1917 Pease; on Taxonomii of Desmarestia 385 



At the end of the period of elongation these hairs are shed, and de- 

 velopment and differentiation of the tissues surrounding the axial filament 

 take place. The summer condition of the plant, therefore, does not at 

 all resemble the spring condition. In fact, plants collected in spring and 

 summer are so unlike that at first they were classified as different species, 

 when the only differences consisted in the presence or absence of these 

 transitory hairs. 



The period of reproduction seems to occur during the winter months, 

 living swarmspores having been seen by Kuckuck (10) at the beginning 

 •of December, and by Rosenvinge (24) in February. So far as known, re- 

 production occurs only thru asexual spores, formed in unilocular sporangia, 

 which occur in sori on the surfaces of the branches and are developed 

 from cortical cells, altho Johnson (7) reports having seen spores formed 

 -in the cells of the terminal hairs of D. ligulata. 



The genus Desmarestia, according to Setchell and Gardner (26), is 

 represented on the north Pacific coast by 5 species, D. aculeata (L). La- 

 mour. ; D. aculeata f. media (Ag.) J. Ag., or D. media (C. A. Ag.) Grev.; 

 D. viridis (Muell.) Lamour. ; /). ligulata (Lightf.) Lamour. ; and D. ligu- 

 lata f. herhacea (Turn.) J. Ag., or D. herbacea (Turn.) Lamour. These 

 species have all been reported from the San Juan Islands, and the present 

 study is based upon material collected during the summer of 1916, while 

 the writer was a research student at the Puget Sound Marine Station, 

 located on San Juan Island, one of the largest of the San Juan group. 



DESMARESTIA ACULEATA (L.) Lamour., Under various names, is includ- 

 ed in practically every list of marine algae collected in northern European 

 -or British waters, back to the earliest published accounts. Tournefort 

 (31) describes it as "Fucus tenuifolius, foliis dentatis." The species name 

 -is credited to Linnaeus, who published it first in the second edition of his 

 Species Plantarum (15). Lamouroux (12) was the first to classify it as 

 Desmarestia aculeata Linn., and his reference (13) is the earliest found 

 by the writer reporting it from the north Pacific (Kamchatka). 



D. aculeata was probably the first member of the genus to be recog- 

 nized and described by the early systematists. It is also the most widely 

 •distributed species, and seems to be at least fairly common thruout its en- 

 tire range. It is not surprising, then, that it has received more attention 

 than other members of the genus, and that its structure, as worked out 

 by Kiitzing (11), Reinke (22), and especially by Sodcrstrom (28) and 

 Jonsson (8), should be considered as typical. 



Soderstrcim was the first to undertake a detailed study of this spe- 

 cies, giving in his carefully worked out paper the origin and d(vel()])nient 

 of the various tissues of the plant. He was the first to distinguish between 



