Winifred K. Brenchley 



165 



supply of prepared nutrient material for building up the tissues and it 

 appears as if the plants attempted to dispose of this restricted quantity 

 in order to combat the disadvantage as much as possible. With increased 

 crowding the tendency is for the weight of the root to decrease more 

 rapidly than that of the shoot, so that the shoot/root ratio goes up. In 

 other words, the plant tends to utilise a larger proportion of its elaborated 

 food in laying down new leaf tissue, possibly in an attempt to increase 

 its assimilatory surface in order to make the most of the diminished 

 supply of light at its disposal. The corresponding reduction in root 

 tissue is economic as it is useless for more dissolved mineral food to be 

 absorbed than can be dealt with by the leaves. The range of variation 

 in the shoot/root ratio is greater with the crowded than with the spaced 

 plants, corresponding again to the greater deviation of the competing 

 plants from the standard type. 



* This plant was so abnormally weak in the shoot that it is not fair to include it in the 

 consideration of the figures as the low shoot/root ratio in this case is simply due to the 

 failure of the shoot to develop. 



These figures of Table XIII lend numerical support to the idea that 

 with increasing competition for light the growth of the shoot is made 

 more and more at the expense of the root, so that the shoot/root ratio 

 gets steadily larger. With an abundant supply of room, on the other hand, 

 a more stable equilibrium is reached, a larger development of root in 

 proportion to shoot occurs, and consequently the shoot/root ratio is 

 lower, particularly when the interquartile range is considered. 



4. Efficiency Index of dry weight production. The efficiency index 

 or rate of addition of dry matter of the individual plant shows more 

 clearly than anything else how much the growth economy is affected by 

 variation in the available light. 



