(8) 
different course, but I am as yet unable thereabout to impart any 
decisive results. 
The experiment now described, is not quite new as to its 
principle. In another form it was already performed in 1892 by 
Scuiésine fils and LAurentT!), not however with a culture liquid, 
but with a solid sand-soil and under conditions much more compli- 
cated than mine. Noteworthy is that also these investigators, culti- 
vating in the light under the exclusion of all compounds of nitrogen, 
obtained Cyanophyceae belonging to the same or almost the same 
genera as those resulting from my experiments. They have moreover 
come to the result that by these Cyanophyceae free nitrogen was 
_assimilated in a slight but distinctly observable quantity, and though 
they have not completely proved this assertion, as their cultures 
must have contained other organisms too, e.g. many bacteria, basing 
also on my own experiences I take their view to be correct. 
My experiment throws some light on the two following obser- 
vations. GRAEBNER*) observed that fresh sandy grounds, which are 
changing into moors, cover in the beginning with a flora of Cyano- 
phyceae; and TrevB*), when visiting the isle of Krakatau after its 
destruction, found that the new flora which first developed on the 
volcanic ashes, likewise consisted of Cyanophyceae, of which he in 
particular mentions Lingbya verbeekiana and L. minutissima. Both, 
the said heathsand and the ashes of Krakatau, have no doubt 
been extremely poor in nitrogen-compounds. 
If absolutely rejecting the theory of spontaneous generation, it 
might be assumed that certain Cyanophyceae, carried over from the 
universe by meteorites, have been the first organisms which peopled 
the earth, as no other living beings are known which, like the 
Cyanophyceae, are able to build up their organic constituents from 
carbonic acid and atmospheric nitrogen. 
Once acquainted with the culture conditions of the Cyanophyceae 
I could easily obtain pure cultures on a solid medium. I therefore 
used as well silica as agar which by long washing with tap-water 
had been freed from the soluble organic substances, but saturated 
with the constituents of the tap-water. Plates of this agar, to 
1) Fixation de l’Azote libre par les plantes. Ann. de l'Institut Pasteur T. 6 pag. 832, 
1892. The authors make special mention of Nostoc punctiforme, N. minutum and 
Cylindrospermum majus. 
*) Studien über die norddeutsche Heide. Bot. Jahrbiicher. Bd. 20, 1891. 
*) Notice sur la nouvelle flore de Krakatau. Ann. d. Jard. Bot. de Buitenzorg: 
T. 7, 1888. 
