( 652 ) 
9 em. diameter was fastened down with resin and wax. Mercury 
was poured into the annular space g and concentrated caustic potash 
into the small Petri dish /. A glass bell-jar 4 of 3.2 litres’ capacity 
was placed in the mercury, so that the air inside the jar was kept 
free from carbon dioxide. It was now possible to introduce the apex 
of a leaf, which had been freed from starch, into the carbon dioxide- 
free space through the mercury. The leaf base and the petiole thus 
remained outside the bell-jar 4, and the petiole was always immersed 
in a dish of water in order to keep the leaf fresh throughout the 
experiment. A piece of metallic gauze was always placed over the 
small Petri dish 4 in order to prevent the leaf from coming into 
contact with the caustic potash. The base of the leaf could now be 
left at will in the open air with its unlimited supply of carbon 
dioxide at great dilution, or the base could be surrounded with an 
atmosphere ricber in carbon dioxide. For the latter purpose the whole 
apparatus was placed on a tripod in a large porcelain dish, partly 
filled with. water. A large glass bell-jar of 38 litres’ capacity was 
placed over the apparatus containing the leaf, so that the space in 
the large bell-jar was cut off by the water in the porcelain dish. 
Into this space any desired quantity of carbon dioxide could be 
introduced. Finally attention may be drawn to the tubes 7 and &, 
which connected the interior of the small jar with the free atmos- 
phere. This prevented differences of pressure between the interior 
and the exterior from raising the jar and establishing a communication 
between the outside and the inside. Moreover a stream of air, free 
from carbon dioxide, could be passed by these tubes through the 
inner jar. For this purpose the tube £ was connected to an aspirator, 
and the tube 7 to absorption tubes for the carbon dioxide of the 
atmosphere. 
With this apparatus a number of experiments were carried out, 
in some of which the base of the leaf was in the ordinary atmosphere, 
and in others in an atmosphere with much carbon dioxide. The 
portion of the leaves which was underneath the mercury had in all 
the experiments a length of 3 centimeters. These experiments led to 
the result, that not only in Dahlia and Pontederia leaves but also 
in all the other leaves investigated, a narrow strip of starch was formed 
in the space free from carbon dioxide at the border of the mercury. 
This strip was generally coloured jet black by iodine. 
The following table summarizes a number of experiments performed 
in this manner. 
In all these experiments the small starch strip was of course bordered 
on the side of the mercury by a straight line, but towards the apex 
heh, har 
