( 665 ) 
species the parenchyma contains air-channels, running continuously 
from the base to the apex and taking up from one third to one half 
of the area of a transverse section. In these channels there are, it is 
true, diaphragms of one cell thick, but these are themselves also 
provided with many wide intercellular spaces. | 
It is therefore merely a matter of course, that in these leaves 
carbon dioxide can be carried over much larger distances; indeed, 
it is clear that this carriage could extend from the lowest part of 
the base to the very tip, given a sufficient duration and suitable 
arrangement of the experiments. 
It is likewise quite natural, that no veins form a sharp boundary 
to the starch strips on the side towards the leaf apex. 
These observations therefore also completely confirmed the view, 
that the above conception of carbon dioxide transport in leaves is the 
correct one. 
At the same time it will be clear that fundamentally this repre- 
sentation is the same for all the leaves examined. In net-veined 
leaves the transport areas are small and very sharply defined; in 
the parallel-veined leaves of Grasses, Acorus and Tradescantia 
they are small but less sharply defined; in the leaves of Hichhornia, 
Eucomis and Pontederia the whole leaf is one transport area. If it 
were possible to make experiments with the two first-named categories 
of leaves in an apparatus of the first type described, but of much 
smaller size, positive results as regards carbon dioxide transportation 
would then be obtained as readily as bas now been the case with 
leaves of the third category only. 
Lastly there is the question over what distance the carbon dioxide 
transport can extend in various leaves. 
We have seen that in Hucomis, Pontederia and Hichhornia carbon 
dioxide can be transported through a piece of leaf 3 cm. long under 
mercury and then even 1.5 em. farther through the apical portion, 
which was placed in air, free from carbon dioxide and of which the 
stomata were closed. As has already been said, we may assume that 
this distance is by no means the maximum one, but that it might be 
increased at will, on condition that the duration of the experiment 
were also increased as much as possible. 
In all the other leaves, however, it was found that the carbon 
dioxide could not reach the apex through the 3 cm. long portion. 
With some of these leaves experiments were now made in order to 
determine the maximum distance, through which carbon dioxide could 
be transported during the course of the experiment. These experi- 
ments were arranged as follows, The leaves, freed from starch, were 
45* 
