MOVEMENT OF WATER IN PLANTS. 
683 
. Among the most remarkable of the phenomena related to this is the fact that the 
younger terminal portions of the stems of large-leaved plants partially lose the power 
of conducting water when cut off in air. If the cut leafy end of the stem of Helianthus 
annuus, H. tuberosus, Aristolochia Sipho, &c. be placed with the cut section in water, the 
suction is not sufficient to compensate the evaporation from the leaves, which therefore 
wither after a shorter or longer time ^. As I have already shown in the second edition 
of this book, the withered shoot may in a short time be revived by forcing in water by 
means of the contrivance represented in Fig. 468. I did not discover till afterwards that 
the shoot remains turgid even when the pressure is reduced to zero, and even when 
the mercury is raised up by the suction of the shoot in the same arm of the tube (^), 
when therefore a force acts on the section of the shoot in the opposite direction. 
This shows that the forcing in of water is only necessary at first, but that the revived 
shoot has itself sufficient power of suction to raise up a column of mercury several 
centimetres in height, and thus to replace the loss by transpiration from the leaves. 
Thus much was known about the phenomenon of the withering of cut shoots placed in 
Fig. 468.— Apparatus for showing the revival of witliered shoots by forcing vi'ater into them. The U-shaped glass 
tube is first filled with water, and the perforated stopper of caoutchouc k in which the stalk of the plant is inserted 
is then fixed in. When the shoot is withered, as represented by a, mercury is poured into tiie other arm of the tube, 
so as to stand at q' some 8 or locm. above q, and the shoot then revives, as represented by b, even when the level <? 
becomes subsequently higher than q'. 
water, when Dr. Hugo de Vries '^ took up the further investigation of it in the laboratory 
of the Würzburg Institute. The results obtained by him I will now quote: — 
* If rapidly-growing shoots of large-leaved plants are cut off at their lower part 
which has become completely lignified, and are placed with the cut surface in water, 
they remain for some time perfectly fresh. But if they are cut through at the younger 
parts of their stem and are then placed in water, they soon begin to wither, and the 
more rapidly and completely the younger and less lignified the part where the section is 
made. This withering can be easily prevented by making the section under water, and 
taking care that the cut surface does not come into contact with the air, the conduction 
^ [Von Höhnel has shown (Bot. Zeitg. 1879) that the rapid loss of conductivity for water shown 
by branches which have been cut off and placed in water is due to the fact th-at the contents of the 
injured cells escape and form a layer on the cut surface ; this becomes infested with Bacteria, and 
these form a membrane (zoogloea) over the surface which prevents the absorption of water.] 
^ [Arb. d, bot. Inst, iu Würzburg, I. 3, 1873; Ueb. das Welken abgeschnittener Sprosse.] 
