20 CIKCULAR NO. 115, BUREAU OF PLANT INDUSTRY. 



Until the habits of branching are taken into account it seems 

 impossible to explain the widely different results that are often 

 secured when the same experiments are repeated in different places 

 or in the same place in different seasons. From the present point 

 of view it is easy to understand that merely statistical experiments 

 made without recognizing the effects of different methods of thin- 

 ning upon the formation of branches would be likely to reach 

 only ambiguous results. The development of the branches, though 

 very easily influenced in the early stages of growth, completely alters 

 the subsequent behavior of the plants. The effect seems out of all 

 proportion to the exciting cause, like touching off a charge of powder 

 or pulling the trigger of a gun. 



Wider spacing appears as the only alternative as long as the young 

 plants are led to put forth a full equipment of vegetative limbs by 

 too much exposure in the early stages of growth. That the develop- 

 ment of these limbs may be avoided by a later and more gradual 

 thinning of the young plants must be recognized before it is possible 

 to understand the advantages of the new system. When good crops 

 are produced on rows that are not thinned at all, it is because the 

 plants remain so close together that no vegetative limbs are devel- 

 oped. The new system provides for a more regular and effective ap- 

 plication of the same principle of suppression of vegetable branches. 



THINNING EXPERIMENTS WITH DURANGO COTTON. 



The behavior of the Durango cotton at Norfolk, Va., in the season 

 of 1912 affords an excellent illustration of the application of the 

 principle of controlling the formation of branches as a means of 

 securing earlier and larger crops of cotton under short-season condi- 

 tions. Planted in a row test with other varieties and thinned in the 

 usual manner to the ordinary distances, the Durango cotton, which 

 is unusually productive for a long-staple variety, yielded at the rate 

 of about 1,175 pounds of seed cotton per acre, though considerably 

 exceeded by the Trice, an extra-early short-staple variety, which 

 produced at the rate of 1.750 pounds per acre. In a field planting 

 on lighter and less fertile soil the rows of the Durango cotton that 

 were thinned in the usual manner to ordinary distances yielded at 

 an average rate of 909 pounds of seed cotton per acre, while alter- 

 nate rows that were thinned late and left with the plants closer 

 together yielded at a rate of 1,391 pounds, or about 53 per cent 

 higher than the others. Table I shows some of the figures obtained 

 from the Norfolk experiment by Mr. G. S. Meloy. 



[Cir. 115] 



