INDICATIONS REGARDING THE SOURCE ОҒ COM- 
BINED NITROGEN FOR ULVA LACTUCA 
G. L. FOSTER 
Teaching Fellow in the Henry Shaw School of Botany of 
Washington University 
INTRODUCTION 
Very little attention has been given the question of the 
sources of nitrogen for marine alge. Nevertheless, the ques- 
tion is an interesting one both physiologically and ecologically, 
because of the extremely small amount of nitrogen supposed 
to be present in sea-water, and because of the very noticeable 
change in the type of algal flora when the nitrogen content of 
the environment is increased, as by the presence of sewage. 
The literature bearing on the subject is practically limited to 
a debate between a few authors as to the amount and form 
of nitrogen in sea-water, and the way in which the supply is 
maintained. This dispute involves some questions of funda- 
mental importance for marine biology; consequently, а brief 
statement of the different views is pertinent. 
Natterer (13) reports that careful analyses of water from 
the high seas show scarcely a trace of nitrates.  Nitrites are 
somewhat more abundant, but not sufficiently so to admit 
of quantitative determination. Ammonium compounds, on the 
other hand, according to Thoulet, are present in sufficient 
amount to be quantitatively determined, and vary from .13 
to .34 mg. per liter (.013-.034 per cent) according to the 
locality. Reinke (15) considers these amounts of nitrogen 
reported to be insufficient for the production of the enormous 
amount of living material in the sea, especially when the activity 
of nitrifying and denitrifying bacteria is taken into account. 
He considers as of prime importance in this question the nitro- 
gen-fixing bacteria which have been demonstrated in sea-water 
by Benecke and Keutner (4), and others. Reinke found Azo- 
tobacter embedded in the gelatinous material on the surface 
of Laminaria fronds and argues for a symbiotic relation between 
the alge and bacteria. 
ANN. Mo. Bor. GARD., Vou. 1, 1914 (229) 
