98 pringsheim's researches on chlorophyll. 



intense light (which in other conditions kills and decolorises 

 them), remain, notwithstanding the carbonic acid present, 

 unchanged and green. This tact, that carbonic acid plays 

 no part in the destruction o' the green colouring matter, is 

 of considerable importance in view of the theory of the 

 function of chlorophyll colouring matter here advanced. 



The cells once decolorised, whether to a great or slight 

 extent, never, even though they be not killed, regenerate 

 the' chlorophyll colouring matter. The decolorisation sets in 

 relatively slowly, becoming manifest only after a minute or 

 so of exposure. The case of Nitella, as previously described, 

 is a very typical one. 



It may, then, be concluded, from such facts, that the 

 destruction in nature of chlorophyll is a pathological 

 process, hurtful to the plant, and not, as has been supposed, 

 a normal process associated wiih the breaking up of carbonic 

 acid, and the fixing of carbon in the green tissues. 



Ever since the days of Senebier opinions have widely 

 differed upon the destruction of chlorophyll in light, upon 

 the relative energy in the process of the different rays of 

 the spectrum, and upon the significance of the process 

 in the life of the plant. Some have tried to settle the 

 question by researches into the changes exhibited by a solu- 

 tion of chlorophyll when exposed to light — a method of no 

 value without further observations upon the behaviour of 

 clilorophyll when attached to the living plant. Others have 

 made observations upon the plants themselves in their 

 natural situations, studying their blanching, yellowing, and 

 the changing in colour of parts exposed, especially in winter, 

 to direct sunlight. But in such cases the conditions are 

 comj)licated, and, moreover, the actual methods employed 

 have been iaulty. Tissues (especially of land plants) have 

 been employed, after maceration for days or weeks in water, 

 which naturally causes disease or death, wherewith are asso- 

 ciated changes of colour, blanching, and destruction" of 

 chlorophyll-coipuscles ; so that, in all sucli researches it has 

 been doubtful whether decolorisation was the direct effect 

 of light or the secondary result of some other injurious cause. 

 Hence it has happened that the decolorisation is ascribed 

 by one to frost, by another to heat, and by others to light. ^ 



' For more detailed informaliou regarding the destruelion of cbloro- 

 phyll iu living plants consult : 



Molil, " Ueber die winterliche Farbung der Blatter," ' Verm. Sehrift./ 

 18:^7, xix. 



Sachs, " Abwechselude^ Erbleichen und Dunkelwerdeu der Blatter 

 bei wechseluder Beleuchtuug," 'Berichte d. Sachs. Gesellsch. d. Wiss./ 



