II2 BOTANICAL GAZETTE [FEBRUARY 
diminished water supply cannot be due to this, since the leaves do 
not wither at once, but remain for some time turgid. I have 
described the progressive effect which steaming the stems of Cyperus 
has on the withering of the leaves, but I attribute this progressive 
injury, which finally results in the death of the leaves, to the intro- 
duction of injurious substances from the dead cells. The presence 
of these poisonous or plasmolyzing substances seems to account 
for the final withering or drying of the leaves. The leaves first 
die and then dry, as Dixon puts it. The leaves do not die from 
lack of water supply, as UrspRUNG would have it, but because they 
are killed. 
Not only are the cavities of the vessels plugged with a brownish 
mass, but the walls of the conducting tubes are tinged with yellow. 
It seems quite probable that the presence of some substance in the 
walls of the tubes may lessen their power of conduction also. DIxoNn 
(10-12), as noted; has observed the presence of a substance which 
stains the walls of the vessels and thinks that “it would be hard to be- 
lieve that the deposit of this colored substance in the walls and lumina 
of the tubes could be without effect on their efficiency in transmit- 
ting water.” I have already described a similar brownish appeat- 
ance of the walls of the vessels as well as the plugging of the lumina 
for some distance above the cut end of a stem of Cyperus standing 
in a sterilized decoction of the same plant. SCHWENDENER’S (28) 
researches, tending to show that heating the stem does not change 
the physical character of the cell walls of the tubes, and that the 
micellar structure and imbibitional power is not affected by such 
treatment, probably do not take sufficient account of the action 
of poisonous substances caused by heating the stem on the structure 
of the walls of the vessels and the efficiency of their conductivity: 
From my experiments it is clear that changes in conductivity and 
in the amount of evaporation are brought about by killing the 
plant with such substances as chromic acid, picric acid, and HgCl,, 
often accelerating evaporation to a very marked degree. 
I have repeatedly shown that when stems are set in a decoction 
of the same plant, the leaves wither much earlier than those set iD 
water. Additional evidence that injurious substances are engen- 
dered by heating the plant was obtained by growing Cyperus 
