(48 ) 
In the following way, however, the experiments with them went 
very satisfactorily. 
Instead of enclosing the leaf on 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 !), 
These experiments confirm the results obtained by SrAnL 2), 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 with its wader 
surface on the gelatin, the oxygen issuing from the stomata directly 
comes into contact with the gelatin, and a luminous spot appears 
shaped like the leaf. 
In performing this experiment it is advisable to cut one and the 
same leave into two halves and press at once both parts on the 
gelatin, one with the upper- the other with the underside. 
The process can, however, become very complicated by the closing 
of the stomata, which are extremely sensitive to the contact of the 
salt-containing culture-gelatin, and evidently also to the absence of 
oxygen in their surrounding, when kept in the dark. 
The fact that nyctitropic leaves evaporate the most vigorously 
1) 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. 
*) Botan. Zeitung, 1894 pag. 117, 1897 pag. 71. 
