1908] JEFF REY—FOLIAR GAPS 243 
related to but a single leaf-trace. If several traces appear in 
relation to a stelar gap, and especially if they are related to the sides 
of the gap, it may be concluded at once that no true foliar gap is 
present. It may be added for the benefit of inexperienced anatomists 
that not all gaps in the wall of the central cylinder are foliar gaps. 
Where the fibrovascular tissues are much reduced in amount, as is not 
unfrequently the case, they often break up into a loose meshwork, 
which has no necessary relation to the vascular supply of the leaves 
or the branches. 
LEPIDODENDREAE AND SIGILLARIAE 
In the memoir cited above, the writer has called attention to the 
fact that in the Lepidodendreae, which are among the oldest of the 
Lycopsida, there are no foliar gaps in the tubular central cylinder, 
when present. Fig. 9 illustrates this feature in Lepidophloios Har- 
courti. Below in the figure is to be seen the woody cylinder, showing 
inferiorly some of the thin-walled tissue of the pith. The cylinder is 
dentate on its outer surface, and the teeth are composed to some 
extent of small-celled protoxylem. Outside the wood may be seen 
nests of small cells, which mainly lie in the intervals between the 
dentations. These are the foliar traces. It is clear that there are 
nO gaps or interruptions in the central cylinder corresponding to 
these. Consequently it may be stated that there are no foliar gaps 
in the species figured. An examination of a considerable number 
of sections of lepidodendrid stems has made it clear that foliar gaps 
are absent in the group. 
In the older Sigillariae the primary wood in the stem ordinarily 
formed a continuous cylinder, and there were, as in Lepidodendron, 
nO gaps of any kind except for the outgoing strands of branches. In 
pea modern Sigillarias, however, the woody cylinder was frequently 
entirely or partially broken up into separate strands. Sigillaria 
‘legans from the Lower Coal Measures had the continuous type of 
"Woody cylinder, while S. Menardi from the Permian had separate 
Strands of wood constituting its tubular stele.3 The leaf-traces in 
both types of Sigillaria stem, however, passed off without leaving any 
foliar gaps in the central cylinder, for in the Sigillarias of the more 
ia Stop R. Internal structure of Sigillaria elegans. Trans. Roy. Soc. 
41 2533-550. 1905. 
