278 Bower . — Studies in the Phytogeny of the Fili cates. 
largest antheridia (cf. Rauwenhoff). Unfortunately, the extreme type in the 
latter respect ( G . laevigata ) has not been examined as regards its spore- 
output. G. linearis i which anatomically and sorally is more primitive than 
G. pectinata , is on the antheridial criterion more advanced. These dis- 
crepancies find some explanation in the irregularity of size of the individual 
antheridia of G. pecthiata , which shows that this criterion must not be 
pressed too hard. It has long been a matter of note that the extent of 
projection and the bulk of sporangia and antheridia show some degree of 
parallelism, the more bulky and deeper sunk being held as the more 
primitive condition. It has also been pointed out at length elsewhere 
(‘ Land Flora \ p. 641, &c.) that the numbers of spores produced in a spor- 
angium give a rough numerical measure of the relative bulk of the spor- 
angium for comparative purposes. It is also the fact that there is a parallel 
between these characters and the segmentation of the apices of axis, leaf, 
and root in the plants in question. To these criteria is now added that of 
the spermatocyte-production of the antheridium. But while we recognize 
these points, they must not be driven to the length of exact numerical com- 
parison. It is becoming apparent that while such parallels are true in 
general, indicating conditions of relatively greater or less bulk of funda- 
mental organization, still they are not invariably exact, and are open 
to exceptions. 
From the details and comparisons advanced in the above pages the 
conclusion may be drawn with some degree of certainty that the Gleicheni- 
aceae occupy a place among the most primitive of the Filicales ; that 
Mertensia is more primitive than Eu-Gleichenia ; and that in many charac- 
ters, though not in all, G . flabellata is a central and an early type. Perhaps 
it may share this position with G. laevigata , which is as yet imperfectly 
investigated. From such forms as central, lines of specialization appear 
to have led, resulting on the one hand in G. linearis , which show various 
features of advance ; on the other hand there is G. pectinata, which may be 
held as the most advanced species of the genus. This appears especially 
from its vascular anatomy, and from its sorus, the latter having arrived 
at the limit of development which can be practically effective in the 
GleicheniaceOus type of soral construction. This species shows, however, 
in its hairs (scales being absent), in the relatively large spore-output of its 
larger sporangia, and in the large number of spermatocytes of its largest 
antheridia, traits that are primitive. But the variability of size of both its 
sporangia and of its antheridia indicates the readiness with which the type 
might advance progressively to characters shared by most Leptosporangiate 
Ferns. The question of genetic relations between the Gleicheniaceae and 
the Cyatheaceae is thus centred definitely upon Gleichenia pectinata above 
all other species of the genus. The next step will be to consider the ques- 
tion from the other side, and to see whether any outstanding species of the 
