Influence of Aeration of Nutrient Solution. 189 
It is now well established that, in all cases so far investigated 
at any rate, changing the culture solution increases the rate of 
growth (2, 7, 10). It is, therefore, interesting to determine whether 
the factor reducing the growth-rate in non-aerated cultures is 
removed when the solutions are constantly renewed, or whether 
aeration still increases the rate of growth even if the solutions are 
frequently renewed. It is also of importance to determine whether 
alteration in other factors produces any difference in the effect of 
aeration, and for this reason different culture solutions were used 
in different experiments. Attempts were made to control the 
temperature and light-intensity under which the cultures were 
grown, but these had to be abandoned owing to a number of 
difficulties which it was found impossible to surmount under 
present conditions. 
These experiments were already in progress when there 
reached us a preliminary statement of the results of experiments 
on the aeration of water cultures grown in Livingston’s laboratory 
at Baltimore (4). In these experiments ordinary aeration of water 
cultures of Buckwheat produced no effect at all on the rate of 
growth, while bubbling oxygen or nitrogen through the cultures 
also produced no result. Carbon dioxide on the other hand caused 
the death of the plant. 
These divergent results of the workers at Rothamsted and 
Baltimore make it all the more desirable that results obtained 
with more numerous individual cultures in which the significance 
of the observed differences is measured should be recorded. In 
the experiments here described we have worked with sets of ten 
plants under the same conditions, and the probable error of results 
has been calculated. 
The bottles used were of one litre capacity, and the usual 
procedure in regard to the bottle and cork was followed. One 
plant was used for each vessel. Aeration was produced by means 
of an air compressor to which was connected “composition” 
tubing provided with a number of branch tubes. These were joined 
by rubber tubing to glass tidies which passed through the corks of the 
bottles to the bottom of the culture vessels. There was no difficulty in 
aerating thirty cultures at once. 
The nutrient solutions were made up from ordinary “ pure ” 
salts and London tap water. The solutions were renewed at frequent 
intervals except in some cases in which no renewal took place. 
Three different solutions were used which will be described under 
