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BULLETIN OF THE BUREAU OF FISHERIES 
growth, and in the long run probably the supply of nitrogenous compounds chiefly 
determines the regional richness and poverty of the phytoplankton as a whole. 
Allen and Nelson’s (1910) experiments on rearing marine diatoms corroborate 
this, for they found it necessary to increase the concentration of nitrates, and 
apparently also of phosphates, above that of normal sea water in order to produce 
active multiplication. Fritz’s (1921a) work along this line is especially pertinent 
here, for she experimented at St. Andrews on the culture of planktonic marine 
diatoms of Gulf of Maine species with similar results, being unable to obtain any 
considerable and persistent growth without the addition to the normal sea water of 
the nutrient salts — nitrates and phosphoric acid — employed by Allen and Nelson. 
With these, however, she obtained flourishing cultures of Thalassiosira nordenslrioldi, 
Skeletonema costatum, Asterionella japonica, Nitschia closterium, Melosira hyperiorea, 
and various other planktonic species. 
NITROGEN 
It has long been known that sea water absorbs nitrogen so readily from the air 
that the surface strata are usually saturated with this element, but it is still question- 
able whether any of the planktonic plants are able to utilize elemental nitrogen first 
hand. It has long been the commonly-accepted belief, also, supported by experiments 
on land, that no chlorophyllous plants can do so, unless, like the Leguminosse, in 
symbiosis with nitrogen-fixing bacteria; but that all others — terrestrial or marine, 
unicellular or multicellular — are dependent on nitrogen compounds elaborated by 
some other means for their food supply of this essential element. 
In 1920, however, Moore and Webster (1920) published the results of experiments 
which seemed to demonstrate that certain green unicellular algae do possess the ability 
to obtain, and to fix by a process of photosynthesis, elemental nitrogen dissolved by 
the water from the air. A year later Moore, Whitley, and Webster (1921) carried out 
further experiments on a marine green alga, which they grew in measured volumes 
of sea water, finding that at the end of the experiment the amount of fixed nitrogen 
in plant and water combined exceeded the nitrite present at the beginning. From 
this they concluded that the excess must have come from the elemental nitrogen 
dissolved in the water, and so, in turn, from the air. These experiments, however, 
were not conclusive, no precaution having been taken to exclude the nitrogen-fixing 
bacteria which Keinke (1904) and Keding (1906) found on the fronds of several 
species of fixed algae at Helgoland, and which, therefore, were probably present on 
the algal fronds used by Moore, Whitley, and Webster in their experiments, or to 
determine their presence or absence. And although Moore and his associates adduce 
several reasons why they think it improbable that the value of their experiments 
is detracted from by this “ loophole” in technique, it remains an open question 
whether the increase in the amount of fixed nitrogen, which they demonstrated, 
did actually result from photosynthesis by the algal fronds experimented upon or 
from activity on the part of bacteria living symbiotic upon them. 
So far as I am aware, the ability of marine phytoplankton to synthesize ele- 
mental nitrogen has not actually been tested by critical experiment directed to this 
definite end. But it has repeatedly been found that very much richer cultures of 
