THE MAIN LINE OF DESCENT THROUGH THE GREEN ALG&. 41 
abundantly on submerged stones and stems of water plants, 
has a flat parenchymatous thallus composed of branched fila- 
ments fused laterally. Biciliated zoospores (zoogonidia) are 
formed reproducing the plant asexually, but the sexual repro- 
duction is heterogamous— highly specialised oogonia after 
being fertilised by antherozoids producing a spermocarp, from 
which biciliated zoospores escape, giving rise to several rudi- 
mentary asexual generations. There is considerable evidence 
that the Cdogoniacee (CEdogonium and Bulbochete) arose 
from ulotrichaceous ancestors, and Prof. Oltmanns has sug- 
gested the origin of the Cladophorales from the line, but 
probably the brief account given will be sufficient to enable 
the botanist with but little knowledge of the green alge to 
glean a general idea of current thought on this subject. 
Somewhere along the line, among the branched forms, there 
seems to have arisen the Bryophytes, which are not far 
removed from it in their protonemal existence. To the ferns 
is not a great remove, and recently it has been shown that 
among the plants of past ages were fern-like plants, at first 
thought to be ferns and named as such, that reproduced by 
seeds, thus bridging over what used to be considered the 
greatest gap in the evolution of the higher plants—that be- 
tween the pteridophytes and the spermaphytes. 
LITERATURE. 
(1) Blackman and Tansley : “ Revision of the Classification of 
the Green Algz.” New Phytologist, 1902. (Not seen.) 
(2) Fritsch: “The Phylogeny and Inter-relationships of the 
Green Algz.” Sc. Prog. 
(3) Oltmanns: ‘‘ Morphologie und Biologie der Algen,” 1904-5. 
(4) West, G. S.: “ British Freshwater Algz,” 1904. 
