1908.] 



PUBLIC DOCUMENT — No. 33. 



77 



It is now an easy matter to draw the lino A B, forming the axis 

 along which these dots cluster, and which may be assumed to 

 be the theoretical locus of them all. 



Having now this average of values shown in the line A B, 

 we may take any time values, as 100 hours and 150 hours, and 

 find immediately the corresponding sum temperatures, — 3,140 



& <3 



Z800 



120 iao 



FIG. 3. 



and 3,445 degree-hours. Substituting these values in the 

 equation already formed, we find the value of x to be 6.2°. 

 Adding this amount to 32°, the base from which we are com- 

 puting, we have 38.2°, the critical temperature for the ger- 

 mination phase of cress. 



The constant sum temperature above 38.2° required for the 

 germination of cress should now be easily found by subtract- 

 ing from each sum temperature as taken the amount of tempera- 

 ture intervening between 32° and 38.2°. This is secured simply 

 by multiplying the elapsed time by 6.2°. 



Applying this method to the records in hand, we find that 



