18 BOTANICAL GAZETTE [JULY 
absolute sterility would be desirable. The bottles were sterilized 
before being used in making culture solutions for the various changes, 
the pans and other apparatus used in germinating the seed were ster- 
ilized from time to time, and corks used for the cultures were always 
clean and sterilized before use. Although all of these precautions 
were taken, it was of course not possible to exclude some micro- 
organisms in such work, as the solutions were exposed from time to 
time to the air. There was in no case any excessive microorganic 
life noticeable. While bacteria and other microorganisms were 
present in the cultures to a slight and, under the conditions, unavoid- 
able extent, it can hardly be said that their influence could have been 
large; that is, such influence as they had was probably so slight as 
to be negligible so far as the general and larger tendencies which are 
shown in this paper to exist are concerned. 
Controls which were set up without having plants grown in them 
were found not to have changed their concentration or proportions 
of the constituents. Moreover, the various cultures support each 
other in their general tendencies. If the disappearance of nitrates 
were to be ascribed to bacterial activity, this should have shown itself 
all the more prominently as the age of the cultures increased. Such 
changes as were noticed from period to period might be ascribed to 
changes in the climatic conditions, thus still further affecting 
the plant’s metabolism. This is very nicely illustrated in a series 
of preliminary experiments in which the solutions were changed 
every day instead of every three days, as was finally done. The dia- 
gram giving the results obtained on a clear day shows strikingly a 
relatively greater nitrogen removal under these conditions. The 
diagram giving the results obtained on the following day, which was 
cloudy and rainy, shows no less strikingly that relatively less nitrogen 
was absorbed on the cloudy and rainy day. It would be obviously 
unfair to conclude that under such conditions bacterial activities 
had been greater on the sunny day than on the following rainy day, 
especially as this result is in harmony with all observations on the 
removal of nitrate from solutions by plants. The processes of nitrogen . 
utilization within the plant are known to be greater under conditions — 
of better illumination. It is fair to assume, therefore, that this same 
general tendency held in all the other cultures, and that whatever — 
