192 Puget Sound Marine Sta. Pub. Vol. 1, No. 17 



Chambers (3) says that currents are beneficial by renewing the COg 

 supply and by removing the depleted water and gas from the surface of 

 aquatic plants. He shows that bicarbonates are a source of COg, as Has- 

 sak, Angelstein and others have already pointed out^ and that a CO2 

 saturated medium does not stimulate growth, which would indicate that 

 the value of currents to plants is not in aeration but in carrying away the 

 water depleted of CO2. Undoubtedly a gas film surrounds the plant and 

 interferes with absorption. But Chambers points out that Schiitzenberger 

 found that the optimum CO2 supply for water plants is only 5% to 10% 

 of complete saturation. Since the tides keep the water around the kelps 

 of the most quiet bays constantly moving it is hard to conceive of a short- 

 age of CO2 except by assuming a depleted layer of water and gas held 

 so tightly to the surface of the plant by cohesion that ordinary tides are 

 not capable of removing it as fast as the gas is taken from it. The facts 

 which must be known before it can be proved conclusively what part cur- 

 rents play in the growth of kelps or any other plant are: the velocity of 

 immediately adjacent water compared with the velocity of the current; the 

 width of the layer held so long that it becomes seriously depleted of gas 

 or saturated with waste products ; the total amount of CO2 available in 

 carbonic acid, bicarbonates, and as free gas ; the rate of their diffusion 

 from the rapidly moving water through the depleted layer to the plant; 

 and the optimum rate of absorption of gas by the plant. 



Temperature may also be a factor in the distribution of Nereocystis 

 (27). The water of the quiet bays is undoubtedly warmer than that of 

 channels where the tides are swift; and it is conceivable that high tem- 

 perature may have something to do with the stunted development of the 

 kelps in the Argyle tide stream, for the lagoon becomes quite warm at 

 times. However an increased temperature of surface water is hardly 

 sufficient to account for the differences in elongation of deeply submerged 

 kelps and those which are near the surface. The slow rate of growth 

 of floating plants may be partly due to their higher temperature and des- 

 iccation. Frye (12) presumes that the difference between the gas pres- 

 sure in floating and submerged pneumatocysts may be attributed to dif- 

 ference in temperature. 



Gravity might also be a factor in the slow elongation of the floating, 

 horizontal kelps, and the more rapid growth of the naturally attached, 

 erect ones. According to Jost, Elfving and Richter found that the growth 

 of Chara and Phycomyces is retarded when the plants are inverted. 



Salinity of the water may not be so large a factor in the distribution 

 of Nereocystis as is generally supposed. Setchell (27) says that the 

 Laminariaceae are most abundant where the salt water is not polluted by 



