994 BIOLOGICAL EFFECTS OF RADIATION 



microcuries per liter of air. These results were in harmony with those 

 reported by Gager. When germinating seeds were exposed in a closed 

 vessel to emanation given off from a solution of a radium salt, Doumer (21) 

 found that germination was favored. Stoklasa (77a) reported similar 

 results the same year. 



Congdon (18, 19) was one of the first to endeavor to analyze the 

 effect of the different types of rays. Using seeds of Sinapis nigra, 

 Panicum germanicum, Amarantus monstrosus, Nicotiana Tabacum, and 

 Papaver somniferum, he found that the effect of beta rays varied with 

 their penetrating power. The slower, less penetrating secondary rays 

 retarded germination more than the more penetrating primary rays and 

 in direct proportion to their ionizing power. As might have been antici- 

 pated, Congdon found the embryos more sensitive than the surrounding 

 endosperm of the seeds, and that the presence or absence of the testa 

 and the position of the radicle toward or away from the source of the 

 radiation affected greatly the sensitiveness of the seeds. 



Molisch, tested, in 1905, the power of radium rays to cause tropistic 

 responses, using seedlings of vetch, lentil, and sunflower, and also 

 Phycomyces nitens, but reported negative results for shoots, as had Gager 

 also. Molisch (52, 52a) returned to this problem in 1911, using stronger 

 radium preparations that gave off a more intense illumination, and found 

 that, at short distances tropistically sensitive plants, such as young 

 seedlings of oat and vetch, gave positively phototropic responses, but 

 others less sensitive, such as barley and sunflower, gave no response. 

 Gager (25) reported a positive tropistic response of roots of Lupinus albus 

 to a sealed tube containing radium bromide of 10,000 activity suspended 

 at distances of 10 mm. to 2 mm. from the tips of the roots. These 

 curvatures were interpreted, not as direct responses to the rays, but as 

 possibly due to ions produced by the rays in the liquid. 



The effect of radium rays in forcing plants was also investigated by 

 Molisch (53). He found that when pipettes containing a small amount of 

 radium bromide were attached to the branches of lilac bushes {Syringa 

 vulgaris), the buds were forced. The longer the exposure (20, 48, 72 lir.), 

 the quicker the response. Similar results were obtained by exposing 

 chestnut branches (Castanea) for one day. Tulip, bladdemut (Staphylea), 

 and maple (Acer) gave indifferent results, and Ginkgo, Platanus, red beech 

 (Fa^us), and Tilia all gave negative results. 



Two years later, Molisch (54) reported that beta and gamma rays 

 of radium stimulate resting buds of Syringa vulgaris, especially when the 

 exposure is made in the second half of November and in December. But 

 in January a longer irradiation (72 hr.) produces no effect, or, if so, an 

 injurious one. Similar but more striking results were produced by 

 radium emanation, using Syringa vulgaris, Aesculus Hippocastanum, 

 Liriodendron tulipifera, Staphylea pinnata, and Acer platanoides. But 



