168 Some Factors in Plant Competition 



Table XVI and Fig. 10 show that in the outer rank, where least com- 

 petition occurs, 50 per cent, of the efficiency indices are in the highest and 

 nearly all the rest in the third quartile. In the second rank where the 

 competition is already rather great, the efficiencies vary considerably, 

 being spread over the whole range with a heavy concentration in the two 

 lowest quartiles. In the two innermost ranks, however, the efficiencies 

 are very low, the larger percentage in each case being in the lowest 

 quartile and none in the uppermost. These results prove graphically 

 that, other things being equal, the degree of competition for light 

 brought about by close spacing or crowding has a direct bearing on the 

 efficiency of the plant in the production of new material. The greater 

 the competition, the lower the efficiency, and consequently the lower 

 the ultimate crop. Furthermore the balance of the plant economy is 

 disturbed, and greater deviations from the standard type are induced, 

 owing to the tendency to individual variation under similar conditions 

 being encouraged and accentuated by the action of a competitive factor, 

 which in this case is light. 



5. Nitrogen Content. The total amount of nitrogen present in the 

 spaced as compared with the crowded plants was 21-22 gms. against 

 18-22 gms., the larger total intake corresponding with the larger crop. 

 The percentage of nitrogen, however, was lower in the spaced plants, 

 being only 1-827 against 2-339. This implies that when the plants had 

 sufficient space they were able to produce a larger amount of dry matter 

 with a lower utilisation of nitrogen, and that although an abundance of 

 nitrogen was supplied they did not make such inroads on it as would 

 correspond with the excess of dry matter ultimately produced. 



The difference in the degree of maturity of the two sets is reflected 

 in the relative percentage of N in the straw and ears. Earlier work at 

 Rothamsted^ has shown that the percentage of nitrogen in the straw 

 falls steadily from the time the grain begins to form, and that in the 

 grain, after a slight initial fall, it rises steadily till maturity is reached. 

 The spaced plants were much the more mature, and whereas the ears 

 contained 3-432 per cent. N, the straw M-as so depleted that only 1-654 

 per cent, was present at the time of cutting. The crowded plants were 

 still green and sappy, and the immigration from straw to ear was far less 

 advanced, so that 2-273 per cent. N was still present in the straw, and 

 the ears only possessed 2-959 per cent. (Separate estimations were made 

 for the different ranks of the crowded square, but no definite gradation 



' Urciiclilt-y, W. E. (1012). "The l)evi-l(.i)mcMil of tlio Chain of !5ailry.'' Ann. But. 

 XXVI, pp. 90G, 917. 



