52 
Lady Isabel Browne. 
Adder’s Tongues ; but Dr. Lang has shown that the symmetry of 
the Ophioglossaceous prothallus is probably not primitive but an 
adaptation to a subterranean habit and that it may be to a certain 
extent induced in dorsiventral prothalli (26). The subterranean 
habit may have caused the radial symmetry of the prothallus of 
Lycopodium, for the most primitive type of prothallus found in the 
genus — that of L. cernuum —is less completely subterranean than 
the other types (except the highly modified type of L. Pldegmaria) 
and forms flattened expansions on reaching the light. Dr. Lang 
has provisionally referred a prothallus essentially similar to that of 
L. cernuum to Psitotum (27). Unfortunately some doubt rests on 
its attribution; otherwise it would be evidence in favour of a closer 
affinity between the Club Mosses and Psilotales than is now usually 
admitted, and might serve to bring the Club Mosses indirectly into 
connection with those probable allies of the Psilotales, the Spheno- 
phyllales, and through them with the Equisetales. Great importance 
has been attached to the biciliate spermatozoids of the Lycopodiaceae 
and Selaginellacese, which are unknown in Ferns or Horsetails. 
Those of Isoetes are, however, multiciliate, and if the Lepidoden- 
draceous descent of Isoetes should be confirmed (it has been 
strengthened quite recently by the discovery of a Mesozoic fossil 
provisionally referred to the Isoetaceous cycle of affinity (30) ) there 
would be a prima facie probability that in this phylum also the 
spermatozoids were multiciliate. 
Still less is it easy to agree with Dr. Campbell’s view that the 
sporophytes of Ferns, Horsetails and Club Mosses originated 
independently from non-vascular forms. The discovery of Proto- 
catamites ( Catamites ) pettycurensis shows that in the Equisetales, as 
in the allied Sphenophyllales, and in the Psilotales and Lycopodiales 
the centre of the axis was primitively occupied by centripetal wood. 
On comparative grounds it seems likely that the primitive type of 
stele, at least in these four phyla, was an exarch protostele. 
Further, though pitted tracheides do not occur in existing Lycopods, 
they were recorded from Sigillariopsis Decaisnei by Renault (38). 
Thus both anatomically and histologically the Lycopods appear to 
be constructed on the same ground plan as the Sphenophyllales, 
Psilotales and Equisetales. In support of the independent origin 
of the Lycopod, Fern and Horsetail sporophytes, Dr. Campbell 
relies on the fact that in Equisetuin the vascular bundles are 
developed from the “ cortical ” region of the apical meristem (13). 
But Dr. Schoute’s very thorough researches seem to show that 
