182 



EXCHANGES AND MOVEMENTS OF FLUIDS 



The turgidity of the active cells is the chief factor in producing 

 the rigidity of the soft-bodied plants. 



253. Estimation of the Force of Turgidity in Tissues. Take an 

 actively growing flower stalk as those of the cowslip, honeysuckle, 

 plantain, or growing petioles of some acaulescent Oxalis, and 

 place in a concentrated solution of cane sugar for four hours. 

 The stalk should be about 100 g. in length. Before placing in 

 the solution, make a thin India ink mark near each end, and 

 measure the distance between the marks accurately with a milli- 

 meter scale. Take the stalk from the 

 solution and note its limp condition. Lay 

 on a piece of glass plate and measure the 

 distance between the marks and determine 

 the amount of shrinkage caused by the 

 plasmolysis of the tissues caused by the 

 cane sugar. Now lay on a board slightly 

 wider than the length of the stalk, and 

 clamp the thin end of the stalk to the 

 board by means of a screw and a piece 

 of wood or cork, leaving the ink mark in 

 sight. Tie a thin cord to the other end 

 and pass it over a small pulley set in the 

 edge of the board. Fix a small scale pan 

 to the cord and load weights into it until 

 the distance between the ink marks is 



restored to the original measurement. The amount of the 

 weights used represents the force exerted by the turgidity of the 

 stem. Measure the diameter of the stalk, and compute area of 

 cross section. Calculate the turgidity in atmospheric pressures. 

 A pressure of one atmosphere is equal to 10.3 grams per sq. milli- 

 meter. The weight of the scale pan should be taken into account. 

 The stalk may be suspended vertically and the pan hung to its 

 lower end when the weight of the pan and a fourth of the weight 

 of the stalk are to be added to the amount, which will still leave 

 a slight error. 



FIG. 88. Apparatus for 

 determining amount of tur- 

 gidity. A, wooden clamp. 

 B, board with pulley at R. 

 G, scale pan with weight. 

 After Detmer. 



