302 Pub. Puget Sound Biol. Sta. Vol. 2, No. 51 



Summary 



1. The growth of sporelings as well as larger plants of Fucus is 

 almost comiDletely inhibited in seawater having a higher pH value than 

 8.6, and is very much inhibited in seawater having a higher pH value 

 than 8.4. 



2. Sporelings as well as larger plants of Fucus will not live in 

 seawater having a pH value of 8.6 when the temperature is higher 

 than 24°C. 



3. Sporelings as well as larger plants of Fucus are very much 

 inhibited in growth when the pH value of the water is below 7.2. Neither 

 will live in seawater having a pH value of 7.0 when the temperature is 

 above 24°C. 



4. Fucus is not found on beaches, even tho there be good attach- 

 ment, where there is much growth of Ulva, since Ulva causes the sea- 

 water to have too high pH values. 



5. The results of the experiments on permeability of the oospores 

 indicate that the plasma membrane is sufficiently permeable to OH and 

 H ions in seawater having pH values above 8.4 and below 6.8 to reduce 

 the percent of germination and to inhibit the growth of sporelings. 



6. Fucus is not found on smooth gravel on beaches even where 

 Ulva is not present, since the high temperatures and extreme desiccation 

 decrease the germination and prevent the growth of sporelings. 



7. The oospores of Fucus in seawater having a pH value of 7.0 

 do not germinate if the the temperature is as high as 30 °C for three hours 

 or longer. Germination is retarded at lower temperatures in seawater 

 liaving pH values below 7.2. 



8. Fucus is not found in tidepools because the temperature of the 

 water is too high and because the extremes of the pH values of the water 

 are too far apart. 



9. Reduced light is a controlling factor in determining the lower 

 limit of Fucus. The probable low pH value and low oxygen content 

 of the seawater at any considerable depth may also be important fac- 

 tors. 



