[Vor. 1 
160 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
plugged with cotton were treated as follows: Two were at once 
placed in the light; the third was covered with black paper and 
without further treatment placed with the first two; the fourth 
was exposed for six hours to a temperature of 100°C. and then 
placed with the rest. In the first two, rich algal growths de- 
veloped, composed of two species of Oscillatoria, a blue-green 
“ Nostoc-Form, " a yellowish green ‘‘Nostoc-Form,”’ a yellowish to 
pure green Microcystis, and a Gleocapsa. In the third and fourth 
flasks no growth of any kind developed. Analyses demonstrated 
that the total nitrogen content in the first two flasks had been 
doubled, whereas that in the latter two had suffered a distinet 
loss. Тһе experiments were repeated with unsterilized soil, 
all air gaining access to the flasks being first passed through 
sulphuric acid to remove any ammonia present. The same 
characteristic algal flora developed and analysis again showed 
a decided increase in total nitrogen. On the basis of these 
experiments, Frank makes the generalization that the soil, as 
such, is unable to fix free atmospheric nitrogen, and that when 
the process does take place, it is effected by means of the vege- 
tation of low alge which develop in the soil, and which pos- 
sess the ability of assimilating free gaseous nitrogen into vege- 
table, nitrogen-containing compounds. He goes still farther and 
states that the fact that low alge utilize free nitrogen makes 
it more and more probable that the assimilation of elementary 
nitrogen is a faculty appertaining to the entire plant world 
provided with chlorophyll, and that, since the simple algal cell 
is endowed with this faculty, the thought is justified that the 
assimilation of free atmospheric nitrogen is as absolute and 
fundamental a process of the entire plant kingdom as is the 
assimilation of carbon dioxide. 
Prantl (27), in cultivating fern prothallia in solutions with and 
without combined nitrogen, observed that whereas an abundant 
algal vegetation appeared in the former, only an Anabena, or 
a Nostoc, grew in the latter. When placed in nitrogen-free media, 
the blue-green alga always grew abundantly. From this 
observation, and without analytical data, Prantl assumes that 
free-nitrogen assimilation had taken place, either a direct one 
by the alga, or an indirect one in which the alga assimilated the 
ammonium nitrite which, according to the theory of Schoenbein, 
