236 PLANT AND ORGANIC CHEMISTRY 



Darwin * has shown that the insectivorous plants, by means 

 of their modified leaves, absorb complex compounds, and that 

 these are of importance in their nutrition. Flies and other small 

 insects may often be found clasped in the tentacles of the 

 Drosera, and in those experiments small pieces of meat, when 

 placed on the leaves, were dissolved after a time by the secre- 

 tions of the leaf glands and absorbed. 



Hydrogen is absorbed by all plants in combination in the 

 form of water or ammonia and its compounds, or in the com- 

 plex substances mentioned above. 



Oxygen is taken up by plants, free or in combination in water 

 or in salts. The free oxygen is especially concerned in destruc- 

 tive metabolic processes. The large quantities of this gas ab- 

 sorbed by plants, and especially by fungi, show conclusively 

 its consumption in metabolic processes. 



The process known as the respiration of plants is the absorp- 

 tion of oxygen and the exhalation of carbon-dioxide. 



The researches of Garreau 2 show that two distinct processes 

 are in operation when leaves are exposed to the light : in the one 

 oxygen is absorbed and carbon-dioxide is exhaled; in the other, 

 carbon-dioxide is absorbed and oxygen is exhaled. When the 

 leaves are exposed to a very bright sunlight, carbon-dioxide is 

 absorbed and oxygen is exhaled, and the activity of these pro- 

 cesses is so much greater than the absorption of oxygen and the 

 exhalation of carbon-dioxide, that it appears as if the former 

 only were in operation. 



Gases, like solids, can be assimilated only in solution, and as 

 they are soluble in water, the cell walls of submerged plants 

 may absorb them, and the sap near the surface of land plants 

 will dissolve the gases from the atmosphere. The sap of plants 

 contains, in solution, carbon-dioxide, oxygen, and also a certain 

 amount of free nitrogen. That this nitrogen does not enter into 

 the metabolism of the plant seems completely decided by the 

 experiments 3 of Lawes, Gilbert, and Pugh; but the more recent 

 experiments of Atwater 4 and Hellriegel 5 should be compared 



1 Insectivorous Plants. 2 Ann. d. Sci. Nat., ser. 3, t. xv. 



3 Phil. Trans., 1860. 4 Amer. Chem. Jour., viii, Nos. 5 and 6. 



5 Zeit. d. Ver. j. d. Rubenzucker Industrie, Nov., 1886. 



