Wet) 
what different. First a rich light-brown culture of Diatomaceae takes 
rise, in which here and there colonies are seen of Chlorophyceae 
belonging to the genera Raphidium, Scenedesmus, Chlorella and 
Chlorococcum, but without their multiplying sufficiently to alter the 
brown colour of the culture. After 8 to 9 weeks however, the colour 
at once grows darker by the then occurring increase of the Cyano- 
phyceae, which increase continues a long time, evidently as long as 
there is a sufficient quantity of kalium phosphate and other mineral food. 
I think the result of this last experiment should be explained 
as follows. Canal-water contains a greater amount of organic sub- 
stances than the tap-water cultures; as long as these substances are 
present the Diatoms are prevailing; they use these substances for 
their carbon-nutrition, together with the carbonic acid from the air, 
and at the same time assimilate the nitrogen-compounds. When these 
are consumed the Cyanophyceae appear. 
That the Diatoms can in fact utilise a fairly high rate of organic 
substances, is well known to the students of that group. The following 
experiment which, to my knowledge, has not yet been described, 
proves that the Diatoms are the very coloured microbes, which 
can, if not assimilate, at least tolerate without injury the full rate 
of organic matter and of nitrate- and ammonia-nitrogen of fertile 
garden-soil. 
A high glasscylinder is filled for one half with garden-soil, for 
the other with pure water. After shaking the thus obtained mud is 
allowed to stand at a sunny. window. After some days or weeks, 
according to season and temperature, one sees at the illumined side 
of the glass a deep brown film appear, consisting of the Diatoms present 
in the garden-soil, which slowly creep towards the light. This film 
increases some months by the multiplication of the Diatoms, but 
finally there appear in it large green spots of various lower Chloro- 
phyceae, whose propagation becomes only vigorous, when the 
Diatoms and other microbes (such as bacteria and monads) have for 
the greater part used the assimilable organic substances and con- 
verted them into unassimilable material. Cyanophyceae do not grow 
under these circumstances, this being prevented by the abundance 
of nitrogen-compounds in the garden-soil. 
Though it is certain, that the flora of Cyanophyceae in my tap- 
and canal-water experiments only develops with an extremely small 
proportion of organic matter in the food, I still consider this pro- 
portion to be of an essential signification for the experiment. I have 
already convinced myself that at as complete an absence as possible 
of organic substances, the development of the flora follows quite a 
