1915 Zeller and Neikirk; on Nereocystis 29 



The high percentage of carbon dioxid in Nereocystis, however, is 

 not sufficient under the low light intensity and low temperatures secured 

 in the sea water, to produce the toxic effects which some have recorded 

 for chlorophyllous terrestrial plants. On the other hand there may be 

 some relation between the high carbon dioxid content of the pneumatocysts 

 of large kelps, such as Nereocystis luetkeana (Mertens) P. & R., Macro- 

 cystic pirifera (Tur.) Aghard, Alaria fistulosa P. & R. and Pelagophycus 

 porta Setchell, and the enormous annual growth of these plants, due to an 

 increased synthesis of carbohydrates. 



The oxygen content of the pneumatocyst proves to be about one-half 

 the percentage found in ordinary air. Our analyses in this respect agree 

 quite consistently with those of Lucas (5) but are surprisingly lower 

 than expected in the light of Wille's investigations. We do not attempt 

 to explain fully this low oxygen content of the bladder. However, we 

 know that very little is absorbed directly from the atmosphere for the 

 pneumatocyst is immersed at high tide and only partially exposed at low 

 tide, and according to Waynick* the amount of oxygen dissolved in sea 

 water is very slight, 9.8 to 16.9 parts per million. 



Our results show that the carbon dioxid and oxygen vary from day 

 to night, and the range of variation is wider for carbon dioxid. As 

 would be expected the maximum increase in oxygen occurs directly after 

 the time of maximum photosynthetic activity, while the maximum increase 

 in carbon dioxid is during the night. The greater range in variation of 

 the carbon dioxide may be due to the greater solubility of the latter and 

 thus the more rapid osmosis to and from the chamber, or it may be due 

 to such unknown factors as the partial pressures of the gases in the mixture, 

 or the varying pressures to which the plants are subjected with the rise 

 and fall of tides. The variation of the two essential gases indicates that 

 their source is to a considerable extent related to the processes of 

 metabolism in the plants. 



In conclusion we may say that our analyses indicate that the pneu- 

 matocyst of Nereocystis is not merely a means by which the plant is 

 buoyed up to the light, but it serves as a reservoir in the gas exchange 

 of the metabolic processes, and this ready supply of essential gases may 

 have a bearing on the enormous annual growth of these plants. 



♦Unpublished data secured on the Expedition of the Alaska Kelp Investi- 

 gation under the direction of Dr. Frank K. Cameron, Bureau of Soils, U. S. 

 Department of Agriculture, in 1913. 



