372 Messrs. F. Kidd, C. West, and G. E. Briggs. 



temperature rooms at low, medium, and high temperatures were utilised. 

 The results are presented in Tables I to III and figs. 1 and 2. 



Table I. — Eespiration of Heliantlms annuus at Low Temperatures. 



No. of 

 experi- 

 ment. 



Days 

 from 

 germina- 

 tion. 



Interral 

 between 

 gathering 

 and 

 placing 

 in 



tempera- 

 ture 

 chamber. 



Time in 

 tempera- 

 ture 



chamber 

 before 



estima- 

 tions 



started. 



No. of 



plants 

 used. 



Dry- 

 weight 

 of an 

 average 

 plant. 



Tempera- 

 ture 

 during 

 experi- 

 ment. 



Duration 



of 

 experi- 

 ment. 



Respiration 

 (Mgrm. CO. 

 per gramme 

 dry- weight 

 per hour). 



1 



12 



hours. 

 2-5 



hours. 1 



6 ' 



20 



mgrm. 

 197 



• C. 

 3-5 



hours. 

 41 -2 



1-28 



2 



14 



0-75 



2 



12 



184 



1 -8 



15 -2 



1042 



3 



15 



0-5 



4-75 



10 



180 



1 -0 



14-6 



0-97 



With regard to the respiration at 25° C, it will be seen that the rate falls 

 continuously after the first period of measurement, and that, as far as our 

 results show, the initial rate of respiration can only be determined approxi- 

 mately at this temperature by extrapolating the curve. In estimating the 

 initial rate of respiration at 25° G., we have assumed that the falling off has 

 been continuous. At 10° C. no falling off occurred for about twelve hours. 

 After this period the rate of respiration falls off, as is shown in Table II, 

 Experiment 3. Presumably, in the case of older plants, where the amount 

 of respirable material relative to respiring cell-matter is greater, the period 

 before the falling off commences would be longer, and such was actually 

 observed. Having found that at 10° C. there is no falling off for several 

 hours in the rate of respiration, we have used that temperature throughout 

 and have adopted it as the standard temperature of the respiratory index. 

 It will be seen later that the index may range from 3'0 to 0*08 for different 

 parts and ages of the plant. 



At this point, the evidence which justifies the application of the tem- 

 perature-respiration relation to the calculation of the respiration under the 

 conditions of fluctuating temperature obtaining in the field may be con- 

 sidered. 



At an early stage in the life of the plant, the actual respiration at the 

 fluctuating temperature obtaining in the field was determined continuously 

 for eight days (June 10, 1920, to June 18, 1920), fresh plants being used 

 every half day. 



The results of these determinations of the actual respiration were 



