414 BOTANICAL GAZETTE [DECEMBER 
The conviction is continually repeated, in recent English publications bearing 
on this subject, that the gaps above the leaf traces in the modern Equisetales, 
but separated from their supposedly corresponding traces by the whole thick- 
ness of the so-called nodal wood, are in reality foliar gaps. An insuperable 
difficulty in this view, in addition to the very important anatomical ones cited 
by the present writer, is the fact that in both paleozoic and mesozoic repre- 
sentatives of the Equisetales the supposed foliar gaps are sometimes twice as 
numerous as the traces. It follows, of course, that some of the putative foliar 
gaps were not in reality leaf gaps in the older representatives of the Equise- 
tales. This state of affairs, brought into strong prominence by recent Swedish 
investigations on mesozoic Equisetales, seems to furnish the necessary coup de 
grace to the views tenaciously held in England. 
SUMMARY 
1. The Pteropsida represent a great natural phylum of vascular 
plants characterized by dorsisporangiate sporophylls and by palin- 
genetically large leaves, as inferred from their anatomical relations. 
2. The pith of the Vasculares, in all cases where definite evidence 
is available, is an inclusion of the fundamental tissues of the cortex 
on the part of the stele. 
3. The concentric type of tubular central cylinder is more ancient 
than the collateral and antedates the latter, as is shown by the 
persistence of the concentric condition in many leaf traces, where 
it has become obsolete in the stem. 
4. So far as the primary bundle system of the Vasculares is 
concerned, they present a reduction series, in which the ferns 
and lower gymnosperms (Archigymnospermae) represent the 
earlier and more complex stages, and the higher gymnosperms 
(Metagymnospermae) and dicotyledons the phases which are more 
recent and more simplified. 
HARVARD UNIVERSITY 
CAMBRIDGE, Mass. 
EXPLANATION OF PLATE XIII 
Fic. 1.—Transverse section of the stem of Onoclea Struthiopteris; X 5- 
Fic. 2.—Transverse section of a part of the stem of the same species; X 10- 
Fic. 3.—Transverse section of the base of the pinnular axis of Anmgiopterts 
evectay X10. + 
Fic. 4.—Transverse section of the same at a higher level, showing the 
fusion of the marginal bundles of the foliar system; X10 
Fie. -s. _{Pranagacse: section of the rachis of Marattia alata; X10. 
_ Fic. ou —The same, showing the exit of the vascular supply of a secondary 
axis; XI 
