378 Bower . — Studies in the Phylogeny of the Fi lie ales* 
which runs below each of the receptacles and extends outwards into the 
indusial flap. The latter is clearly of the nature of a portion of the leaf 
surface, for the tissues of the thicker portion of the median region of the 
pinna extend out into it, without any sudden change, graduating imper- 
ceptibly into the flap, till at last a single layer of cells is reached. There is, 
however, a preponderance of lacunar mesophyll in the median region. The 
sori are restricted to the thinner region, where the mesophyll is either 
reduced or absent. But they extend for a considerable distance along the 
flaps, while a vascular supply stretches beneath them outwards from the 
commissures. Thus the character of the flaps suggests that they are lateral 
regions of the pinna expanse. 
The development of the fertile pinna has been traced in PI. XXIV, 
Fig. 7, a-e , and it has been found that the marginal cell, with its usual 
alternating cleavages (m), finally takes its place at the extremity of one of 
the rounded ridges. The indusial flap is here of later origin, as the figures 
themselves will show. In the young state (Fig. 7, a) the foliar wing is 
clearly referable in origin to cleavages from a marginal cell (m). As the 
development proceeds, an upgrowth appears at some distance from the 
margin and upon the lower surface. This is the indusial flap (*'), which is 
thus initiated as a superficial outgrowth (Fig. 7, b,c\ It gradually increases, 
with inclined cleavages (c, d ), thinning out to only two layers (d) and finally 
to a single one. It thus appears that the indusial flap is no longer the direct 
product of a marginal segmentation, but is slightly deferred in its time of 
appearance and is produced as an upgrowth from the lower surface. 
The sporangia arise almost simultaneously, and, though they do not 
exactly synchronize in their segmentation, there is not any marked ‘ mixed 5 
condition of the sorus. Fig. 7,^, shows the early cleavages which define the 
procambial strands, one of these leading to the gland (k) t the other passing 
to the receptacle of the sorus. 
(E) Bleckmim U Her minieri (Bory), Mett. 
Material of this species was obtained from the Blue Mountains, 
Jamaica, and from the Glasgow Botanic Garden. The plant is erect and 
subdendroid, but does not assume a climbing habit. The axis and leaf-base 
are covered with dark scales, and the leaves are dimorphic, the pinnae of 
the fertile leaves being very narrow. Hooker remarks (Syn. Fil., p. 176) 
that it ‘ is probably the same species as the Australian and Polynesian 
Icmceolata \ But this identity was not actually adopted by Hooker himself or 
by later writers. 
The fertile pinnae show in transverse section a similar outline to those 
of B. attenuatum , but on a less bulky scale of construction. There is no 
flange that can be observed externally. The very youngest stages were not 
observed in this species. In the earliest seen there were already two 
