OF FILICALES 151 
In the Ophioglossales the structure of the shoot at large is open to 
various interpretations; but without entering here into questions which 
will be taken up in detail later it will suffice to mention that in 
flelminthostachys there are sporangiophores which are broadly similar 
in outline to those of Lguisedum, but they are borne in_ irregularly 
disposed bands on the lateral margins of the fertile spike (Fig. 83). 
It may at first sight seem difficult to bring the very varied disposition 
of the sporangia upon the enlarged sporophyll in modern Ferns into line 
with these examples of spore- : 
bearing bodies in smaller-leaved 
types. But it is to be remem- 
bered that in Palaeozoic Ferns 
definite common ; 
they were as a rule of circular 
form, and all their sporangia 
were produced simultaneously. 
The wide-extended sori, such 
as are frequently found among 
sori were 
the Polypodiaceae, were pro- 
bably of relatively late and 
secondary origin, by extension 
of the sori of the circumscribed 
type. Now, a circular sorus, 
with relatively few sporangia 
formed simultaneously and 
borne upon a more or less pro- 
jecting receptacle, into which, 
as may often be seen, a vascular 
supply extends, differs in no 
such bodies as 
considering. A 
simple type is B 
seen, for instance, in Kaw/fussza, 
which is closely similar to that 
essential from 
we have been 
sorus of this 
Ptychocarpus unitus. Fructification. A, part of a fertile 
of the Palaeozoic Fern, Ptycho- 
carpus unitus (Fig. 84). It has 
been seen that spore-bearing 
pinoule (lower surface), showing numerous synangia. #4, 
synangia in side view. (4 and & x about 6.) (After Grand! 
Eury.) C,a synangium in section parallel to the surface of 
the leaf, showing seven confluent sporangia. a, bundle of 
receptacle; 4, its parenchyma; c, tapetum; a, spores; ¢,//, 
common envelope of synangium. ™ about 60. (After 
bodies may be borne directly Renault.) From Scott’s Studies in Fossil Botany. 
on the axis or on the appen- 
dages; the latter is the case in the Ferns, the chief difference between 
them and the strobiloid forms being that the appendages here are large 
and the sori, or sporangiophores, very numerous. Regarded in this light, 
the Fern-type is not a thing distinct or apart; the difference from other 
types is mainly one of the degree of development of the sporophyll which 
bears the sori. 
