1920 Pease; on Desmarestia 321 



Superficially, this species is distinguished from jD. herbacea, which it 

 most resembles, by its extreme size. Specimens of typical D. herbacea 

 have not been collected in the San Juan Islands with fronds longer than 

 one meter, nor wider than 3 cm., and all the specimens collected were of 

 about the same size and general appearance. Specimens of D. latissima 

 with fronds up to 8 meters in length and 40 cm. in width were collected 

 by the writer during the summer of 1918; several specimens were found in 

 the summer of 1916 from 40 to 60 cm. in width, and during that same 

 summer Muenscher (1917) collected one specimen 1 m. wide. Setchell 

 and Gardner (1903) mention plants of D. ligulata f. herbacea "cast ashore 

 at Esquimalt, B. C, in fragments several meters long and full 30 cm. wide." 

 Rigg (1912) says it "sometimes reaches a length of 8 to 10 feet and a 

 width of from 12 to 16 inches (about 3 m. long and 30 to 40 cm. wide — 

 Author), although it is usually much smaller." The figures given apply to 

 the main axis of the plant. This axis bears opposite lateral branches 

 which may attain a length of 2.5 m. and a width of over 20 cm. 



The lateral branches begin to appear quite close to the holdfast, are at 

 first small and rather crowded, but soon become farther apart and much 

 longer. Well developed branches are usually separated by from one to 

 three pairs of spines, which are merely abortive branches. Practically all 

 of the lateral branches are borne within one meter of the holdfast, plants 

 3 and 4 meters long having no more branches than those from a meter to 

 a meter and a half in length (table 1). The same thing is true also of 

 young plants, fhose with a main axis measuring less than 10 cm. bearing as 

 many branches as plants four times as long. Also the main axis usually 

 attains its maximum width within one meter of the holdfast. The occur- 

 rence of wider intervals between the upper branches is due to two factors: 

 (!). A larger number of abortive branches between the long branches; 

 (2). Greater elongation of the thallus of the main axis between the 

 branches of the midrib, which form the midribs of the lateral branches. 



Abortive branches vary from short sliarp spines to flattened out- 

 growths 3 to 4 cm. long and several mm. wide, which give no external 

 evidence of venation, and do not bear spines along their margins. Normal 

 branches, especially on the narrower forms, are sometimes no larger, but 

 have a definite midrib with visible lateral branches which run out to spines 

 olong the margins. 



All occasional plant was found in which one or two of the lower pairs 

 ol" lateral brandies were themselves branched, but this is not common and 

 seems to take ])]aee wlien the main axis has been broken off rather close 

 to the holdfast, a ])lHiioineiH)n which reminds one forcibly of the growth 

 l-abits of liigh( r |)l;iiits. 



