1915] /. Arthur Harris and Ross /iiken Gortner 59 



loss of water but by the evaporation of some volatile constituent, or 

 eise by the decomposition of organic Compounds. There seems to 

 be some decomposition even when the drying is done in a water 

 Oven. Perhaps a more ideal method would be to dry in vacuo over 

 sulfuric acid without the aid of heat, but owing to the large num- 

 ber of samples with which we had to deal such a procedure was not 

 feasible. 



c 



Concentration = 



lod — 5 



where s is the solids in 10 c.c. and d is the specific gravity at 20°. 



G. Determination of the mean molecular weicht of 



THE SOLUTES. The average molecular weight of the dissolved 



substances is given by 



,, ^ 1860 



M = Conc. X ~7~> 



I 

 the calculation of which is facilitated by tables published else- 

 where in this Journal: 3, p. 259-263, 1914. 



4. Discussion of data. The individual constants are given in 

 the accompanying series of tables (2-21). Numbers in the left 

 hand columns are the laboratory numbers of the samples. 



A. Specific gravity and concentration. (Data, Tables 

 2-6 and 17-21.) These are the simplest possible measures of the 

 properties of the sap of the two kinds of tissues. 



It would be surprising if there were not distinct differences be- 

 tween the means of the specific gravities of samples taken from 

 separate cultures and at different times. The data for mean spe- 

 cific gravities in the appended summary are for the three larger 

 series : 



Experiment Wall Prolificatioa 



C 1.020168 + 0.000154 1.017831 + 0.000156 



D 1.019225 + o.oooiis 1.018125 + 0.000119 



E 1.020636 + 0.000231 1.019500 ± 0.000247 



