Vascular System of Pteris. i 7 
The probability of the modification of vascular structure at 
the node of a plant, in relation to an alteration of the leaf-trace, and 
the effect of leaf-traces in modifying stem-structure generally, has 
been pointed out in one form or another by nearly all recent writers 
on vascular morphology. In ferns the principle of the decurrency 
of such a new structure from the node into the internode below, 
and its eventual establishment throughout the internode to join a 
similar structure at the next node below was tentatively suggested 
by Boodle (’01, pp. 737-8) and by ourselves in reference to Lindsaya 
and Davallia pinnata These suggestions have been confirmed and 
greatly extended by Gwynne-Vaughan (’03). There can now be 
little doubt that we have here a principle of very wide application, at 
least within the Filicinean series. The particular instance of it 
described in the present paper is of special interest, since it brings 
before us a mode of origin of an internal system of rhizomic vas¬ 
cular strands differing from that described by Gwynne-Vaughan in 
a number of types. Whereas the internal ridges and strands in the 
Dicksonias, in Cyathea, and in Pteris data var. Karsteniana arise at 
the node as a local thickening of the leaf-gap, those of the plants 
we have described arise as lateral elaborations of the leaf-trace 
itself. 
1 Tansley and I.ulham. On a New Type of Fern-Stele, Ami. of 
Bot., XV., 1902. 
University College, London. December, 1903. 
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