RESULTS OF COTTON EXPERIMENTS IN 1911. 15 



tliat plants less exposed to the sun show less of the leaf-curl, while 

 those that are well shaded or gi'ow in diffuse light, as in a greenliouse, 

 are not affected. If too mucli exposure of the young plants to the 

 sun is the cause of the injury it may be possible to secure protection 

 by later planting or more gradual thinnmg. It is to be considered 

 that the gi-o\ving tissues of the young seedlings are probably exposed 

 to greater extremes of heat and dryness than those of more mature 

 plants, because they are closer to the heated surface of the soil. 

 After a cold night the young plants often appear badly wilted in the 

 morning, an liour or two after sunrise, perhaps because the leaves are 

 heated before the roots are warm enough to absorb water ra])idly. 

 Injuries due to sudden exposure in the morning are often ascribed to 

 frost. Cotton seedlings may be killed in this way although the night 

 temperatures remain above the frost line. This fact was shown some 

 years ago in cxperunents with cotton in Guatemala. 



METHODS OF UTILIZING FIRST-GENERATION HYBRIDS. 



It has long been known that hybrids between Upland and Egj'ptian 

 cotton i)roduce lint of superior quality. The hybrids are also more 

 vigorous and productive than pure-bred varieties, and better able to 

 withstand unfavorable conditions. Many attempts have been made 

 to breed superior hybrid varieties, but the later generations always 

 prove inferior to the first, or to the ])arent varieties. Many of the 

 plants have short or sparse lint or are weak and infertile. 



Accepting the fact that the superiority of the hybrids is limited to 

 the first generation, otlier possibilities of utilization are being investi- 

 gated in southern California. Experiments have been made by 

 ^Ir, Arg}de McLachlan with two methods of j^roducing hybrid seed, 

 hand pollination and natural crossing by bees. The former process 

 would be rather expensive, but the methods have been so simplified 

 that the cost would not be prohibitive. 



The production of hybrid seed through natural crossing by insects 

 is facilitated by planting the parent varieties in alternate rows. As 

 only a part of the seed will produce hybrid plants, the feasibility of 

 this method depends on the possibility of recognizing the hybrids in 

 the early stages of development and pulling out the remainder of the 

 plants. Studies of the characters of young seedlings have shown that 

 the hybrids can be distinguished in the early stages of growth. The 

 proportion of hybrids in any particular lot of seed would depend, of 

 course, on the number and activity of the bees or other cross-fertilizing 

 insects at the time of flowering, and this varies greatlj^ in different 

 localities and in different parts of the season. 



The utility of the hybrids would be increased if two or more crops 

 of cotton could be obtained from the same plants. The Avinters of 

 southern California are not cold enough to kUl the roots, and the 



[Cir. 96] 



