374 Bower. — Studies in the Phytogeny of the Filicales. 
the gap first opens, shows it giving off at its base the stele of a root. This 
is a very usual feature in Blechnum. In 2 the root-stele is seen passing 
outwards, while from the sides of the gap the initiation of the foliar trace 
may be noted. In 3 the two strands which constitute it are more clearly 
defined, while in 4 they have separated from the axial meristeles, and 
have already subdivided. The traces 4-8 indicate the behaviour usual 
for the leaf-trace in the larger types of the genus. The two larger strands 
of the series into which the trace divides are on the adaxial side, and show 
the usual hooks of xylem ; the smaller strands vary in number and in size. 
As the trace emerges into the 
petiole, it usually consists of 
the two adaxial strands with 
five or six smaller strands 
disposed in a curve between 
them (compare 7 and 8). It 
may be added that the vas- 
cular supply from the rachis 
to the pinna consists in this 
species of two equal strands. 
Plainly the vascular system is 
essentially of the same type 
as that seen in Matteuccia , 
but here the vascular tracts 
are more subdivided, in ac- 
cordance with an hypothe- 
tical advance, and perhaps 
also the large size. Still 
more does B. tabidare show 
an advance in vascular structure as compared with Plagiogyria. 
The species is strongly dimorphic, the fertile leaves standing more 
erect than the sterile. The development of the fertile pinna shows the 
usual marginal segmentation of the wings. But the relation of the protective 
4 indusial * flaps to the marginal cells does not appear to be constant. 
Sometimes the 4 indusial 5 structure seems plainly to be derived from the 
marginal cell itself (PI. XXIII, P'ig. 4, a, b ) ; in other cases it seems to arise 
as clearly from an abaxial segment (Fig. 4, c y d , e y f), so that the true 
margin as defined by segmentation lies towards the upper, or adaxial face 
of the developing pinna. It is possible that this apparent variability may 
have its explanation in differences of position of the actual sections relatively 
to the apex and base of the pinna, a point which will come out more clearly 
in the description of the facts to be given for B. lanceolatum. Probably the 
sections a , b y where the flap is truly marginal, came from the middle region 
of the pinna, and those shown in c, d y e y f from points nearer the apex 
Text-fig. 3. Transverse section of the stock of 
Blechnum tabulare (Thunb.), Kuhn. The numbers indicate 
the succession of the leaf-gaps from below upwards, x 4. 
