[Vor. 1 
158 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
HISTORICAL 
As early as 1854 Laurent (20, 21), and Morren (24) occupied 
themselves indirectly with the relation of alge to free atmos- 
рһегіс nitrogen. Morren was led to the conclusion that the 
sudden death of cultures of infusoria and alge was due to 
the insufficient quantity of combined nitrogen furnished when 
the number of organisms became considerable. The nitrogen 
requirement, he found, could be satisfied by ammonium car- 
bonate, organic nitrogenous compounds (decaying insects), and 
other nitrogenous substances in the water; but in no case did 
he find that free nitrogen from the atmosphere could serve as 
the source of nitrogen. While it is difficult to say with what 
organisms Morren worked, it is altogether probable that mem- 
bers of the Volvocacee were present among his "green," "brown," 
and “тей іпѓиѕогіа.” 
No additional contribution to the subject, so far as the author 
is aware, was made until the appearance of Frank’s paper (9) 
in 1888. In his investigation of the question of a possible 
fixation of free atmospheric nitrogen in natural soil without the 
instrumentality of cultivated plants, Frank exposed samples of 
unsterilized soil, poor in organic matter, in containers under a 
glass roof, watering them only with distilled water. During 
the 134 days that the experiment was continued, no phanero- 
gams appeared, but in all cases the surfaces of the soil samples 
became covered with a thin, crustlike, greenish layer composed 
of ‘‘zwei spangrüne Oscillariaformen, die eine dick-, die andere 
sehr dünnfádig; ferner grünes Chlorococcum humicola, viel- 
leicht auch Pleurococcus, sowie Vorkeimfüden von Моовеп, 
also kryptogame Gewáüchse . . .  Diatomaceen waren nicht 
zu finden." Analysis showed an undoubted increase іп total 
nitrogen in the experiments. No increase in the nitrate content 
was observed,—the additional nitrogen being wholly in the form 
of organic nitrogenous compounds. These facts led the author 
to the conclusion that the abundance of algal cells, which are 
rich in protoplasm and therefore in organic nitrogen, accounts 
for the presence of the increased nitrogen in an organic form. 
That the appearance of the nitrogen in an organic form (algal 
substance) does not represent the primary fixation of free nitro- 
