520 Bower.—SHi dies in the Phytogeny of the Filicales. 
The lower surface of the leaf is covered by the dense sorus, which 
is not limited to any position above the veins, but is spread uniformly over 
the whole area. It consists of (a) very numerous paraphyses, simple un¬ 
branched hairs, each terminating in a glandular cell ; ( b ) isolated sporangia 
disposed with no definite regularity among them. The relations of these 
are shown in transverse section in Text-fig. 17, and in vertical section in 
Text-fig. 15. The sporangia are seen in the latter to be sometimes seated 
over the vascular tracts ; but they appear to be equally common in the 
areas between them. Further, as they are not disposed in any order of 
age, the soral areas are of the ‘ mixed ’ type. Thus there is a definite 
‘ Acrostichoid 5 condition of the sorus in Cheiropleuria . 
While young, the sporangia are efficiently covered by the paraphyses, 
which are taller than they. But as maturity approaches, the sporangial 
stalk elongates, so that the sporangial head comes to be level with their 
ends, and can discharge its spores freely, while those which are younger 
are still protected below. This arrangement is closely parallel with that 
of the asci in any of the Discomycetous Fungi. 
The sporangium originates from a single superficial cell. In a large 
number which have been examined, the segmentation appears to show 
a regular cleavage of the segments in two opposite rows. Naturally, those 
selected for drawing show these right and left, for thus they present the 
most definite appearance. The first of such segment-walls cuts obliquely 
down to the base of the square mother-cell (Fig. 17, a). The number of 
the cleavages does not appear to be constant (compare Fig. 17, b-e). After 
the number of the cells in each row, either by primary cleavage or by 
subdivision, has reached four to six, the wedge-shaped cell which occupies 
the apex undergoes periclinal division (d), which is followed by further 
segmentations parallel to the last, giving rise to the tapetum, and the 
central sporogenous cell (/). Later development follows the course usual 
in Leptosporangiate sporangia. Meanwhile, subdivision of the two rows 
of segments of the stalk by walls in the plane of the drawings has given 
rise to the four rows of cells of the stalk, as seen in the later stages 
(Text-fig. 17, d). 
The cleavages thus described are so peculiar and exceptional among 
Leptosporangiate Ferns that it was thought well to compare them with 
those seen in Dipteris , in which a like structure of the sporangial stalk has 
been seen. Here again the storage tracheides of the receptacle lie closely 
below the surface where the sporangia are borne (Fig. 18, a). The sporangia 
arise from single cells, which may here have an oblique base, and the first 
oblique segment-wall impinges upon that oblique face; thus the type of 
sporangium is from the first less robust than that of Cheiropleuria. 
Alternate segments in two rows then follow, as in Cheiropleuria . In order 
to check the fact of this alternate segmentation, sporangia were examined 
