Bozver . — Studies in the Phytogeny of the Filicales . 315 
both sources the result is arrived at that the dendroid character is secondary 
for the Gradate Ferns. 1 
It also appears from the sequence in question that a natural progres- 
sion is illustrated from the protostelic to the solenostelic, and finally to the 
dictyostelic type of vascular arrangement. Lastly, there is the further step 
to a dictyostelic state with accessory strands in pith and cortex. There is 
probably no series of nearly related Ferns which shows such progressions as 
these so clearly. 
It is also indicated that while the hair is present in the lower members 
of the sequence, broad scales become a later feature, and that though these 
at their first appearance in Alsophila do not form an ‘ indusium ’, in the more 
advanced types they become specialized for that duty. 
Finally, the sequence illustrates the progression from the simple to the 
gradate sorus, and from sporangia with large spore-output and median 
dehiscence to those with greatly restricted output and lateral dehiscence. 
It is the consistent parallelism of all these progressions, in characters physio- 
logically quite distinct from one another, which gives them their special 
cogency as evidence, and forbids any of the progressions being read in 
converse. 
Unfortunately the evidence from the fossils, which would be so 
valuable an adjunct to comparison, and especially in deciding whether 
or not the sequences contemplated were really progressive, is not of a dis- 
tinctive character. As to the Cyatheaceae, Seward states ( c Fossil Plants ’, 
vol. ii, p. 366) that ‘it is not until we reach the Jurassic Period that trust- 
worthy data are obtained ’. The evidence as to the existence of the 
Gleicheniaceae, such as we at present know them, earlier than the Jurassic 
Period, where they are certainly represented, is not convincing. It turns 
upon the interpretation of specimens of Oligocarpia , which bear sori with 
a small number of sporangia, and have been referred by some authors 
to the Gleicheniaceae. But opinion as to their Gleicheniaceous character is 
divided. Zeiller and Scott (see Seward, 1. c., p. 352) uphold the presence of 
an annulus such as would be indicative of a Gleicheniaceous affinity. But 
this is not admitted by Solms-Laubach, Stur, or Schenk. It cannot there- 
fore be used as direct evidence here. Nevertheless the comparative con- 
siderations which have been advanced would make the occurrence of 
ancestral representatives of the family earlier than the Jurassic Period seem 
probable. And the character of the sorus of Oligocarpia suggests at least 
some such ancestral form, whether or not the sporangia have the exact type 
of annulus now recognized as characteristic of the Gleicheniaceae. There 
is no doubt that they had the median dehiscence ; this is clear from speci- 
mens shown me by Dr. Kidston. There is, however, reason to think that 
the annulus in these early types may not have consisted of a single row of 
1 Compare footnote on p. 293, above ; also Ann. of Bot., xxv, pp. 567-8. 
