116 Plant Biology 



which produce the sex cells in green algae are unicellular; hence they 

 cannot be called sex "organs" in the true sense. 



Most green algae live in fresh water^ although a few live in the water of 

 the ocean (marine). Other species live in soils, on rocks or trees, in 

 ice or snow. Some species live in salt lake waters whose concentration of 

 salt is much greater than that of ocean water. A few species live on 

 other plants or animals. A few live symbiotically with such animals as 

 protozoa, sponges, and Hydra. Sometimes certain types may live sym- 

 biotically with certain species of chlorophyll-less fungi to form plants 

 called lichens (Fig. 327). Green algae, together with other algae and 

 animals, may supply foods for fresh-water and marine animals. Certain 

 marine forms in conjunction with red algae may secrete lime salts which 

 assist in the formation of reefs in the ocean. There are approximately 

 5,700 species. 



Examples: Chlamydomonas (Fig. 61), Ulothrix (Fig. 30), Protococ- 

 cus (Fig. 30), Spirogyra (Figs. 30 and 62), and desmids (Fig. 30). 



3. Phylum Chrysophyta (kris -of i ta) (Gr. chrysos, gold; phyta, 

 plants) . — In the yellow-green algae, or golden-brown algae, or diatoms, 

 the yellowish-brown pigments known as carotinoid pigments are more 

 abundant than the chlorophyll so that they may have yellowish-green or 

 golden-brown colors. The pigments are contained in special bodies called 

 plastids. A well- organized nucleus is characteristic. The cell walls may 

 be composed of a pair of overlapping halves (valves) which are fre- 

 quently impregnated with glasslike silica (Fig. 31), Depending upon 

 the species, these algae may be unicellular, colonial, or, in a few instances, 

 multicellular individuals. The stored foods are oils and an insoluble 

 carbohydrate called leucosin (lu'kosin) (Gr. leukos, white). 



Asexual reproduction occurs by cell division, by motile zoospores, or by 

 nonmotile spores. When present, sexual reproduction occurs by isogamy 

 (fusion of similar gametes). The method or methods of reproduction 

 depend upon the species. There are approximately 5,700 species. 



Example: Diatoms (Fig. 31). 



4. Phylum Phaeophyta (fe-of'ita) (Gr. phaios, brown or dusky; 

 phyta, plants) . — The brown algae are multicellular, some species being 

 quite large. They are nonmotile (sessile), being attached by rootlike 

 holdfasts. Depending upon the species, the plant body may be composed 

 of a few cells or it may be over a hundred feet long, as in some of the 

 kelps. Brown algae are marine, usually present in colder waters. The 

 chlorophyll is masked by a golden-brownish pigment called fucoxanthin 



