Bower.—Shidies in the Phytogeny of the Filicales. 515 
show a mixed condition, as regards the order of appearance of the sporangia 
(Land Flora, p. 621). But this is not actually an £ Acrostichoid ’ condition, 
for the sori are still circumscribed, and the receptacles are quite distinct, 
as is shown in Text-fig. 2 ; and individual sporangia do not occur as a rule 
upon the areas between the receptacles. In Cheiropleuria the venation is 
the same as that in D. conjugata ; but the sori are not circumscribed. They 
are merged into a continuous mass of sporangia and paraphyses, which 
covers the whole surface, the identity of the sori being completely lost. 
The sporangia are borne indiscriminately over the whole surface, and not 
only at points above the vascular receptacles. Further, sporangia of very 
various ages are found in juxtaposition, giving a pronounced £ mixed ’ 
character to the whole mass (Text-fig. 15). Thus Cheiropleuria is fully 
‘ Acrostichoid and non-soral, and 
shows a marked advance upon 
the other types as regards these 
characters. 
Platycerium , on the other hand, 
is not truly £ Acrostichoid ’, though 
it has often been assumed to be so. 
It has already been shown that the 
fertile patches of this genus are not 
continuous, but that the sporangia 
are disposed along definite lines, 
which are really extended sori (Phil. 
Trans., B, vol. 192, p. 86). They lie 
above those vascular strands, which 
constitute in each case an elongated 
receptacle, and form collectively the lower vascular reticulum (see Text- 
fig. 15). The sporangia are disposed upon these in two more or less 
definite rows, one on either side of these elongated receptacles. Moreover, 
they originate for the most part, if not wholly, simultaneously. Thus 
the fertile patches of Platycerium are really composed of closely placed 
aggregates of greatly extended sori, themselves essentially of the type of 
the Simplices, so far as the origin of their sporangia is concerned. 
It thus appears from the facts adduced that the soral condition of the 
Ferns under discussion is referable in origin to a primitive state seen 
typically in Gleichenia , with a single row of circumscribed sori on either 
side of the relative midrib ; and with few sporangia produced simultaneously 
in the sorus. It has been shown (Studies, II, Ann. of Bot., xxvi, p. 275) 
that in G. pectinata , by crowding of the sorus, it had become mechanically 
inefficient, since there is not sufficient room for median dehiscence of its 
sporangia. From this relief might be found (1) by increasing the length of 
the sporangial stalk, (2) by adopting lateral dehiscence, (3) by extending 
Text-fig. 15. Transverse section of part of a 
fertile lamina of Cheiropleuria. x 50. 
