THE PLANT 31 



This closure of the stomata brings about other effects 

 which may be roughly described as starvation, since 

 carbon dioxide gas can no longer pass into the leaf, 

 where it would be built up into sugar for the food of the 

 plant. The result is that the plant, as a result of its 

 water-greed, leads a rather miserable existence every 

 afternoon in hot sunny weather. 



The story of its average day is roughly thus : Stomata 



open with the sunrise, and open wider as the light gets 



stronger, the formation of sugars beginning 



ay s and increasing as the day gets warmer, till 

 Events. 



carbon dioxide may be taken up as fast as 



a free surface of caustic potash could take it, and the 

 weight of the leaves increases rapidly. Growth has mean- 

 while slowed down or stopped entirely, according to the 

 wetness of the soil and the humidity of the air. Presently, 

 at some hour after 9 a.m., depending on the same con- 

 ditions, the plant has dried up the soil in the immediate 

 vicinity of its roots by taking away more water than can 

 be replaced by capillary movements among the soil 

 particles, and the stomata begin to close, while growth is 

 entirely stopped. This closure of the stomata checks 

 the formation of sugars, by cutting off the supply of 

 carbon dioxide, and the transport of sugars, etc., into the 

 body of the plant being no longer compensated by the 

 formation of new supplies, the dry-weight of the leaf de- 

 creases. The plant remains thus during the afternoon 

 until sunset, when the water-loss ceasing growth is 

 resumed, often quite suddenly. During the night the 

 rate pf growth is controlled by the night temperature 



