242 HISTORY OF BOTANY 



viz. those between B and C, as the most important, 

 though Engelmann claimed there was a second photo- 

 synthetic maximum in the blue violet region. The 

 subject was re-investigated by Kniep and Minder in 1909, 

 and from their experiments they conclude that, provided 

 the light is of the same intensity, red and blue light 

 produce the same photosynthetic results, but as they 

 used the old gas-bubble method for estimating the 

 intensity of photosynthesis, their conclusions cannot be 

 said to be beyond criticism. You will see, therefore, 

 that the new century has not as yet provided us with 

 data on the energy relations of the leaf at all comparable 

 with those of Willstatter on the chemical side, and it is 

 more than strange that no one with the requisite physical 

 knowledge seems to have considered it worth while to 

 determine whether any of the radiant energy is trans- 

 formed into electric energy — taking into account at the 

 same time the old work of Brodie and the newer experi- 

 ments of Loeb on the decomposition of carbon dioxide 

 and water by silent electric discharge. I drew attention 

 to this point in 1908, but, so far as I know, the matter 

 has been left untouched, and various circumstances have 

 prevented me from following up the subject. 



I am not going to trouble you with the speculations 

 of Van't Hoff , Siegfried, and Willstatter on the mode by 

 which photosynthesis is carried out, for, in the words of 

 a recent writer, " It can safely be said at the outset 

 that, when critically considered from a physiological 

 view point, none of the existing theories is even moderately 

 well estabUshed by observations of facts." In the 

 Croonian lecture to the Royal Society in 1903 Timiriazeff 

 made a witty reference to the philosophers of Balnibarbi, 

 whom GulHver in his travels found instructing their 

 pupils how to extract sunbeams from green cucumbers, 

 and suggested that we also must rest content to con- 

 template for a Uttle while longer green leaves locked 

 up in glass bottles, ere we reached a clear interpretation 



