Ld 
( 664 ) 
also formed rather narrow and not very sharply defined starch strips. 
As regards the grass leaves of Hordeum, Triticum and Zea Mays, 
the transverse veins, which connect the longitudinal veins, are here 
indeed insignificant; the vascular bundles by no means fill up the 
whole thickness of the leaf and much parenchyma remains above 
and below. Investigation showed, however, that in transverse section 
the intercellular spaces of this latter parenchyma are very narrow, 
although they extend pretty far longitudinally. When passing through 
this parenchyma above and below the veins, the carbon dioxide is 
therefore checked very much more than in the general parenchyma 
between the veins, and its course must be much less rapid, although 
it is not stopped completely. In accordance with this, only narrow 
starch strips were formed in these leaves in the limited duration of 
the experiments, which lasted generally for 6, or at most for 7 hours. 
In other words, the carbon dioxide transportation was very limited, 
so that a transference of carbon dioxide across a greater interval 
than 3 em, in the apparatus first described, was an impossibility. 
The transverse anastomoses of the veins did not however, sharply 
define the starch strips. 
The leaves of Acorus and Tradescantia behaved similarly in the 
experiments performed. In the green parenchyma of Acorus only small 
intercellular spaces occur and here some veins moreover take up 
the whole thickness of the leaf, the colourless central parenchyma of 
the leaf contains it is true many large spaces which extend longi- 
tudinally, but at frequent intervals they are shut off by transverse 
cell-layers, diaphragms without intercellular spaces. Lastly Tradescantia 
has a very spongy assimilating tissue, but in it many vein-anasto- 
moses occur, which only have minute intercellular spaces. In these 
cases too therefore the agreement between the anatomical structure 
and the experimental result was sufficient to warrant the acceptance 
of the above view. 
Finally the question arose how the intercellular spaces are distri- 
buted in the leaves of Pontederia, EHucomis and Eichhornia, which, 
as is evident from the experiments of table 2, are much better 
adapted for carbon dioxide transportation, so that in the apparatus 
employed this gas could he carried from the leaf base to the apex. 
The anatomical investigation of these leaves yielded the following 
result. The leaf of Mucomis is parallel-veined, the whole of the 
leaf-parenchyma is very spongy, and the longitudinal as well as 
the transverse veins are very insignificant, so that carbon dioxide can 
everywhere pass freely. There are still better gas passages in the 
curved-veined leaves of Eichhornia and Pontederia. In both these 
