Phylum Phaeophyta [ 83 



The cells are walled chiefly with readily hydrolyzable modified polysaccharides. 

 Algin, the soda extract of kelps, consists of chains of oxidized mannose units. A poly- 

 saccharide of the sugar fucose, with a sulfate radicle to each sugar unit, is also present. 

 A small percentage of cellulose is present, apparently as the immediate investment 

 of each protoplast. A glycogen- or dextrin-like dextrosan, laminarin, is stored (Miwa, 

 1940; Tseng, 1945). The plastids contain chlorophylls a and c (Strain, in Franck 

 and Loomis, 1949) and carotin; xanthophyll is also present in the more primitive 

 examples. In all examples, there is an additional carotinoid called fucoxanthin, which 

 produces the brown color. The analytic process of separating the pigments yields 

 also a sterol, fucosterol, not found in green plants; but this substance, and fucoxanthin, 

 are found in chrysomonads, green Heterokonta, and diatoms (Carter, Heilbron, and 

 Lythgoe, 1939). 



Cytological study of a considerable variety of brown algae (Swingle, 1897; Farmer 

 and Williams, 1896; Mottier, 1898, 1900; Simons, 1906; Yamanouchi, 1909, 1912; 

 McKay, 1933) has shown that the spindle and chromosomes appear within an intact 

 nuclear membrane which disappears during the later stages of division. A centrosome, 

 usually with radiating rays, is present outside of the membrane at each pole of the 

 spindle. In Stypocaulon, a comparatively primitive brown alga, Swingle found the 

 centrosome to be a permanent structure, dividing as a preliminary to each division 

 of the nucleus. In the generality of brown algae, the centrosomes appear de novo as 

 division begins. 



Swimming cells are produced by primitive brown algae as spores and as morpholo- 

 gically undifferentiated gametes; in the most advanced brown algae, such cells are 

 produced only as sperms. The flagella are attached laterally. The anterior flagellum 

 is the longer except in order Fucoidea (Kylin, 1916). Longest (1946) found in 

 Ectocarpus that the anterior flagellum is pantoneme, and the posterior one acroneme. 

 The swimming cells are without walls, and contain, beside the nucleus, usually one 

 plastid and a light-sentitive speck, the stigma or eyespot. They are quite small. No 

 system of structures linking the nuclei, centrosomes, and flagella has been discovered. 



Thuret (1850) discovered that most brown algae produce swimming cells from 

 structures of two different sorts, which he named (1855) respectively plurilocular 

 sporangia and unilocular sporangia. The difference between them is this. In the 

 developing plurilocular structure, each division of the nucleus is followed by division 

 of the protoplast and deposition of a wall, with the result that the swimming cells 

 emerge from separate walled spaces. In the unilocular structure, the nucleus divides 

 repeatedly before the protoplast divides; the protoplast then undergoes cleavage to 

 produce swimming cells which emerge from a single walled space. A number of 

 studies (Clint. 1927; Higgins, 1931; Knight, 1923, 1929) have shown that the first 

 two nuclear divisions in the unilocular structure are normally meiotic. Unilocular 

 structures occur normally only on diploid individuals and release haploid swimming 

 cells. A few exceptional species, however, are known to bear unilocular structures 

 which produce swimming cells without the intervention of meiosis. 



In Ectocarpus siliculosus as studied by Berthold (1881) at Naples, the swimming 

 cells from unilocular structures are spores which give rise to haploid individuals. In 

 the same species as studied in the Irish Sea by Knight (1929), they were found to 

 act as gametes, conjugating and giving rise to diploid individuals. Diploid and hap- 

 loid individuals of Ectocarpus are alike, and E. siliculosus may be said to have a 

 facultatively complete homologous life cycle. The haploid individuals produce pluri- 

 locular reproductive structures; the swarmers from these act either as spores, re- 



