62 Lady Isabel Browne. 
Equisetales, may prove to be interesting ; for its sporangia appear 
to have been borne on the lower surface of small sporangiophores. 
Unfortunately the interpretation of this cone, known only in 
impressions, is doubtful. If the marginal position of some Fern 
sori is primitive, the sporangia have in most ferns undergone shifting 
—such shifting has actually been traced in certain Polypodiaceae 
(10). A similar shifting in other directions might have brought 
about the adaxial position of the Spenophyllaceous sporangiophore 
or have produced a marginal and abaxial position of the sorus from 
an adaxial position. If Mr. Tansley is right in regarding the 
branching of the frond of many Botryopterideae in more than 
one plane as a vestige of a primitively radial construction the 
branching of the sporophylls of some Sphenopyllales in the dorsi- 
ventral and lateral planes may be an indication of primitively 
radial symmetry. Such radially symmetrical sporangiophores 
occur in the Equisetales, and if primitive, a point in favour of 
which we have little or no evidence, they might afford an explana¬ 
tion of the different position of the sporangia in the Ferns and 
Lycopsida, since in acquiring dorsiventral symmetry the appendage 
might well cease to form sporangia on the upper surface in one 
case and on the lower in the other. All such suggestions are of 
the most tentative, not to say imaginary nature, and even the 
homology of the “ sporangiophore ” and “ sorus ” which gave rise to 
them is but a doubtful hypothesis in favour of which we have as 
yet little evidence. 
Professor Lignier regards the matter from a different stand¬ 
point. He has drawn attention to the large size and dichotomous 
venation of the leaves of the more primitive Sphenophyllales and 
Equisetales, to the fern-like nature of the spermatozoids of the latter 
phylum and to several less important points indicating, as already 
noted, a certain affinity between the Equisetales and Spheno¬ 
phyllales, constituting Professor Lignier’s group of the Articulate, 
and the Ferns. His suggested derivation of the fructifications of 
the Sphenophyllales and Equisetales from a filicinean type is less 
convincing. As already explained Professor Lignier has shown 
that the species of Sphenophyllum with small and simple leaves were 
probably evolved from forms with a smaller number of more highly 
compound leaves by the precocious division of the leaf-trace within 
the tissues of the stem, and by the subsequent separation of the 
lobes of such leaves round the periphery of the stem so as to 
simulate whole and independent leaves. He has brought forward 
