162 Some Factors in Plant Competition 



the difference between individuals and also prevents all the growth 

 possible being made. The extreme range of weight is large even under 

 favourable circumstances, but is greatly increased when the competition 

 for light comes into play. The figures in Table IX show that this is the 

 case with both the root and shoot, the extension of range in both cases 

 being chiefly downwards owing to the hindrance to growth caused by 

 crowding. 



Table IX. Total range of dry weights. 



64 crowded plants G4 spaced plants 



gms. gms. 



Shoot .50—24-44 9-72— 24-47 



Root -37— 5-57 1-52— 6-27 



Whole plant -97—30-01 12-34—28-74 



The result of this downward range is to decrease the total amount 

 of dry matter produced by a given number of crowded plants, and so to 

 lower the average weight, as is shown in Table X. 



Table X. Total and average dry iveights. 



64 crowded plants 64 spaced plants 



The total range and average weights, however, hardly give a fair 

 picture of the general effect of overcrowding on the majority of the 

 plants, and with such a large variation in weight the average is in 

 reality of little value. A much clearer idea is obtained by a comparison 

 of the interquartile range of the weights under the different conditions, 

 as by this means the most abnormal plants, both large and small, are 

 ruled out and only the more representative specimens come under 

 consideration (Table XI). 



Table XI. Interquartile range {of 32 intermediate plants in each case). 



64 crowded plants 64 spaced plants 



