516 Bower.—-Studies in the Phytogeny of the Filicales. 
the area of the sorus, or (4) by elongating the receptacle. Gleichenia did 
not adopt any of these devices, but other Ferns did, and have succeeded. 
The Matonia-Dipteris-Cheiropleuria Series has adopted the three first 
named, but not the last, for none of them have developed as Gradate types. 
Mcitonia itself retained the circumscribed sorus, but adopted a lateral 
dehiscence of its short-stalked, but large and few sporangia. In Dipteris 
the number of the laterally dehiscent sporangia is larger, their size smaller, 
their stalks longer, and the area of the sorus larger, especially as seen in 
D. Lobbiana, and quinquefurcata. In D . conjugata the less size of the sorus 
is balanced against their much greater number spread over the webbed 
lamina. In Cheiropleuria the laterally dehiscent sporangia are still longer- 
stalked, and the confluent sori are spread continuously over the leaf-surface, 
giving a fully ‘ Acrostichoid ’ character. In Plotycerium , however, the sori 
are merely elongated, not confluent, the large number of the sporangia 
being accommodated by the extension of the area of their elongated 
receptacles. The latter types appear to have diverged far from the simple 
Gleichenioid source, which would hardly be recognized in them were it not 
for the intermediate states which some of them show, and also the comparisons 
which may be based on other characters. 
The Sporangia. 
The sporangia of Matonia are well known, and need no fresh descrip¬ 
tion (see Seward, Phil. Trans., vol. 191, p. 171 ; Studies, IV, Phil. Trans., 
B, vol. 129, PI. 4, Figs. 59-62, and Land Flora, p. 565). But those of 
Dipteris are less fully investigated. They have been figured and described 
by Seward (Phil. Trans., vol. cxciv, PI. 48, Figs. 11-16) and by Miss Armour 
(New Phyt, 1907). But these analyses were not exhaustive, and their 
development has never been fully traced. It will be seen that their seg¬ 
mentation gives an important line of comparison with Cheiropleuria . The 
sporangia of Dipteris Lobbiana are shown from their ‘peripheral’ side in 
Text-fig. 16, a , b, and it is apparent that the annulus is a complete ring of 
cells, though the induration of those opposite the stalk is incompletely 
carried out. A comparison may be made with a similar view of the sporan¬ 
gium of Gleichenia lineata (— Gl. dichotoma) (Land Flora, p. 555, Fig. 3io) s 
which shows similarity of form and of position of the annulus ; but there 
the induration is complete, and the dehiscence distal and median. In 
Dipteris Lobbiana the dehiscence is obliquely lateral and, as the Text- 
figs. 16, a,b show, either right or left of the median line. The stomium is 
not well defined, a character shown also in Matonia and Gleichenia. The 
stalk is short, and shows two rows of cells, as seen from the peripheral 
side. Fig. c shows a similar view of a sporangium already dehisced. In 
P'ig. d is a view from the ‘ central ’ side, but with the annulus hidden on the 
dehiscent margin. Again the stalk appears as two rows of cells. Since 
