28 



Pucjet Sound Marine Sta. Pub. Vol. 1, No. 5 



Table II Showing the analyses for oxygen. 



Analyses of gas collected 

 at 3:00 — 4:00 a. m. 



Analyses of gas collected 

 at 3:00 — 4:00 p. m. 



Average variation of O^ from day to night 1.398*7^ • 



The average amount of carbon dioxid and oxvgen taken together is 

 about 13 percent of the whole gas content with a remainder of about 87 

 percent which we consider as nitrogen. We find here a carbon dioxid con- 

 tent far above that of ordinary air, varying from 10 to 100 times that of 

 air at Kew reported by Brown and Escombe (2). The maximum amount 

 of carbon dioxid which we obtained in any one analysis was 3.45 percent 

 while the average amount at night proved to be 2.5 percent. 



It has been found that for terrestrial green plants the amount of 

 carbon dioxid in ordinary air is inadequate for a maximum of photosyn- 

 thetic activity. Under these conditions the limited carbon dioxid pres- 

 sure is one of the limiting factors in growth when the plant is strongly 

 illuminated at favorable temjjeratures and with good water supply. On 

 the other hand it has been shown by Godlewski, Kreussler, Blackman, 

 Pantanelli and others that an increase in the amount of carbon dioxid 

 above that ordinarily found in air increases assimilation, assuming the 

 other factors were favorable. According to Kreussler's researches the 

 optimal percentage seems to lie at about 10 percent while de Saussure and 

 others have found that the growth of plants is retarded in the presence 

 of high percentages of carbon dioxid. Blackman ( 1 ) points out that the 

 optimum is dependent on limiting factors, especially light and temperature. 

 Thus a tension of carbon dioxid which might give a maximum 

 photosynthetic activity at a certain light intensity, would become a limiting 

 factor at higher intensities. 



