LUMINOSITV IN PLANTS. 357 



As the light produced l)y these substances has an external and spec- 

 troscopic likeness to that produced by living organisms, and as some 

 of the substances in the list of Radziszewski which are capable of 

 luminosity exist also in living cells (I mention lecithin, fats, choles- 

 terine, ethereal oils, and grape sugar) that investigator has come to 

 the conclusion that light development in living organisms can be 

 explained as an oxydation of these same substances. Radziszewski 

 looks upon the jn-oblem, therefore, as solved. We have, however, as 

 yet hardly gotten that far. The question of whether Radziszewski 

 is in the right could be definitely settled if we could extract from the 

 living cell a photogen material which would show luminosit}^ outside 

 of the cell. But up to the present time the attempt has not been 

 successful. Furthermore, according to Pfeffer, no actiA'e light-caus- 

 ing oxygen exists in the living plant cell, which does not square with 

 the theory on which Radziszewski's explanation rests, inasmuch as 

 his light-producing substance is luminous only when in contact with 

 active oxygen. Nevertheless, I look upon the photogen theor}' as 

 the most plausible, though we at present have no knowledge as to 

 the nature of photogen. Possibly it is a material in no sense similar 

 to the luminous substances previously mentioned ; perhaps something 

 capable of giving light without active oxygen. 



There are certain facts which appear to me to directly support the 

 idea of a photogen. Thus certain animal organisms give out a non- 

 cellular luminous secretion, and certain cells together with their 

 contents are capable of producing light when no longer living. Men- 

 tion can be made of P/toIas, certain of the insects, myriapods, and 

 many of the worms. A fact of significance and too little noted is 

 that certain tissues and cells have the power of producing light in a 

 lifeless condition. Thus manuscript written w^ith the luminous mate- 

 rial obtained from Liiciola italica gives off light when it is dampened. 

 The light organs of Lanvpyris noct'duca lose their luminosity when 

 thoroughly dried and kept in a vacuum. But, according to Bongardt, 

 if after a year's time they are taken out and moistened with a drop of 

 distilled water the light reappears. If filter paper is impregnated 

 with the secretions of certain myriapods, it can, after t\Yo months' 

 time, be made luminous by moistening. It is impossible in such in- 

 stances to talk longer about " living cells " or " living cell contents," 

 for it is impossible to describe as living the luminous material from 

 an insect that has been dried and kept for a year in a vacuum. In 

 such instances we are no longer dealing with a vital l)ut with a purely 

 chemical process; we are dealing with a substance which produces 

 light in the presence of water and free oxygen. 



In the case of luminous plants no such thing as a luminous excre- 

 tion exists, though such is erroneously stated to be the case, for the 

 light exists only within the cell. In other words, it has never been 

 seen outside of the living plant cell, and to that extent luminosity in 



