DENNSTAEDTIA-DAVALLIA SERIES 613 
cases from the type of the Gradatae, but might also be produced directly 
from the sorus of the type of the Simplices. It must suffice here to trace 
some probable lines of phyletic origin which have so far emerged, though 
others may eventually be recognised. 
DENNSTAEDTIA-DAVALLIA SERIES. 
The best accredited case is seen in Ferns with marginal sori, and it 
has been found that among them there are forms which lead from the 
Gradatae towards those genera with mixed sori which have been grouped 
by Prantl as the Pterideae.! It has already been seen that though the 
sorus of Dennstaedtia is typically basipetal (see Fig. 332 42s, a), occasional 
departures from the strict sequence exist in D. apiifolia, while in D. rudz- 
ginosa the sorus retains some signs of the basipetal sequence, but younger 
sporangia occur interpolated without order among those pre-existent, while 
the receptacle is more flattened (Fig. 339 4). It will be seen that these 
characters approach those seen in Davadiia. 
The genus Davallia, as it stands in the Synopsis Filicum, is a compre- 
‘hensive one. Sir William Hooker remarks? of the Davalliae: ‘‘No two 
authors are agreed as to the limits of this group, nor of the genera which 
compose it; and no wonder, seeing how gradually the genera seem to 
run one into another. To me the genera seem to have been need- 
lessly multiplied, upon very insufficient grounds, so that in many cases 
I cannot even adopt them as sub-genera.” The result of Sir William 
Hooker’s view, as thus expressed, has been that he grouped several genera 
of other authors under the comprehensive genus Davadia. But the 
tendency has since been to reinstate some of his sub-genera as substantive 
genera, the most prominent case being that of Aicrokpia: the characters 
derived from the sorus have been described above, and justify the removal 
of Microlepia from the genus Davaliza. 
From the § £u-Davallia of the Synopsis Filicum, observations have been 
made on D. griffithiana, Hook, pyxidata, Car., canartensis, Smith, sodida, 
Swartz, and diwvaricata, Blume. In all of these the sorus shows various 
ages of sporangia intermixed, while they are inserted upon a wide, flat 
receptacle. The sporangia themselves have long stalks when mature, so 
that the ripe sporangial head is raised far above those of the younger 
sporangia, and thus scattering of the spores is ensured without an elongated 
receptacle. 
The development has been specially studied in D. Griffithiana. Fig. 3398 
shows a young sorus with the first sporangia appearing. It may be noted 
that on the flat receptacle the first sporangium is in a median position, 
and this may be taken as a slight trace of basipetal succession; but even 
this is not constant, and as the development proceeds any superficial cell 
14rd. K. Bot. Gart. Breslau, vol. i. (1892), p. 17. 
2 Species Filicum, i., Pp. 150. 
