HOW TO KNOW THE SEAWEEDS 



3a Entire thallus hollow, subglobular to tubular, or the thallus with hol- 

 low, septate or unseptate branches, or provided with hollow blad- 

 ders, bulbs or vesicles. Fig. 14 82 



Fig. 14. Several examples of hollow struc- 

 tures in the algae. 



A. A hollow tubular thallus as in Enteio- 

 morpha. B. A hollow branch provided with 

 septation or diaphragms as in Gastrocloni- 

 um. C. A solitary, hollow vesicle as in 

 Botryocladia. D. A hollow vesicle (pneu- 

 matocyst) at the base of a vegetative blade 

 as in MacTOcystis. 



Figure 14 



3b Thallus without hollow structures or parts (except sometimes the 

 coarse stipe, as in Postelsia) 4 



4a Thallus crustose, forming a thin, adherent expanse on the substrate, 

 or, prostrate and coarsely net-like 78 



4b Thallus not crustose or net-like, free except for one or more basal 

 attachmentsi 5 



5a Thallus consisting of one or more branched 

 or unbranched uniseriate filaments Fig. 15, 

 or consisting of a variously branched, free, 

 essentially cylindrical filament without cellu- 

 lar septations (coenocytic) (See Figs. 89-92) 

 58 



Fig. 15. Two forms of uniseriate filaments. A. 

 An unbranched uniseriate filament as in 

 Chaetomorpha. B. A branched uniseriate 

 filament as in Callithamnion. 



Figure 15 



29 



