5 H Bower—Studies in the Phytogeny of the Filicales. 
but in Lindsaya they are laterally confluent; the vascular system of their 
receptacles is there linked by commissures, so as to form a continuous 
strand. The origin of this state is by lateral spreading of the isolated sori 
of the Saccoloma-type (Studies, III, Figs. 20, 21). Similarly in the 
Pterideae, as was long ago pointed out by Prantl (Engler’s Bot. Jahrb. iii, 
p. 403, &c.), while Pellaea has the sori separate, at the distal ends of veins, 
in Pteris they are confluent. The veins are linked by vascular commissures, 
which are really lateral extensions of the vascular supply of the receptacle. 
Again, in Studies, IV, a strong probability has been advanced that the 
primitive condition from which the Blechnoid Ferns have been derived was 
that with isolated sori, such as are seen in Matteuccia intermedia. By 
lateral extension of their receptacles, and especially of their vascular systems, 
the fusion-sori typical of the Blechnoids was produced. It has also been 
shown (Ann. of Bot., vol. xxviii, PL XXIX, Fig. 20 f) y that occasionally the 
tracheidal system of the receptacle in these Ferns may extend separately from 
the conducting venation of the leaf, and pursue a course of its own in a slightly 
different (lower) plane. This, though slight in extent in the case quoted, is 
similar in essential character to the larger receptacular extensions described 
for Platycerium. And thus it appears that in a number of distinct phyla 
of Ferns, the receptacle, and very markedly the vascular system of the 
receptacle, is liable to extension. This may result in a mere linking 
together of isolated sori, as suggested by comparison of Matteuccia with 
Blechnum , or of Pellaea with Pteris ; or it may lead to an extensive 
vascular system with elongated sori attached, as in Cheiropleuria and 
Platycerium. However peculiar the latter case may itself appear, the 
above comparisons indicate that it cannot be held to stand absolutely 
alone. It may be held to be a specially pronounced example of a wide¬ 
spread phenomenon, viz., the extension of the individual sorus. 
The sori of the series of Ferns at present under discussion show 
a forward progression in several features. The most important are, (i) the 
number of the sporangia, (ii) the order and time of their appearance, and 
(iii) the extent of the receptacle which bears them. The number of the 
sporangia in the sorus of Gleichenia is small, though it rises in certain 
species, which are on that and other grounds held to be in advance 
of the rest (Studies, II, Ann. of Bot., xxvi, pp. 274-5). In Matonia also 
the number is only from six to nine, and they are individually large, and 
are produced simultaneously. In Dipteris the number may be larger, 
and the individual sporangia small. In point of order and time of appear¬ 
ance of the sporangia, the simpler species correspond to the type of 
Gleichenia , or Matonia ; this is so for D. Lobbiana , where the sori are 
disposed as in these Ferns in a simple series on either side of the mid-rib, 
and the sporangia arise simultaneously. But in D. conjugata , with its 
broad-webbed leaf, the sori are scattered over the enlarged surface, and 
