654 University of Calif ornia Publications in Botany [Vol.8 



p. 73) and related to D. pi^matifida Kuetzing (Tab. Phyc, vol. 9, 1859, 

 p. 16, pi. 39, fig. 1), to Z). Pappeana. Kuetzing (loc cit,, pi. 38, fig. 2), 

 and to D. liturata Kuetzing (loc. cit., fig. 1). The cross-section in 

 the central and lower parts of the frond has a structure similar to 

 that shown by Okamura (1913, p. 33, pi. 109, figs. 3, 7) for D. 

 mnrginata. In Z>. Johnstonii the margins are thickened by divisions 

 of the cells of both the medulla and the surface, while in D. marginata 

 increase in thickness is brought about by division of the medullary 

 cells only. 



4. Dictyota Vivesii Howe 



Fronds densely caespitose, stupose at the base, 7-9 cm. high, 135- 

 160/A thick (240ja at the base), collapsed and thin on drying, somewhat 

 regularly 3-6 times dichotomous below, the branches then rather 

 closely 3 or 4 times subflabellately or subpinnately dichotomous, 

 sinuses mostly rather acute, margins entire or slightly undulate ; main 

 segments oblong or obcuneate, 3-8 mm. broad, diminishing in length 

 and width upward, terminal segments 1-2 mm. wide; cortical cells 

 nearly uniform in size, 19-65ju, long, 11-27^ wide, interior cells much 

 larger and very thin-walled ; aplanospores forming small, scattered, 

 inconspicuous sori. 



Collected by Senor G. V. Vives at La Paz, Lower California, in 

 February, 1911. 



Howe, Phyc. Stud. V, 1911, p. 497, pi. 27. 



Dictyota Vivesii seems to be a near relative to D. Bartayresiana 

 Lamour. from the West Indies. According to Howe (1911, p, 498) : 

 "It is more caespitose in habit of growth than D. Bartayresiana, more 

 stupose at the base, less regularly dichotomous towards the apices, 

 rather broader in its broadest parts and more conspicuously dwindling 

 in width as the ultimate segments are approached, the axils (the 

 upper at least) are more acute and the segments less patent or divari- 

 cate, the apices are less acute, and both the cortical and the interior 

 cells are for the most part narrower and the cortical cells overlaying 

 the septa and lumina of the interior cells show scarcely any of that 

 differentiation in form and translucency that led J. Agardh to 

 describe B. Bartayresiana as 'fenestrate.' " 



