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USE OF RADIOACTIVE SUBSTANCES AS FERTILIZERS, 5 
same as that given off from the preparation before the separation. 
The total radiation has thus not been either increased or decreased 
by the treatment, and as far as the use of the rays is concerned it 
must necessarily be just as expensive, although possibly at times 
more convenient, to treat plants with radium emanation as with the 
radiation from the equilibrium amount of radium. 
THE INFLUENCE OF RADIOACTIVE RAYS ON PLANTS. 
Every physical agent known when exceeding a certain minimum 
intensity is able to affect in a marked degree the germination of seeds 
and the growth of plants. It would therefore be expected that the 
rays from radioactive substances, when present in sufficient intensity, 
would likewise have an influence on plant growth. A great many 
experiments have been made along this line, and the literature on 
the subject is already very extensive. Unfortunately in many of the 
experiments which have been made, no mention is made of the 
amount of radioactive material used nor of the intensity of the 
radiations emitted by it. Consequently such experiments can not 
be duplicated by others, and the results reported are therefore of 
little value, for it could have been predicted that a very intense 
radiation would have an injurious effect on plant growth, while ra- 
diations of moderate intensity might exert a beneficial effect. Fur- 
thermore, owing to an insufficient knowledge of the properties of 
radioactive rays, Many experiments have been carried out in such a 
way that the effects which were attributed to the rays could not 
possibly have been due to this influence. 
The most extensive experiments in this field which have been de- 
scribed in this country were carried out by Gager! at the New York 
Botanical Garden. In one set of pot experiments a quantity of 
polonium (activity not given) inclosed in a sealed glass tube was in- 
serted in the soil at the center of the pot, with the end containing the 
radioactive material about 10 millimeters below the surface. Twelve 
grains of wheat were then planted without soaking in the soil around 
the tube. Three other pots were also prepared in the same way with 
the same number of wheat grains; in one of the pots was placed a 
tube containing 10 milligrams of radium bromide of 1,800,000 ac- 
tivity; in another, a tube containing 10 milligrams of radium bro- 
mide of 1,500,000 activity, while the remaining pot was used as a 
control. On the fourth day measurements were made of the height of 
the seedlings, and it was found that the average growth was greatest 
in the pot containing the polonium and least in the control pot. It 
is known, however, that polonium gives off alpha rays only, and that 
these rays are so lacking in penetrating power that they could not 
1 Effects of the Rays of Radium on Plants, Memoirs of the N. Y. Botanical Garden, 
vol. 4 (1908). 
