52 EVOLUTION OF PLANTS 
the filament shows a distinction between base and apex. 
The most specialized forms, e.g. Coleochete (Fig. 10), 
have the form of a flattened disk, and recall somewhat 
the structure found in 
iB the simplest mosses. 
Within the Confer- 
vacee there is found a 
similar advance in the 
reproductive parts to 
that described in the 
Volvocinee. Some of 
the lowest forms have as 
yet shown only non-sex- 
ual reproductive cells, 
Fig. 8 (Confervacee).— A, a filament but it is not improbable 
of Microspora, composed of entirely 
uniform cells; B, part of a plant of hat sexuali will 
Cladophora, showing the branching that: See ty be 
habit; C, a zodspore of Cladophora, shown for all of them. 
showing the two cilia, the eye-spot, 
e, and the ae D, eames, In these forms where 
or sexual cells, of Ulothrix, showing 
the process of conjugation. , (Fig. D, only non-sexual —0- 
mtter Dorleh) ‘dspores have been ob- 
served, they may be 
either uniciliate or biciliate. These zodspores may arise 
singly, by the escape of the whole of the contents of 
a cell as a single zodspore; or there may be a division 
of the cell-contents into two or more parts which then 
escape. When the zodspores are large (Fig. 9, D), they 
sometimes have more than two cilia, but otherwise 
resemble closely the typical Volvox cell. 
The simplest type of sexual reproduction among the 
Confervacez consists in the formation of cells (gametes), 
which differ from the zodéspores only in being, as a rule, 
smaller, but with no distinction of sex. These gametes 
