The Plant Kingdom - 599 



PLATES 



Fig. 31-4. Flame algae (Pyrrophyta). The dinoflagel- 

 lates (shown above) are the most important of the 

 flame algae. Note the unique arrangement of the 

 flagella and the overlapping cellulose plates. Some 

 dinoflagellates produce toxic substances and are re- 

 sponsible for "mussel poisoning" and "red tides" (see 

 text). 



the millions when an upsurging population 

 of dinoflagellates becomes so great that it is 

 described as a "red tide." Also "mussel poi- 

 soning" may result when people eat mussels 

 that have been feeding mainly upon toxic 

 dinoflagellates. 



The Dinoflagellata and other Pyrrophyta 

 appear to have initiated a separate path of 

 evolution at a very early date, as is indicated 

 in Figure 29-11. 



The Phaeophytes (Brown Algae). About 

 1000 species of these marine algae are found, 

 mainly in shallow coastal waters, although 

 some species extend their range to depths 

 approaching 100 feet. The species vary widely 

 from small branching filamentous forms, such 

 as Ectocarpus (Fig. 31-5), to large expansive 



plants, such as Laminaria (Fig. 31-5). All 

 possess fucoxanthin and chlorophyll in vary- 

 ing proportions; and the color ranges from 

 light greenish brown to very dark, almost 

 blackish green. 



The larger brown algae, which sometimes 

 are called kelps, may show a considerable 

 differentiation of their organs. Character- 

 istically, there is a holdfast (Figs. 13-3 and 

 31-5), a branching stemlike stipe, and a num- 

 ber of broad leaflike blades. Also there may 

 be a number of gas bladders (Fig. 31-5), 

 which buoy up the thallus, so that the blades 

 receive a maximum share of the weak light 

 that filters down through the overlying 

 water. Some brown algae, compared to other 

 algal forms, display a high degree of cellular 

 differentiation. At the center of the stipe in 

 some brown algae, are found a number of 

 elongate cells with perforated end walls, 

 somewhat like the sieve tubes of higher 

 plants; and these probably serve to convey 

 organic materials from the upper to the 

 lower parts of the plant. Also meristem cells, 

 somewhat similar to the cambium of higher 

 plants, are found in a few of the larger 

 phaeophytes. 



The brown algae generally display sexual 

 as well as asexual methods of reproduction; 

 and some (for example, Ectocarpus) show a 

 regular alternation between diploid spore- 

 forming and haploid gamete-forming genera- 

 tions. And even forms such as Fucus (Fig. 

 31-5), in which the cells of the thallus are 

 consistently diploid, are considered to have a 

 transient unicellular haploid stage, repre- 

 sented by the reproductive cells just before 

 the eggs and sperm are produced. 



The brown algae, especially the kelps, 

 are of some practical importance: as a food 

 base for marine fish; as food for cattle, and 

 even man (China and Japan); as sources of 

 iodine and mineral salts; and in the produc- 

 tion of algin, a carbohydrate derivative quite 

 widely used to improve the "creamy" quali- 

 ties of ice cream, candies, and hand lotions. 



Like other thallophyte groups, the brown 

 algae started an independent line of evolu- 



