206 



THE ALG^E 



can withstand the beating of the heaviest surf because of their 

 firm texture and strong holdfasts, and some of them grow on 

 the most exposed points and reefs. There are, however, many 

 smaller brown algae, membranous and cord-like forms, and some 



delicate filamentous 

 types (Ectocarpus) 

 which are as simple as 

 many green algae and 

 grow generallyin 

 rather quiet waters. 



We can only illus- 

 trate the brown algee 

 by representatives of 

 three orders, the 

 Ectocarpus group, the 

 kelps, and the rock- 

 weeds. 



235. Ectocarpus. 

 This alga (order Ecto- 



A $'I^iyf \ \ -B carpales) is a branching 



filamentous type which 

 forms tufts attached 



to the larger algae, eel- 

 FIG. 193. A filamentous brown alga (Ecto- 

 carpus siliculosus) g rass > and to the wood - 

 A, unilocular sporangia, one containing zoospores, WOTK OI wnarves. 

 the other empty ; a zoospore, z, shown at the left ; chief interest for US lies 

 B, plurilocular sporangia, the larger mature, the . , 

 smaller still showing the outlines of the original m the reproductive OT- 

 cells in the branch from, which it arose; C, the p;anS which are of two 

 union of the gametes to form the zygospore; 



note that the chromatophores with the pigment SOTtS, and illustrate 



spots remain separate. C, after Oltmanns verv well the reproduC- 



tive processes of the lower brown algae. The asexual organs are 

 one-celled sporangia (Fig. 193, A), which develop large numbers 

 of kidney-shaped zoospores, each with a pair of cilia attached 

 at the side (Fig. 193, A, z). Because the zoospores are all de- 

 veloped in a single cell, the sporangia are called unilocular 



