134 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.3 



analysis has been verified by cross sections of tetrasporic sori in European 

 material of R. pabnetta (figs. 5-6) which showed the soriferous frond 

 only slightly thicker than the sterile, and the cortical layer of small, oval 

 cells entirely unmodified except through displacements by the enlarging 

 tetraspores. There is apparently no stimulation to extra cell division in 

 the cortex and hence no strings or rows of cells in which the tetraspores 

 are imbedded as in Sec. Palmatae (figs. 3-4). Tetraspores may also be 

 borne on lateral lobules proliferating from the upper segments. 



(15) RHODYMENIA PALMETTA (Esp.) Grev., Alg. Brit. 

 (1830), p. 88, pi. Xll;Fucus palmetto Esper, Icon. Fuc. (1800), 

 p. 84, pi. XL. 



Plate 18, Figs. 5-6 



This assemblage is another one which has caused considerable con- 

 fusion in the treatment of the Pacific Coast species of Rhodymenia. 

 Numerous specimens with only superficial resemblance have been re- 

 ferred to this species. In the type locality it is rather polymorphic, a fact 

 which has allowed a broad basis for the interpretation of forms. Fertile 

 material is rare ; not only in this species but throughout the section cysto- 

 carps are largely unknown. We must depend then upon gross morphology 

 for specific taxonomic characters ; and, since this section contains so many 

 forms of similar habit, separation is difficult. 



When more complete collections are available and the extent of vari- 

 ation in Rhodymenia in response to the environment is more fully under- 

 stood, rearrangements will undoubtedly be necessary. The section Pal- 

 mettae is the most difficult section of the genus to interpret because it 

 seems to be a center of variation in which the variants are distinguished 

 with difficulty and about which the morphological differentiation into 

 other sections of the genus radiates. It is a fortunate coincidence that this 

 median species was illustrated by Greville as the type of the genus. 



Distribution. — Coasts of England and France; the Mediterranean. 



(16) RHODYMENIA CORALLICOLA Ardiss., Florid. Ital., II 

 (1868-1878), p. 55, pi. IX (ex synon.). 



Distribution. — The Mediterranean. 



(17) RHODYMENIA LIGULATA Zanard., Saggio (1843), p. 

 46; J. Ag., Sp. II (1851), p. 382; Sphaerococcus ligulatus 

 Kuetz., Tab. Phyc. XVIII, t. 96. 



Distribution. — The Mediterranean. 



