536 FILICALES 
To form an estimate, the number of spores produced in a single 
sporangium may be actually counted, or an estimate of the potential 
number may be based upon the number of spore-mother-cells as shown 
in sections. By the latter method, as applied 
to Osmunda regalis, since the number of spore- 
mother-cells in a median section is 30 to 32 
(Fig. 297), and the sporogenous mass is 
approximately spherical with the diameter of 
each cell about jth that of the whole sphere, 
the total number would approximate to 128, 
though probably somewhat below that number. 
Actual countings of spores showed figures 
about midway between 256 and 512, distinctly 
below the estimate of Russow. In TZodea 
barbara, while some sporangia approximate to 
those of Osmunda, others fall far short, and 
approximate to 256; but in Z: superba and 
fe Gen eacaamening See, hymenophyllordes, which are “filmy” in habit, 
See o et tee layan (After Geeta)” the output is still lower, approximating in the 
last species to 128. The bearing of these 
facts will be discussed below; the results are such as coincide readily 
with the relatively robust structure and variable details of the sporangial 
development.! 
Fic. 297. 
ANATOMY. 
The vascular structure of the axis in the Osmundaceae has long been 
an object of interest, on the ground of its distinctness from that of other 
Ferns, and its apparent analogy with that commonly seen in Dicotyledons. 
But in the form of the leaf-trace, and the way in which it breaks up as 
it passes into the leaf, the Osmundaceae present features which are more 
readily matched among known Filicineous types. Starting from the peri- 
phery of the leaf, the numerous forked veins fuse, on passing downwards 
from pinnule and pinna to leaf-stalk, into a single half-cylindrical strand 
with its concave channel directed adaxially. This strand consists of a 
continuous band of metaxylem, with numerous protoxylem-groups at its 
concave limit, which alternate in position with groups of mucilage-sacs. 
Peripherally is a mantle of phloem, thicker on the adaxial side, and 
surrounding the whole is a continuous endodermis. As it passes down to 
the base of the petiole the strand contracts, and the protoxylems unite 
into a single one in a median adaxial position, while in transverse section 
it assumes a deep U-shaped outline (Fig. 298 a, B). It is in this neighbour- 
hood that the vascular supply to the roots is given off laterally from the 
strand of the leaf-trace (Fig. 2984 ut.). The strand thus contracted, after 
entering the axis, takes its place in a ring of similar traces surrounding a 
1For a more full statement see Stzdzes, iv., pp. 38-42. 
