BUREAU OF PLANT INDUSTRY. 265 



other similar materials containing appreciable quantities of magnesia, 

 it is apparent that there will be greater necessity for making special 

 provision for magnesia in the fertilizer mixture. 



COTTON. 



Cultural control of the holl iveevil. — The general value of varie- 

 ties and agronomic methods for obtaining an early short-season crop 

 of cotton in the presence of the boll weevil is now widely recognized, 

 but there are special problems to solve in determining the full advan- 

 tage that can be gained by cultural methods of control. One of the 

 problems is to determine more definitely the time when cotton may 

 be planted with the best prospect of fruiting rapidly and of being 

 least exposed to weevil injury. Very early and very late planting 

 have both been advocated as measures for avoiding weevil injury, 

 with various arguments in support of the different views, but satis- 

 factory experimental evidence has not been secured. 



The difficulty encountered in the past in such experiments is that 

 later plantings when compared side by side with early plantings 

 usually suffer most, because more weevils are bred on tlie early 

 plantings, but this difficulty may now be avoided by using poison on 

 the early cotton. The productiveness of the later plantings will 

 determine the practical advantage to be gained by planting all the 

 cotton of a community rather late, to avoid the breeding of more 

 weevils in early-planted fields. If found to be equally effective in 

 avoiding weevil injury, simultaneous later planting, of course, 

 would be much cheaper than the protection of early plantings by 

 poison, though poison might be used effectively later in the season 

 if the crop required protection. To the extent that later planting is 

 shown to be practicable the system of control may be rendered more 

 effective in allowing more of the weevils to emerge and starve for 

 lack of food before the plants are large enough to produce flower 

 buds, which are the food as well as the breeding places of the weevils. 

 A series of such tests of late-planting possibilities has been arranged 

 in cooperation with the Florida Agricultural Experiment Station, 

 with similar experiments at field stations of the department in South 

 Carolina and Texas. 



DeveloyTTient of finiiting parts. — Careful determination of the 

 rates of growth and periods required for the development of 

 branches, buds, flowers, and bolls has been made with different vari- 

 eties and in different cotton-growing regions, and a collection of such 

 data is being published. This information is of use in determining 

 the feasibility of various methods that have been suggested for 

 avoiding or reducing weevil injury and also in relation to varieties 

 and cultural questions. A new explanation of the advantage of vari- 

 eties with upright habits of growth over varieties with wider and 

 more spreading habits and longer fruiting branches is afforded. The 

 relation of the upward growth of the plants to the production of an 

 early crop is shown by the fact that the average interval between 

 the first flowers of successive branches is about three days, while the 

 average interval between successive flowers of the same branch is 

 about six days. This also shows why it is possible to produce more 

 flowers and more bolls in short periods by using close-spaced single- 

 stalk plants and why long-season conditions are required to secure 

 good crops from large spreading plants. 



