MINERAL COMPOSITION OF CROPS 49 



fertilization with copper resulted in increased copper assimilation by 

 the plant, but Rademacher (4-73) observed no such increase, even 

 when increased yields resulted from the use of copper. 



Iodine added as a fertilizer seems to be easily assimilated by the 

 plant, and some investigators have reported manyfold increases in the 

 iodine content of plants in this way. The work of Stoklasa (542) in 

 1926, Scharrer and Strobel (510) in 1927, Scharrer and Schwaibold 

 (509) in 1927, Pfeiffer and Courth (463) in 1929, and Balks (45) in 

 1935 in Germany, Orr and coworkers in England (447) in 1928, and 

 Beaumont and Karns (49) in the United States in 1932, may be cited 

 as examples. McHargue, Young, and Calfee (383) in 1935 added 

 potassium iodide from time to time to soils in which corn plants were 

 growing, and they obtained, according to their report, an iodine con- 

 tent in the leaves of these plants of as much as 30,000 p. p. b. at one 

 time during the season. 



When no iodine was included in the fertilizer mixture, neither 

 McHargue (383) nor Mack and Brasher (385) reported any relation- 

 ship between the fertilizer treatment and the iodine in crops. The 

 latter investigators, however, obtained large increases in iodine in 

 beans and turnips by applying potassium iodide about 30 days after 

 planting. Dietz (153) in 1938 was able to increase the iodine content 

 of head lettuce (grown in pots) from 4,620 p. p. b. to 91,560 p. p. b. 

 by applying 20 pounds of potassium iodide per acre 4 days before 

 harvest. 



Claims that Chile saltpeter contains sufficient iodine for plant 

 growth have been disputed and affirmed by several authors (150, 206, 

 604). In general, it would seem that there are so many factors 

 involved in determining the specific value of any trace element in such 

 a material that no sound conclusions could be reached as to its effect 

 on plant growth or composition. 



Cook and Wilson (121) reported in 1917 the presence of boron in 

 wheat grown in soils fertilized with borax and colemanite. No boron 

 was found in plants grown without the use of this element as a ferti- 

 lizer. Increased concentrations of boron in both leaves and stems of 

 alfalfa were obtained by McLarty, Wilcox, and Woodbridge (387) 

 after treating the soil with boric acid. The boron in the leaves of 

 untreated plants was 11. 4 p. p. m., while that of treated plants ranged 

 from 214 to 734 p. p. m., depending upon the amount of boron added. 

 Askew, Thomson, and Chittenden (29) reported in 1938 that the boron 

 content of apples in areas top-dressed with boron was appreciably 

 greater than that of the control fruit. Applications of 100 pounds of 

 borax per acre had no greater influence on the boron content of the 

 apple, however, than did 50 pounds of borax per acre. Hudig and 

 Lehr (280), studying soils in the Netherlands, claim to have shown that 

 the boron in Chile saltpeter was responsible for increased growth and 

 boron content of plants. 



Studies of the effect of arsenic on plant composition have originated 

 with the problem of spraying. Pirotta (468) investigated this prob- 

 lem in Italy in 1906 and reported that the application of a dilute 

 arsenical spray to plants resulted in an increase in the arsenic content 

 of the plant. Increase of arsenic in the plant resulting from spray on 

 the soil has not been reported, and Jones and Hatch (307) stated in 

 1937: " Analytical data on commercial orchard soils and fruits indicate 



257897°— 41 4 



