206 



THE ALGJE 



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 alga?, membranous and cord-like forms, and some 



delicate filamentous 

 types (Ectocarpus) 

 which are as simple as 

 many green algae and 

 g row 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 algre, eel- 



g rass > and fco the wood - 

 WOl'lv OI Wlianes. 



chief interest for US lies 



the reproductive Or- 



FIG. 193. A filamentous brown alga (Ecto- 

 carpus siliculosus) 



A, unilocular sporangia, one containing zoospores, 

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

 /, plurilocular sporangia, the larger mature, the 

 smaller still showing the outlines of the original 

 cells in the branch from which it arose; C, the <rans which are of two 

 union of the gametes to form the zygospore; 



note that the chromatophores with the pigment SOrtS, aim illustrate 

 spots remain separate. C, after Oltmanns vei'V well the reproduc- 



tive processes of the lower brown alga?. 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 iii a single cell, the sporangia are called unilocular 



