212 



COTTON 



at maturity they burst open and the locks of fiber, attached to the 

 seeds, are easily gathered (Fig. 79). 



Since the fiber and seeds constitute the cotton crop, it is impor- 

 tant to consider them separately and in greater detail. 



Fiber. The fiber constitutes about 10 per cent, by weight, of 



FIG. 79. Showing the opening of the cotton boll; and the lock-cotton, or seed-cotton; 

 A, the unopened boll; B, the boll partly opened; C, the boll fully opened, and the locks of 

 fiber; D, the empty pod after the lock-cotton has been gathered. 



the mature plant. It is poor in fertilizing constituents, a bale of 

 lint (500 pounds) containing only: 



Nitrogen 1.7 pounds 



Phosphoric acid 0.6 pound 



Potash 2.3 pounds 



Lime 1.6 pounds 



Proportion of Fiber to Seed. The proportion of fibers to seeds in 

 lock-cotton is usually 33 to 35 per cent of the total weight, although 

 extreme proportions of 30 to 40 per cent are often found. The pro- 

 duction of a large proportion of fiber is a very desirable varietal 

 characteristic. 



Dimensions and Strength of the Fiber. Each cotton fiber is a 

 tubular, hair-like cell 0.001 to 0.025 inch in diameter. Its length 

 varies among different species and varieties. The average length 

 of the fiber of American upland short-staple varieties is from 

 0.80 to 0.95 inch, while in long-staple varieties it is from 0.90 to 

 1.50 inches (Figs. 80 and 81). The fiber of Sea Island cotton is 



