50 Dr. H. T. Brown and Mr. F. Escombe. [Jan. 9, 
Table IIJ.—Total Assimilation per Square Decimetre of Leaf per Hour, 
according to Sachs. 




_ Grammes increase per Equivalent of CO, 
Be ae a ee cimetre per in cubic centimetres. 
our. 
Helianthus annuus  ..cccccceese 0:01882 15:00 
CMBUDULG RCD Oly ae sacetorescteh desc 0°01502 | 19g 



In repeating these experiments in 1892, Brown and Morris* obtained the 
following results by the Sachs method, in which no correction is made for 
the assumed simultaneous depletion in the case of the leaves still attached to 
the plant. 
Table IV. 

| 
Grammes increase per 
Equivalent of CO, 
in cubic centimetres. 
square decimetre per 
hour. 
Expt. 1. Helianthus annuus— 
| SAL Detached leat ............ 0-00985 7°85 
| B. Still attached to plant .. 0-00460 3°66 
| Expt. I. Helianthus annuus— 
i SAY Detached leatec. 3s. t-5. 0:0100 or OF 
|B. Still attached to plant... 0:0071 5°66 


When we compare the results of Table I obtained for Helianthus by direct 
determination of the carbon dioxide taken in by the leaf with those deduced 
by Sachs from his weighing method, we find a very great discrepancy, the 
apparent rate of assimilation in the former case being only one-third to one-fifth 
of what it is in the latter. On the other hand, in the experiments of Brown 
and Morris, where diurnal depletion of the leaf is not assumed, the discrepancy 
is less, but even here, in the case of the detached leaves, the weighing method 
has given an apparent rate of assimilation about double that of the direct 
method by CO, measurement. | 
In considering the probable cause of these discrepancies we must first 
* * Journ. Chem, Soc.,’ 1893, Trans., p. 625. 
