50 



carbonic acid are a little smaller than the}' 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, akhough 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. 8 and 4 confirm in the most 

 l^recise 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 i^lant. (a) by 

 increasing the absorption of oxygen and {b) 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. 



CO. 

 (o) In tlie dark the ratio T) ^' as determined l>y four experiments 



divided equally between the seed of the castor-oil plant and those of 

 the haricot bean, was at least a third more in favor of the latter thari 

 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 0.7T1 in experiment No. 8, 

 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 



tends to render the ratio -t^ equal to unity. With tiie duration of 



the experiment this ratio rises in those cases Avhere 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 M'hich latter 

 time the final limit may be reached when the quantities of oxygen 

 absorbed and the carbonic acid exhaled balance perfectly. 



(4) In the light the ratio - - is about a third more for the 



