550 



1 . Carbonic acid within growing vegetable cells and intercellular 

 passages suffers decomposition very rapidly on the penetration of 

 the sun's rays, oxygen being evolved. 



2. Living vegetable cells, in the dark, or not penetrated by the 

 direct rays of the sun, consume oxygen very rapidly, carbonic acid 

 being formed. 



3. Hence, the proportion of oxygen must vary greatly according 

 to the position of the cell, and to the external conditions of light, and 

 it will oscillate under the influence of the reducing force of carbon- 

 matter (forming carbonic acid) on the one hand, and of that of the 

 sun's rays (liberating oxygen) on the other. Both actions may 

 go on simultaneously according to the depth of the cell ; and the 

 once outer cells may gradually pass from the state in which the 

 sunlight is the greater reducing agent to that in which the carbon- 

 matter becomes the greater. 



4. The great reducing power operating in those parts of the plant 

 where ozone is most likely, if at all, to be evolved, seems unfavour- 

 able to the oxidation of nitrogen ; that is under circumstances in 

 which carbon-matter is not oxidized, but on the contrary, carbonic 

 acid reduced. And where beyond the influence of the direct rays of 

 the sun, the cells seeni to supply an abundance of more easily oxi- 

 dized carbon-matter, available for oxidation, should free oxygen or 

 ozone be present. As nitrates are available as a source of nitrogen 

 to plants, if it were admitted that nitrogen is oxidated within the 

 plant, it must be supposed (as in the case of carbon) that there are 

 conditions under which the oxygen compound of nitrogen may be re- 

 duced within the organism, and that there are others in which the 

 reverse action, namely, the oxidation of nitrogen, can take place. 



5. So great is the reducing power of certain carbon-compounds of 

 vegetable substances, that when the growing process has ceased, and 

 all the free oxygen in the cells has been consumed, water is for a 

 time decomposed, carbonic acid formed, and hydrogen evolved. 



The suggestion arises, whether ozone may not be formed under 

 the influence of the powerful reducing action of the carbon-com- 

 pounds of the cell on the oxygen eliminated from carbonic acid by 

 sunlight, rather than under the direct action of the sunlight itself 

 in a manner analogous to that in which it is ordinarily obtained 

 under the influence of the active reducing agency of phosphorus 



