288 Boiver . — Studies in the Phytogeny of the Fi tic ales. 
sporangium which is directed obliquely outwards from the centre of the 
sorus in the normal orientation; this orientation we have seen to be 
habitual in those of the lower tier in Lophosoria . The central is the oppo- 
site face, which is directed obliquely inwards, to the centre of the sorus, just 
as in Gleichenia. It is shown for Lophosoria in Fig. 19. In Fig. 20, where 
the sporangium is seen from the side, showing clearly its turgid form, the 
two opposite faces are indicated by words. The annulus consists as a rule 
of a single row of cells of regular sequence ; but in the neighbourhood 
of the stomium irregularities appear. In Figs. 19, 20, certain cells are 
divided, while in close proximity there appears a break in the regularity of 
the sequence. It is as though the distal part of the annulus were more 
nearly vertical than the proximal part. Such facts indicate an instability 
of exact position of the annulus such as might be anticipated in a case 
where that structure is in course of change from an inherited to a 
novel position ; in fact, swinging from an oblique towards a vertical 
position. 
The stomium is lateral in position — a marked difference from the case of 
Gleichenia , where the dehiscence is median. It is not exactly differentiated, 
and appears to be variable in the number as well as in the exact position of 
its cells. It serves, however, as a structural definition of the lateral dehis- 
cence, though not with the constancy of structure seen in more advanced 
Ferns. Such a condition is what might have been expected in a type 
in which a recent change of the point of dehiscence from a distal to a lateral 
position had occurred. 
The number of tabular cells covering the faces of the sporangium 
is relatively large, and it is markedly so when a comparison is made with 
the sporangia of the Cyatheaceae. Thus, over fifty cells are shown on the 
peripheral face of Fig. 18 of Lophosoria. In Studies, IV, Fig. 83 of Cyathea 
there are only six, in Fig. 86 of Hemitelia there are eight. The correspon- 
dence is, however, a closer one with the large sporangia of Gleichenia. 
Having noted thus the large size of the sporangium, and its complexity of 
structure, it was a matter of some surprise to find that the output of spores 
is low. Several countings gave figures closely approximating to, but not 
exceeding sixty-four, which appears to be the typical number in each 
sporangium. 
The development of the sorus and sporangium has been studied 
in sufficient detail for bringing out the points that are essential for 
comparison. As in Gleichenia the receptacle makes its appearance on 
the lower surface of the pinnule, at some distance from the margin, as 
a multicellular upgrowth of rounded form (Figs. 21-2). Certain of its 
superficial cells begin to grow out as hairs (Figs. 24-6), while others become 
soon recognizable as the parent cells of sporangia (marked x in Fig. 23). 
These undergo divisions by walls inclined to one another, leaving a pyra- 
