THE METABOLISM OF PLANTS. 



201 



2. When seeds are deprived of free oxygen the amount of CO 2 which 

 they exhale gradually diminishes. 



Seeds of Vicia Faba exhaled, in a Torricellian vacuum, for each 

 gramme weight, 



During the ist hour, 0*124 c.cm. CO 2 

 2nd 0*117 

 3rd 0-105 

 4th 0-098 

 5th 0-071 

 6th 0-071 

 7th 0-066 



Broughton obtained the following results with leaves of the Box : 

 5 grammes of leaves were placed under two bell-jars over water, the one 

 containing air, the other nitrogen ; the amounts of CO 2 in cubic centi- 

 metres evolved in 24 hours are given in the columns headed "Air" and 

 " Nitrogen." 



The gradual decrease, in both cases, in the volume of CO 2 - exhaled is 

 due to the diminished vitality of the leaves in consequence of their sepa- 

 ration from the plant. 



In concluding our consideration of respiration, we may 

 enquire whether or not the gaseous interchange of the plant 

 is affected by variations of the proportion of oxygen in the 

 surrounding atmosphere. It appears from the researches of 

 Rischawi and of Godlewski that the relation, whatever it may 

 be, between the amount of oxygen actually absorbed and that 

 of the carbon dioxide evolved, is unaffected by variations in 

 the composition of the atmosphere, except when those varia- 

 tions are so great as materially to affect the absorption of 

 oxygen (see p. 74). 



