584 Puget Sound Marine Sta. Pub. Vol. 1, No. 31 



(>r numerous exploring expeditions, especially those in Antarctic regions, 

 others have been added from time to time, until, according to De Toni 

 (4), the genus consists of 14 species and 4 varieties. Of these only one, 

 D. media (C. A. Agardh) Grev., in addition to the 4 already named, has 

 been reported from the north Pacific coast; but Okamura (19) has pro- 

 posed a new Pacific species, D. tahaccndes, which may occur on American 

 as well as Japanese shores. 



The Desmarestias are all sublittoral, growing from just below low 

 tide line to a depth of 20 to 25 fathoms. They occur most abundantly 

 in cool temperate and polar regions, and are not found in the tropics. 

 In northern waters, according to Kjellman (9) and Muenscher (17), 

 they occur usually as secondary species in the Laminaria association, or 

 in deeper water just below the Laminarias, but in antarctic and sub- 

 antarctic regions they form the dominant sublittoral vegetation, being as 

 abundant, according to Skottsberg (27) as are the Laminarias in arctic 

 regions. They prefer exposed situations in strong currents, but some- 

 times flourish in quieter waters. In still water or on exposure to the air 

 they soften, change color, and decompose rapidly. 



There are 2 types of thallus in the Desmarestias: (a) the filiform, 

 in which the main axis and all its branches to the last order are slender 

 and terete or only slightly flattened, with the axial filament and its sur- 

 rounding tissues, the so-called midrib, not at all evident from the surface, 

 as in D. media; (b) the plane type, in which the main axis and all its 

 branches are much flattened, with a very evident midrib, as in Z). herbacea. 

 The plant rises from a simple disk-shaped or flattened-conical holdfast. 

 The plant body consists of an axial row of articulate cells, surrounded by 

 layers of more or less differentiated tissue and covered by a cortical layer 

 from one to several cells thick. According to Oltraanns (20), the Des- 

 Tiiarestias may be likened to a huge Ectocarpiis with a cortical growth, 

 finding its analogy in the corticated Callithamnions. The main axis bears 

 branches to the fifth and sixth degrees and during the growing season all 

 the branches and branchlets are tipped by confervoid branching filaments, 

 whose cells are densely filled with small lens-shaped chloroplasts. Ac- 

 cording to Soderstrom, these filaments function As assimilation organs 

 during the season of rapid growth. 



The growing region is intercalary, and located at the bases of the 

 hairs, which are thus continuous with the axillary row of cells in-the older 

 parts of the plant. Branches appear on the axis both above and below 

 the growing region, and cortication begins at most only a few cells back 

 of this point, so that the lateral branches which arise below the growing 

 region appear on superficial examination to be lateral outgrowths from the 

 corticated thallus. 



