192 BOTANICAL GAZETTE [September 



A young branch of Eucalyptus globulus, with ten pairs of 

 expanded leaves, all horizontal, stood in water four hours. The 

 xylem was then full of water, excepting the large pitted vessels 

 which contained bubbles occupying about half of their volume. 

 Both sides of the stem for 2*="" were cut away almost half through, 

 leaving only a very thin strip, whicli was protected against desicca- 

 tion wjth vaseline. The structure was so fine that in the outer part 

 of the xylem only the pitted vessels were clear cut and individ- 

 ually distinct. The lower end of the branch was tied into a glass 

 tube containing a little water over a meter of Hg, the other end of 

 which tube was swung down so as to subject the cut end to a pres- 

 sure of 9^°" Hg instead of 74"^™ (the atmosphere). Within five min- 

 utes the water began to disappear from the pitted vessels, which 

 were soon visibly empty. The spiral vessels (primary) were but 

 little later losing their water ; while it was more than half an hour 

 before the lumina of the wood fibers became generally empty. 

 During the first part of this time the cut end was in contact with 

 water, the rubber tube connecting the plant with the glass tube 

 being bent i8o°, so that air escaping from the branch would not 

 collect against it. The branch used up its stored water, then, 

 not because other water was not at hand, but because it cannot 

 absorb it when the pressure is only 9*=°" Hg. After about fifteen 

 minutes the subject was kept horizontal under the microscope 

 and very likely water was no longer kept against the cut end. 

 To this point the experiment showed that, as Strasburgeriound, 

 while the conducting part of the wood fills with water when it 

 may be absorbed under the full atmospheric pressure, its lumina 

 become empty again when this pressure is removed. When the 

 leaves are called upon to exert a great suction, the continuous 

 threads of water whose cohesion might transmit it do not exist. 

 After the lumina became free of visible water, the suction 

 was removed, and the branch set in water for three minutes. Then 

 eosin was given drop by drop to the cut end. It was eagerly 

 absorbed, showing that the lumina had not filled to any con- 

 siderable extent with air from outside. Watching for the eosin 

 with the naked eve, it was between four and five minutes before 



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