HOWARD AND HOWARD. 27 



5. A POSSIBLE EXTENSION OF THE METHOD OF PURE 

 LINE CULTURES. 



The constant differences observed between the seedlings of the 

 types of H. cannahinus are of importance from two points of view. 

 In the first place, they render the production of uniform fibre and 

 pure seed a comparatively easy matter. In the second place, and 

 this is by far the more important, they suggest a method by which 

 the system of pure line cultures can be applied to some extent to 

 the improvement of plants like cotton in which a certain amount 

 of natural crossing takes place and in which it is essential to pre- 

 serve uniformity in any improved type. 



Uniformity is of great importance in fibre plants. Not only 

 is it necessary for the crop to ripen at the same time so that it can 

 be cut and retted at once but also the quality of the fibre must be 

 uniform. Branched and straight growing forms growing together 

 do not give fibre of even length while a mixture of different types 

 even if they ripen together gives a product of uneven quality. The 

 immediate loss of quality which results from growing an improved 

 type with a small admixture of other forms is, however, small com- 

 pared with the consequences of this proceeding which are only to 

 be seen in succeeding crops. Not only do the constituents of the 

 mixture appear in the next generations but also new forms arise 

 from crossing between the original constituents. The quality 

 of the fibre rapidly changes and is not consta)it from year to year. 

 Any improvement observed in the first year is soon lost and the 

 quality rapidly degenerates. 



The differences between the seedlings and young plants of the 

 various types of this crop enable a piire culture to be maintained 

 without much trouble. Most of the stray plants which arise from 

 accidental admixture can be detected by the differences they show 

 in the seedling stage. Any which escape the first rogueing dis- 

 close themselves before the crop is a foot high. No difficulty 

 would be experienced in carrying out this work in practice as the 

 ordinary labour is easily trained to the work. Indeed the boys if 



