69 
Inter-relationships of the Phyla . 
cauline in the Sphenophyllales, the dorsal lobe of the sporophyll of 
S. fertile must also be cauline, since the sporangiophores of which it 
is composed appear to be identical with the ventral ones; but it is 
difficult to doubt the homology of the dorsal segments of the sporo¬ 
phyll of S. fertile with the leaf-like dorsal segments of Cheirostrobus, 
or of such a form as 5. Dawsoni. These dorsal segments are 
termed bracts by Miss Sykes. In the case of Tmesipteris Miss 
Sykes has shown that the bundle entering the synangium divides 
into three, of which the lateral ones run round the periphery of the 
septum, while the third terminates in the pedicel. She adds: 
“ The central trace, described now for the first time, seems an 
important piece of evidence in favour of the axial theory of the 
sporophyll in the Psilotales, and is here regarded as representing 
the vascular supply of the apex of the branch ” (39). Such a third 
bundle might, however, equally be regarded as evidence of reduction 
from the Sphenophyllales, since in Cheirostrobus and Sphenophyllum 
fertile (which on other grounds are probably primitive) the ventral 
sporangiophores as well as the dorsal bracts were branched. 
Another difference between the sporophyll traces (fertile branch- 
traces of Miss Sykes) and leaf traces in Tmesipteris , recorded by 
Miss Sykes, is the presence at the departure of the former of a gap 
in the stele, not occurring at the departure of the latter. Dr. 
Jeffrey, after an examination of her slides, asserts that in neither 
case is there a gap (21). It is fair to add that Miss Sykes attaches 
little or no importance to this difference, regarding it as due to the 
earlier preparation for the formation of sporophyll traces (39). 
But even if we accept the affinity suggested between the 
Sphenophyllales and Psilotales, founded on the homology of the 
stalked synangium with the sporangiophore, but supported by other 
similarities, we must remember that in the Sphenophyllales the 
leaves were whorled, the fructifications, strobili and the stem 
branched monopodially, while in the Psilotaceae the leaves are 
alternate, the fructifications non-strobiloid, and the stem branches 
dichotomously. It is curious that this last character, often regarded 
as primitive, should not be found in the fossil phylum (31). These 
differences indicate that the common stock of the two phyla lies 
very far back. 
Dr. Hallier’s views of the affinities of the phyla are in such 
marked contrast to those of other botanists that it appears 
preferable to notice them briefly and separately. He would derive 
all the non-filicinean phyla from the Marattiacese (17). His choice 
