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Igtt] OVERTON—TRANSPIRATION AND SAP-FLOW 57 
the withering and final drying of the leaves, as has already been 
suggested by Dixon, is a difficult question. Although UrspRUNG 
and ROsHARDT were unable to observe such clogging substances 
in all of the plants experimented upon by them, they are entirely 
too conspicuous to be disregarded in Cyperus. Drxon (10) has 
also found clogging substances in Populus stems which have been 
treated with steam or hot water. 
I have also made experiments using decoctions of the stems of 
these plants as a water supply. After thorough sterilization of the 
decoction, cut stems were set init. Ina very short time the xylem 
becomes plugged for some distance with the same resinous sub- 
stance, judging from its reactions to alkanin, as stops the passages 
when steam is applied to a normal plant, while the phloem remains 
unstained. The leaves above soon lose their turgescence and 
rapidly fall off in the amount of water transpired. 
When fresh stems are set in water, the xylem vessels finally 
become plugged with dark-colored material, which is probably a 
decomposition product, due to decay or bacterial action. In order 
to be sure that the plugging of the stems set in the decoction was 
not due to bacteria, as UrspRUNG believes to be the case in Drxon’s 
experiments, I have examined both the solutions and the stems 
for the presence of bacteria and always with negative results. 
To further test Drxon’s hypothesis that heating a section of 
the stems causes substances to be formed which poison the plant, 
I have performed a series of experiments as follows. Nutrient 
solutions were made, in which a sterilized plant decoction instead 
of distilled water was used and the requisite salts added thereto.. 
Plants grown in such nutrient solutions very soon show signs of fad- 
ing and the leaves become discolored, behaving in all respects much 
like those with steamed stems. A plant was sealed in such a culture 
solution on June 3 and kept under the most favorable conditions; 
the bottle was sealed to keep the solution sterile. In 3 days there- 
after the leaves began to droop, and in 5 days began to show signs 
of discoloration along the veins; in 7 days the leaves were streaked 
with yellow and. appeared like those on steamed stems. A con- 
trol plant, which was set up in an ordinary nutrient solution in the 
same way at the same time, remained perfectly normal. The con- 
