186 FIXATION OF CARBON FROM THE ATMOSPHERE. DIGESTION. 



oxygen, which is absorbed ; and this appears to be principally 

 effected by the interior organs of the flower. It has been found 

 that an Arum-flower, whilst in bud, consumed in twenty-four 

 hours 5 or 6 times its bulk of oxygen ; during the expansion of 

 the flower 30 times; and during its withering, 5 times. When 

 the outer leafy parts of the flower were removed, it was found 

 that the oxygen consumed by the interior organs was much 

 greater in proportion. In one instance, the stamens and pistil 

 of an Arum consumed in twenty-four hours 132 times their bulk 

 of oxygen. It has also been observed that double flowers, in 

 which these internal organs are replaced by leafy parts, vitiate 

 the air much less than the single flowers, in which the former 

 are perfect. 



Fixation of Carbon. 



286. The process of Respiration, then, in Plants as in Ani- 

 mals, appears essential to the life and health of the system ; and, 

 though more energetic at some periods than at others, it is con- 

 stantly performed. If a plant be surrounded by an atmosphere 

 already vitiated, and be secluded from the influence of light, its 

 respiration will be (like that of an animal in similar circum- 

 stances) so much impeded, that its speedy death will follow. 

 But a very different result occurs, if it be exposed to strong or 

 even moderate daylight. The carbonic acid of the air will be 

 decomposed by the green parts of the surface of the plant ; and 

 the solid carbon will be fixed within its tissues, while the oxygen 

 will be set free, so as to restore the purity of the air. It is in 

 the performance of this function, that the leaves, from the extent 

 of the green surface they present, are peculiarly energetic ; for in 

 that of respiration, they only share with all the rest of the softer 

 portions of the exterior ; and in fact the dark surfaces seem to 

 have more to do in it than the light. 



287. Now this Fixation of carbon, as it is termed, which 

 antagonises so remarkably the effects of the process of respiration, 

 may be regarded as in some degree analogous to the function of 

 digestion in animals. In the solid food of all animals, whether 

 it be of an animal or vegetable character, carbon is one of the 



