352 PHOTOSYNTHESIS 



in living leaves, on similar deductions. He examined in the spectroscope 

 the fluorescence of solutions of chlorophyll of various degrees of disper- 

 sion. Neither solid chlorophyll nor colloidal solutions thereof show any 

 fluorescence. Stern argues that if chlorophyll in the living plant is in 

 the form of a colloidal solution, there must be present in the cells sub- 

 stances which afifect the colloidal chlorophyll in a manner to produce fluores- 

 cence. He tested colloidal solutions of chlorophyll to which had been 

 added various substances in order to determine whether these produce 

 fluorescence. Proteins, carbohydrates, glycerine and lipoids were added. 

 Stern concludes that chlorophyll fluoresces only when it is in true solu- 

 tion. By the addition of lipoids to colloidal chlorophyll solutions and 

 shaking the mixture for a few minutes, an emulsion was produced in 

 which some chlorophyll passed into the lipoid phase. These solutions 

 showed the characteristic fluorescence. Thus lecithin, cholestrine, linseed 

 oil, oleic acid, soap, etc., gave positive results. Stern concludes from 

 this that in the living plant chlorophyll is not in a colloidal solution, but 

 that in the intact chloroplast the chlorophyll is dissolved in a lipoid phase 

 in true solution and consequently shows fluorescence. Photosynthesis, 

 according to this view, would take place partly in a lipoidal and partly 

 in an aqueous phase. The lipoidal solutions of chlorophyll also show a 

 shifting of the absorption bands toward the red end of the spectrum as 

 compared with true solutions. This Stern ascribes to the difiference in 

 the index of refraction between alcohol and the lipoids. This is in agree- 

 ment with Kundt's law which states that the absorption maxima are dis- 

 placed to the red in proportion as the refractivity of the solvent in- 

 creases. The refractive index of alcohol may be taken as 1.36, that of 

 the lipoid as about 1.46. The position of the fluorescent band of a solu- 

 tion of chlorophyll in alcohol is at 654 ^n, chlorophyll in lecithin at 677 \i\i, 

 and in the living Chlorella cells it is at 681 \i\i; these are the positions of 

 maximum intensity of the bands. It should, perhaps, be recalled that 

 Iwanowski pointed out that the position of the absorption bands of a 

 colloidal solution of chlorophyll and of a living leaf do not precisely 

 coincide, but that the position of the absorption bands of a colloidal solu- 

 tion is between that of the leaf and that of a true solution. Liebaldt^^ 

 also considers it probable that chlorophyll in the chloroplasts is in a lipoid 



solution. 



The question of the fluorescence of chlorophyll solutions in different 

 degree of dispersion is in need of further intensive study. It is a 

 familiar fact that the fluorescence of chlorophyll solutions is greatly 

 affected by the presence of finely divided particles. Whether this is due 

 to dispersion of the fluorescent light or some other. cause has not been 

 definitelv established. 



Solutions of chlorophyll exhibit the Becquerel effect.^*^ If two elec- 

 trodes are placed in a solution of chlorophyll and one electrode is illumi- 



^Liebaldt, Zeit. Bot., 5, 65 (1913). 



=" Samsonow, Zeit. iviss. Phot., 11, 33 (1912). 



