160 ANNUAL EEPOETS OF DEPARTMENT OF AGEICULTXJRE. 



sues, as the affected areas enlarge. Such an origin explains why the 

 disorder may be restricted to cotton, the oil glands being a peculiar 

 feature of the species of Gossj^pium and a few closely related genera. 



PHYSIOLOGICAI, REQUIREMENTS OF THE DATE PALM. 



The experiments to determine the physiological requirements of 

 the date palm have shown that under partial shade and with con- 

 trolled humidity the rootings of offshoots give high percentages of 

 success. The relation of offshoot production to a broad leaf area 

 in the parent tree has been demonstrated, as well as the advantage of 

 a high nitrogenous fertility in the soil. 



Observations of the leaf growth of date palms in relation to cur- 

 rent temperatures have brought out the fact that under the. higher 

 temperatures, involving low humidity and greatly increased tran- 

 spiration, the water supply becomes the limiting factor governing 

 growth; hence at this season increased irrigation and especial atten- 

 tion to the permeability of the soil and to maintaining by culture a 

 proper soil mulch are indicated. 



FERTILIZER STUDIES. 



The enormous fertilizer consumption in the United States, amount- 

 ing to upward of a hundred million dollars prior to the war, has in 

 the course of the last few years undergone a decided change, not so 

 much in volume of fertilizer consumed as in the composition of the 

 fertilizing materials. This has forced a careful study of ratios of 

 essential plant-food constituents on prominent and essential crops. 

 Accordingly, small field plats for the study of fertilizers have been 

 established at many points on different soils and under different 

 agricultural conditions. The test fields now in operation are at 

 Presque Isle, Me. ; State College, Pa. ; Norfolk, Va. ; Florence, S. C. ; 

 Pecan City, Ga. ; Putney, Ga. ; Thomasville, Ga. ; Monticello, Fla. ; 

 Orlando, Fla.; Ashland Wis.; and Scottsburg, Ind. 



Special field tests have been conducted to determine the smallest 

 quantities of potash as a fertilizer which will meet the requirements 

 of the tobacco plant, more especially on the lighter soils of the flue- 

 cured district. Marked responses have been obtained with only 24 

 pounds, and even as low as 12 pounds, of potash per acre. These 

 applications have sufficed to prevent the appearance of the character- 

 istic symptoms of potash deficiency which the plant shows when no 

 potash is supplied in the fertilizer. It has been possible also to estab- 

 lish an appreciable difference between the sulphate and the muriate 

 of potash in their action on the plant. 



EXAMINATION OF MATERIALS OFFERED AS FERTILIZER SUBSTITUTES. 



The unusual fertilizer situation has brought forth numerous fer- 

 tilizer substitutes of more or less doubtful merit for which extrava- 

 gant claims are made. Companies are organizing to exploit fertilizer 

 materials concerning the value of which little is known, and it would 

 seem that a very considerable increase in such test work is necessary. 

 Several such products have been investigated and tested. Some of 

 them are practically worthless and others of value entirely out of 

 proportion to the price charged. 



