Bower . — Studies in the Phytogeny of the Filicales. 271 
rest. But they share the general characteristics of Gleichenia so fully that 
there is no question of their real affinity with it. Both have the creeping 
rhizome, bearing upon it at intervals leaves which are endowed with the 
continued apical growth so characteristic of the genus. As in other species, 
the circinate apex of the leaf rests from active growth at intervals, appearing 
as a bud dormant between the last developed pinnules, and then resuming 
again its activity (Goebel, ‘ Organography/ ii, p. 318). In the disposition 
and development of the ultimate branchings of the leaf, these species have 
been recognized by systematists as forming each a separate section of the 
genus. Their segregation has also been based upon the fact that in the 
number of sporangia in the sorus they exceed the rest. Of G. pectinata 
Sir Wm. Hooker wrote that ‘ it is the only species of this section (§ 3), and 
not to be confounded with any other ’ ; while he further remarked of his 
§ 4, that ‘ as G. pectinata is a solitary species in its section, so is G. dichotoma 
of the present one ’ (‘ Syn. Fil. ’, p. 1 5). 
Branching of the axis may be in G. pectinata either dichotomous in 
a horizontal plane, or monopodial in a vertical plane. Of the former 
branching Boodle and Hiley remark that c it appears not to be known to 
occur in the rhizome of any other species of the genus ’ (‘Ann. of Bot.’, 1909, 
p. 426). It is true that collectors and systematic botanists have commonly 
neglected to provide evidence of, or to describe such features. But I have 
specimens of very perfect dichotomy of the axis in Dicranopteris fulva , 
Desv. Underw. (— Gleichenia pnbescens , H. Bk.), and the same branching 
exists also in G . flabellata. Probably dichotomy of the axis is frequent 
within the genus. In the leaf, on the other hand, it is stated by Goebel 
(‘Organography’, ii, p. 319, footnote) that ‘no species in Gleichenia has 
a dichotomous leaf’, and these species appear to be no exceptions. More- 
over, as Campbell has observed (‘Ann. Jard. Bot. Buit. 2 e serie, vol. viii, 
p. 98), ‘ the cotyledon in G. pectinata , G. dichotoma , and G. laevigata shows 
a prolonged apical growth like that found in the adult leaves of the young 
sporophyte’. He notes ( 1 . c., p. 94) that ‘the cotyledon of Gleichenia , 
especially in the section Mertensia , differs from that of most Ferns. In the 
majority of Ferns the cotyledon is fan-shaped, the result of an early 
dichotomy. In Gleichenia the original apex seems to persist.’ The complex 
leaf-forms of the genus are the result of repeated pinnation, modified, but 
not in any genetic sense altered, by unequal development of the parts, 
varied distribution of intercalary growth, and periodic arrest of apical 
activity. In G. linearis the unequal development of parts of the leaf makes 
itself apparent in the specialization of certain pinnules as a protection to 
the resting apex of the leaf. Goebel points out that these are neither 
‘ adventitious structures ’ nor ‘ vestiges ’, but only pinnules which are de- 
veloped for the protective function ; and that they vary in different species 
according to the size of the resting apex, being absent where it is small, or 
