2 Bower. — S Hedies in the Phytogeny of the Fili cates. VI. 
The case of Acrostichum is parallel with that of Polypodhnn. This 
comprehensive genus was based upon the definite sorus, consisting of 
numerous sporangia, without any protective indusium. It is obvious that 
such a condition may have been primitive in types which never had an 
indusium at all, such as Gleichenia , Matonia , Dipteris , Metaxya , &c. : or it 
may have resulted from abortion of an indusium previously present, as 
in Dryopteris : there is reason to hold that this latter state may have arisen 
along more than one phyletic line. Such single characters as those defining 
Acrostichum , or Poly podium in the old sense, are in fact too wide to be of 
service in a system which aims at a true phyletic grouping. Moreover 
these, though the most prominent of the ‘ false 5 genera, are by no means the 
only ones that will have to be broken up as the basis of comparison is 
extended. In proportion as a larger number of characters are used in the 
comparisons, the relations of the plants to their phyletic sources will become 
clearer, and the classification will be a more natural one. To this end the 
definite intention should be to bring a larger number of characters into our 
comparisons. Among these, anatomical data will be of the first importance. 
In the present memoir the observations relate chiefly to representatives 
of the old comprehensive genus, Acrostichum . The attempt will be made 
to refer certain of its forms to their phyletic source, and to suggest their 
inter-relations. It will then become apparent that while certain Acro- 
stichoid Ferns may have sprung from an indusiate ancestry, others have 
sprung from a primitively Polypodioid or Matonioid-Dipterid source, where 
no indusium was ever present, by a simple spread of the soral area from 
the vascular receptacle to the non-vascular surface of the sporophyll. This 
source has already been suggested for Cheiropleuria } 
Gymnopteris ( Leptochilus ) tricuspis (Hook.), C. Chr. 
In No. Ill of these Studies 1 2 it was suggested that a phyletic relation 
exists between Metaxya and certain types of the comprehensive but false 
genus Polypodium . Reference was also made to Neocheirop ter is , but the 
relation of this plant to the Ferns named was held to be obscure and in need 
of further inquiry. Since then opportunity has been found for the investi- 
gation of Cheiropleuria , 3 and this led to a suggestion of its affinity on the one 
hand to Dipteris , on the other to Platy cerium. All of these are Ferns with 
superficial, non-indusiate sori. This character, as well as some others, 
indicates relationship downwards with Gleicheniaceous and Matonioid types, 
though such relationship can hardly be regarded as one of near affinity. 
In resolving such questions of affinity an increase in the number of the 
1 No. V of these Studies. Ann. of Bot., vol. xxix, p. 475. 
2 On Metaxya and certain other relatively Primitive Ferns. Ann. of Bot., vol. xxvii, 1913, 
P- 473 - 
3 Studies, V. Ann. of Bot., vol. xxix, 1915, p. 495. 
