Eooliition of Oxygen hy Sea- JFecds. 



249 



mercury in tlie eudiometer has to be deducted from the 

 reading of the barometer in making the calculations. 



A. Unteromorpha com'pressa (L.) Grev. 

 [u this case the results of seven experiments are given, 

 diiferent plants being employed on each occasion. Good 

 specimens were procured in the immediate vicinity of this 

 station, all being in full vigour of growth. The first experi- 

 ment gave the following statistics: — 



Correcting according to the formula, 



yi_ 12-6x(755-TV of 4-8 -13-710) 

 ~760 X (1 + 0-003665 X 16-2). 

 = log A — log B. 

 = x-y. 



Hence the number whose log. is z is the number required. 

 Tn this instance it is found to be 11*5 approx. 



The variations in the percentages of oxygen shown by the 

 following table are indeed considerable, but perhaps cannot 

 be looked upon as abnormal. The maximum, 61-2, was 

 obtained in the second experiment, the minimun in the 

 third, namely, 51-7. On comparing the condition of the 

 plants in these two cases, a very remarkable difference was 

 recorded. Both were in an exceedingly perfect condition 

 of health, and had not been injured in any part by impact 

 of foreign bodies, but on examining the former under the 

 microscope, the spores were found to be just moving out of 

 the cells. That a plant at the acme of its vigour was thus 

 observed is of interest, as proving that in such a condition 

 its efficacy as an oxygenator is very great — higher indeed 

 than in any previous, and, of necessity, than in any 

 subsequent period of its existence. In the second instance 

 referred to, the stage for emission of spores had not yet 

 arrived, nor did this occur during the week following, while 



