PREFACE IX 



concordant testimony could leave no doubt as to the 

 authenticity of the newly discovered facts. Advanced in- 

 vestigation necessarily depends on the use of specially devised 

 instrumental appliances and on the proper understanding 

 of the technique of new methods, which can only be acquired 

 after sufficient training. The perfect reliability of my highly 

 sensitive instruments has been repeatedly verified at various 

 scientific centres both in the West and in the East. The 

 technical knowledge of the new methods can be gained 

 after a certain amount of practice. Professor Hans Molisch, 

 lately Director of the Plant-Physiological Institute, Vienna 

 University, during his recent visit to my Institute, was 

 able to repeat, with invariable success, many of the experi- 

 ments described in this volume. His account of some of 

 these will be found in Nature of August 4, 1928, and of 

 April 13, 1929. 



It must be confessed that I was completely baffled, at 

 the beginning of my researches, by many results which were 

 as astonishing as they were unexpected. It was long per- 

 sistence and careful comparison of numerous records that 

 ultimately led to the elucidation of all anomalies. Attention 

 had hitherto been centred on the end-effects, which, taken 

 alone, are misleading. Examination of continuous records 

 under prolonged stimulation showed clearly the gradual 

 transformation of what may be regarded as the normal 

 reaction to its very opposite. With such basic facts to 

 work upon, it was afterwards possible to discover the causes 

 of transformation. 



I may here briefly refer to a few of the more important 

 results. For instance, the excitation of plants by radiation 

 had come to be regarded as more or less confined within 

 the narrow range of the visible spectrum. Experiments on 

 the effects of wireless waves and of a high-frequency alter- 

 nating field of electric force prove, on the contrary, that 

 the sensitivity of plants to the ethereal spectrum extends 

 far beyond the infra-red region. 



An unexpected factor in the modification of normal 



