322 



THALLOPHYTES 



smaller. Although strictly aquatic, they produce no zoospores 

 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 



FIG. 278. Reproduction in Fucus vesiculosus. a, section through a 

 swollen tip, showing sections through some of the conceptacles; b, much 

 enlarged section through an oogonial conceptacle, showing the pore-like open- 

 ing to the exterior and the oogonia within; c, a 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, oogonium from which 

 the eggs are escaping; /, sperms swarming around an egg; g, a sperm. 



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 



