290 



Pub. Pnget Sound Biol. Sta. 



Vol. 2, No. 51 



Table 1. Average monthly p H values of seawater 

 June 15 to August 15, 1919. 



June 



July 



August 



Av. for Per. 



Time of Testing 



a.m. 

 5-6 



p.m. 

 1-4 



a.m. 

 5-6 



p.m. 

 1-4 



a.m. 

 5-6 



p.m. 

 1-4 



a.m. 

 5-6 



p.m. 

 1-4 



Little or no Fucus 



Table 1 shows the different pH values of the seawater and the loca- 

 tions are referred to by numbers which correspond to those above. The 

 pH value of the locations having much Fucus does not vary much either 

 side of 8.0 in the afternoons. The average difference between the forenoon 

 and the afternoon is 0.50. In case of tidepools and of beaches having 

 much Ulva, but neither having Fucus, the pH values of the water in the 

 afternoons is considerably above that of 8.00. The average difference 

 between the forenoon and afternoon is 1.09, which is much greater than 

 the average difference where much Fucus is found. This would seem to 

 indicate that the pH values of the water were not favorable since all other 

 conditions were good. 



The last three locations, namely (7) out in the Sound away from 

 visible vegetation, (8) on beaches having no Ulva and (9) on exposures 

 receiving little or no direct sunlight, have pH values well within the 

 limits for a good growth of Fucus. They have an average difference 

 between the morning and afternoon of only 0.035. There must be other 

 factors which prohibit the growth of Fucus in these locations, and these 

 factors will be considered in a later part of this paper. 



Effects of Ulva on Fucus 

 To study the effect that Ulva might produce on Fucus, 2-4-lobed 

 plants, and more mature ones but not fruiting, with their natural attach- 

 ments, were selected. These were placed in the Sound, where much Ulva 

 was growing, others in Fucus beds. All plants were apparently of equal 

 vigor. A stout cord was tied to each rock containing the Fucus plants 

 which were placed among the Ulva. To the other end of each cord a 

 piece of Avood was tied. The cord was of sufficient length to permit the 

 wood to float at high tide. Thus the Fucus could readily be found. The 

 rocks containing the Fucus which was placed in the Fucus beds were suffi- 



