322 THALLOPHYTES 
smaller. Although strictly aquatic, they produce no zoéspores 
and their sexual reproduction is much specialized. 
Rockweeds. — These are very common Seaweeds and are 
especially abundant on rocky shores. The plant body, sometimes 
a foot or more in length, is much branched and has bladder- 
like floats and commonly special reproductive structures. The 
Rockweeds are common in fish markets, being used as a packing 
[LA 
SIFY 
Fic. 278. — Reproduction in Fucus vesiculosus. a, section through a 
swollen tip, showing sections through some of the conceptacles; b, much 
enlarged section through an oégonial conceptacle, showing the pore-like open- 
ing to the exterior and the odgonia within; c, « similar section through a 
conceptacle containing antheridia which appear as small bodies on the fila- 
ments projecting from the walls of the conceptacle; d, antheridia much en- 
larged and one antheridium shedding its sperms; e, odgonium from which 
the eggs are escaping; f, sperms swarming around an egg. 
in the shipment of crabs and other shell fish. Along the west 
coast of South America and also in other countries, Fucus is used 
for food by the inhabitants, and it is also used as a fertilizer and 
as a source of iodine. 
Fucus vesiculosus, one of the commonest of the Rockweeds, will 
serve to illustrate the character of the plant body and the peculiar 
features of reproduction, the former being shown in Figure 277 
and the latter in Figure 278. The gametes are differentiated 
