MISCELLANEOUS EXPERIMENTS 



187 



accelerated by rays from radium bromide of 10,000 activity. These 

 rays produced no apparent morphological change in the yeast under 

 the conditions of the exposure. 



Mushroom spawn (^Agartcus ca7npestris L.) was killed by rays 

 from 15 mg. of radium bromide of 1,500,000 x, while rays of the 

 same activity passing through water produced no apparent morpho- 

 logical change in Sptrogyra. 



When the end of the glass tube containing 10 mg. of radium 

 bromide of 1,500,000 x was placed a few millimeters above the 

 gemmae of Liiniilaria an exposure of 48 hours retarded the growth 

 of the gemmae, and one of 67 hours completely inhibited it. The 

 reaction of chloroplastids to radium rays is similar to their reaction to 

 too intense sunlight (figure \^a). This indicates that the gemmae 

 are rather resistant to the rays. Cupules with brood-buds formed 

 sooner than normally on thalli grown from the gemmae exposed for 

 48 hours. When the same radium tube was placed in contact with 

 these gemmae they were killed within at least 19 hours, or possibly 

 sooner. Growth of the gemmae was retarded when'they were sown 

 on the surface of soil into which the tube was inserted for five and 

 one half weeks. 



Fig. 47a. Experiment 60. Response of Chloroplasts to Radium Rajs. 



The sprouting of a potato was evidently not affected by having 

 the radium tube (1,500,000 x) inserted into the tissue of the tuber 

 about 10 mm. from the " eye." 



No effect on germination followed an exposure of dry timothy 

 grass seed for 161 hours to the a rays from a rod coated with 

 polonium. 



The thorium rays from a Welsbach gas mantle retarded the 

 growth of timothy grass when the mantle was placed over the seeds 

 germinating on the surface of soil, but germination and growth did 

 not appear to be affected in the least by burying the mantle in the 

 soil. 



