146 M. Marc Micheli on some Recent 



passing the observations of M. Bert* on those of the so-called 

 sensitive organs in coloured light. These are the only re- 

 searches upon this subject with which we are at present 

 acquainted. According to this author, plants of Mimosa pu- 

 dica kept in the dark died at the end of twelve days, having 

 lost all sensibility after the seventh. Other individuals of the 

 same species were enclosed in lanterns of coloured glass, which 

 was, as far as possible, monochromatic ; and the following is 

 a summary of the results obtained : — 



In green light the plants died in sixteen days ; sensibility 

 persisted for twelve days. 



In violet light the plants lived three months without any 

 development, and then jierished ; sensibility persisted to the 

 end. 



In blue light the plants continued to live without develop- 

 ment ; they constantly retained a certain degree of sensibility. 



Lastly, in yellow and red light the plants not only live but 

 become slightly developed ; ^\^QJ retain their sensibility. 



If we now approach the important subject of the decompo- 

 sition of carbonic acid and the assimilation in the grains of 

 chlorophyl, we shall find that here also some advances have 

 been made, and we shall have to refer to works of greater 

 importance. 



It is a fact that often presents itself in the history of the 

 sciences, that the first observers, perhaps carried away by the 

 charm of discovery and by the desire to render it as evident 

 as possible, give a somewhat too absolute value to the results 

 which they have obtained, and it is only at a later period and 

 by little and little that the facts appear in a perfectly correct 

 light. Thus it was formerly regarded as a perfectly positive 

 law that the most luminous rays of the spectrum alone acted 

 in the phenomenon of assimilation, a different part being as- 

 signed to the more refrangible rays. In other words, the action 

 of light upon chlorophyl seemed to be directly opposite to its 

 influence upon chloride of silver. Repeated and more pro- 

 found researches have already greatly modified this notion. 

 We shall now endeavour to give an exact idea of the state of 

 the question by rapidly going through the various works 

 which have come to our knowledge. We shall simply follow 

 the chronological order, leaving entirely on one side the ques- 

 tions of priority which, as a matter of course, have sprung up. 



The first in point of date is M. Gregor Kraussf, one of the 

 most accurate of observers, and author of several important 

 treatises. He resumed the investigations of M. Famintzin 



* Comptes Rendus, 1870, tome Ixx. 

 t Pringsheim's Jahrb. vii. p. 511. 



