362 BOTANICAL GAZETTE [may 



was calculated from the tangents of the curves of intake, using 

 a string and protractor for measuring the tangents. This is a 

 very crude and inaccurate method, especially in unskilled hands, 

 but one easily used. They assert that the velocity of water absorp- 

 tion is almost exactly an exponential function of the temperature. 



A short time previous to the appearance of this work the 

 writer (3) had found that the seeds of Xanthium have semipermeable 

 coats, and experiments on the influence of temperature on the rate 

 of moisture intake by these seeds were in progress at about the 

 time that Brown and Worley's paper appeared. The results of 

 the work, however, did not receive careful mathematical considera- 

 tion until about two years later, when it was found that the con- 

 clusions reached by Brown and Worley from their work on barley 

 seeds could not be drawn from the data which had been obtained 

 from Xanthium seeds. A preliminary report of the work was 

 made before the Botanical Society of America at the Columbus 

 meeting in 191 5. The data which had been obtained indicated 

 that the value of Q I0 was approximately 1.5, somewhat higher 

 than the temperature coefficient of diffusion, but notably lower 

 than that of chemical processes. This situation is very similar to 

 that later reported by Denny (2) for the effect of temperature on 

 the rate of permeability of certain plant membranes to water. 



Shortly following the Columbus meeting a few tests were run 

 on seeds of Xanthium having a somewhat different environmental 

 history. Mainly, the seeds were older than those previously used. 

 The intake curves did not check very well with the former data, 

 and it was thought desirable to repeat the experiments with seeds 

 of the same species of Xanthium but of different genetic origin and 



environmental history. In this way it was felt that data might 



* 



be obtained regarding the variability in the rate of water absorption 

 in these seeds. The data which have been accumulated have been 

 subjected to a critical analysis, principally to insure accuracy in 

 the measurements of tangents. At the same time the possibility 

 of a rate law has been kept in mind; but from a study of absorption 

 in a number of cases I have decided that it would be unsafe or at 

 least premature to propose a rate law on the basis of data now 

 obtained. At the same time, the formulae presented may have 



