66 PREVIOUS INVESTIGATIONS UPON PLANTS 



longitudinal splitting and distribution to the daughter-nuclei these 

 segments moved irregularly, some lagging behind on the equator, 

 or appearing distributed along the spindle between the equator and 

 the poles. Several cases were observed where two and three 

 daughter-nuclei were formed on each side of the cell-plate. In 

 some cases an increased number of tetrads resulted from the division 

 of the pollen-mother-cell. Following the exposure to the rays, there 

 was observed a tendency to a stronger formation of kinoplasm than 

 formerly. 



The first recorded experiments of the effect of radium rays on 

 plant respiration are those of Micheels and de Heen,*^ who found that 

 the respiratory energy of germinating pea seeds was diminished by 

 exposure to the rays from 0.5 mg. of a radium preparation of 240 

 activity. The authors describe this result as being in good agree- 

 ment with other physiological phenomena due to radium. 



Molisch^^ was not successful in any attempts to produce a tropistic 

 curvature by the direct influence of the rays of radium, but found 

 that the phosphorescent light produced by mixing radium bromide of 

 3,000 activity with zinc blend in a sealed glass tube, caused positive 

 phototropism of stems in Vic/a sa/i'va, and £rvum I^ens, but called 

 forth no curvatures in Helianthus anniius. In the case of Phy- 

 comycesnitens^ sporangiophores were positively, and mycelium nega- 

 tively phototropic. The phototropic sensibility of the seedlings above 

 mentioned was greatly intensified by exposure to the rays. As Molish 

 indicates in the title of his paper, these curvatures may be attributed 

 only indirectly to the radium ; they are responses only to the phos- 

 phorescent light caused in the zinc-blend by the rays. 



The ability of Bacillus pyocyaneiis to secrete its characteristic 

 pigments was found by Bouchard and Balthazard ''^ to be diminished 

 by exposure to radium emanation, and the power of reproduction 

 and division was diminished and finally destroyed, Rays from 

 "the radioactive residues from the treatment of pitchblend from 

 Joachimsthal " affected various species of Aspergillus in a similar 

 manner (Dauwitz ''). Sensitiveness to the rays varies according to 

 the species, A. niger and A. Juinigalus being most sensitive, and A. 

 ochraceus, A. clavatus, and A. varians less so, in the order named. 

 Spores formed while the plant was under the influence of the radio- 

 active bodies germinated poorly, and produced a meager mycelium 

 that bore no spores. Analogous effects followed the treatment of 



