1920 Pease; on Desmarestia 319 



color, with a greenish tone; has a narrow thallus, not exceeding 6-8 mm. 

 in the widest parts ; and has a firmer, heavier texture, with the midrib 

 much more prominent in the older basal portion of the plant. D. herbacea 

 is lighter in color, a yellowish brown, with a comparatively broad 

 thallus, 10 to 30 mm. wide; and a much thinner, more delicate texture. 



d. Desmarestia latissima Setchell and Gardner in Litt. n. sp. 



(Plates 55, 5G, 57; Plate 58, Figs. 1-4; Plate 60, Figs. 5-9; 

 Plate 62, Figs. 8-10.) 



Fronde magna, foliacea, latissima, inferne sub-coriacea et evidenter 

 costata ; pinnis distantibus, margine dentis distantibus. 



Plant body very large, length up to 8 m. ; frond membranaceous, sub- 

 coriaceous at base, foliaceous, very wide, diam. 4-100 cm.; with an evident 

 midrib and lateral veins ; occasionally bipinnate ; pinnae and pinnules 

 widely separated, either blunt or pointed, with margins coarsely spinulose- 

 serrate; veins branching from the midrib, giving off secondary branches 

 which break up into fine veinlets and form a network in the broad thin 

 tissue of the lamina, visible to the eye in both fresh and dry material as 

 faint branching lines. 



The species name is credited to Drs. W. A. Setchell and N. L. Gardner 

 of the University of California, who were kind enough to furnish the 

 writer with a brief outline of their provisional arrangement of the Pacific 

 coast species of the genus Desmarestia. Type specimens are deposited 

 in the Alga Herbarium of the University of Minnesota. 



The writer believes that this species should be set off from D. herbacea 

 en account of its extreme size and the heavier, coarser texture of the 

 thallus ; also because it has fewer branches, more widely separated, and 

 cnly in rare instances do the lateral branches bear branches of the second 

 order. 



The species, as designated, includes a wide range of forms, and 

 further study may make it necessary to subdivide still more or at least to 

 segregate one or two varieties, but up to tlic present time a sufficient number 

 of examples have not been examined and compared so that definite limits 

 can be set, and it is not the writer's intention to split up the genus un- 

 necessarily. 



In a series of 25 young plants collected by the writer the length of 

 the main axis varies from 1 to 50 cm. and the width from 0.2 to 13 cm. 

 While in general an increase in width accompanies one in length, the two 

 are not proportional. In these young plants the number of pairs of 

 lateral branches varies from 2 to 11, without any apparent relation to the 

 length or width of tlic main axis from which they arise. These lateral 

 branches vary in length from 0.5 to 22.5 em., and in width from 0.2 to 8 cm. 



