558 University of California Piiblications in Botany [Vol. 8 



FAMILY 15. DESMAE.ESTIACEAE kjellm. 



Fronds erect, sparsely branched in some species, profusely branched 

 in others, from cylindrical through compressed to broadly membran- 

 aceous, solid, arising- from a simple monosiphonous branched filament 

 of trichothallic growth in length, soon becoming complex through the 

 downward growth of closely applied branching corticating filaments 

 which results in the production of several distinct tissues; central 

 monosiphonous and branching filament remaining distinct, although, 

 at times, becoming obscured through thylose growth filling the cavities 

 of the large cells; tissues outside the central monosiphonous axis, 

 various, usually large celled and more or less regular, the outer being 

 smaller and forming a distinct outer tissue of one, or few, layers of 

 cells ; zoosporangia known in only a few species scattered or in small 

 patches, arising by direct transformation of the outer cells; plants 

 mostly undergoing change of color (to verdigris green) and odor 

 (''sharp") soon after being removed from the water and exercising 

 a bleaching effect on other algae with which they come into contact. 



Kjellman, Enum. PL Scand., 1880, p. 10, Alg. Arctic Sea, 1883, 

 p. 261. 



The Desmarestiaceae form a very distinct group and one which is 

 readily separable from that of the Myriogloiaceae. It represents a 

 very distinct type of frond development, at least so far as the final 

 product is concerned. There are two centers of distribution, viz., 

 North Atlantic and North Pacific as contrasted with the Antarctic and 

 Subantarctic regions, and it is doubtful whether there are any species 

 common to the two centers. 



There are, at present, referred to the Desmarestiaceae three genera, 

 Desmarestia, the type genus, Arthracladia, by some referred to a 

 separate family, and the Phaeurus of Skottsberg. The first is from 

 both Arctic and Anarctic centers, the second is North Atlantic 

 (European and American) while Phaeurus is from Fuegia. While 

 the Myriogloiaceae are seemingly the more primitive and related to 

 such forms as ^giraeeae, the Desmarestiaceae are more complex, at 

 least, with Phaeurus as the more simple and the ligulate Desmarestias 

 as the more complex. 



