88 



durchgefiihrte Ansicht des Parallelismus von Algen und Pilzen eine 

 empirische Basis erhalten hat." 



In 1902 BEIJERINCK obtained a pure culture also of Cyanophyceae, 

 after he had indicated in 1901 how to obtain these organisms from 

 garden soil by enrichment culture in a liquid medium. It became 

 apparent to him, namely, that various Cyanophyceae were able to 

 develop in liquids in which only traces of nitrogen were present. If a 

 flask of water from the Delft municipal water supply (this contained 

 approximately 0.42 mg N per liter) to which a small amount of di- 

 potassium phosphate was added (0.02 per cent), was inoculated with 

 garden soil (this contained 0.56 per cent N on the dry matter) and 

 was placed in the light, then therein developed a rich flora which 

 contained many Cyanophyceae (viz., species of Anabaena and of 

 Nostoc). BEIJERINCK considered these organisms as oligonitrophils, 

 and he considered the growth of these cultures so strong that fixation 

 of atmospheric nitrogen had to be assumed. In 1901 he states in a 

 footnote that he will return later to the question as to whether the 

 Cyanophyceae themselves fix nitrogen, or whether they do this in 

 symbiosis with other microbes. As appears from his publication of 

 1902, BEIJERINCK considered the latter the more probable. In 1904 

 also he states this very distinctly ; but attention must be called to the 

 fact that he has not proved this fixation with analytical data. 



By spreading the above-mentioned cultures on well-washed plates 

 of agar or silica-gel, to which only 0.02 per cent of dipotassium phos- 

 phate had been added, and by cultivating in the light, BEIJERINCK 

 obtained large colonies of bacteria-free Anabaena. He adds that his 

 assistant A. VAN DELDEN isolated a blue-green organism on a similar 

 agar medium to which a trace of ammonium nitrate had been added, 

 \vhich organism was related to Oscillaria. It is to be regretted that 

 these interesting cultures have not been described more extensively. 



Not less important than the isolation of these organisms in pure 

 culture, are the considerations which BEIJERINCK adds to his obser- 

 vations on the possibility that the Cyanophyceae, which are apparent- 

 ly satisfied with such simple conditions of life, belong to the oldest 

 organisms on earth. Perhaps even to those which, according to 

 the bold hypothesis of H. E. RICHTER (1865 and 1870), later on 

 independently raised by VON HELMHOLTZ and by WILLIAM THOMP- 

 SON, might be distributed through the universe by meteorites. But 

 BEIJERINCK withdrew the latter view in his fundamental publication on 

 "Mutation bei Mikroben" in 1912, and he states that it is much more 

 probable that "abiogenesis" has occurred on earth, be it in earlier 

 geological periods, or that it still occurs. 



In a short communication of 1904 1 ) BEIJERINCK describes the 



i) Das Assimilationsprodukt der Kohlensaure in den Chromatophoren der Diato- 

 meen, Recueil travaux botaniques neerlandais 1, 28-32, 1904 (Verzamelde Geschrif- 

 ten 4, 239-241). 



