CHAP ii Photosynthesis 279 



indeed he entertained doubts as to the significance of chloro- 

 phyll and even as to the necessity for its presence, for he 

 noticed that the red garden Orache (Atriplex hortensis) 

 behaved like an ordinary green plant, and not knowing 

 that chlorophyll is present with the red pigment, he failed 

 to recognize its importance. 



A certain connexion between chlorophyll and nutritive 

 processes had become apparent a little later, when Dutrochet 

 discovered that it was only in cells containing the pigment 

 that the absorption of carbon dioxide and the concomitant 

 exhalation of oxygen were noticeable. Von Mohl had 

 observed the almost universal presence of starch grains in 

 the substance of the chloroplasts, or chlorophyll corpuscles, 

 as they were then called. Naegeli, Cramer, and Boehm 

 had noticed the same appearance. The significance of the 

 observation had, however, eluded the grasp of all, for 

 Naegeli, writing in 1858, did not associate the construction 

 of the starch in any way with the pigment. 



Liebig had reaffirmed De Saussure's statement that the 

 source of the carbon dioxide is the air and not the soil ; 

 in opposition to the adherents of the theory of the nutri- 

 tion of plants entirely from the humus of the latter. 



No correlation of these isolated facts had been forth- 

 coming ; no one had appeared apparently capable of making 

 the great generalization to which, in the light of subsequent 

 researches, we can see they pointed. It was reserved for 

 Sachs to lead the way, and to bring forward the idea that 

 these isolated and dimly-connected facts are severally 

 parts of one great process, the formation of organic sub- 

 stance from inorganic materials, the fundamental process 

 underlying all organic life, whether animal or vegetable. 

 Sachs' work in this direction gave a new starting-point and 

 a fresh impetus to the series of laborious investigations 

 into these great problems, and directed them into the 

 channels which have to-day brought the story of the con- 



