chapti:r X 



PHYLUM IV. SIPHONOPHYCEAE 



THE TUBE ALGAE 



264. These plants are filamentous, saccate or erect- 

 dendroid, and are composed of coenocytes instead of dis- 

 tinct cells. In the first (primitive) forms the plant body 

 consists of a row of long bi- or poly-nucleated segments 

 (coenocytes) arranged in a simple or branched filament, 

 which is more commonly rooted below. When the fila- 

 ment has cross partitions it is said to be septated. In 

 many Tube Algae there are no partitions in the vegeta- 

 tive portions of the plant, and such are said to be 

 continuous. 



265. They are propagated (1) by the internal division 

 of the protoplasm of a coenocyte (sporangium), or even of 

 the whole plant into spores (ciliated zoospores in the 

 water — walled spores in the air) ; (2) by the condensation 

 of definite masses of protoplasm directly into thick-walled 

 spores (chlamydospores). Their generation shows all 

 gradations including the union of (1) ciliated isogametes; 

 (2) ciliated heterogametes; (3) ciliated sperms, with eggs; 

 (4) antherid nuclei, with eggs — in all cases producing 

 zygotes, which usually become thick-walled resting 

 spores. 



266. The dominant idea here is the development of 

 coenocytes instead of distinct cells, and this has been 

 consistently adhered to even when the plant body has 

 shown otherwise a considera])le amount of differentiation. 



184 



