The Work of the Leaves 



active months evaporates about 28,000 gallons of water" — an 

 average of about 187 gallons a day. 



In the making of starch there is oxygen left over — just the 

 amount there is left of the carbon dioxide when the carbon is 

 seized for starch making. This accumulating gas passes into the 

 air as free oxygen, "purifying" it for the use of all animal life, 

 even as the absorption of carbon dioxide does. 



When daylight is gone, the exchange of these two gases ceases. 

 There is no excess of oxygen nor demand for carbon dioxide until 

 business begins in the morning. But now a process is detected 

 that the day's activities had obscured. 



The living tree breathes — inhales oxygen and exhales carbonic- 

 acid gas. Because the leaves exercise the function of respiration, 

 they may properly be called the lungs of trees. For the respira- 

 tion of animals differs in no essential from that of plants. 



The bulk of the work of the leaves is accomplished before 

 midsummer. They are damaged by whipping in the wind, by 

 the ravages of fungi and insects of many kinds. Soot and dust 

 clog the stomates. Mineral deposits cumber the working cells. 

 Finally they become sere and russet or "die like the dolphin," 

 passing in all the splendour of sunset skies to oblivion on the leaf 

 mould under the trees. 



555 



