Bower.—Studies in the Phytogeny of the Filicales . VII. 65 
Blechneae, and is a feature of relatively recent types of Ferns. It must 
accordingly be used with discrimination. But his table certainly demon¬ 
strates its constancy in several large series, and in none better than in the 
Pteroideae. It is accordingly of some interest to note that Acrostichum 
( Chrysodium ) aureum and praestantissimum agree in this respect with the 
Pterid series, in the absence of a perispore, therein differing from all other 
Acrostichoid Ferns examined. This fact detaches them from the latter, and 
indicates relationship to the Pterid series. 1 
It is thus seen that by comparison in respect of several distinct criteria 
drawn from the sporophyte generation, the Dicksonioids may be seriated 
inter se, and related with the Schizaeaceae, as suggesting with some degree 
of probability their phyletic source. The main sequence of the Dicksonioi- 
deae is based upon the maintenance of the individuality of the sorus. It is 
indicated roughly by the genera named in order thus :— Thyrsopteris , 
Cibotium, Dicksonia, Dennstaedtia , Microlepia, Davallia , Nephrolepis , 
Oteandra. A second series of Dennstaedtiinae, springing from Dennstaed¬ 
tia or Microlepia , leads to Hypolepis and Polypodium punctatnm , and related 
to these is also Monachosorum . 
Another line is the Pterid series, based upon the formation of fusion- 
sori; it is probably related in origin through the lower Dicksonioids to some 
Schizaeoid source. There seems to be a probability of the attachment of 
Saccoloma to Microlepia . The relation of Lindsay a is more problematical, 
but that genus occupies some place relatively low in the scale of the Pterid 
series. The main series of the latter consists of Paesia , Pteridimn , 
Lonchiiis , Histiopteris , Anopteris ) and Pteris ; it also includes Acrostichum , 
L. It has clearly sprung from Ferns with a Dicksonioid, two-lipped, 
marginal sorus, by their lateral fusion and passage to a superficial origin, 
with abortion of the inner indusium. Thus the Dicksonioids lead to an 
ultimate Polypodioid sorus, and the Pteroids to an Acrostichoid state. 
And both in course of their elaboration have been seen to lose their inner 
indusium by abortion, consequent upon the phyletic slide of the sorus to 
the lower surface of the leaf. 
Comparison thus shows that a sorus with a single indusium may 
originate along more than one line from a bi-indusial source. The question 
will be whether all Ferns with a sorus near to the margin, and protected 
by a single indusium, are to be credited with a similar phyletic history. 
The practice of systematists has hitherto been to group all such together. 
It is not explicitly stated that this grouping implies their phyletic unity, 
but at least it may be held as indicating a view of substantial alliance. 
The consequence has been that under the heading of the Pterideae 
there have been placed as subdivisions, in addition to the Pteridinae, the 
1 Compare Frau Schumann, Flora, 1915, p. 208. 
F 
