Bower. — Studies in the Phytogeny of the Filicales. 475 
2. The characters which distinguish it from Alsophila are the creeping 
habit, the unbranched hairs and absence of scales, the solenostelic structure 
of the axis and undivided leaf-trace, the flat receptacle and simultaneous 
origin of the numerous sporangia, and the almost vertical annulus, interrupted 
at the insertion of the sporangial stalk. 
3. These characters collectively place it in a position phyletically more 
primitive than the true Cyatheae, in a somewhat similar independent 
position to that held by Lophosoria. 
4. Notwithstanding the dictyostelic structure with medullary strands 
shown in their upright axes, all the genera of the true Cyatheae may 
at times show a solenostelic structure in their runners, which arise from 
dorsal buds, as in Lophosoria and Metaxya . 
5. Thyrsopteris shows a solenostelic structure of its axis, with a medul- 
lary system built up from ‘ compensation strands Its leaf-trace is undivided 
at the base. This structure closely corresponds to that of Saccoloma. 
6. The sori of all such species of Thyrsopteris , Dicksonia , Saccoloma , 
Odontosoria, Lindsay a, and Davallia as have been examined developmental^ 
arise from the actual leaf-margin, their indusia being of the nature of surface 
growths. 
7. The sori are quite separate in Thyrsopteris and Dicksonia : but they 
have their upper indusial flaps fused laterally in Saccoloma ; both flaps are 
fused, and their receptacles also in Lindsay a, while a vascular commissure 
may join the distal ends of the veins, which are elsewhere free. These 
fusions are secondary and derivative characters which indicate phyletic 
advance. 
8. The first sporangia of the sori of the genera named appear to be 
strictly marginal in their origin, followed by a ‘ gradate ’ sequence in the 
more primitive types, such as Thyrsopteris and Dicksonia , but becoming 
‘ mixed’ in more specialized types, such as Lindsay a and Davallia. 
9. The sporangia of Thyrsopteris and Dicksonia have a complete 
oblique annulus, but in the more advanced types it tends to become 
vertical, and is interrupted at the stalk as in Davallia. 
10. In all the more advanced types, and particularly in Davallia , 
the sorus, though developmentally marginal, is diverted to the lower surface 
by the advance in strength and complexity of the upper indusial flap which 
forms a false margin of the leaf. 
11. This appears to have become accentuated further in Nephrolepis, 
and probably also in Oleandra , and thus the sori have the appearance 
of being superficial. 
12. Except for this phyletic slide of the sorus to the lower surface 
in these relatively advanced types, the sorus is constantly of marginal origin 
in all the Dicksonioid and Davallioid series, as it is also in Loxsoma , in the 
Hymenophyllaceae, and in the Schizaeaceae. 
