584 FILICALES 
arrested leaf-tip developing equally, and so strongly as to exceed the actual 
apex which lies between them. But on the other hand, as the result of 
comparison apparently of mature specimens, Tansley refers the leaf-architec- 
ture ultimately to dichotomy. He states that ‘a bud normally arises from 
the angle of the primary dichotomy.”! In face of such diametrically opposite 
statements the accurate observation of the ontogeny is most desirable; 
hitherto the details of development of the Gleicheniaceous leaf have never 
been worked out. 
The degrees of branching of the leaves have been made the basis of 
subdivision of the genus into four sections (Fig. 308).? Goebel has described 
the mode of protection of the resting bud seen in some species: the pinnules 
which stand nearest to the apex form protec- 
tive scales, and they have been mistaken for 
adventitious or aphleboid growths? As a 
matter of fact, the whole structure can be 
referred to a normal pinnate development of 
the leaf, altered by temporary arrest of the 
apex, and by precocious development of 
certain pinnae. Hairs and paleae are found 
on the surface both of rhizome and leaf. 
The sori are always superficial, disposed 
in a single row on either side of the midrib 
of the fertile segment (Fig. 309). Typically 
they are radiate-uniseriate, the sporangia 
being attached in a ring round a central 
receptacle: they are without indusium. The 
ee a number of sporangia varies in different 
Gleichenia flabellata, Br. Midrib and 6 A 
three pinnules, showing the arrangement Species, two to five being common numbers; 
and constitution of the sori, with vagiable 
number of sporangia. but the sorus may often be represented by 
a solitary sporangium (monangial  sorus), 
especially towards the distal end of the segment, a fact pointing in the 
direction of the Schizaeaceae: or the number may be larger than five 
or six, as in G. pectinata and dichotoma (Fig. 310, a—h), and this points in 
the direction of the Cyatheaceae. 
The existence of the fossil Fern with fructification designated Oligocarpia 
has been held as evidence of the existence of Gleicheniaceous Ferns as 
early as the Palaeozoic period. But the fact that the Gleicheniaceous and 
Marattiaceous sori are of the same type throws the burden of proof upon 
the sporangial structure, on which point it may be admitted that there is 
some doubt.4 But the Gleicheniaceous habit of frond is seen in the 
Palaeozoic genus Dzflotmema and other types, while certain Carboniferous 
stems had an anatomical structure like that of the Gleicheniaceae.6 But 
FIG. 309. 
1 Ann. of Bot., xix., 1895, p. 479. ’ Diels, Wat. Pflanzenfam., i. 4, p. 352+ 
° Goebel, 2.c., pe 318. +See below, p. 560. 
5 Scott, Studies, p. 263. 
