(47) 
carbonic acid, and a local spot of light appears, which may be 
caused to come and to vanish at will as often as desired. 
This apparatus was set up in a simple camera and could be 
locally illumined by withdrawing a slide. When the slide was 
closed the camera was quite dark, by which the eye of the observer 
became sensible to the light. Prof. OnNEs himself supplied spectral 
colours of known refrangebility, taken from the spectrum of an 
electric arc-light, and projected them on the Ulva in the gelatin. 
By me was then observed what coloured lights were well, and what 
were not able to cause the decomposition of carbonic acid. The 
result was the following: Only red light decomposes carbonic acid, 
for only in it the phosphorescent bacteria emit a strong light; the 
maximum of decomposition was found near the chief absorption- 
band of the chlorophyll-pigment, situated between B and C, and this 
maximum coincides about with C itself, certainly it was somewhat 
out of the middle of B—C. Decomposition of carbonic acid in 
other coloured lights could not be detected. 
If the Chlorophycee was replaced by a Rhodophycee, which I 
determined as Porphyra vulgaris, and which, like the Ulva, is common 
on the stone piers at Scheveningen, the process was nearly the 
same, but with this difference that the maximum of decomposition 
does not coincide with C but lies quite in the orange. 
As the chromatophores of Porphyra, besides the chlorophyll- 
pigment, contain a red pigment soluble in water, and of which two 
chief absorption-bands are situated in the yellow, it is obvious that 
the maximum of carbonic-acid decomposition is in this case deter- 
mined by the co-operation of the coloured rays which both pigments 
by preference absorb. | 
Our results, accordingly, correspond in the main point with those 
obtained by Prof. ENGELMANN '), by his method based on the motion 
of bacteria, with this difference that the production of oxygen in 
two other absorption-bands, situated in the blue, as described by 
him, could not be observed by us. 
In opposition to the sea-algae and likewise to the crushed leaves of 
landplants, whole leaves of the latter, immersed in luminous fish- 
bouillon, or in gelatin mixed with phosphorescent bacteria, do not 
distinctly, or only for a very short time, produce oxygen, when 
they are illumined after being freed from the air enclosed in their 
tissues. 
') Botanische Zeitung. 1883 pag. 1, 1884 pag. 81. 
