ENVIRONMENT OF THE BOLL 121 



The first cannot be eliminated in field crop conditions. 

 If the plants were separated by intervals so wide that 

 Plant-to- eac ^ one k a d a ^ the soil it could occupy, if 

 Plant such spacing did not bring in secondary 

 Fluctuation, difficulties, and if the soil were absolutely 

 uniform to a depth of 3 metres, then there would be 

 no fluctuation from plant to plant, but there might still 

 be differences from boll to boll. Conversely, there is a 

 strenuous struggle for existence between plants crowded 

 in field crop. This struggle is subterranean and invisible, 

 but none the less bitter. Under Egyptian conditions, 

 the success of any individual over its neighbours is partly 

 rectified above-ground, since its consequently greater 

 growth brings shade to them and lessens the strain on 

 their root systems ; but if a pure-strain population is closely 

 crowded in a shallow soil, it will be found by the end of the 

 season that a few plants have alone survived to mature 

 their seed, the remainder being wizened sticks. 



The last component of "regularity " is the distribution 



over the seed. This can be partly controlled by the use 



of suitable strains, since the character of 



the distribution is inherited, and strains can 

 Fluctuation. 



consequently be isolated in which when 



properly grown the mean length and strength of the 

 lint varies but little from the tip to the butt of the seed. 

 In periods of unsuitable nurture, however, even these 

 strains will make poor lint at the tip of the seed, farthest 

 away from the food-distributing centre, which is situated 

 where the incoming vascular bundles ramify in the butt- 

 end of the seed-coat. All the changes we described in 



