itself, certainly it was somewhat out of the middle of B C. Decomposition of car- 

 bonic acid in other coloured lights could not be detected. 



If the Chlorophycee was replaced by a Rhodophycee, which 1 determined as 

 Porphyra vulgaris, and which, like the Ulva, is common on the stone piers at Sche- 

 veningen, 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 determined 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 1 ), 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 fishbouillon, 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. 



In the following way, however, the experiments with them went very satis- 

 factorily. 



Instead of enclosing the leaf in the strongly phosphorescent gelatin it is simply 

 laid on the surface, and firmly pressed to it by means of a solid glass-plate. 



Kept in the dark, after some time all the oxygen originally enclosed in the 

 tissues of the leaf is utilised by the phosphorescent bacteria and everything under 

 the glass-plate grows dark. If now the leaf is illumined, oxygen is formed, and 

 when transferred to the dark, the bacteria will be seen to continue emitting light 

 for some time 2 ). 



These experiments confirm the results obtained by S t a h 1 "'). which demonstrate 

 that the stomata are the ways by which the gases enter and leave the leaf. For when 

 suitable leaves are selected with about an equal number of stomata on both surfaces, 

 and examined after our method, it appears to be all the same, whether the leaf is 

 pressed with its under or upper side against the gelatin, in both cases a luminous spot 

 of the shape of the leaf appears, after illumination. If. on the other hand, the stomata 

 are only, or for the greater part, at the under surface, and the leaf is pressed with 

 its upper surface on the gelatin, thus with its underside against the glass-plate, then 

 the oxygen accumulates between the latter and the leaf, and does not, or only partly 

 pass through the lamina but, reaching the gelatin along the margin of the leaf, a 

 luminous line following this margin is produced. 



If such a leaf is illumined after being pressed Avith its under surface on the ge- 



') Botanische Zeitung. 1883 pag. i, 1884 pag. 81. 



2 ) For the right performance of this experiment some practice is required as the 

 layers of air, adhering to the leaves, and which are greatly different at the upper and 

 under surface, influence largely on the course of the process. 



s ) Botan. Zeitung. 1894 pag. 117, 1897 pag. 71. 



9* 



