992 BIOLOGICAL EFFECTS OF RADIATION 



much as 2.5 per cent of the compound was appUed to a soil. In agricul- 

 tural practice this would require about 25 tons to the acre, at a cost to 

 the farmer of about $5000 per acre. 



The practicability of radioactive compounds for fertilizing on a com- 

 mercial scale was tested by Hopkins and Sachs (36, 37). They also 

 critically reviewed the previous work and reached the conclusion that 

 there is no foundation in fact for reasonable expectation of increased 

 crop yields, when financial possibilities are considered. They pointed 

 out that radium to the value of $1000 (10 mg.) on one acre would, during 

 100 days of good crop-growing weather give off energy equal to only 

 1 hp. for 22 sec; and that the heat given off to the soil by that much 

 radium in 100 days "would be less than the heat received from the sun 

 on one square foot in thirty seconds." 



Later, Ramsey (65) calculated that the average soil of a field contains 

 10 times as much radium naturally as is contained in the amount of a 

 certain "radium fertilizer" recommended by the commercial concern 

 offering it for sale. 



Pilz (64) concluded from experiments that the utilization of mineral 

 nutrients bj'' plants "fertilized by radium" was better than with plants 

 not so fertilized, so far as nitrogen, potassium, and sodium are concerned, 

 but poorer for phosphoric acid. Miklauz and Zailer (49) reported no 

 increase in crop production when oats (Avena saliva) were grown in soil 

 containing radioactive residues from Joachimsthal. 



The relative sensitivity of green plants in light and darkness was 

 tested by Packard (61). Willcox had shown in 1904 that the green 

 Hydra viridis was much more resistant to radium rays than the brown 

 form {Hydra fusca). Packard tested Spirogyra and Volvox and found 

 that the deleterious effects observed began to be manifested much more 

 quickly when the exposure was made in the dark. "It is very evident," 

 he said, "that the life of the cell is prolonged by some condition connected 

 with photosynthesis." 



Since this is not intended to be an exhaustive digest of the literature, 

 other papers must be passed over. Some of them are reviewed by 

 Gager (26), especially one by Ramsay (65), in which he pointed out that, 

 in order to double the amount of radioactive emanation normally in the 

 soil, "one must use about 75 mg. of radium per acre," at a cost of several 

 thousand dollars per acre. Therefore, whether crop yield could be 

 increased by adding radioactive preparations to the soil can have only 

 academic, if any, interest. Experiments of the writer with a commercial 

 "fertilizer" advertised as radioactive were reported in 1916 as giving 

 absolutely negative results when the "fertilizer" was mixed with garden 

 soil. A similar conclusion was stated by E. J. Russel in 1916, who cau- 

 tioned against "the danger of arguing from a simple physiological 

 observation to a complex phenomenon like the growth of a plant in 

 soil." 



