324 A TEXTBOOK OF GENERAL BOTANY 

Fig. 329. Pediastrum, 
a colonial green alga. 
(x 210) 
In the same. species of Ulothrix there 
may be a fusion of similar gametes, and 
in that case there is no differentiation of 
sexes; or there may be a fusion of micro- 
gametes (small gametes) and megagam- 
etes (large gametes), which indicates an 
early state of differentiation of sexes. 
Relationship of Ulothrix. ‘The simuilar- 
ity of the reproductive cells of Ulothrix 
to the mature individuals of such forms 
as Chlamydomonas and the Flagellata in- 
dicates that Ulothriz was derived from a 
flagellate ancestor. The vegetative plant of Ulothriv may be 
regarded as interposed between motile states in the same way as 
the palmella state is inter- 
posed between motile states 
in Chlamydomonas. 
OEDOGONIUM 
Vegetative structure. 
Oedogonium is avery com- 
mon genus of fresh-water 
alge. A plant consists of 
an unbranched filament 
which when young is at- 
tached to the substratum by 
means of a basal cell. When 
the filaments become older 
they may float freely in the 
water. Each cell contains 
a single nucleus and a 

Fic. 3830. Oedogonium 
single large chloroplastid, Above, formation and escape of zoéspore ; 
which is composed of anas- 
tomosing strands. 
below, germination of zodspore. (Redrawn 
after Hirn) 
Reproduction. Asexual reproduction is by means of zodspores 
which are formed singly in vegetative cells (Fig. 330). The 
