the Periderm of Fossil Lycopodiales . 285 
the view supported is that the phellogen was just inside the leaf-bases, and 
that the corky nature, even of the little tissue on the outer side, is very 
doubtful. With regard to Stigmaria, Scott agrees with Solms and differs 
from Williamson in believing that remains of the phellogen can be traced 
on the inner edge, but that the tissue was not impermeable. He gives 
a brief description of the periderm of species of Sigillaria , and points out 
that in all these plants the functions of the secondary cortex were probably 
very different, and much more important than in recent vegetation. 
The periderm of Lepidophloios fuliginosus next received attention in 
the paper by Weiss on a Halonial branch of the species. 1 Here no 
phellogen layer can be distinguished, though the tissue is regarded as being 
probably phelloderm, but Weiss considers it (unlike the periderm of the 
Dalmeny specimen) a closely-set, protective layer which would prevent the 
passage of air to the interior tissues ; and, in a paper on the parichnos 
written a few years later, he says, ‘A respiratory passage through the dense 
outer cortex and the impervious periderm would seem to be an essential 
requirement of the Lepidodendroid stem.’ 2 
In 1906 Seward noted the formation of a wound periderm in Lepido- 
dendron aculeatump and Scott the presence in places of a second periderm 
in L. obovatump but the next detailed account of the tissue is to be found 
in 1907 in Arber and Thomas’s paper on Sigillaria scictellataP Here the 
secondary cortex forms the bulk of the ribs of the species, and is regarded 
as phelloderm, because the tangential walls of the outer layers are closer 
together and thinner than those of the more internal elements, and the 
parenchyma outside remains unchanged. In the same year an account was 
given by Watson of his new species, Lepidodendron Hickii , which had been 
included in the L . Harcourtii of Williamson. One specimen shows the 
first beginnings of the periderm, and it is stated that ‘ the central cell 
becomes the meristem and cuts off new cells on both sides ’ ; G but that in 
older sections it is impossible to locate the phellogen. 
In 1908 Gordon described another new species, Lepidophloios Scottii, 
in the periderm of which there are zones of clear cells alternating with zones 
filled with dark material, which are taken as an indication of some sort of 
periodic rest. 7 In 1908 also, besides a paper by Weiss on a Stigmaria 
with centripetal wood possibly belonging to Bothrodendron , 8 where the thin- 
walled periderm with its outer cells tangentially extended is taken as 
evidence of Stigmarian nature, there was published the second edition of 
Scott’s ‘Studies’. In this, however, little is added to the original account 
of the periderm of the fossil Lycopods beyond bringing the book up to 
date by references to recent work. 
1 Weiss (33). 2 Weiss (85), p. 7. 3 Seward (27). 
4 Scott (25). 5 Arber and Thomas (1). 6 Watson (32), p. 9. 
7 Gordon (12). 8 Weiss (36). 
