1919 Gail; on Fucus and Hiidrogen Ion 299 



1. The maximum growth is found in seawater having a temperature 

 not higher than 17°C. 



2. The largest plants as a rule are found in seawater having a pH 

 value of 8.0-8.2, in any of the temperatures considered. 



3. The growth in width of the sporeling is small in comparison 

 with the growth in length. The greatest growth in width is found 

 where the temperature of the water is not higher than 17°C, and where 

 the pH value of the water is 8.0-8.2. Plate 51 shows a graphic repre- 

 sentation of the size of the sporelings as affected by the different tem- 

 peratures and the various pH values. It will be observed that in this 

 particular set the sporelings made little or no growth where the tem- 

 perature ranged from ll'^-17"C and the water had a pH value of 6.8. 

 The sets were all run in duplicate and there was a more normal growth 

 in the corresponding set of the same pH. 



Study of beaches 



In the case of beaches having neither Ulva nor Fucus and only 

 smooth rolling stones for attachment, some other factor or factors than 

 that of the pH value of the water must be responsible since the average 

 pH value of the water at such places was 8.07, which is well within the 

 limits for an abundant growth of Fucus. Experiments previously con- 

 ducted by the writer (Gail, 1918) threw some light on the situation. 

 It was then believed that desiccation was the limiting factor. Consider- 

 ing the evidence presented in this paper, it is now considered tha^ tem- 

 perature is also an important factor. 



As during the previous summer, oospores were planted on smooth 

 flat stones which were firmly attached to the beach, a 10 per cent ger- 

 mination resulted on two different occasions when the temperatures did 

 not go above 19° or 20°C. At another time scarcely a 1 per cent ger- 

 mination resulted, when the temperature remained at 26 °C for nearly 4 

 hours. In one case all of the sporelings disappeared in five days. In 

 another trial they disappeared in eight days. In the last trial, during 

 which it was more cloudy than usual, most of the sporelings remained 

 on the stones until the thirteenth day. The temperature in the first case 

 went up to 24°, 24.5° and 26°C, during the first three days. When the 

 sporelings remained on the stones eight days the temperature rose to 

 26°C on two different days, but only for about an hour on each occasion. 

 In the last case the temperature did not go higher than 20 °C until the 

 last two days, when it rose to 25'"C and 28°C, respectively. The tem- 

 perature of 28°C was maintained for over two hours. 



In order to determine whether desiccation or temperature was the 

 limiting factor experiments were started as follows. Oospores were 



