Simple Plants With Chlorophyll — Algae 155 



Occasionally a heterocyst may germinate to form a new filament, thus 

 functioning as a spore. Nostoc is common in ponds and pools of fresh 

 water. 



Anabena (ana-be'na) (Gr. anahainein, to go up). — This blue-green 

 alga resembles Nostoc in its beadlike strands, pigments, heterocysts, and 

 jelly covering (Fig. 29). It differs in that certain enlarged, thick- walled 

 cells, known as spores, contain much food and may separate from the 

 filament and form a new colony. 



GREEN ALGAE (PHYLUM CHLOROPHYTA) 



In certain species of green algae the chlorophyll may be associated 

 with additional pigments known as carotinoids (carotene and xantho- 

 phyll). The chlorophyll is localized in definite bodies known as chloro- 

 plasts (klo' ro plast) (Gr. kloros, green; plastos, moulded or body). The 

 nucleus is well organized (Fig. 30). The cell wall consists of cellulose 

 (sel'ulosz) (L. cellula, little cell), and the stored food is starch. The 

 latter is formed by structures on the chloroplasts known as pyrenoids 

 (pi'renoid) (Gr. pyren, fruit-stone; eidos, resemblance). Green algae 

 vary in structure, and the plant body may be unicellular, colonial, or 

 multicellular, depending upon the species. When the reproductive or 

 vegetative (body) cells are motile, each bears two to four anterior flagella, 

 usually of equal length. 



Reproduction occurs (1) asexually by cell division, by fragmentation, 

 by motile zoospores, or by nonmotile spores or (2) sexually by isogamy 

 (i -sog' a my) (Gr. isos, equal; gamos, marriage) with the fusion of 

 gametes (sex cells) of equal size, by heterogamy (het er -og' a my) (Gr. 

 heteros, different) with the fusion of gametes of unequal size, or by oog- 

 amy (o-og'amy) (Gr. oon, ^gg) which is a special type of heterogamy 

 in which the egg (female gamete) is nonmotile. The structures which 

 produce the sex cells in green algae are always unicellular. 



Most green algae live in fresh water, but some are marine, while others 

 grow in soil, on rocks, or on trees. Several species live in snow or ice. 

 Some live in salt lake waters whose concentration of salt is much greater 

 than that of the ocean. A few species may grow on other plants or ani- 

 mals. A few live symbiotically with such animals as protozoa, sponges, 

 and Hydra. Certain types may live together with chlorophyll-less fungi 

 to form plants called lichens (Fig. 327). Green algae, as well as other 

 algae, supply foods for fresh-water and marine animals. Marine green 

 algae in conjunction with red algae secrete lime salts which assist in the 



