Carbon- A ssimiiation of Marine Algae . 679 
This is marked even in Ulva , and as I showed in a previous 
paper, formed one of the chief difficulties of the work. The 
Alga had to be darkened for several weeks before becoming 
starch-free. At the conclusion of the work on Ulva , I was very 
anxious to make similar observations on other marine Chloro- 
phyceae. Unfortunately very few members of this group are at 
all suitable for such a purpose, and in none is the form of the 
thallus so favourable for observation as in Ulva. Enteromorpha 
intestinalis , Link, was tried, but abandoned as I was unable, even 
after weeks or months of darkening, to get all the starch out. 
Not having the time at my disposal to attempt a direct 
estimation of the amount of carbon assimilated, — a problem 
seemingly of great difficulty when the plant is immersed in 
a liquid, — I determined to try Cladophora rupestris , Kg. 
Material, which was very kindly sent me by Professor Phillips, 
was completely darkened in sea water in the laboratory, but 
after two months the Alga still contained starch and was 
becoming so unhealthy that, although another and equally 
unsuccessful attempt was made in very diffuse light, the work 
had to be abandoned. It had occurred to me that want of 
oxygen, or insufficiency of salts in a limited quantity of sea- 
water, might account for this. Pennington 1 , in regard to 
similar difficulties with the destarching of Spirogyra, found 
that the former played a very important part in the process. 
I therefore arranged, through the courtesy of the Director, 
for the destarching to be carried out at the Marine Biological 
Laboratory at Plymouth. A large tank there was almost 
completely darkened, and through it a supply of sea-water 
was pumped continuously, the inflow impinging sharply on 
the surface of the water in the tank, and thus ensuring 
sufficient saturation with air. The tank was stocked early in 
January with Cladophora which I obtained from the neigh- 
bouring coast. After five months’ darkening, while the Alga 
continued healthy, and in good condition, it still contained 
starch. In a few experiments which I made with the partially 
destarched Alga, by exposing it to light in sea water, I found 
1 Pennington (’97). 
