THALLOPHYTA: ALGAE 85 



Summary of Phaeophyceae 



The Phaeophyceae are algae having in their plastids an excess of 

 carotin and a brown xanthophyll pigment (fucoxanthin) over the chloro- 

 phyll. All of them are multicellular, the thallus being filamentous, 

 plate-like, or massive, often with differentiated tissues. The cells contain 

 a definite nucleus, generally several or many plastids, and a distinct cell 

 wall. Reserve food is stored chiefly as laminarin (a dextrin-like carbo- 

 hydrate) or oil. Except in the Fucales, zoospores are produced or, in the 

 Dictyotales, aplanospores. Gametic reproduction may occur either by 

 isogametes or heterogametes. In the heterogamous forms the eggs may 

 be ciliated but are generally nonciliated. All motile reproductive cells 

 are laterally biciliate, the cilia being unequal in length. No resting cells 

 are formed. Most members exhibit an alternation of generations, the 

 Fucales, with only a diploid plant body, being a notable exception. The 

 gametophyte and sporophyte are either similar or dissimilar vegetatively. 



10. RHODOPHYCEAE 



Like the Phaeophyceae, the Rhodophyceae, or red algae, are almost all 

 marine in distribution but, as a rule, live in deeper and warmer waters 

 than the brown algae. They include the majority of the seaweeds. 

 Most of the Rhodophyceae are rose red or violet, but some are dark 

 purple, reddish brown, or olive green. In addition to chlorophyll and its 

 associated carotinoids, a red pigment, phycoerythrin, is present in the 

 cells. This more or less obscures the chlorophyll. Many of the Rhodo- 

 phyceae also contain a small amount of phycocyanin, the blue pigment 

 of the Cyanophyceae. Except for several unicellular forms, whose 

 inclusion in the group is doubtful, all the red algae are multicellular. 

 Their bodies are not large, most of them being less than 30 cm. in length, 

 while only a few are as long as 1 m. They are rather varied in form, how- 

 ever, being fdamentous, ribbon-like, or plate-like, but never massive. 

 They are always attached. Some are heavily impregnated with lime. 

 Lime-secreting forms are known as fossils as far back as the Ordovician. 

 The Rhodophyceae are the most highly specialized of all the algae. They 

 are probably not related to any of the higher plants except, perhaps, to 

 some of the fungi. They include about 3,000 species. 



There are seven orders of Rhodophyceae. These, together with one 

 or more representative genera, are as follows: (1) Bangiales — Bangia, 

 Porphyra,'Porphyridium; (2 )Nemalionales — Nemalion, Batrachospermum; 

 (3) Gelidiales — Gelidium; (4) Cryptonemiales — Corallina, Lithothamnion; 

 (5) Gigartinales — Plocamium, Gracilaria, Chondrus, Gigartina; (6) Rhody- 

 meniales — Rhodymenia; (7) Ceramiales — Callithamnion, Ceramium, Poly- 

 siphonia, Delessaria. 



