GLEICHENIACEAE 559 
in advance of the latter. G. dichotoma shows individual fluctuations in 
size of the sporogenous group, while the number of spore-mother-cells is 
considerably below that in G. flabellata. Subsequently, the spore-mother- 
cells separate, becoming rounded off, and undergo the usual tetrad 
division. Prior to this, the tapetal nuclei make their way in among the 
developing spore-mother-cells, as has been described for other sporangia. 
In order to test the results obtained from sections, and the estimates 
of potential spore-production based on them, countings of the actual spores 
produced from single sporangia have been made in various species of 
Gleichenia, with the following results : 
Gl. flabellata, 794, 698, 838, 634. 
Gl. circinata, 241, 242. 
Gl. rupestris, var. glaucescens, 220, 232, 244. 
Gl. hecistophylla, 265, 272. 
Gl. dichotoma, 251, 319. 
From the figures it appears that the output is very irregular; but consider- 
ably in excess of that in most Leptosporangiate Ferns; that the high 
estimated number in GZ flabellata is not actually attained; and that though 
in the four latter species the numbers approximate to 256, that figure is 
liable to be exceeded. That the actual figure in GZ flabellata falls below 
the estimate may be accounted for partly by the abortion of some spore- 
mother-cells, or young spores, of which there is evidence; partly by errors 
in counting such large numbers; but it may also be due to the number 
of spore-mother-cells being inconstant, or being actually not so large as 
the estimate, which is necessarily only a rough one; another reason for 
the deficiency is the frequently incomplete division of the spores of single 
tetrads. There-is no exact proportion between the size of the individual 
sporangium and its output of spores in this genus as a whole. G/. circinata, 
with its large sporangium, has a smaller output than GZ /ladellata, of 
which the sporangium is a medium size. It is, however, to be noted that 
the spores in the latter species are smaller than in the former. 
The dehiscence of the sporangium takes place by a slit in the median 
radial plane; the annulus, which is continuous all round, except along 
the line of rupture, becomes gradually straightened on drying, or even 
everted, the whole sporangium thus widening laterally so as to elbow 
aside the other sporangia in cases where these are numerous. Then a 
sudden jerk on both sides of the slit throws the spores out, right and 
left. Plainly, this mode of dehiscence requires lateral space, to allow of 
the widening before the jerk, and it is thus ill-suited for a crowded sorus. 
Its existence here indicates that the Gleicheniaceae are in the upgrade, 
not in the downgrade, of soral complexity. The facts point to the radiate- 
uniseriate type of sorus as being the primitive state, while the spore-numbers 
would indicate that of the species examined, G. flabellata, in which that 
type of sorus is represented in its most regular form, is probably the most 
