1925] Setchell-Gardner : Melanophyceae 629 



character of the attaching portion— "rhizome" and hapteres. In the 

 deep sea species, there is no rhizome and the mass of hapteres developed 

 often becomes several decimeters in thickness and up to a meter in 

 diameter, while in the shore species the conspicuous ' ' rhizome ' ' is flat 

 and adheres closely to the rock, dying and decaying at the rear as it 

 advances and spreads out in all directions. We have had an excellent 

 opportunity to study what might be considered a natural experiment 

 upon the effect of changing the deep sea species to the habitat of the 

 shore species at San Pedro, where a government breakwater was 

 extended out from the shore a long distance in the vicinity of a large 

 "kelp bed" of Macrocystis pyrifera. Thousands of plants attach 

 themselves to the rocks along low-tide level and persist until they are 

 torn loose. In not a single instance has the nature of the holdfast 

 been changed. It thus seems perfectly definite that the shore species 

 is a distinct entity, as well as the deep sea species. We have never 

 seen any specimens of either species which would seem to represent 

 transition stages between the two. 



53. Pelagophycus Aresch. 



Holdfast of several whorls of strong, dichotomously branched 

 hapteres diminishing in size toward their termini ; stipe solid at the 

 base, hollow above, constricted at the summit just below the large 

 spherical bladder, again becoming smaller and solid for a few centi- 

 meters beyond the bladder at its summit, dividing once dichotomously, 

 each branch again dividing unilaterally 4-6 times and each branch 

 bearing a single large terminal blade. 



Areschoug, in Botaniska Notiser, 1881, p. 49 ; Observ. Phycol., 

 part 5, 1884, p. 6. 



Pelagophycus is one of the large, conspicuous, monotypic kelp 

 genera confined to a relatively small area on the Pacific coast of North 

 America. Its resemblance to Nere&cystis is striking so far as the main 

 stipe up to the first dichotomy is concerned. Above the first, or occa- 

 sionally, the second dichotomy, however, the unilateral splitting and 

 sympodial character of the stipe clearly places the genus with the 

 Macrocysteae. 



