376 



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



determining variations with age in the value of the respiratory index and for 

 calculating the respiration in the field of a mean plant, the objection may be 

 raised that no allowance is made for the probable error of the respiration 

 value determined from a single plant. It is true that it would have been 

 hetter to have determined simultaneously the respiration of several indi- 

 vidual plants, and from the results obtained to have calculated the mean 

 result with its probable error. Such a procedure was impossible with the 

 facilities at our disposal. We can, however, apply the following correction to 

 our figures. Probably a principal cause of any extensive difference between 

 the respiratory index of one plant and that of another is the difference in 

 the relative proportion of stem to leaf, when the respiration of the stem 

 differs from that of the leaves. Knowing the difference between the 

 relative proportion of stem to leaf in the plant used for determining the 

 respiration and that in a mean plant, and having after the thirty-fourth day 

 from germination determined the respiration of the stem and leaves 

 separately, we have from this date onwards been able to make an allowance 

 for the effect of a difference in proportion of stem to leaf in calculating the 

 respiratory index of a mean plant. This correction, however, makes very 

 little difference. The figures for the respiratory index of a mean plant of 

 the harvest are given in Table 5. 



Table V. — Calculated Eespiratory Index of an Average Harvested Plant. 



Days from 

 germination. 



Dry-weight 

 ■of plant. 



Respiration per hour at 

 10° C. of an average plant. 



Respiratory index of an average 

 plant (mgrm. CO^ per gramme 

 dry- weight per hour). 





grm. 



mgrm. COj. 





1 



-0238 



0-071 



2-9 



8 



-0707 



0-212 



2-9 



22 



1 -128 



3-38 



3-0 



29 



4-53 



10 -4 



2-3 



36 



12-35 



14-9 



1 -2 



43 



26 '9 



27 -7 



1-03 



50 



60 -1 



56-1 



0-93 



57 



92 -8 



68 -8 



0-74 



64 



133 



91 -5 



0-69 



85 



352 



176 



0-53 



i 99 



559 



198 



0-35 



1 113 



765 



233 



0-31 



127 



873 



1 



345 



0-39 



It will be seen from the above Table that the value for the respiratory 

 index of the mean plant falls off continuously from 3 to about one-tenth of 

 that amount at the end of the life-cycle. 



■ When in the second place we consider the respiration of the various 

 parts of a plant, such as the stem, leaves, and flowers, we find a similar 



