198 



PHYSIOLOGY OF NUTRITION. 



convenient to direct our attention first to the phenomena resulting 

 from root pressure. Vigorous pot plants of Cucurbita, Helianthus, 

 Bicinus or Begonia, or willow cuttings well rooted in flower pots, 

 are decapitated, i.e. the stem of the plant is cut through at a 

 point a few centimetres above the soil. In winter we may also 

 experiment with pot plants of Sanchezia nobilis (belonging to the 

 Acanthaceae).* Over the stump projecting from the soil is now 



FIG. 73. Appara- 

 tus for experiments 

 on root pressure. 



FIG. 74. Apparatus for experi- 

 ments on root pressure. (After 

 Pfeffer.) 



FIG. 75. Apparatus 

 for researches on root 

 pressure. (After Pfeffer.) 



slipped a short rubber tube (Fig. 73), fr, which serves to connect 

 it with a glass tube, st. In order to make the connections air- 

 tight, the rubber tubing is bound over the stem-stump and over 

 the glass tube with thread, or better with elastic. Just above the 

 connection tubing the glass tube is provided with a mark, m, easily 

 made with a three-cornered file. On filling the tube up to the 

 mark with water, we shall observe, if the plant had not been 

 transpiring too strongly before the commencement of the experi- 



* This plant, which serves exceedingly well, can be readily propagated by 

 cuttings. I found that a plant investigated in January gave sap for fourteen 

 days. 



