( 662 ) 
Mr. Zijrsrra succeeded in giving a complete account of these 
phenomena by the study of the anatomical structures of the various 
leaves used in the experiments. 
The speaker begins with those cases, constituting the majority, in 
which starch-formation only took place at the expense of the 
respiratory carbon dioxide. 
The carbon dioxide of respiration, produced by the living cells, 
will of course diffuse into the intercellular spaces, and as these are 
connected up for longer or shorter distances, we may indeed assume 
that a transportation of carbon dioxide will in the first place take 
place by diffusion along this route. 
Further we must consider, that the veins generally have far fewer 
intercellular spaces than the parenchyma; indeed, they may have 
none at all. 
In this connexion a fact deserves notice, to which repeated attention 
has already been drawn in the above, namely, that the starch strips 
were generally sharply defined by veins on the side opposite to 
the carbon dioxide supply, so that it gave the impression, as if these 
formed a barrier across which the starch-formation could not 
extend. The edge of the starch strip was therefore frequently toothed 
in an irregular manner. In the Dahlia leaf, which is coarsely 
reticulate, the strips of starch came out largest in all experiments; 
especially in those places where the veins happened to be a little 
more remote from the border-line between carbon dioxide production 
and carbon dioxide consumption, the starch had spread furthest, and 
then there was often no sharp delimitation. In leaves with very fine 
meshes between the veins, such as those of Aesculus and Acer, the 
starch zones were correspondingly narrow. 
In parallel-veined Monocotyledonous leaves on the other hand, 
as for instance in the experiments with Acorus, Zea, Hordeum, 
Triticum and Tradescantia, there was no relation between the edge 
of the starch strip and the small transverse veins. On the contrary, 
in these leaves the starch strip was generally seen to be straight on 
the side facing the apex of the leaf and not sharply defined; it faded 
away gradually, albeit fairly rapidly. 8 
These observations led to an anatomical investigation of the various 
leaves used in the experiments, especially with a view to answering 
the question, to what extent their veins, in the absence of intercel- 
lular spaces, formed barriers, across which the carbon dioxide could 
not move at all, or only very slowly. Should this really prove to 
be the case witb the leaves employed, then the simplest interpretation 
of the observed facts would be, that the carbon dioxide can indeed 
