Relations of Higher Plants to the Formation of Nitrates 103 



In these tests the primary and the secondary crops were planted at 

 the same time. The growth was more rapid than in the soil. Again in 

 about half of the tests the primary crop gave larger yields when grown in 

 the mixture than when grown alone. As any benefit to the primary crop 

 by a stimulation of nitrate formation through the growth of the secondary 

 crop is precluded by the fact that the entire supply of nitrogen was in 

 the form of nitrate, the evidence is opposed to the supposition that any 

 increased growth of the primary crop in the mixtures grown in soil was 

 due to such a process. 



An examination of the data recorded reveals two conditions that influence 

 the growth of the primary crop in mixtures. These are the length of the 

 period of growth and the relative growth of the secondary crop. The 

 benefit to the primary crop from a longer period of growth may be due 

 either to a slower growth or to harvesting at a later period of development 

 of the plant. It will be noticed that for any given mixture a very large 

 gro^vth of the secondary crop is usually accompanied by a relatively 

 smaller growth of the primary crop. This holds true only when the yield 

 of the secondary crop is very large, and is presumably due to the com- 

 petition of the plants for food and water. 



It was decided to repeat these tests in the field, where there would be 

 a large body of soil from which the plants could obtain nourishment and 

 where the conditions would be more nearly normal than in the green- 

 house. The plants v/ere grown in squares six feet each way and usually 

 twenty-five primary plants were placed in each square. Whether grown 

 alone or in a mixture, the number of primary and secondary plants in 

 each square was the same. The plants were not watered artificially, 

 and as the summer was a very dry one they suffered from lack of moisture. 

 Each combination of plants was repeated on four squares. Two of these 

 were harvested at or near the flowering stage and the other two were 

 allowed to ripen fully. Jn Table 43 the yields are given for only the squares 

 that were harvested before the plants were mature, as in almost all cases 

 the mature plants yielded more in single cultures than in combination. 

 This may have been due to the severe drought or it may be the natural 

 result under any conditions. At least it is what would have been expected. 

 The relative yields are based on the oven-dry weights of the plants. In 

 choosing the plants for this experiment, combinations were used which 

 previous experience or observation indicated would give larger yields 



