148 Some Factors in Plant Competition 



of the alteration in the efficiency index, as the working capacity of the 

 plant in this case is limited by the material with which it can build up 

 its tissues. 



Table II. Efficiency indices for 10 pots. 

 Mustard. 



Table II and Fig. 2 show graphically the steady fall in the efficiency 

 index as the food supply gets less. The close correlation of cause and 

 effect is shewn by the dotted curve which represents the relative actual 

 food supply per plant. Though the steepness of the curves varies, especi- 

 ally in the initial drop from 1 to 2 seeds, the direction changes in the 

 same sense in every case, as the one factor follows in the wake of the 

 other. 



Experiment II. 



Barley. 



Narrow pots. 10 kilos soil. 



Seeds sown March 21st, 1917. One to five per jwt after thinning. 



Plants cut July 16th, 1917. 

 Broad pots. 20 kilos soil. 



Seeds sown March 21st, 1917. One to eight per pot after thinnins. 



Plants cut July 16th, 1917. 



This test resembled Experiment I, but was carried out with a different 

 plant, barley, to ascertain whether the response to competition was 

 similar in two widely varying species. Two sizes of pots were used in 

 this case in order to obtain further evidence cf the correlation between 

 the amount of growth and the quantity of available food. 



From an early stage in the experiment the strength of the individual 

 barley plants varied inversely as the rate of seeding, though the superi- 

 ority of the thinly seeded plants was not so markedly evident as in the 

 case of mustard. The same relative position was maintained to the time 

 of harvesting, when the thinly seeded plants were better developed and 

 much less mature than the more crowded specimens. In all cases the 

 lower leaves were ripe and brown, but the ears varied considerably in 

 maturity from greenish grains with green awns (1 plant per pot) through 



