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 alga3, membranous and cord-like forms, and some 



delicate filamentous 

 types (Ectocarpus) 

 which are as simple as 

 many green algae and 

 grow generally in 

 rather quiet waters. 



We can only illus- 

 trate the brown algae 

 by representatives of 

 three orders, the 

 Ectocarpus group, the 

 kelps, and the rock- 

 weeds. 



235. Ectocarpus. 

 This alga (order Ecto- 

 carpales) is a branching 

 filamentous type which 

 forms tufts attached 



to the larger alg;e, eel- 



, J ,. , 



g rass > and to the wood - 

 work ot wharves. Its 



chief interest for US lies 

 m the reproductive or- 



which are of two 



FIG. 193. A filamentous brown alga (Ecto- 

 carpus siliculozics) 



A, unilocular sporangia, one containing zoospores, 

 the other empty ; a zoospore, z, shown at the left ; 

 B, plurilocular sporangia, the larger mature, the 

 smaller still showing the outlines of the original 

 cells in the branch from which it arose; C, the 

 union of the gametes to form the zygospore; 

 note that the chromatophores with the pigment Sorts, and illustrate 

 spots remain separate. C, after Oltmanns very well the reproduc- 



tive processes of the lower brown algse. 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 



