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 



ABC D 



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 



