Table II.

Model choice: Comparison between models fitted to data of Figure 5

Model Class	I	II				III
Model No.	1	2	3	4	5	6
No. of Parameters Varying during Fit	1	1	2	2	3	3
	3.42 (ft)	3.36 (ft)	−2.5 (ft)	8.2 (ft)	3.01 (ft)	0.001 (ft)
	0 (fx)	0 (fx)	0.33 (ft)	0 (fx)	0.31 (ft)	0.38 (ft)
Delay (s)	0 (fx)	0 (fx)	0 (fx)	19.5 (ft)	15.4 (ft)	9.9 (ft)
Err (rel)	7.1222	6.9671	0.095	0.25542	0.04365	0.057295
Preferred model	−	−	−	−	+++	++

Six different models were fitted to 60-s-long records (including the delay) of volume changes of protoplasts exposed to hypotonic solution shown in Figure 5. The classes of models are based on different assumptions with regard to the dynamics of the specific osmotic permeability of the membrane, P_f (see text for details, and, in particular, Eqs. 5–7 in “Materials and Methods”). In all models, was a variable parameter and the other parameters, and delay, were either fixed (fx) or obtained as best-fit (ft) parameters in fitting the data of Figure 5. Err is the sum of squared departures of the data from the model, normalized, for the sake of comparison among various cells, to the number of points (hence independent of the duration of the data record or the sampling frequency) and to the value of baseline volume (hence independent of initial cell size).