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



Table VII. 



Dates and tunes of experiment. 



Dry- 

 weight 



or a 

 single 

 plant. 



Physio- 

 logical 

 mean 

 tempera- 

 ture. 



Mgrm. of COo 

 per gramme 

 dry-weight 



per hour 

 calculated 



for 10' C. 



Respira- 

 tory 



index for 

 mean 

 plant. 





grm. 



° C. 







5 P.M., June 26, to 10.5 a.m., June 27 



5-68 



16 -0 



1 -58 



2-00 



4.20 P.M., July 15, to 7.10 A.M., July 16 



51 -4 



12 -G 



1 -28 



0-96 



4.3 P.M., July 19, to 12.10 p.m., July 20 



62 -5 



15-3 



0-94 



0-97 



2.3 p.m., Aug. 17, to 8.26 p.m., Aug. 17 



227 



16 -7 



0-69 



0-58 



7.32 P.M., Sept. 11, to 9.34 a.m., Sept. 12 ... 



354 



6 -8 



0-26 



0-30 



The evidence from uncut plants in the field corroborates that derived from 

 cut plants in the laboratory to the extent that there is continuous falling off 

 in the respiration with age, and, moreover, the values given are of the same 

 order. The agreement is not very close, three being higher and two lower 

 than the respiratory index of the average plant at the same date. In view 

 of the following considerations, a close agreement is not to be expected. 

 Whilst in the case of the laboratory experiments the temperature of the 

 tissues was presumably that of the chamber, since suitable precautions were 

 taken, in the case of the field experiments there must have been a consider- 

 able lag before the cooling down or warming up of the bulky tissues was 

 accomplished. Again, whilst in the laboratory the volume of the respiration 

 chamber was minimal, the airtight fabric collapsing closely round the plant 

 tissue, such a condition was impossible in the field without unduly damaging 

 the plants. Further, by tying the leaves up they were subjected to a 

 continuous geotropic stimulus, which was exhibited when the plants were 

 untied by a decided downward movement of the leaves, which took up a fixed 

 position with the petioles pointing almost vertically downwards. Another 

 possible source of error attaching to the field experiments lies in a possible 

 inaccuracy in the allowance made for the carbon dioxide-content of the air; 

 but this, however, could only slightly affect the results. Finally, the propor- 

 tion of leaf to stem was not that of a mean plant and could not be allowed 

 for, since the respiration of the leaves and stem could not be determined 

 separately. 



