this is an uncommon con- 
dition, but it exists, in point of fact, in Zygopteris and the Hymenophyllacese. It 
is not suggested that there is any near affinity between Stromatopteris and either 
Zygopteris or the Hymenophyllacese, but the similarity of the disposition of axis and 
leaf in all of these is sufficiently striking to justify the comparison, and the case of 
Stromatopteris may help to elucidate what in these other plants has been regarded 
as an exceptional state for relatively primitive ferns. 
The presence of both hairs and scales accords with what is seen in certain 
Gleichenias. But- apart from these extreme types of appendages, Stromatopteris 
possesses a curious assemblage of irregular transitional forms, which have not been 
matched from any other known Gleicheniaceous plant. These transitional forms 
