Studies in the Morphology of Spore-producing Members. 27 



towards the centre of the sorus. By periclinal division this forms 

 internally the archesporium, externally that part of the -wall where 

 dehiscence takes place. The tapetum arises, typically in them all, 

 from the cells surrounding the archesporium. The dehiscence is iu 

 all by a slit in a radial plane, which may widen to a circular pore in 

 Dancea. In those sori where the sporangia are united laterally there 

 is no annulus ; it is present only where the sporangia are separate, as 

 in Angiopteris. 



An interesting feature is disclosed by estimates of the potential 

 spore-production of the single average sporangium in the four 

 genera; the results in round numbers are, in Angiopteris 1,450, in 

 Dancea 1,750, in Marattia 2,500, in Kaidfussia 7,850. It is to be 

 remembered that the usual numbers in Leptosporangiate ferns are 

 48 — 64; in some Leptosporangiate ferns (Osmunda) the number may 

 rise to 500. I have ascertained in Gleichenia, however, that the 

 number may be as high as in Angiopteris. This large potential out- 

 put of spores goes parallel with the broad base of the sporangia; in 

 fact, the Eusporangiate condition is that best adapted for maturing 

 large numbers of spores in the individual loculus. 



Frequent deviations from the type have, however, been observed, 

 as well as variations of size and mode of segmentation of the 

 sporangia, and it is not possible in certain cases to refer the whole 

 sporogenous tissue of one sporangium to a single parent cell. A 

 special study of the irregularities has been made in Dancea, in which 

 geim'i they are most marked ; incomplete septa are frequent, and the 

 sporangia are of very unequal size. The main features have already 

 been noted in the preliminary statement on that genus, where it has 

 been pointed out that comparison of the details with those of the 

 septate anthers of some Angiosperms shows that there is a remark- 

 able resemblance between the two cases. Similar irregularities have 

 been noted, though less commonly, in Kaidfussia, and Marattia, and 

 rarely in Angiopteris. 



Those fossil Marattiacese which are best known as to the details of 

 the sorus have been compared, and the substantial similarity of the 

 sori in certain cases to those of the modern genera recognised. The 

 facts from fossils and from the modern Marattiacese have been made 

 the basis for a fresh discussion of the theoretical question, whether 

 the synangium is or is not a result of coalescence of sporangia ? It 

 is concluded that the palasophytological evidence leaves the question 

 open as to the priority of existence of forms with synangia, or with 

 separate sporangia, in the Marattiaceee. Notwithstanding that 

 writers of authority have treated the question as decided, that the 

 synangia are a result of fusion of distinct sporangia, it is held with 

 some persistence that it is still open; the paleeophytological evidence 

 is inconclusive, while the comparative evidence from the living 



