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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
plicated later by the formation of "commissural" strands, which are of 
cauline origin. 
The " dictyostele " of Ophioglossum and most Marattiales is in no sense 
a monostele. The "foliar gaps" are not breaks in a single tubular stele, 
but are merely spaces between the coalescent leaf-traces, and the pith is 
part of the ground tissue included within the cylindrical network formed 
by the united bundles derived from the leaves. 
In short, the condition found in the axis of the eusporangiate ferns is 
more in accord with the older theory of "common" bundles traversing a 
ground tissue, and united to form the woody cylinder of the axis, than with 
the assumption o a true cauline stele. 
The condition existing in the eusporangiate ferns by no means implies 
that the stelar hypothesis must be completely discarded. There seems to 
be no question of its application to the Lycopods, Conifers, and many Angio- 
sperms; but in all of these, the relative importance of stem and leaf is very 
different from the condition in the ferns; and it will not be surprising if, 
when the different types of the Leptosporangiatae are subjected to a thor- 
ough examination of the origin of the stelar tissues in the young sporophyte, 
it will be found that in these, as well as in the Eusporangiatae, the axial 
stelar tissues are largely, at least, of foliar origin. 
Stanford University 
