PHOTOSYNTHESIS 207 



of view, I may be justified in spending a few moments 

 on this remarkable theory. 



With the aid of a lens and a heliostat Pringsheim 

 exposed green tissue to highly concentrated Hght, and 

 found that after a few minutes the chlorophyll was 

 completely destroyed, although the protoplasm at first 

 suffered Httle alteration. He convinced himself that this 

 destructive effect was not due to high temperature and 

 was dependent on the presence of oxygen. On the 

 strength of these observations he suggested that chloro- 

 phyll operated as a protective screen, moderating the 

 injurious effect of light on the protoplasm and, by its 

 absorption of the so-called chemical rays, acting as a 

 regulator of respiration. He also claimed to have dis- 

 covered a new substance of a hydrocarbon nature which 

 he called hypochlorin, which he thought was the first 

 product of assimilation, and from which starch and other 

 compounds were derived. This hypochlorin was obtained 

 by heating green cells with dilute hydrochloric acid or 

 treating them with steam ; it appeared on the margins 

 of the chloroplasts as small glutinous red-brown droplets 

 or needles. It formed the oily basis of the plastid, and 

 was soluble in alcohol, ether, and benzin, but insoluble 

 in water. After separation it soUdified into an obscurely 

 crystalhne resinous or waxy substance. Increase in 

 starch, Pringsheim claimed, was accompanied by decrease 

 in hypochlorin. Yellow seedhngs contained no h^'po- 

 chlorin, but it at once made its appearance in light and 

 as soon as the chlorophyll became evident. It did not, 

 however, occur in the dark in the case of Gymnosperm 

 seedhngs, which develop chlorophyll in darkness. When 

 hypochlorin was removed from the chloroplast there was 

 left a spongy framework, the plastid proper. Thus the 

 green pigment in absorbing light protected the hypo- 

 chlorin from oxidation. 



For five years or more paper after paper appeared 

 on this subject, indeed much of the Hterature pubhshed 



