235 
Algal Ancestry of the Higher Plants. 
and reproductive tissues and gradual assertion of a main axis. A 
likely algal ancestry might, therefore, be expected to display these 
tendencies:—Differentiation of prostrate dorsiventral and radial 
upright systems, assertion of a main axis in the latter, and restric¬ 
tion of sexual organs to the prostrate portion, and of asexual organs 
to the appendages of the upright system. We may, perhaps, add 
to this, evidence of a terrestrial tendency, with corresponding 
adaptations. 
The filamentous Algre among the Isokontae, to which we may 
now turn, include a number of separate series, viz., Ulotrichales, 
Chaetophorales, Siphonales, CEdogoniales, and Conjugate. The 
last three are obviously specialised along lines of their own, in fact, 
some algologists are inclined to regard the last two as originating 
from ancestries independent of that of the remaining Isokontae, a 
view which the writer does not share. Ruling out these three 
groups we are left with the Ulotrichales and Chaetophorales, which 
are probably best regarded as distinct, though closely related, 
series. 1 The former are, on the whole, very uniform, and display 
little morphological differentiation, and what there is is scarcely 
relevant in the present connection. In the Chaetophorales, on the 
other hand, we have a group with very considerable morphological 
differentiation and one, moreover, showing a very wide range of 
construction and a great diversity of habitat. 
As a relatively primitive and central member of this group, we 
may regard the genus Myxonema (Stigeoclonium) . In this genus 
the typical thallus consists of two portions, a prostrate system 
attached to the substratum (in the following, briefly referred to as 
the creeping base), and a more or less elaborate, branched, upright 
part, arising from the base and extending out into the water (Fig. 
1, a); the former is dorsiventral, the latter essentially radial. 
Among the known species of Myxonema there are all possible 
variations in the degree of relative development of the base and 
the upright system. In some ( e.g ., M. tenue (Fig. 1 , a), M.falk- 
1 It will probably be useful to give the following outline sketch of the 
classification of the Chaetophorales: — 
(a) OuetophoracecB :—Myxonema (Stigeoclonium), Chaetophora, Drap- 
arnaldia, Gongrosira, Protoderma, Endoderma, Gomontia, Tellamia, 
Acrochaete, Ectochaete, Pseudochaete, Ochlochaete, Pringsheimia, Aphano- 
chaete, etc. 
(b) CJuetosphceridiacece: —Chaetosphaeridium, etc. 
(c) Cluetopeltidacea Chaetopeltis, etc. 
(d) Coleochcetacea: —Coleochaete. 
(e) Chatosiphonacea: —Chaetosiphon. 
(f) Trentepohliacece: —Trentepohlia, Cephaleuros, etc. 
