4 H Dixon and Joly. — The Path of 
E was placed in mixed solution of tartaric acid and sodium 
bicarbonate which had ceased effervescing. 
After 1 1 hours A and C were interchanged in the solutions ; 
thus, in these two only was C0 2 developed. B served as 
a control regarding the effects of sodium bicarbonate alone, 
D ditto for tartaric acid, E ditto for the effect of the mixed 
solution without development of gas. In five hours A and 
C were very much, and about equally flagged, while the rest 
remained fresh. Next morning, however, all were drooped, 
showing that prolonged treatment with any or both of these 
salts is injurious in any case. It was evident also that the 
stoppage of the lumina by the gas had greatly accelerated the 
flagging. 
It is not probable that the check upon aeration of the tissues 
involved in all of the foregoing experiments wherein the lumen 
is choked could account for so rapid a flagging of the soft 
parts. However, to set this doubt at rest, we inserted branches 
in water which had been boiled and cooled in vacuo and coated 
with oil after the insertion of the branch. These, however, 
remained perfectly fresh, indeed they seemed in no way 
affected. 
Choking the Lumen by means of Ice or Water Vapour . 
In order to investigate this subject more fully an additional 
series of experiments were devised and carried out upon the 
passage of water through the wood of Taxus at very low and 
at very high temperatures. For it was very certain that in 
the one case the formation of ice, and in the other the forma- 
tion of steam, would occur in the lumen before occurring in 
the wall, rendering the former non-conducting without the 
introduction of any foreign substance. 
It was necessary to determine first of all the freezing-point 
of water in the lumen by direct microscopic observation. To 
effect this we used a form of cold stage which possesses certain 
advantages which induce us to add the accompanying figure 
(Woodcut 6) showing its construction. In this stage the object 
