50 
carbonic acid are a little smaller than they should be in reality, in 
consequence of peculiarities inherent to the method and already 
explained; but as this diminution, which is almost insignificant, is 
equally present in all the quantities, the result is that the numerical 
quantities are always comparable, although the ratio may be dimin- 
ished in an inappreciable degree. Finally, I may add that the con- 
clusions which follow are only applicable to plants under precisely 
the same conditions as those under which my experiments were 
conducted. 
(1) I note, first, that experiments Nos. 3 and 4 confirm in the most 
precise manner the general fact of the accelerating influence exer- 
cised by light upon the absorption of oxygen; but, these experiments 
having been carried out at a higher mean temperature, the differences 
in the quantity of oxygen absorbed in the light and in the dark are 
generally less than in the first series of experiments. 
-(2) As to the exact relative quantities of carbonic acid exhaled, 
it was a little more for the castor-oil plant in the dark than in the 
light, the contrary being the case for the scarlet runner bean. From 
this we might conclude that the influence of light produces doubly 
favorable effects upon the germination of the castor-oil plant, (a) by 
increasing the absorption of oxygen and (0) by diminishing the 
exhalation of carbonic acid, thereby increasing the gain of oxygen 
by reducing the expenditure of carbon and oxygen. (It must not 
be forgotten, in this explanation, that one volume of carbonic acid gas 
contains one volume of oxygen.) From this particular point of 
view the scarlet runner bean seems to be less favored than the castor- 
oil plant, although the excess of the quantity of carbonic acid exhaled 
by either placed in the light is nearly insignificant when compared 
with that exhaled by the same species kept in the dark. 
a: 
nO: , 
(3) In the dark the ratio Ra as determined by four experiments 
divided equally between the seed of the castor-o1l plant and those of 
the haricot bean, was at least a third more in favor of the latter than 
the ratio obtained for the castor-oil plant. The length of the experi- 
ment appears to me to have exercised a certain influence upon this ratio. 
Thus, for the castor-oil plant the figures reached 0.586 in experiment 
No. 2, which lasted about four days, and 0.771 in experiment No. 3, 
which lasted five days. The same was the case with the haricot bean; 
the result was 1.138 for experiment No. 4, which terminated during 
the fourth day, and 1.034 for experiment No. 5, which was prolonged 
until the sixth day. In a word, the prolongation of the experiment 
COs cs ; BA 
tends to render the ratio ~¢~ equal to unity. With the duration of 
the experiment this ratio rises in those cases where it is below 1, but 
diminishes where it is above 1, until the seed is consumed and the 
period of vegetation, properly so called, arrives, during which latter 
time the final limit may be reached when the quantities of oxygen 
absorbed and the carbonic acid exhaled balance perfectly. 
i 
(4) In the light the ratio a is about a third more for the 
