Gas Pressure in Nereocystis 



T. C. Frye, 



University of Washington, Seattle. 



So far as the writer has been able to find there is no literature on 

 the gas pressure within the air cavities of marine algae. Yet daily con- 

 tact with Nereocystis soon makes it evident that the pressure inside the 

 plant is not usually the same as that outside. 



The air cavity of Nereocystis is estimated by Zeller and Xeikirk^ 

 to have a volume of about 4 liters or less, depending upon the size of 

 ilie plant. Normally the bulbous end either floats on the surface of the 

 water or is submerged below it, depending upon the tides, the length of 

 stalk produced by the individual, and the depth of the water. 



Fallis- and Sheldon^ have shown that the plant is independent of its 

 holdfast, also that its parts are largely independent of each other. The 

 most serious thing about cutting or otherwise injuring it, seems to be 

 the paving of the way for the entrance of bacteria. 



We have, therefore, a plant containing a great quantity of gas, living 

 in a medium whose temperature changes little, a plant which may be 

 torn loose and moved about freely without stopping or materially hin- 

 dering its growth, and which may be greatly injured without seriously 

 affecting its physiological activities. These conditions seemed favorable 

 for experimenting on the gas pressure within the bulb. Experiments 

 were undertakeng during July, 1915, at the Puget Sound Marine Station, 

 to determine the variations in pressure within the gas cavity. 



The apparatus used was essentially a U-tube half full of mercury, 

 with some form of puncturing apparatus to connect it with a kelp. At 

 first a continuous glass tube was bent to form the whole apparatus, to- 

 gether with the puncturing tip. But this was so difficult to handle from 

 a rowboat, and thus so often broken, that it was abandoned. In the 

 final form a pressure rubber tube of small bore was used to connect the 

 kelp with the U-tube. The difficulties of exact measurements on the bob- 

 bing boat were sueli that no difference could be observed between the 

 results of the two kinds of a])))aratus. The small amount of gas in the 



iZeller, S. M., and Neikirk, Abigail. Gas exchange in the pneumatocyst 

 of Nereocystis. Puget Sound Marine Sta. Pub. 1:25-30. 191. ""i. 



2Fallis, Annie L. Growth of the fronds of Nereocvstis luetkeana. Puget 

 Sound Marine Sta. Pub. 1:1-8. 1915. 



3Sheldon, Sarah M. Notes on the growth of the stipe of Nereocvstis luet- 

 keana. Puget Sound Marine Sta. Pub. 1:15-18. 1915. 



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