MORPHOLOGY 
In either case the zoospores produced are laterally biciliate (fig. 121) 
and develop new filaments directly. 
Gametangium. The gametangium is a many-celled structure, and, 
like the sporangium, is developed either from ordinary cells of the fila- 
ment or at the end of a short lateral branch 
(fig. 122). The small cells composing it are 
cubical, being packed together closely, and each 
one produces a biciliate, zoospore-like gamete. 
Upon escaping, the gametes pair and fuse, and 
a zygospore is formed. This gametangium is of 
great interest on account of the variations that 
occur, leading sometimes to uncertainty as to 
whether the structure should be called a 
gametangium or a sporangium ; in fact, it is 
often called a plurilocular sporangium, in dis- 
tinction from the true unilocular sporangium. 
In some cases the gametangium is reported to 
produce both zoospores and gametes, judged 
by their behavior. The question might be 
raised whether the so-called zoospores in this 
case are not parthenogenetic gametes (see p. 
V ^C^C 4)' Other cases are reported in which the 
gametangium is said to produce motile cells of 
three sizes, the medium-sized ones germinating 
directly, and the largest and smallest ones 
pairing. In this case, we should have not only 
zoospores, but also dissimilar gametes. In 
another case it is reported that the larger 
gamete comes to rest and is fertilized in this 
quiescent condition ; in which case heterogamy 
would be very apparent. In the same genus, 
therefore, there occur both zygospore and 
oospore formation, and more or less confusion 
of gametes and zoospores. The group would 
seem to be an unusually favorable one for ob- 
serving both sex origin and sex differentiation. 
FIG. 123. Laminaria: 
showing bladelike body, 
stipe, and holdfast. 
Sphacelaria. In general structure and reproductive 
habits this form resembles Ectocarpus, but it may be 
used to illustrate the appearance and powers of an apical 
