[Vor. 1 
234 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Acetanilid and dimethylanilin are in a separate class,—being 
decidedly toxic at all the concentrations used. At the lowest 
concentrations there was slight growth at first, but in ten days 
all cultures were dead and discolored. The results with these 
last two compounds are comparable to those obtained with 
similar substances by Czapek (10) and by Lutz (12) working 
on fungi and fresh-water alge. They found that compounds 
having the nitrogen attached directly to a benzene nucleus are 
toxic. 
Pure culture methods were not attempted on account of the 
brief time available for this work, and the question of the pos- 
sible interaction of ammonifying bacteria is therefore pertinent. 
However, the rapid augmentation of growth upon the addition 
of the amido compounds, and the comparative absence of 
bacteria both suggest a direct absorption of these substances. 
Moreover, since rapid growth of the alga occurs in concentra- 
tions of the amido compounds considerably greater than the 
toxic limit for ammonium salts, and since, further, no evi- 
dence of toxicity of fairly strong solutions of urea and aceta- 
mid developed during the interval of these experiments, no 
support is given to the thought that ammonification may be 
an important factor. However, in further continuation of this 
work it is proposed to control this possibility by quantitative 
tests. 
It seems probable from the facts brought out here, as well 
as from the work of Letts and Richards, that Ulva is not lim- 
ited to an inorganic nitrogen supply, since growth occurs with 
urea or acetamid as the sole source of nitrogen, and, as Letts 
and Richards have shown, that it grows more rapidly in sewage- 
polluted water than in pure sea-water. Undoubtedly, further 
experiments would show that other organic compounds can 
supply available nitrogen for Ulva. 
The results also indicate that for Ulva, at least, the amount 
of available nitrogen in the water is the limiting factor in growth. 
This is shown by the fact that growth is more rapid in sea- 
water containing additional nitrogen (ammonium nitrate, or 
urea) than in pure sea-water. The above mentioned results 
of Letts and Richards also point to the same conclusion, as does 
