410 PROTOPLASM 



Some interesting work has been done upon the effects of 

 X rays on the hereditary characters of plants and animals. 

 Among the first outstanding pieces of research of this sort was 

 that of Goodspeed, working on tobacco, and that of Muller, 

 with the fruit fly, Drosophila, as his material. The former 

 found that when the reproductive cells of Nicotiana, whose many 

 (24) pairs of chromosomes might well exhibit irregular behavior 

 though actually very few mutations occur, are subjected to 

 X rays and radium emanations, chromosome disturbances are 

 rather frequent and result in changes in leaf and flower form and 

 plant size. 



Muller, in his work on the fruit fly, found that mutations, or 

 permanent changes, particularly in the eyes, can be induced by 

 radiation with X rays. The changes cannot be distinguished 

 from those arising spontaneously. 



Other portions of the spectrum having wave lengths shorter 

 than X rays produce little effect upon the genes, or hereditary 

 units of organisms, but longer rays, viz., the ultraviolet, have 

 been shown to have an effect similar to that of X rays. 



Alpha, Beta, and Gamma Rays. — Of the three types of radia- 

 tion from radium — alpha and beta particles and gamma rays 

 — only the last is included in the spectrum of electromagnetic 

 radiation. It is customary to refer to alpha and beta particles 

 as particles, but as beta radiations are free electrons, the dis- 

 tinction between particle and wave is not definite. As a result, 

 beta radiations are often referred to as rays, though neither 

 they nor alpha particles have yet been given a place in the 

 spectrum. 



Alpha particles are of no special medical value but may 

 influence vital processes. R. E. Zirkle has shown that alpha 

 particles emitted from polonium (radium F), at an average rate 

 of 100,000 particles per second, retard or completely inhibit the 

 germination of fern spores. The effect is more severe when the 

 nucleus and not the cytoplasm alone is irradiated. 



Beta and gamma rays also ordinarily affect plants in such a 

 way as to retard growth. Blaauw and van Heymingen find this 

 to be true of certain fungi. 



The usually observed effect of radium radiation on living 

 matter is a harmful one, but certain forms are extremely resistant; 

 this is true of Protozoa and even more so of Myxomycetes (slime 



