NITROGENOUS SOIL CONSTITUENTS 



47 



The culture solutions were changed every three days, four changes 

 being made in the course of the experiment. The solutions were 

 analyzed for nitrates immediately after each change. 



In making these cultural tests in which appreciable quantities 

 of nucleic acid are required, the compound prepared from yeast 

 was used. In order to counteract the acidity, calcium carbonate 

 was added to each nucleic acid culture and also to each culture 

 in the control set for the purpose of better comparison. Both 

 sets of cultures grew, therefore, under the slight physiologically 

 alkaline conditions imposed by the calcium carbonate. Wheat « 

 seedlings were grown in both sets of culture solutions from April 

 8 to April 21, the solutions being changed every three days. 



Effect on growth 



When the two sets of cultures had grown in the greenhouse 

 under identical conditions for several days the effect of the nucleic 

 acid was already noticeable by a much superior growth in the 

 nucleic acid cultures, an effect which became quite marked as 

 the growth continued. This was more marked in some of the 

 fertilizer combinations than in others, but consistentlj^ so, as 

 will be shown. Direct comparison between the two sets showed 

 the effect of nucleic acid in producing increased growth to be 

 most pronounced in those fertilizers which contained no nitrate 

 and in those low in nitrate. 



At the end of the experiment the green weight of the tops was 

 taken of both sets and the results obtained will be found in the 

 following tables. The total growth in the 66 cultures of nutrient 

 salts without nucleic acid, designated as normal or control cul- 

 tures, was 163.3 grams, against 200.7 grams in the case of the 

 66 cultures with 100 parts per million of nucleic acid. Putting 

 the normal at 100, the latter becomes 122, or an increase of 22 

 per cent in green weight, as an average of the 66 cultures, although 

 as before mentioned, this increase is more marked in those cul- 

 tures low in nitrates than in those high in nitrates, a fact which 

 will be amply shown by the tabular results presented. 



