54 
Lady Isabel Browne. 
Almost as much importance has been attached to the absence 
of a leaf-gap in the Lycopsida as to their microphylly. Dr. Jeffrey 
has recently asserted that the gap in the wood reported by Miss 
Sykes (39) at the departure of the sporophyll trace of Tmesipteris , 
and the so-called leaf-gap figured by Professor Bower from the 
upper part of a stem of this plant (10) have been misinterpreted. 
Dr. Jeffrey claims that the traces always originate opposite a 
cauline strand ( i.e ., leave no gap) but owing to their oblique course 
they may appear, while in the cortex, to be opposite the gaps; he 
also urges that these cannot be foliar since they occur mainly on 
one side of the stele and more than one trace may be related to 
each gap (21). There is much force in these objections, but as 
regards Equisetum the case is different. Dr. Scott and Dr. 
Campbell believe that leaf-gaps are present here (34) (13). The 
I 
latter urges that the gaps between the vascular strands occur alike 
in branched and unbranched axes and that it is hardly reasonable 
to suppose that “ an ideal branch—so to speak—could cause the 
development of a ramular gap where no actual branch is present ” 
(13). This refutation of the ramular nature of the gaps in the stele 
of Equisetum seems convincing, and in recently reasserting that 
these gaps are not foliar, Dr. Jeffrey relies chiefly on the fact that 
they are not immediately superposed to the departing traces, but are 
separated from them by the thickness of the “ nodal ” wood. In 
the cone he holds that the frequent continuity of the carinal canal 
through the node proves the absence of a gap (21). The facts are 
not yet clear—for if the gaps are not foliar it is very remarkable 
that they should always be equal in number to the leaves ; but if 
Dr. Jeffrey’s conclusions are correct, the gaps in the stele of 
Equisetum would be neither ramular nor foliar, but more of the 
nature of the gaps occurring in the rhizomes of many Ferns, to 
which gaps Mr. Tansley has given the name of perforations. 
Actually the presence of a leaf-gap is chiefly important, in so far 
that it supports the primitive megaphylly of the phylum in which 
it occurs. The absence of a gap in protostelic forms is, as pointed 
out by Mr. Tansley (41) and Dr. Jeffrey (21), no proof of microphylly, 
since leaf-gaps cannot occur in a solid stele. The above discussion 
seems to show that even if they never possessed leaf-gaps, the 
Sphenophyllales (and therefore probably their allies the Psilotales) 
and the Equisetales primitively bore large compound leaves; at the 
same time we have no evidence that the relatively small and simple 
leaved Lycopods were evolved from forms with large or compound 
leaves. 
