PHOTOSYNTHESIS 201 



light retards the development of the pigment. In 1860, 

 Sachs, with the aid of an instrument he termed a diaphano- 

 scope, estimated the degree of penetration of light through 

 tissues of varied thickness, and showed that light did 

 actually pass through structures that were opaque to the 

 eye. He also determined which rays of the spectrum 

 penetrated most deeply, and showed that the spectrum 

 of the leaf was identical with that of an alcoholic solution 

 of chlorophyll. 



In the same year Fremy analysed the green pigment 

 by shaking up an alcoholic solution with ether and 

 hydrochloric acid and obtained a blue-green acid alcoholic 

 solution and a yellow ether solution ; the blue - green 

 pigment he termed phyllocyanin and the yellow one 

 phylloxanthin. 



In 1862-63 Sachs published a series of important 

 papers dealing with the intimate structure of the chloro- 

 plast and the origin of the starch grains in it, and showed 

 that the appearance of the starch was associated with 

 illumination ; in his own words, " the starch in the 

 chlorophyll body is a product of the living -chlorophyll 

 and it may be said in general that starch in the chlorophyll 

 arises by the assimilatory capacity of the latter." From 

 the leaves the starch is transported to wherever it is 

 required, and travels in the form of glucose, dextrin, 

 cane-sugar, etc., and may be redeposited as starch in 

 other organs. He also discussed the chemical and 

 physical properties of the pigment and confirmed the 

 earlier observation that iron was essential to its formation. 



In 1864 Stokes published a paper on the constitution 

 of chlorophyll, which, in a very remarkable way, anti- 

 cipated the work of the most recent chemical investigators 

 of plant pigments, viz. Willstatter and his pupils. ,S_tokes 

 affirmed that chlorophyll was a mixture of two green and 

 two yellow pigments, the former being fluorescent but 

 the latter not. This was not only true of leaf green 

 taken from land plants but also of the pigments extractable 



