MARINE ALGAL VEGETATION 87 



phyte: the remaining 4 species are common in the lower littoral 

 zone, and occur in pools in the upper littoral zone, consequently 

 they cannot, strictly speaking, he reckoned as belonging to the upper 

 littoral zone. 



Chlorophyceae. In the table, 36 species of green alga? are 

 mentioned from the upper littoral zone. Of these, 15 are charac- 

 terized as common and 21 as rarer. 31 species are recorded ex- 

 clusively from the upper littoral zone; 2 species, Entoderma and 

 Bolbocoleon are more frequent in the lower littoral zone; one species 

 Chlorochytrium dermatocolax is as frequent in the lower littoral zone 

 as in the upper littoral zone, one species Ulothrix flacca, which 

 must be considered a decidedly littoral species, grows to a depth 

 of about 10 metres. Ulvella fucicola also grows to a depth of 5 

 metres, but must nevertheless be considered littoral. In addition 

 to these 36 species, others may be found in the upper littoral zone, 

 which have a more downward extension (e. g. Monostroma Greoillei 

 var. aretica , M. fuscum , Acrosiphonia incurva, and others), but they 

 generally keep to the pools. 



Cyanophy cese. All the species hitherto found (6) grow in 

 the upper littoral zone. 



The species which are recorded from the upper littoral zone 

 may be put into two divisions. The one comprises the species 

 which are common in the upper littoral zone and are adapted to 

 growth in places exposed to the light and the wind during the 

 period of exposure; these species, then, might be termed strictly 

 littoral. The other division comprises species which are common 

 in the lower littoral zone or extend even further downwards. The 

 greater number of these species does not occur in the open littoral 

 zone, but is found as an undergrowth or in shady clefts, or in 

 pools. The real home of these species is lower down than in the 

 upper littoral zone, and for this reason they can scarcely be de- 

 signated littoral species. 



According to the above, there are in all 58 strictly littoral species : 

 Rhodophycece 5 species, Phceophycece 14 species, Chlorophycece 33 

 species and Cyanophycece 6 species. 



The upper littoral zone is thus essentially characterized by a 

 paucity of species of red alga?, by many species of green algse and 

 by a preponderance of Facacece. The number of the species of 

 brown algse is of less importance; it is three times as large as that 

 of the red algse and about half as large as that of the green algae. 



