68 previous investigations upon plants 



3. Effects of Radium Rays on Plant Fibers 



In addition to the physiological results reviewed above, the action 

 of radium ra3's on vegetable fibers is both interesting and pertinent in 

 this connection. This effect was first noticed by Giesel,"* and after- 

 ward accidentally by Lord Blythswood,^^ in 1904. "I happened," 

 says the latter, " to replace the usual mica plates, used to keep in the 

 small quantity of radium in its ebonite box, with a piece of cambric, so 

 as to permit the whole of the emanations to pass out, mica stopping 

 the a. rays. In four days the cambric was rotted away. I have 

 replaced it now several times with the same result." 



In the following year Martin and Morton ^^ experimented on the 

 effect of the rays on unspun silk fibers and ordinary unbleached cot- 

 ton thread. The threads were exposed to " bare radium," at a dis- 

 tance of about one half centimeter. After a certain period of expo- 

 sure the average breaking strength of the threads was taken and 

 plotted against time. The points obtained lay closely on a smoothly 

 descending curve. In the case of the silk the loss of strength went 

 on at a practically uniform rate from the beginning up to the end of 

 the longest exposure given (seven days). The initial strength of 78 

 gm. decreased by about 4 gm. per day. The cotton threads gave 

 a curve which fell more rapidly in the early than in the later stages. 

 The strength began at 370 gm., and decreased at first by about 60 

 gm. per day. After ten days the rate of weakening was about half 

 this. At the end of 17 days the strength was reduced to 17 gm. 

 The difference in behavior of the two kinds of fibers is attributed to 

 the greater thickness of the cotton threads. The effect is due en- 

 tirely to the a rays, for only negative results were obtained when 

 those rays were screened out. 



Wet threads, with the same length of exposure, were less weak- 

 ened, and this, the authors state, was plainly due to the decreased 

 emission of rays on account of the solution of the radium salt, and 

 the consequent removal of the emanation.* 



In a subsequent paper, McKee and Morton"^ state that the con- 

 stant removal of the emanation does not affect the result. It was 

 further found that when threads or a piece of filter paper, after 

 exposure to the rays are dyed with methylene blue, the exposed part 

 takes a deeper color than the rest, thus indicating the presence of 



* " The rate of escape of emanation is much increased by solution of the com- 

 pound." Rutherford, p. 255 (see Bibliography, p. 20, No. 115). 



