7 2 



end until it stands in the open limb at a rather higher level 

 than in the closed limb — viz., by eight to ten centimetres. A 

 pressure is consequently set up and water is forced into the 

 drooping shoot, which gradually revives and becomes turgid 

 again, a series of spasmodic jerks occurring as the plant gra- 

 dually becomes erect. The Indian Cress {Tropceolum ma/us) 

 is a very good plant to perform an experiment of this kind 

 on. It is noteworthy that the shoot remains turgid after the 

 pressure has become reduced to zero by the mercury in the two 

 sides of the tube coming to the same level, and even when the 

 mercury is raised up by the suction of the shoot in the same 

 arm of the tube to which the shoot is attached, so that a force 

 is now acting upon the section of the shoot in an exactly op- 

 posite direction to that in which it previously acted. This 

 shows that the forcing in of water is necessary only at first ; 

 afterwards the revived shoot has sufficient power of suction 

 even to raise a column of mercury to a height of several centi- 

 metres, and thus to replace the loss occasioned by transpiration 

 from the leaves. Hugo De Vries found that if rapidly-growing 

 shoots of plants with large leaves are cut off at the lower part, 

 which has become completely lignified, and are placed with the 

 cut surface in Avater, they remain for some time perfectly fresh. If, 

 however, they are cut through at the younger parts of their stem 

 and placed in water, they soon begin to wither, as we have seen. 

 This withering takes place more rapidly and more thoroughly 

 in proportion as the part where the cut is made is young and 

 not lignified. We can easily prevent this withering, however, 

 by making the section under water, and taking care that the 

 cut surface does not come into contact with the air. By these 

 precautions, the disturbing influences are reduced to a mini- 

 mum, and the conduction of water through the stem suffers no 

 interruption. For if we compare the length of time during 

 which a stem cut in water remains fresh, with that during 

 which a similar stem cut in air does the same, we will find 

 that the former will be much the greater. Or if we take 

 care while we are making the cut in air, that the leaves and 

 upper parts of the shoot lose only a very small quantity of 



