CHAPTER XIX 



THEORETICAL CONSIDERATIONS 



It has been clearly shown that radium rays act as a stimulus to 

 plants, and are therefore able to modify their life processes. In cer- 

 tain cases the reaction to the rays is an excitation of function, in other 

 cases a depression. But as to the method by which the stimulation 

 is brought about, as to just how the protoplast is affected by the 

 rays, we are in almost complete ignorance. Nor is the wriier bold 

 enough to essay an answer to these questions here. The final solu- 

 tion of the problem, however, will involve a careful consideration 

 of certain facts and theories which may now be reviewed. 



The term stimulus is employed here and throughout in the 

 sense emphasized by Verworn,^- * as any " change in the external 

 agencies that act upon an organism." With reference to any indi- 

 vidual protoplast this change will involve factors outside the proto- 

 plast, but not necessarily outside the organism of which it is a part. 

 These external agencies are forms of energy,! of which Verworn'- X 

 lists eight, viz., chemical, molecular, mechanical, thermal, photic, 

 electrical, magnetic, § and energy of gravitation. In Chapter II of 

 this Memoir, it was pointed out that to these forms of energy, hitherto 

 commonly recognized, must be added that of radioactivity. It was 

 furthermore shown that radioactivity is a factor in the nornial environ- 

 ment of probably all plants. Any change, therefore, in this factor 

 becomes a stimulus. 



The Biogen Hypothesis : Before we can form any conception 

 of the modus operandi of any stimulus we must have some sort of 

 picture of the constitution of the cell. That protoplasm is not a 

 chemical entity, but a morphological one, is generally accepted. It is 

 also recognized that that which fundamentally distinguishes it from 

 lifeless matter is its power of metabolism. One of the most thor- 



* Loc. cit. , p. 34S. 



t Or modify some form of energy, as when one plant is shaded by another. 



J Loc. cit., p. 209. 



§ Verworn ^ later (1. c, p. 348-349) states that the only ones of the above classes 

 that come into relation with the organism are the first six and the last, but Ewart ^' 

 succeeded in modifying the rate of streaming of protoplasm in living cells and the rate 

 of motion of spermatozoids by the influence of strong magnets. 



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