STRUCTURE OF THE BOLL 79 



ject of twist. Given such pits, the fibre must twist when 

 it dries, unless the wall has been thickened so much as 

 to obliterate the central cavity almost entirely. Whether 

 the twist is right or left handed in any part of the fibre 

 is determined by whether the pits are laid down with an 

 inclination in one direction or the other. This direction 

 appears to be accidental. It might be well if someone 

 would re-examine the useless wild-cottons, which have 

 weak twist or none, on these lines, and see if, as is 

 probable, the pits are set too obliquely or too trans- 

 versely to effect a good convolution of the hairs. It 

 should be noticed that the twisting of the cell -wall may 

 take place completely before collapse begins. Unripe 

 lint kept in pickle behaves thus. The subsequent 

 collapse which renders the convolutions visible when the 

 boll opens can thus take place without further twisting. 



The actual mode of thickening is open to further investiga- 

 tion; a well-thickened wall is about 0-004 millimetre thick, or 

 about one-six-thousandth of an inch. This wall is probably 

 composed of concentric layers, laid down during the active 

 growth of each successive night, and numbering about twenty- 

 five in all, of which a dozen phould be of appreciable thickness. 

 The daily or nightly layers would thus at the most be about 

 0-0004 millimetre in depth, so that their resolution by the 

 microscope is highly improbable, without some previous treat- 

 ment. Having been led to consider the existence of such 

 concentric layers as probable, the author made several 

 attempts to see if they could be recognized, but without 

 success. Indications are sometimes seen when a section 

 across a fibre has been torn slightly by the razor in cutting. 

 If they exist, it is possible that some of the finer details of 

 grading may be concerned with their arrangement, and the 



