290 The Physiology of Plants BOOK in 



haphazard place in the cell containing chlorophyll, but in 

 the chlorophyll body itself. 



Though Sachs was for so many years indefatigable in 

 the prosecution of research, it will be generally admitted 

 that his work upon this particular subject constitutes one 

 of his greatest claims to eminence. During the greater 

 part of the sixties it was engaging his attention, and in the 

 earlier years especially his discoveries were very far-reaching. 



During these early years, as we have already seen, Sachs 

 showed that chlorophyll can be formed only in the light, 

 except in rare cases, and he distinguished between the role 

 of the light in such formation and the part which it plays 

 in its subsequent activity, showing that the former process 

 is not in any way directly connected with the exhalation 

 of oxygen. 



Starting from these discoveries and conclusions of Sachs 

 the trend of thought has been gradually shaping itself 

 through a period of nearly fifty years in the direction of 

 the recognition of the mechanism or, as it is now called, 

 the chlorophyll apparatus, as an independent machine for 

 the performance of certain work, viz. the construction of 

 organic substance from inorganic materials ; this mechan- 

 ism, though present for the most part only in plants, is 

 not an essential feature of the vegetable organism, for it is 

 occasionally and exceptionally present in some members 

 of the animal kingdom, and is, also exceptionally, absent 

 from some plants, and in all the higher ones at any rate 

 appears only after they have reached a certain degree of 

 development. The plants permanently without it are 

 usually held to be degraded forms, but this need not affect 

 the view of its independence. Originally present in the 

 primordial ancestor of both animals and plants, it has come 

 to be localized almost entirely in the latter as evolution and 

 development have proceeded ; nearly all animals and some 

 plants ceasing to contain it. The process of parting from 



