Evolution of Oxygen hy Sea- Weeds. 257 



is clecar that 58'5 per cent, of oxygen was originally 

 present. 



A similar method has been adopted in the case of the first 

 five experiments on this table, the last two being calculated 

 in the ordinary manner already described. 



Seeing that no spores wej'e observed in connection with 

 the plants employed, the high percentages of oxygen arc 

 somewhat striking. 



Good tufts of the closely allied Chcetomorpa melagonium 

 were also procured from the same locality, but the 

 difficulties connected with their manipulation precluded an 

 extensive series of ex[)eriments from being made. So far as 

 my observations went, an average percentage of about 54 

 was obtained. 



The experiments made on Fttcus canaliculatns, Linn., 

 had unfortunately to be conducted somewhat late in the 

 season, during the earlier part of November. They cannot 

 accordingly be taken as indicative of the average summer 

 or early autumn conditions of the plant, yet they demon- 

 strate that the oxygen-emitting power is not eclipsed by the 

 advent of a little frost during night, or by the presence of con- 

 ditions which cannot be looked upon as so favourable as in 

 the earlier parts of the year. That the part played by the 

 various i)erennial algai in the oxygenation of ocean water, 

 even during winter, is a very important one, cannot longer be 

 doubted, nor is it unlikely that it may yet be shown that in 

 the cases of those which emit their spores in the cold season 

 their maximun power as oxygenators may be attained at 

 the same time. 



The single experiment recorded in the case of Chondrus 

 cripits (L.), Stackh., was also made in the early part of 

 November, but a little later than those recorded for Fucus 

 canalimdatus. That this is sufficient to account for the low 

 percentage, as in the former cases, can hardly be doubted ; 

 but unfortunately I have as yet been unable to collect data 

 l)earing on the summer evolution of oxygen iu this common 

 but interesting species. 



In conclusion, it must be pointed out that the figures 

 given in the preceding lists cannot be regarded as of 

 absolute but only of relative importance. That more exact 

 methods of analysis would probably give results varying 



