G. E. Briggs, F. Kidd, and C. West 217 



with temperature may mean, either that it is temperature acting upon 

 stomatal opening or that it is growth (i.e. utilization of assimilated 

 material) governed by temperature which controls assimilation. More 

 definite evidence is required before an opinion can be given on this point. 

 We are attempting to obtain such evidence in the case of Helianihus. 



IV. A Comparison of Assimilation Values Determined by the 

 "Growth" Method with those Determined by "Gasometric" 

 and "Half-Leaf" Methods. 



We have thought it interesting to make a comparison of values of 

 assimilation calculated from results of growth experiments with values 

 obtained by the " half-leaf" method, with leaves attached to or detached 

 from the plant, and by the "gasometric" method with cut leaves. 



Unit Leaf Rate, as already stated, is the resultant of the real assimi- 

 lation, of salt-uptake and of the respiration of the whole plant per cm. 2 

 per week. The former takes place only during the hours of light; the two 

 latter proceed during the whole twenty-four hours of each day. If the 

 hours of illumination and the values for the respiration of the leaves and 

 of the whole plant and also the value for salt-uptake are known we can 

 calculate a value for the real assimilation or for the apparent assimilation 

 of the leaves. 



In arriving at our estimate of the real assimilation for maize we have 

 used Kreusler's data for the year 1877 since this is the only year for which 

 a full record of the light is available. We have utilised the values of 

 the Unit Leaf Rate for the eleven weeks subsequent to the fourth week 

 from sowing, thus omitting the low initial values, which we have good 

 reason to suppose are not the values for normal leaves, and the excep- 

 tionally high value at the end. The results from the "nach Auswahl" 

 experiment were used. 



The average Unit Leaf Rate for this period is 4-62 1 , and the total hours 

 of light for the eleven weeks number 1118, or a weekly average of 101-7. 

 The total of hours of light after allowance has been made as in column 4, 

 Table VI, is 959, or a weekly average of 87. Using the former value for 

 the light we obtain an average rate for increase in dry-weight per cm. 2 

 per hour of light of -0456, which is equivalent to 3-65 mgs. C0 2 per 

 50 cm. 2 per hour. Adopting the other figure for the light we obtain a 

 value of 4-25 mgs. CO., per 50 cm. 2 per hour. Making allowance for the 



1 The Unit Leaf Kate calculated on the exponential basis gives a value about -t % 

 smaller. The real value is intermediate between these two. 



