692 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
ternary branch x" of fig. 35 D has also evidently escaped from the periphery of the 
petiole at the interval between the points at which the sections fig. 35 D & E were 
made. 
On tracing the further development of one of the secondary petioles in the same 
series of sections, we obtain yet further information respecting their modes of branching. 
Plate LV. fig. 35 F is the lowermost of several sections of one petiole, which, though 
virtually transverse, are nevertheless slightly oblique ones. In it we have the secondary 
crescentic bundle ( aa ), corresponding to the bundles aa in figures 35 A, B, C, D, & E. 
At x we have a ternary bundle passing out of the petiole, the bark of which latter again 
is much enlarged at this point. At x' we see a second ternary bundle lying immediately 
outside the uncurved horn of the crescent (aa), and evidently preparing to pass off towards 
the periphery as the bundle x had done, but from the opposite horn of the crescent aa. 
At x 1 " we find a quaternary bundle evidently going off to supply either a lateral pinnule 
or a leaflet. In Plate LVI. fig. 35 G we see the ternary bundle x! of Plate LV. 
fig. 35 F moving outwards, but in the opposite direction to that taken by x in that 
figure. The latter bundle, with its enlarged mass of cortical cells, has now become 
altogether detached, and is seen to be a separate rachis, having the relative size and 
form, compared with that from which it springs, of Plate LV. fig. 40 and of Plate LVI. 
fig. 35 H, both of which represent sections of similar twigs. Its central bundle has 
acquired the gutter-shaped section seen in fig. 40*. Plate LVI. fig. 351 is the next 
section in this ascending series. The central bundle retains its place at aa, whilst its 
ternary branch (x 1 ) with its investing cortex has not only become of considerable size, 
but is giving off at x 11 ' a quaternary twig, which may either have been the petiole of a 
leaflet or, more probably, the rachis of an ultimate pinnule. The vascular bundle 
supplying this quaternary subdivision of the rachis has obviously corresponded to x" in 
Plate LV. fig. 35 F, only opposite sides of the rachis are thus occupied in the two ex- 
amples. But this section (fig. 35 I) shows that whilst this ascending branch of the petiole 
has thus enlarged, the central vascular bundle (aa) is now throwing off at x" a corre- 
sponding bundle to x', only destined for the opposite direction, being now detached 
from the lower horn of the crescentic bundle as x' was from the upper one. In Plate LVI. 
fig. 35 K, which is the fourth of this ascending series of transverse sections, we again 
find the rachis much reduced in size, owing to the entire separation of the large branch 
x 1 of fig. 35 I. In the original specimen this latter is now seen to be a small, detached 
cylindrical rachis corresponding in size and form with fig. 35 H. In fig. 35 K the small 
cluster of vessels x", seen in fig. 35 I, x", is now larger, and more nearly detached than 
before from the crescent aa. In all these specimens, as in all similar recent ferns, the 
two extreme horns of the crescentic bundle (aa), which alternately become detached to 
form the ternary bundles, are entirely composed of barred vessels, whilst those forming 
the central part of the crescent are of the reticulated type. 
* It is possible that fig. 40 may be the upper portion of a secondary rachis, since at x we find it detaching 
a bundle like that shown in fig. 35 K. 
