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 

 Gfezchema, with the following results : 



Gl. flabellata, 794, 695, 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 Gl. 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 GL 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. Gl. circinata, 

 with its large sporangium, has a smaller output than Gl. flabellata, 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 



