THALLOPHYTES 



45 



been derived from the Chlorophyceae, and it has possibly developed 

 independently from such organisms as gave rise to the green algae. 

 None of the true brown algae are one-celled, the simplest being a simple 

 conferva-like filament, and the group also includes forms with very com- 

 plex bodies. Sexual reproduction is probably present in all the forms, 

 having been discovered recently in Laminaria, and is chiefly repre- 

 sented by isogamy, but a small group has attained heterogamy. 



The two orders of brown algae are distinguished by their methods of 

 reproduction : Phaeosporales, characterized by the formation of zoo- 

 spores and by prevailing isogamy; Fucales, characterized by the absence 

 of zoospores and by well-developed heterogamy. 



(a) Phaeosporales 



General character. — This group includes the large majority of brown 

 algae and also the most bulky. The zoospores and gametes are alike, 

 and are produced in special 

 organs — the sporangium 

 and the gametangium. It 

 will not be possible or profit- 

 able to give an account of the 

 numerous families, but the 

 general features of the group 

 may be indicated by the 

 following illustrations: 



Ectocarpus. — This form 

 occurs as tufts of branching, 

 many-celled filaments. The 

 filament may consist of a 

 single row of cells, in which 

 case the body is called 

 monosiphonous ; or it may 

 consist of several parallel 

 rows of cells, in which case pj^g ^2o-T22. — Ectocarpus: I20, monosipho- 

 the body is polysiphonous. nous filament bearing a sporangium on a short 



Sporangium. — The spo- ^^"^^ ^'^"^^^ ^ " ' ■ "^ 2°°spore, showing the laterally 



' . 11 1 1 biciliate character (after Kuckuck); 122, filament 



rangmmisasmglecell, which bearingagametangiumCplurilocularsporangium"). 



in some forms is a cell of 



the filament changed in function and usually in size; and in other 



forms is developed at the end of a special short lateral branch (fig. 120). 



