NUTRITIVE FUNCTIONS OF SALTS 107 



blue flowers and, as the result of various soil analyses and ferti- 

 lizing experiments, it was determined that the blue color was pro- 

 duced when the soil contained soluble aluminum salts. In green- 

 house practice this is now the established method of producing 

 blue-flowered hydrangeas, and provides a striking illustration of 

 how a nonessential element may influence plant metabolism. 

 But iron salts may also cause Hydrangea flowers to become blue, 

 and Atkins finds that they are blue in any distinctly acid soil. 

 This effect thus seems to be a question of acidity rather than a 

 specific mineral effect. 



Although aluminum is stimulating to plants in very low con- 

 centrations it is very toxic above 15 p. p. m. Since it is only slightly 

 soluble in soils near the neutral point, i. e., in tillable soils, it is 

 thought by Magistad (1925) that it can seldom cause much harm. 

 What has been called aluminum poisoning is more frequently 

 either an acid effect or phosphorus starvation, due to the precip- 

 itation of the phosphorus as aluminum phosphate. 



Some plants, e. g., Eurya japonica of Java, absorb aluminum 

 in great quantities; in such an " aluminum plant," over 45% of 

 the ash may consist of aluminum oxide. 



Chlorine. — This element does not enter into the composition 

 of many organic compounds and, although essential in animal 

 nutrition, is not essential for plants. When grown in saline condi- 

 tions, plants absorb much chlorine, which raises the osmotic pres- 

 sure within the cells (Chap. XIX) and thus enables them to re- 

 tain their turgescence. Chlorine applied at the rate of 20-30 

 pounds per acre increased the yield of tobacco 10%, but 40-60 

 pounds resulted in a distinct injury to the crop. Although Knop 

 and Livingston have grown buckwheat to maturity in the absence 

 of chlorides, Nobbe obtained contrary results and attributed this 

 lack of development to a favorable influence of chlorides upon 

 translocation. These results are confirmed by work done upon 

 the mango and coconuts, where chlorides in the fertilizer gave an 

 improved yield, and by that of Tottingham (1918), who attributes 

 the favorable results found to the effect of the chlorides upon 

 enzyme activity; but they are not in agreement with the ob- 

 servations of potato growers who find that potatoes grown in soils 

 containing an abundant supply of chlorides show a smaller yield 

 than where chlorides are lacking. Both chlorine and iodine have 

 been found beneficial to sugar beets. 



