EFFECTS PRODUCED BY PINK BOLLWORM ON THE YIELD OF COTTON SEED. 299 



one pan of the balance, equilibrated by one gramme of lint and a gramme weight 

 on the other. In this case the hygrograph record is obviously very different from 

 the record of the variations of the percentage of lint. 



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Fig. 4. Simultaneous fluctuations in humidity (solid line) and 



percentage lint (broken line) ; rising percentage lint is shown by 



fall in curve. 



From the figures given for the fluctuations in the weight of seed, it would appear 

 that the fluctuations increase with increasing temperatures. This is probably 

 the meaning of the steady fall of seed-weight shown in Table V. In this case a 

 sample of seed and its lint were weighed on 31 occasions between 11th February 

 and 24th March 1917. The lint showed correlation (r = 0"46) with the atmospheric 

 humidity recorded at Gizeh (according to Mr. Hurst, who kindly had the calculation 

 made), but the seed could not be correlated either with the humidity of the same 

 morning, or with a lag of 24 hours. The reason for this is obvious now that we know 

 that seed-weight and atmospheric humidity are correlated but with a lag of about 

 three hours. The steady fall of the seed-weight produced a total rise of the 

 percentage lint of 0"5 per cent, due to climatic changes alone, probably in part to 

 temperature and in part to humidity. 



The effect of Gelechia attack on seed cotton is to decrease the production of seed 

 and of lint. For the seed we have already shown a decrease (1) in numbers 

 matured, (2) in weight of the sound seed matured, and (3) actual loss of substance 

 produced in attacked seeds. The effect on the quantities of lint produced has 

 been studied indirectly by examination of the percentages of lint. 



Obviously the suppressed seeds mature no lint, and are pure loss. It has not 

 been possible to find any evidence that the reduction in weight of sound seeds 

 from attacked bolls is accompanied by any change in the percentage of lint pro- 

 duced by such seeds. The loss of lint in such sound seeds may be considered 

 proportionate to their loss of weight. 



The changes in the percentage of lint produced by damaged seeds are more 

 difficult to summarise, and depend to some extent on the age of the seed at the 

 time of the attack. 



(1) If the seed is attacked at a very early stage, it disappears entirely, thus 

 causing the reduction observed in the average number of seeds set. 



(2) Attacked slightly later, part of the seed remains but sets no lint, thus 

 causing the percentage to fall to per cent. 



