200 HISTORY OF BOTANY 



(in contrast to photosynthesis), and shown to be carried 

 out by energy supplied by the oxidation of ammonia. 



Winogradski also investigated the nutritive phenomena 

 of so-called iron and sulphur bacteria. The latter were 

 known to belong to the genus Beggiatoa, which were fila- 

 mentous forms growing in water containing sulphuretted 

 hydrogen. The energy in this case is obtained by oxida- 

 tion of sulphur. Synthesis of organic material may thus 

 take place without the presence of chlorophyll or light, 

 and you will see how fundamentally important the 

 study of these synthetic processes becomes in view of the 

 speculations on the origin of life on the earth. 



THE PROBLEM OF PHOTOSYNTHESIS 



During the past few years I have had occasion to 

 collect all the references I could find connected with the 

 subject of photosynthesis or carbon assimilation, from 

 the earliest times to the present day. On looking through 

 the volumes of notes I have accumulated I find I have 

 the titles and abstracts of no less than 756 papers on 

 the subject for the period 1860-1900. Quite half of these 

 are probably of no importance, but I almost despair 

 of doing anything like justice in the time at my disposal 

 to the labour and energy represented by even a fraction 

 of the remainder. 



After 1859 the*name of Sachs confronts us at every 

 turn, and, whatever we may think of him as a historian, 

 we must assign to him the place of honour as the first 

 since De Saussure to revive the experimental side of 

 plant physiology and submit the phenomena of living 

 nature to critical laboratory investigation and analysis. 

 His first contribution to the elucidation of the photo- 

 synthetic problem dealt with the influence of light on 

 chlorophyll. He showed that the colourless plastid 

 may form in darkness, but that light is essential to green- 

 ing ; that the light need only be feeble, and that intense 



