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 gametangiiim. It 

 will not be possible or profit- 

 able to gi ve 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 consists of a single 

 row of cells, the body being 

 called monosiphonous. If 

 the body consists of several 

 parallel rows of cells, as in 

 certain other brown algae, ~ 



° ' rics. 120-122. — Ectocarpus: 120, monosipho- 



it is called polysiphonous. nous filament bearing a sporangiurr on a short 



Sporangium. — The Spo- kteral branch; 121, a zoospore, showirg the laterally 



• • • , n , . , biciliate character (after Kuckuck); 122, filament 



rangium is a single cell, which bcaring . 

 in some forms is a cell of 



;agametangium ("plurilocular sporangium"). 



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). 



