COTTON. 173 



alone, possess hairs of nearly normal length, though abnormally 

 weak. Mean lint-lengths is an inherited character. The final 

 attainment of the lint cell in the matter of length is effected by 

 intercalary growth, the form of the tip and the base being deter- 

 mined at an early stage. The cessation of this growth is thus 

 the result of internal constitution, though environmental 

 changes exercise a limited effect. Probably linear extension 

 has ceased before thickening of the wall commences. It is this 

 thickening which determines the strength of the individual 

 fibre. The strength of the commercial sample depends not 

 only on thickness, but also on uniformity of strength as between 

 different fibres. Moreover, commercial strength does not 

 merely result from the thickness of the cell wall, but also from 

 the uniformity of that thickness over the whole length of the 

 cell, and possibly is also affected by the texture of the thicken- 

 ing layers. 



" Concentric layers of cellulose probably delimited from 

 night to night are laid down on the interior of the delicate 

 cellulose-cuticle wall until a certain thickness is reached. This 

 disposition is not uniform , but results in the formation of simple 

 pits at intervals, elongated obliquely. 



" In consequence of this thickening we find that fibres 

 devoid of secondary thickening show no twisting when extri- 

 cated from the unripe boll and dried, while fibres taken from 

 a boll which is nearly ripe exhibit rapid and uniform twisting 

 as they dry, owing to the closure of the solid portions of the 

 cell wall into the minute spaces formerly occupied by the pits." 



Morgan states : " If the fibre is mature, examination will 

 show it to be somewhat flattened and irregularly twisted. It 

 is claimed that the number of twists varies from 300-500 to an 

 inch. The amount of twist in the cotton fibre is very important 

 in determining its spinning qualities, and hence its value. The 

 degree of twisting is to a large extent determined by the stage 

 of maturity of the fibre. The immature fibres, on drying, 

 form almost flat, structureless ribbons, with very little twist. 

 The strength of the cotton fibre varies according to its ripeness 

 and fineness. From 2"5 to 15 grams represent its breaking 

 strength. The cotton fibre in proportion to its size is stronger 

 than jute or flax and is three times as strong as wool. It is 

 surpassed in strength bv the fibre of hemp, Manila hemp and 

 silk. 



" Length of lint varies with the variety and to a certain 

 extent with soil fertility. Some strains produce lint of the 



