IV THE COTTON FIBRE 83 



after the third day it takes its place in the middle of the 

 cell axis, and there remains, either slung in cytoplasmic 

 bridles, or at the side. The cytoplasm, of course^ 

 lines the whole cell-wall, and appears to remain, ajive 

 until the boll cracks. : _ 



The growth of the fibre is at first confined to linear 

 extension. In fact, it seeins that the bojl attains 1 almost 

 to its full size before any secondary thickening of the 

 fibre wall begins. By this time the fibre has .reached 

 to rather more than its final ripe length. ThiSr,peripd 

 embraces about half the total maturation period, being 

 some twenty-five days. Presumably it is during this 

 period that unfavourable environment, such as is made 

 manifest by a mode in the Shedding Curve, could produce 

 irregularity in length from boll to boll. The final length 

 is of course constitutional, and can only be deflected from 

 this constitutional basis to a relatively slight extent. 

 Even seeds which have not been fertilised, and consist of 

 empty, undeveloped seed-coats alone, possess hairs of 

 nearly normal length, though abnormally weak. The 

 best evidence in respect of this constitutional basis for 

 length is given by measurements on the ripe seed. Thus, 

 a random selection of data for maximum lint-lengths, 

 in five seeds per plant in a pure strain grown under 

 conditions favouring maximum fluctuation, has given the 

 following figures on a total of 210 seeds. 



Mean length 33 '50 mm. 



Extremes 27 and 39 mm. 



Standard deviation 2 '14 mm. 



Probable error 1'44 mm. 



Probable error as percentage of mean = ±4"3 per cent. 



Comparison of one strain with another in this way 

 shows that the mean lint-length is an inherited character- 

 istic. The final attainment of the lint cell in the matter 

 of length is effected by intercalary growth, the form of 

 the tip and of the base being determined at an early stage. 



G 2 



