CHAPTER IV 



• PREVIOUS INVESTIGATIONS UPON PLANTS 

 I. Effects of Rontgen Rays on Plants 



In the year 1892 Leo Errera, ^- * by a series of painstaking ex- 

 periments with Phycomyces nitens and other plants, demonstrated the 

 fallacy of the notion of " physiological-action-at-a-distance," which 

 had been put forward in 1890 by Elfving/' ^* It is not surprising, 

 then, to find him one of the first investigators to study the physiolog- 

 ical action of the then new kind of rays, the X rays, on living plants, 

 for Rontgen's discovery belonged to a series of brilliant investigations 

 which have resulted in the almost, if not wholly, complete abandon- 

 ment of the idea of action-at-a-distance of any kind. Errera, ^^ how- 

 ever, was unable to determine the slightest response of Phycomyces 

 niteiis when it was exposed to these rays. 



Soon after the discovery that Rontgen rays are a component of 

 sunbeams, Miiller^" raised the question as to whether or not the ra3's 

 thus occurring exerted any influence upon plants. He placed speci- 

 mens of garden cress in a dark chamber, protected from sunlight, 

 and found that their stems turned towards the rays as in phototro- 

 pism. By this means, and also by using phosphorescent substances, 

 Muller reached the conclusion that the X rays present in sunbeams 

 do act upon plants. 



Contrary to these results, Schober^'^ failed to observe in oats any 

 tropistic response with reference to X rays, but found that an expo- 

 sure of one hour to the rays did not cause the seedlings to lose their 

 phototropic sensitiveness. 



Studies of the action of X rays on bacteria also began in the year 

 1896. The literature on this subject alone has become so volumi- 

 nous that it would not be desirable nor profitable to review it here in 

 detail, and no attempt is made even to cite all of the published papers. 

 Practically all investigators have obtained one or the other of two 

 kinds of results ; either negative results, or an injurious effect on the 

 bacteria. Among those who have obtained negative results are Mink *^ 



*Errera's interpretation of " pliysiological-action-at-a-distance " as merely a special 

 case of hydrotropism, was confirmed by Stryer '' in 1901. 



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