Simple Plants With Chlorophyll — Algae 161 



gamos, marriage; phyta, plants) alternates with a free-living, multicellu- 

 lar, spore-producing sporophyte (spor'ofite) (Gr. spora, spore; phyta, 

 plants). Reproduction may occur asexually by jragmentatioiij by motile 

 zoospores, by nonmotile spores; or sexually by isogamy (i -sog' a my) (Gr. 

 isos, equal; gamos, marriage or gametes) in which gametes of equal size 

 fuse, by heterogamy (het er -og' a my) (Gr. heteros, different) in which 

 gametes of unequal size fuse, or by oogamy (o -og' amy) (Gr. oon, egg) 

 which is a special type of heterogamy with a nonmotile egg. The motile, 

 pear-shaped reproductive cells bear two lateral flagella of unequal length. 



Certain brown algae are important sources of iodine, potassium, fer- 

 tilizers, and foods for animals and man. About 900 species are classified 

 in 190 genera. The following typical examples will be considered: 

 Laminaria and Fucus. 



Laminaria (lam i -na' ri a) (L. lamina, flat blade). — These brown 

 algae or kelps, known as "devil's-aprons," are common on our seacoasts 

 and may be over six feet long. The sporophyte plants consist of long, 

 flat blades, stalklike stipes, and branched, rootlike holdfasts. Patches of 

 zoosporangia (zoo spo -ran' ji a) (Gr. zoon, animal; spora, spore or seed; 

 angos, vessel) on the blades produce numerous zoospores. The latter 

 produce two types of microscopic gametophytes: (1) the simple, 

 branched, filamentous male gametophyte which bears terminal anther- 

 idia (an ther -id' i a) (Gr. anthos, "flower"; idion, small) and (2) the 

 female gametophyte which is a short filament with one-celled oogonia 

 (oo-gon'ia) (Gr. oon, egg; gonos, offspring). Each antheridium pro- 

 duces a sperm, with two flagella of unequal length. Each oogonium pro- 

 duces an egg. Oogamous fertilization produces a zygote, which germi- 

 nates to form the sporophyte plant. Hence, there is alternation between 

 the large, conspicuous sporophyte and the microscopic gametophytes 

 (Fig. 32). 



Fucus (fiu' kus) (Gr. phykos, seaweed). — This marine brown alga or 

 rockweed is commonly attached to rocks along seacoasts. The plant is 

 leathery and dichotomously forked and is attached by a disklike holdfast. 

 The green chlorophyll is usually masked by a brown pigment called 

 fucoxanthin (fu ko -zan' thin) (L. fucus, alga or sea weed; xanthos, yel- 

 low) and carried in special bodies known as chromoplasts (Gr. chroma, 

 color) . Bladderlike floats filled with gas buoy up the multicellular plant 

 (Fig. 32). Every body cell has an organized nucleus. Stored foods con- 

 sist of fats and soluble sugars. Enlarged tips called receptacles (re -sep'- 

 takl) (L. recipere, to receive) contain numerous openings which lead 



