158 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



what one could expect under such conditions, regardless of the 

 presence of a radioactive substance in the soil. In discussing 

 his mutation experiments, deVries has called attention to the 

 necessity of extreme care in securing an equable distribution of 

 moisture, and to the fact that the common slight irregularities 

 in the surface of the soil in seed-pans may cause marked differences 

 in the rate of growth of seedlings. 



If the application of minute traces of radioactive substances 

 to the soil can produce an increase of yield, the fact would be of 

 very great scientific as well as economic importance, more especi- 

 ally if, as Rusby states (p. 21) "The beneficial effects continue 

 over successive crops, perhaps for many years," while "The 

 largest amount required by any crop would cost less than the 

 increased market value of such crop the first year." The author 

 well says (p. 21) that radium is not a plant food, and that the 

 necessity of fertilizer is but little decreased by its use. But 

 that "The fertility of unused ground will spontaneously increase 

 at a much greater rate when treated by radium," is not self evi- 

 dent from any facts that have been obtained by observation or 

 experiment, though it ought not to be difficult to refute or to 

 confirm it experimentally. 



"But let us analyze the situation a little more thoroughly. The 

 second chapter of the Garden Memoir reviewed a large literature, 

 covering 149 titles, showing that radioactivity is normally a factor 

 of plant environment; that freshly fallen rain and snow, soil, 

 common rocks, soil-air, and, in fact, practically every kind and 

 form of matter is more or less radioactive. The magazine adver- 

 tisements of the radioactive compound employed by Rusby 

 recommend that one pound will fertilize 50 sq. ft. of soil. The 

 compound is claimed to contain 0.05-0.08 microgram (5 to 8 X io~^ 

 gram) per pound. Now fifty square feet of ordinary top soil has 

 been found by experiment to contain approximately two mil- 

 lionths (5 X io~^) grams of radium. In other words the use of 

 the radioactive fertilizer according to the directions of its manu- 

 facturers would increase the radioactivity of the soil by only one 

 tenth of the: normal amount. 



Ross' has also called attention to the fact that "the radium 

 present, on an average, in an acre-foot of soil, is about 100 times 



' U. S. Dept. Agr. Bull. 149: 13. 11 D 1914. 



