.32 EXPERIMENTAL PLANT PHYSIOLOGY. 



Cut off a shoot of some woody plant with tender leaves (Loni- 

 cera), and place the lower end in a vessel of water. Now cut off 

 the top and fasten to the end of the shoot, by means of a piece of 

 rubber tubing, a glass tube bent twice at right angles. Place the end 

 of the perpendicular long arm in a vessel of mercury. In a short 

 time the fluid ascends in the tube. 



EXPERIMENT 36. 



RESTORATION OF SAP-CURRENT. 



Fix an excised shoot of Coleus or Helianthus (Sunflower) by 

 means of a rubber stopper in one arm of a U tube and fill with water. 



Its power of conduction has been de- 

 stroyed and it wilts (See Experiment 28). 

 Now pour mercury into the free arm of 

 the tube. The turgor is restored, and is 

 retained until the mercury is higher 

 under the plant than in the other arm. 



EXPERIMENT 37. 



RATE OF ASCENT OF SAP. 



Water copiously the soil in which 2 

 herbaceous plant i meter in height is 

 growing, with a solution of lithium ni- 

 trate. In an hour cut a portion from 

 the tip and at successive intervals 

 toward the root. Burn these pieces 

 in the flame of an alcohol-lamp or Bun- 

 sen burner, and by the characteristic 

 red flame of lithium ascertain to what 



Restoration of sap-current, height the lithium has ascended in the 

 (Sachs.) stem< 



EXPERIMENT 38. 



MOVEMENT OF FLUIDS IN CONTINUOUS VESSELS. 



Cut away the stem of a Euphorbia (Spurge), Sonchus (Wild 

 Lettuce), or Asclepias (Milkweed). The milky juice exudes rapidly 

 from both the upper and lower cut surfaces in a manner indicative 

 of pressure. Cut away the stem of a Gourd or Pumpkin and note 

 the large drops of slime which must have been forced from some 

 distance, since that amount would not be found in the cells of the 

 part cut across. 



