CHAP, ii Photosynthesis 299 



purin accordingly. The matter was explained, however, by 

 Ewart's discovery in 1897 that the bacteria contain a 

 little chlorophyll, which is masked in the normal condition 

 by the purple pigment. 



THE PROCESSES OF PHOTOSYNTHESIS. As has already 

 been mentioned, the first investigations in this direction 

 which led to definite results were those of Sachs, which 

 were undertaken and carried to such conspicuous success 

 in the years 1860-5. Not that the work in any way 

 reached finality on the other hand, but little of its result 

 remains exactly as Sachs left it. It was, however, work 

 on which all the accurate knowledge of more recent times 

 has been based. 



Sachs' views based upon these researches were stated by 

 him in the Vorlesungen (Eng. ed., p. 307), in the following 

 terms : 



' In a long series of micro-chemical and experimental 

 researches on the growth of starch and sugar, ... I came to 

 the conclusion in 1862 that the enclosed starch, which had 

 already been observed in the chlorophyll corpuscles by 

 Naegeli and Von Mohl, is to be regarded as the first evident 

 product of assimilation formed by the decomposition of 

 carbon dioxide. I said to myself, if this view is right, 

 the formation of starch in the chlorophyll corpuscles must 

 cease on the exclusion of light, since the decomposition of 

 carbon dioxide can then no longer take place ; and that 

 in like manner renewed access of light to the chlorophyll 

 corpuscles must also bring about a renewal of the formation 

 of starch in them. These and similar deductions were con- 

 firmed by appropriate investigations.' 



Again he said : 



' In the nutrition of plants it is only necessary in the 

 first place to decompose carbon dioxide under the influence 

 of light in the cells containing chlorophyll, with the co- 

 operation of certain mineral matters absorbed by the roots, 

 and to produce at the cost of its carbon an organic sub- 

 stance starch which then represents the starting-point, 



