24 Martin J. Prucha 



EXPERIMENT 3 

 INFLUENCE OF POTASSIUM NITRATE IN LIGHT AND IN DARKNESS 



In this experiment twelve glass cylinders, each of 5 liters capacity and 

 50 centimeters in height, were used. Six of these were filled with Crone's 

 full nutrient solution, and the other six were filled with the same solution 

 except that potassium chloride was substituted m place of potassium 

 nitrate. Five plants were grown in each cylinder. The experiment was 

 arranged in the following manner; 



Series 1. Three of the cylinders filled with Crone's full nutrient solution 

 were covered with black paper. Two of these were inoculated, and one 

 was not inoculated. 



Series 2. The other three cylinders filled with Crone's full nutrient 

 solution were treated as was series 1, but were not covered with black 

 paper. 



Series 3. Three of the cylinders filled with Crone's solution in which 

 potassium nitrate was replaced by potassium chloride, were covered with 

 black paper. Two of these were inoculated, and one was not inoculated. 



Series 4. The remaining three cylinders, with the same solution as was 

 used for series 3, were treated as was series 3 but were not covered with 

 black paper. 



Results 

 When the plants were three weeks old, those grown in the solution 

 with nitrate looked green and healthy, while those grown in the solution 

 without nitrate were turning yellow and the lower leaves were dropping 

 off. No difference in appearance was observed between the inoculated 

 and the uninoculated plants. The uninoculafced plants had no nodules; 

 those grown in the presence of nitrate and inoculated had one or two 

 nodules each ; those grown in nitrate-free solution had about fifteen nodules 

 each. Six weeks after planting, the plants grown in nitrate solution had 

 thick, green leaves and thick roots, and no more nodules had developed 

 on the inoculated plants. The plants grown in nitrate-free solution were 

 yellowish except for the upper leaves, which were green; the roots were 

 longer and more abundant than on the plants grown in nitrate solution. 

 Nodules were abundant, continually developing on the new roots. The 

 uninoculated plants in nitrate-free solution had no nodules and were 

 practically dead. 



