LITTORAL ALGAB OF PUGET SOUND 95 



species with much variation due to difference of environment. 



IX. Sucia Islands, south side. 



This was excellent ground for this study. The rock is softer 

 and larger pools have been worn in them. They are more exposed 

 to the sweep and surge of the tide and surf and better test the 

 character of Prioniis. This region is a resume of all the others 

 with enough new features to settle some of the problems raised 

 by them. In other places the plants were more protected, which 

 seemed to account for the presence of Prionitis rather than the 

 higher temperatures or better light exposures. Long troughs 

 are cut in the sea-floor which retain sufficient water at lowtide 

 to support large quantities of Prionitis, but none is found there, 

 evidently because the waves and tide sweeping the full length 

 of the troughs sweep out this seemingly fragile plant, which is 

 not adapted to such a strenuous existence. Why it has not become 

 so adapted is another question. 



DISCUSSION. 



Prionitis is probably the only alga found exclusively in tide- 

 pools and not elsewhere. It is found outside of tide-pools, properly 

 so called and at greater depths than these, but in tide-pool con- 

 ditions, essentially, and hence real tide-pools. Rhodomela seems 

 to prefer the pools and probably for the same reason as Prionitis. 

 Although abundant and nearly always found associated with the 

 former, it is also found in crevices and protected places, in essen- 

 tially tide-pool conditions, but deeper than its associate. It seems 

 to shun extreme light and higher temperatures, which are found 

 at higher altitudes. I thought at first that the plant went deeper 

 only to find a firmer anchorage and shunned loose rocks, but I 

 afterwards found it on rock fragments and shells; but these must, 

 however, be protected from rolling and abrasion. 



Prionitis is also more abundant where Rhodomela or like 

 plants are present to afford protection; whether as points of 

 attachment for young plants or later against strong currents 

 is not apparent. It is preeminently not a surge-plant. It must 

 have a protected nook or hollow. It does not grow on a sloping 

 ledge as does Calpomenia; nor on a sheer rock wall as does Fucus; 

 nor on a surf-beaten shore as does Postelsia. It exudes no slime 

 and can not endure exposure to the air as does Fucus. It must grow 

 in a pool or some protected place where it may secure much flowing 



