Elementary Plant Physiology. 



although it might be done with equally marked results on 

 branches or trunks of any vigorous plant with a good absorbing 

 system, before the appearance of the leaves. 



52. Amount of liquid exuded in bleeding. — Cut off 

 the stem of an actively growing spec- 

 imen of Dahlia, Geranium, sun- 

 flower [Helianthus), grape (Vitis), 

 or tomato a short distance above 

 the ground, and fasten a long glass 

 tube to the stump by means of a 

 short section of rubber tubing passed 

 over the ends of both. Support 

 the tube in an upright position, and 

 keep the preparation well suppUed 

 with water, and place in a warm 

 room. Note the gradual rise of 

 exuded sap in the tube. A drop 

 or two of oil on the liquid in the 

 tube will prevent evaporation. 

 Four or five days later mark the 

 height of the column on the tube 

 and remove. Now determine the 

 amount of water necessary to fill 

 the tube to the given height (Fig. 



35)- 



The above experiment may also 

 be performed in another manner 

 by the use of a bent tube, the 

 end of which projects into a test 

 tube into which the exuding sap will flow (Fig. 36). 



53. Measurement of exudation pressure. — The force 

 with which hquids are thrown out of turgid cells may be meas- 

 ured approximately if some form of a gauge is attached to the 

 cut end of a stem, and the exuding liquid confined. It will be 



Fig. 35. — Glass tube attached 

 to stump of plant to collect the 

 sap exuded in bleeding. After 

 Detmer. 



