Bower .—Studies in the Phytogeny of the Filicales. 379 
distinct projections on the developing wing (PI. XXIV, Fig. 8, a). They 
are plainly the indusial flap (i) and the margin ( m ), as in B. attenuahim , and 
their ultimate origin is probably the same. The indusium soon projects as 
a protective covering over the region where the sporangia arise. They are 
formed from the deep prismatic cells seen in Fig. 8, a , b , and usually show 
some indication of a gradate sequence (Fig. 8, c ), but this is not constant, 
and in Fig. 8, which shows a rather more advanced condition, there are 
signs of irregularity. The wedge-shaped cell marked m is a fairly constant 
and easily recognized feature, and marks the structural margin. This is 
specially noted for comparison with other cases, such as B. filiforme and 
Stenochlaena . There are evidences of branchings of the vascular supply 
below the sorus to supply glands, as in B. attenuatum (Fig. 7, e), but the 
whole structure, though very like that species, is on a less elaborate scale. 
(F) Blechnum spicant (L.), Wither. 
This familiar species corresponds in essentials to those above described, 
but, as will be seen, it shows a slight degree of advance in the complexity 
of its fertile pinnae. 1 The mature stem is up- 
right and contains much sclerenchyma, which 
forms an external cortical band, and a medullary 
mass with projecting angles. Its vascular system, 
consisting of the usual dictyostele, lies between 
these, surrounded by softer parenchyma (Text- 
fig. 5). The meristeles vary in number in the 
transverse section according to the leaf arrange- 
ment ; they are usually about four in number 
and have a form similar to those in B. attenuatum . 
Here, as elsewhere in the genus and with striking 
regularity, each meristele first gives off a root- 
trace from its central region, which passes bodily 
out. A leaf-gap is thus formed, the sides of which, at a slightly higher 
point, give off the leaf-trace itself as two strap-shaped strands, which 
enter the leaf-base without further division. But here one of them may 
give off a single smaller strand, which usually splits into two (see Luerssen, 
Rab. Kr.-Fl., vol. iii, p. 114). These lie between the larger strands, forming 
with them a simple horseshoe. This is a rather simpler structure than in 
the larger B. tabulare , or attenuatum , while all may be held as derivatives of 
the type seen in its simple form in Matteuccia , or still more simply in 
Plagiogyria. 
The general characters of the fertile pinna are adequately shown in the 
Text-fig. 5. Transverse 
section of the stock of Blechmun 
spicant (L.), Wither, x 8. 
1 For habit of pinnae of this species see Rab. Krypt.-Flora, vol. iii, p. 109, and Figs. 84, 85 ; 
for an account of the vascular system, 1 . c., p. no. For the vascular condition of the seedling see 
Chandler, Ann. of Bot., vol. xix, p. 373. 
D d 
