28 PLANT LIFE ON THE FARM. 



the existence of any direct connection between the absorption 

 of oxygen and the emission of carbonic acid, in plants, 

 because it has been shown that a green leaf placed in dark- 

 ness and in an atmosphere deprived of oxygen nevertheless 

 exhales carbonic acid, the emission of which under such 

 circumstances cannot of course be connected with any cor- 

 responding inhalation of oxygen. 



Though going on constantly, the energy of the oxidising 

 process is much less than that of the opposite deoxidising 

 process, carried on when the chlorophyll cells are exposed 

 to the light. Deprived of oxygen, the movements of the 

 protoplasm, the movements of the roots and of the leaves 

 cease, other manifestations of activity are put a stop to, 

 and the plant dies of suffocation. Moreover, it has been 

 shown that each cell consumes its own supply of oxygen, and 

 if that fails it will die, even though adjoining cells be pro- 

 vided with the gas. In this particular then the cells act, 

 not in concert, but individually (Van Tieghem). It is not 

 essential that the oxygen should be in a free state ; it may 

 be utilised by plants from a compound containing oxygen, 

 and from which it may easily be obtained. An instance of 

 this is afforded in the case of the disease of animals known 

 as " charbon," which is now known to be caused by the 

 existence in the blood of the animal affected of a microscopic 

 plant (Bacillus anthracis), which lives in the blood, and 

 which, not finding sufficient oxygen in its serum or liquid 

 portion, decomposes the matter contained in the red cor- 

 puscles and utilises the oxygen they afford. To live itself, 

 it deprives the creature in which it is established of its 

 oxygen, and thus not only kills it by suffocation, but 

 eventually cuts off its own supply of food. 



The effect of depming a plant which contains glucose of 



