58 Dr. H. T. Brown and Mr. F. Escombe. [Jan.. 9, 
Table VIII.—Direct Compsrison of the Increase in Weight during Insolation 
of the Leaf-Lamina of Catalpa bignonioides, with the Intake of CO, from 
ordinary Air, and the corresponding Amount of Carbohydrate formed. 





Carbohydrate 
Increased weight | CO2absorbed | formed per square 
of leaf-lamina by leaf per decimetre per 
per square square decimetre | hour deduced 
decimetre per per hour in from CO, 
hour in grammes. | cubic centimetres. absorbed, in 
| grammes. 
Experiment (1)......... 0:00983 1°41 0-00176 
, (ON ier aie 0:-00714 1°48 0:°00179 
7 CON ee 0-00260 2°35 0:°00294 
5: (Aig She 0:00722 2°33 0 -00292 
| INGA meer ee | 0:00669 0°00235 



A comparison of the first and third columns in the above table shows 
a very considerable discrepancy between these two methods of estimating the 
rate of assimilation. 
In only one case, that of Experiment (3), is there any kind of agreement 
between the results of the weighing method and that based on intake of 
carbon dioxide: in all other instances the Sachs’ method gives results which 
are far in excess of the direct method. If we take the mean of all four 
experiments we find that the Sachs’ method gives an estimate of the 
assimilation rate between two and three times greater than that deduced 
from the intake of carbon dioxide, a result which agrees fairly well with the 
previous experiments which were not carried out under conditions admitting 
of such rigorous comparison as those of Table VIII. 
The discrepancy is far too great to be accounted for by any under-estimate 
of the amount of carbohydrate equivalent to the fixation of a given amount 
of carbon dioxide, and can only be explained by some error incident to the 
Sachs’ method of determination. This is the more certain since in one 
experiment, the results of which are not recorded in Table VIII, the apparent 
dry weight of the leaf-lamina per unit-area was actually less after insolation 
of the leaf than it was before, although there had been an intake of carbon 
dioxide corresponding to the assimilation of 0:003 gramme per square decimetre 
per hour. Ae 
The great objection to the Sachs’ method is that all the various errors to 
