1908] JEFFREY—FOLIAR GAPS 253 
setum, represented in fl. 1, fig. 16.” It is obvious from the data of 
Srur, which have never been called in question, that the older 
Calamites were without the alternation of the strands in the region 
of the nodes which is characteristic of the more modern Calamites 
and the stem of the living Equisetum. It will be clear from the 
description of the anatomical conditions present in the cone of Equi- 
setum that absence of alternation brings with it the complete 
absence of foliar gaps. The writer in his memoir has suggested 
that the explanation of the peculiar features of the foliar traces 
in the vegetative stem of Equisetum is to be found in the past 
history of the phylum to which it belongs. Dr. Scorr would prob- 
ably agree to the soundness of this proposition, for example, in the 
case of the older living gymnosperms. ‘There appears to be no reason 
to make an exception in a group which has at least so long a past as 
the Gymnospermae. In the non-alternating arrangement of the inter- 
nodal strands, characteristic of the stems of the older Calamites 
(which is still largely represented in the cone axis of the living genus), 
there were no foliar gaps immediately above the outgoing foliar traces. 
As the relations of the internodal strands of one internode to those 
of the next became changed in the progression from the archeocala- 
mital to the equisetal mode of arrangement, the leaf-traces naturally 
came to lie opposite the gaps between the internodal strands of the 
next higher segment of the stem. But with the conservatism which is 
one of the most interesting characters of leaf-traces in general, they 
retained in Equisetum their old anatomical relations to the central 
cylinder of the stem. ‘That is, they still pass off in the vegetative stem 
of Equisetum without leaving any true foliar gaps. The lacunae in 
the internodes cannot be regarded as foliar gaps, since they are not 
immediately above the foliar traces, but are separated from them by 
the depth of the so-called “nodal” wood! The explanation offered 
'S a reasonable one in view of the past history of the group, and on 
those who do not accept it is placed the burden of some other more 
teasonable elucidation of the peculiar anatomical relations of the 
leaf-traces in the genus Equisetum. a 
The writer is credibly informed that Dr. ScoTT is of the opinion 
that the internodal gaps in the genus under discussion are de facto 
foliar gaps. This is a somewhat surprising opinion on the part of 
