304 SCIENCE PROGRESS 



uniform cotton of different kinds from the same pure strain by 

 controlling its environment, so as to maintain a constant degree 

 of ill-health. 



Apart from these internal problems of growth there is also 

 the obvious direct play of external limiting factors on the growth 

 and functions of the plant. The aim in this connection of the 

 scientist who would be a cultivator, is to maintain the growth- 

 rates of the lint-hairs at the same mean daily velocity day in and 

 day out, either by maintaining a uniform control through a single 

 limiting factor of growth, or by controlling first one factor and 

 then another, when it in its turn becomes limiting, so as still to 

 keep the growth-rates constant. 



The problem of the production of uniform cotton on a pure 

 strain is essentially very simple. Flowers open day after day, 

 set fruit, and the lint-hairs sprout on the seeds ; these hairs grow 

 up to their full length, provided that there is no internal poison- 

 ing, and subsequently thicken to their full strength, with the 

 same reservation. The full strength and length revealed at the 

 end of the seven weeks of maturation depend on the environ- 

 mental conditions, acting directly, or indirectly through the 

 nutrition of the plant on which the fruits are borne. If all the 

 flowers opened and ripened simultaneously, the production of a 

 uniform sample would be simple, but since they continue to 

 open for a space of two months, the environmental conditions 

 on any given day will affect the length in young fruits, and the 

 strength in old ones, and each of these again in varying degree 

 according to their age. If we confine our attention to the two 

 characteristics of length and strength (as tested by breaking- 

 strain of single fibres), and neglect all the minor features, it is 

 still easy to prepare a most complicated sample of cotton. If, 

 as is actually the case in good cultivation, the mean length 

 swings steadily up and down about 5 per cent, in fortnightly 

 oscillations, while the strength changes as much as 40 per cent, 

 in the same way (but in fruits which are some three weeks 

 older), the result cannot be a uniform series of fruits from day 

 to day, even if plant-to-plant fluctuation is excluded. The aim 

 of the grower is to smooth out these oscillations, so that the 

 fruits of several successive days may all produce the same kind 

 of lint, and it is in this respect that any physiological work will 

 find a direct application. 



The obvious answer to the spinner's request for more regular 



