548 



Prof. A. J. Brown and Mr. F. P. Worley. [Aug. 9, 



temperatures are the same only when equal quantities of water have been 

 absorbed, the rates of entry of water at the three temperatures were deduced 

 at points where amounts of water corresponding to 5, 7'5, 10, 15, 20, and 

 25 per cent, increase in weight had been absorbed in each case. Higher 

 percentages were not dealt with, on account of the possible influence of 

 secondary changes in the latter parts of the experiments. 



The rates were deduced from the curves drawn carefully to express the 

 result (Diagram I), by finding the values of the tangents at the required 

 points by means of a stretched thread. The rates thus obtained, expressed 

 in terms of the amount of water (percentages of initial weight) absorbed per 

 hour, are given in the following table : — 



Table II. 







Velocity. 









Water already 









Velocity at 21 -1° 



Velocity at 34 -6° 



absorbed. 



At 3 -8°. 



At 21 -1°. 



At 34 -6°. 



Velocity at 3 -8°. 



Velocity at 21 -1°' 



per cent. 

 5-0 



0-506 



1-72 



4-50 



3-40 



2-62 



7-5 



0-416 



1-51 



3-83 



3-63 



2-54 



10-0 



0-356 



1-27 



3-07 



3-57 



2-42 



15-0 



0-282 



0-897 



2 -30 



3 -18 



2-56 



20 -0 



0-216 



0-679 



1-68 



3-14 



2-47 



25 -0 



0-164 



0-570 



1-16 



3-48 



2-04 



Mean 



3-40 



2-44 



If the sequence of ratios at the three different temperatures be compared, 

 it will be seen that there is an approach to constancy in their relation ; that 

 this is the case is more clearly seen, however, on examination of the numbers 

 in the fifth and sixth columns of the table, which express the proportional 

 values obtained from a comparison of the three series of ratios. 



Taking the mean values of the ratios, it appears that the velocities with 

 which absorption takes place at the three temperatures 3-8°, 21'1°, and 34-6° 

 are in the proportion of 1 : 3"40 : 3-40 x 2'44, i.e. 1 : 3"40 : 8-30. 



The temperature coefficient is obviously high and of the order of that of a 

 number of chemical actions occurring in solution. Moreover the velocity with 

 which water is absorbed by the seeds is almost exactly an exponential function 

 of the temperature. If this be so, the logarithms of the velocities plotted 

 against the temperature should lie on a straight line. The results obtained 

 on plotting the logarithms of the velocities given in Table II, including those 

 of mean ratio of the velocities, are given in the following diagram. 



