Studies of Photo-synthesis in Marine AlgoB. 



55 



together. As there were two similarly treated jars in each set, the Kjeldahl 

 determinations for nitrogen came to be made upon the contents of four jars ; 

 thus a good average was obtained. 



The green sea-weed utilised was Enteromorpha. compressus, which grows 

 abundantly in the open wooden runnels supplying the freshly-pumped-up 

 sea water to the ponds of the Fish Hatchery. This weed is well suited to 

 the purpose because it is easily divided and can be accurately weighed out in 

 definite amount. A quantity of the Enteromorpha was gathered and relieved 

 of excess of sea water by pressing gently between folds of filter paper. It 

 was then weighed out into 0'5-grm. quantities, and one of these quantities 

 was placed in 200 c.c. of fresh sea water in each Kilner jar. Nothing save 

 the weed and water was added to any jar.. The first dozen jars were started 

 on the morning of March 28th, and the second set on the afternoon of the 

 same day ; they were pickled together in absolute alcohol as preservative on 

 the morning of April 5th, and also the waters in which they had grown were 

 taken away for analysis, with the results given below. 



The two sets were treated identically as to exposures, and the first set may 

 be taken as an example for both : — 



Nos. 1 and 2. — Kept with lids tightly screwed on in such daylight and 

 sunlight as were available outdoors. 



Nos. 3 and 4. — Ditto, but instead of tightly screwed-on lids, these were 

 covered above only with a double layer of muslin, so that there was free 

 access of atmosphere. 



Nos. 5 and 6. — Exposed to diffuse light only indoors on shelf in laboratory, 

 with lids tightly screwed on. 



Nos. 7 and 8. — The same as to light, but open, with muslin covers only. 



Nos. 9 and 10. — Kept in complete darkness in cupboard with lids tightly 

 screwed on. 



Nos. 11 and 12. — Also kept in darkness in cupboard with muslin covers 

 only. 



At intervals, as noted in the subjoined Table, a quantity of 100 c.c. of 

 sea water was taken from one jar of each type of exposure, four drops of 

 0'5 per cent, of phenolphthalein were added, and the water was titrated to 

 neutrality with the results shown. Then 100 c.c. of fresh sea water were 

 added to restore the former volume, and the jar restored to statu qii.o as to 

 exposure. The samples of weed in each set of four jars with identical 

 exposures did not during the experiment ever receive more than 1000 c.c. of 

 sea water in all. Samples of fresh sea water, and of that from the jars open 

 in sunlight, were analysed for amino-nitrogen by Kjeldahl destruction and 



