ASSIMILATION. 43 



paratively feeble in plants, and the great amount of surface 

 favours rapid cooling, no rise in the temperature is observ- 

 able except under special conditions, as in the case of 

 flowers at the time of fertilization, where a proper heat, that 

 is, the amount above that of the surrounding air of from 4° 

 to ro° C, has been observed. 



Assimilation. — Inorganic plant-food consists of com- 

 pounds usually containing a large amount of oxygen, and 

 as the substances formed by the plant from these compounds 

 contain very little oxygen, it follows that a large amount of 

 the last-named element is liberated by the plant and restored 

 to the atmosphere. The decomposition of carbonic dioxide 

 by the green parts of plants under the influence of light is 

 a rapid process, consequently the amount of oxygen liberated 

 into the air by this process during the day is greatly in excess 

 of the amount of oxygen removed during the same period 

 in the act of respiration. As the assimilation of carbonic 

 dioxide cannot be carried on by the plant in darkness, while 

 respiration continues, it follows that during the night the 

 vegetable kingdom produces the same effect on the atmo- 

 sphere as the animal kingdom does, that is, takes away 

 oxygen and adds carbonic dioxide. As already stated, 

 all fungi, and some flowering plants that are destitute of 

 chlorophyll, cannot assimilate carbonic dioxide, hence never 

 restore oxygen to the atmosphere, although such constantly 

 remove it in the act of respiration. 



Although carbonic dioxide is the staple substance from 

 which plants obtain the carbon and part of the oxygen 

 required for the formation of starch, yet the interesting 

 discovery has been made that the chlorophyllous cells of 

 many plants, both Cryptogams and Phanerogams, can form 

 starch from various organic compounds, such as cane-sugar, 



