90 SOIL CONDITIONS AND PLANT GRO WTH 



of growth in those within I cm. radius of the tube. As 

 stronger preparations of radium became available more 

 definite retardations and inhibitions were observed ; thus 

 Gager, in an elaborate report, 1 noted a more or less complete 

 inhibition in cell activities in younger and especially embryonic 

 tissues, with a few exceptions. The action of radium through 

 the soil, however, was different ; germination and growth 

 were both accelerated, and the plants farthest away were 

 stimulated most. Acqua 2 found that different plants, and 

 even different organs of the same plant, were differently 

 affected, the root system in general responding more markedly 

 than the aerial parts, and in his experiments being arrested in 

 their development. The intensity of the radiation, however, 

 is important, and G. Fabre, 3 using Linum catharticum as a 

 test plant, was able to obtain increased development and 

 germination of seedlings by working with emanations up to 

 I -5 microcuries per 2 litres of air, and to retard development 

 by using emanations of 40 microcuries per litre of air. H. 

 Molisch 4 obtained a like result ; young plants of vetches, 

 beans, sunflower, etc., were stimulated in growth by weak 

 emanations, but checked, or entirely stopped, by stronger 

 ones. He further claimed that the " rest period " could be 

 broken by the radium emanation, and he forced lilac into bloom 

 in November by attaching pipettes containing small quantities 

 of radium chloride to the terminal buds. 5 In his earlier 

 experiments he, like Dixon and Wigham, failed to detect any 

 radiotropism, but later on he found indications in the case of 

 certain heliotropically-sensitive plants, e.g. oats and vetches. 6 

 These, and similar results, naturally suggested that the 

 residues left after the extraction of radium, but still containing 

 radio-active material, might have definite manurial value, and 

 it was not long before definite statements were forthcoming. 

 Baker 7 claimed that increased yields of wheat and radishes 



1 Mem. New York Bot. Gard., 1908. 



z Ann. Bot. (Rome), 1910, 8, 223-238. 



8 Compt. Rend. Soc. Biol. (Paris), 1911, 70, 187-188. 



4 Umschau, 1913, 17, 95-98. *Oesterr. Gart. Ztg., 1912, 7, 197-202. 



8 Sitzber. K. Akad. Wiss. (Vienna), 1911, 120, 305-318. 



7 Journ. Roy. Soc. Arts, 1913, 62, 70-78. 



