CHAPTER XVIII 
LIFE HISTORIES OF ALG^E (CONCLUDED) 
DICTYOTA DICHOTOMA 
227. Habitat. Like Ascophyllum and Fucus, Dictyota 
dichotoma grows chiefly along the ocean margins in the 
zone between the lines of Jiigh and low tide. It is thus 
subjected to alternate wetting and drying, and to rhyth- 
mically alternating changes of light and temperature. It 
FIG. 177. Dictyota dichotoma. Left, sporogonial plant; right sperma- 
gonial (gametophytic) plant. (After W. D. Hoyt.) 
is found from as far north as the middle of the Scandi- 
navian peninsula to about 40 south latitude. 
228. Description. The plant body (Fig. 177) is a 
thallus, flat, and branching profusely by forking at the 
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