STRUCTURE OF THE BOLL 77 



Some bolls and seeds stopped before reaching 30 milli- 

 metres, and some extended beyond it, the extreme lengths 

 ultimately attained by sixty seeds which were measured 

 when ripe being 24 and 35 millimetres, twenty of these 

 being 29, 30, or 31 millimetres in length. These devia- 

 tions from the mean are, of course, due to accidental 

 circumstances, such as a check in growth from any cause, 

 affecting the boll locally or the plant generally. 



It should be noticed that the rate of growth is at its 

 maximum somewhere near the fifteenth day, and is slow 

 at the beginning. This should be borne in mind, as it 

 will recur in the next chapter. Obviously, any cause 

 affecting lint length will have most influence if it is 

 acting on a boll which is fifteen days old. 



Up to the twelfth day the delicate lint is firmly attached 

 to the seed, and can only be torn away with some diffi- 

 culty. By the fifteenth day, however, a noticeable change 

 has taken place, and the lint can be stripped off with 

 great ease during the next fortnight, leaving a smooth, 

 shiny seed-coat behind. The subsequent firmer adhesion 

 of the lint is due to the thickening of the epidermal cell 

 walls, but it never again is so firmly held as during these 

 first two weeks. 



The first signs of thickening of the lint are apparent on 

 the twenty-first day, though no visible increase in wall 

 thickness can be seen. This first sign is a very simple 

 one. Material which has been pickled in alcohol dries 

 very quickly, especially when single hairs are removed 

 and held in the air. Hairs thus treated from material 

 earlier than the twenty-first day are contorted in all 



