376 Fawner and Hill. — Arrangement and Structure 
The vascular skeleton of the young sporophytes of Angiopteris 
evecta and Marattia fraxinea , and of the adult stem of 
K aulfussia. 
The vascular skeleton in the young plant of Angiopteris 
consists of an axile rod of tissue from which strands are 
given off to the roots and leaves respectively. The first 
lateral root is given off, as previously stated by one of us 1 , at 
a point not quite opposite the formation of the first leaf- 
trace. It is separated from it by about 130°. The regular 
relation between the leaf and the corresponding root is, how- 
ever, soon lost. The gaps produced by the early leaf-traces 
are very small and are immediately made good above. The 
first deeply depressed aperture or gap occurs at about the 
sixth or seventh leaf. The leaf-traces still continue to issue 
from the stele as single strands till a varying number have 
been formed, but they begin to bifurcate whilst still within the 
cortex of the stem. (PI. XVI, figs. 1, 2, 3.) 
As the stem increases, the leaf-traces become more numerous 
and crowded, and they take away a larger portion of the 
vascular tissue from the axile strand. The result is that the 
leaf-gaps become less rapidly repaired. The stele is already 
hollow in this region (Fig. 3), that is, it consists of a cylindrical 
vascular mass with perforations corresponding to foliar gaps 
and enclosing a core of parenchyma. Sooner or later the gap 
above one leaf fails to be repaired till after the exit of the 
trace of the next leaf, and then the original vascular cylinder 
becomes broken up, and assumes a condition in transverse 
section conforming with that of polystely or dialystely. 
When once this condition has supervened, the vascular ring 
is never again completely repaired ; on the contrary, owing to 
the crowding of the leaves, more and more apertures or foliar 
gaps are visible at any one level in the cylinder. Finally, 
across the intervening parenchyma commissural vascular 
strands are differentiated, and these connect the opposite sides 
of the cylinder, which now exhibits the appearance of a coarse 
1 J. B. Farmer, On the embryogeny of Angiopteris evecta. Annals of Bot., vi, 1892. 
