ALG 107 
It has been observed that these small swimming cells come 
together in pairs and fuse (Fig. 97, C, d), each pair thus 
forming one new cell (Fig. 97, C, e). The cell thus formed 
passes through a resting period (usually during winter), 
then begins to grow (Fig. 97, #), and finally produces four 
swimming spores (Fig. 97, F), each of which is able to pro- 
duce a new filament of Ulothriz. Here is evidently a third 
method of reproduction, which is peculiar in the fact that 
two special cells unite to form the spore that produces the 
new plant. These two special cells are gametes (sexual 
cells); their act of fusion is fertilization; the spore thus 
formed is the odspore (egg-spore); and this kind of re- 
production is called serual reproduction.* It should be 
observed that the swimming spores and the odspores of 
Ulothrix do not differ in what they are able to do, but in 
the method of their formation, one being formed by cell- 
division and the other by cell-fusion; but to distinguish re- 
production by spores from sexual reproduction by odspores, 
the former is called asexual reproduction, and the spores are 
often spoken of as asexual spores; although when the word 
“spore’’ is used it generally implies an asexual spore. 
The three methods of reproduction found in Ulothriz 
may be summarized in the following graphic way: 
(1) Vegetative multiplication is indicated by P—P— 
P—P—, in which P stands for the plant, there being a 
succession of plants arising directly one from the other 
without the interposition of any special cells. 
(2) Reproduction by asexual spores is indicated by 
P—o—P—o—P—o—P —, indicating that new plants are 
not produced directly from the old ones, but that between 
the successive generations there is the asexual spore. 
* It does not seem wise to multiply terms at this point, and hence 
the more general terms “‘fertilization”’ and ‘‘odspore’’ are used as in- 
cluding the more special terms ‘‘conjugation”’ and “zygospore.”’ 
