Anatomy of Solenostelic Ferns: /. Loxsoma . 8r 
root-steles arise from the under-surface and sides of the 
solenostele of the rhizome, and the long axes of their diarch 
xylem-plates are so arranged that they are tangential to the 
solenostele in a transverse plane. The root-steles pass out 
in a very slightly oblique direction towards the apex. 
The Petiole. 
The only points at which the perfect continuity of the 
closed solenostele is interrupted are the points of insertion 
of the leaf-traces. At each node the departure of a vascular 
strand to supply the leaf removes a portion of the vascular 
ring bodily from the stem, leaving a gap through which the 
parenchyma and sclerenchyma of the ground-tissue lying 
within the vascular ring communicate with the corresponding 
tissues lying without it, while at the same time the internal 
endodermis, pericycle, and phloem become continuous with 
the external, around the margins of the gap. The leaf-gap 
thus formed persists for some little distance (6-8 mm.) into 
the internode above, but gradually becomes closed up again. 
The manner in which the leaf-trace actually arises from the 
solenostele of the stem was ascertained by the comparison of 
a number of consecutive transverse sections taken through 
a node, and the conclusion confirmed by rough dissections. 
As a result, Fig. 4 was drawn as the representation of the 
form taken up by the vascular system of the rhizome at the 
nodes, and it is hoped that a reference to it will facilitate 
further description. It is seen in the diagram that the portion 
of the vascular system of the stem destined to pass off as 
a leaf-trace is clearly indicated for a short time previous to 
its departure as a protuberance on the upper side of the 
solenostele, and a reference to transverse sections shows that 
this leaf-trace portion rapidly diminishes in thickness as the 
point of departure is approached. The drawing is further 
intended to show that the leaf-trace (which has the form of 
a trough, or in transverse section that of a horseshoe) is 
seated upon the vascular tube of the stem almost in the 
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