66 AERATION AND AIR-CONTENT. 



Pfeffer showed that the evolution of carbon dioxid in the air was 

 several times greater than in hydrogen, and Pasteur, Borodin, 

 Dehe'rain and Moissan, Vesque, and others that it is greatly reduced 

 in an atmosphere of CO 2 itself, continued exposure resulting in the 

 death of the plant. Pfeffer (1900) has stated that most land-plants 

 die eventually in an atmosphere containing from 4 to 20 per cent of 

 carbon dioxid. 



As would be expected, respiration under anaerobic conditions dif- 

 fers with the species, much as does normal respiration. This fact 

 may be readily gained from practically all experiments dealing with 

 two or more species, and it has been studied especially by several 

 investigators. De.herain and Moissan stated that in the absence of 

 oxygen the resistance of leaves to death varied greatly from species 

 to species and they confirmed this for roots as well. 



Godlewski found that the energy of respiration was much smaller in 

 starchy than in oily seeds during germination under reduced oxygen- 

 pressure, and starchy seeds also differed much among themselves. 

 The increased evolution of carbon dioxid under oxygen-pressure up 

 to 5 atmospheres varied with the species in the investigations of 

 Johannsen, while Pfeffer observed a wide range in the amount evolved 

 by seedlings in hydrogen from Vicia faba, which gave nearly equal 

 amounts in air and in hydrogen, to those in which the normal respi- 

 ration was several times greater. At 2 per cent of oxygen, Stich 

 showed that certain flowers, fruits, and seedlings respired normal 

 amounts of C0 2 , while others showed a marked decrease. Hill found 

 that ripe fruits which spoil quickly, such as cherries, respired more 

 intensely under anaerobic conditions than those that keep better, 

 such as grapes. 



Finally, Stoklasa and Ernest have determined that the roots of 

 rye secrete both formic and acetic acid in the absence of oxygen, but 

 those of buckwheat, oats, and corn acetic acid alone. 



Carbon dioxid and alcohol are the regular products of anaerobic 

 respiration, and the latter is consequently regarded by most investi- 

 gators as essentially identical with alcoholic fermentation when 

 carbohydrates are present. Under certain conditions it approaches 

 other types of fermentation, and acetic, formic, and lactic acids have 

 frequently been noted as excretions from the roots and other parts 

 of flowering plants. Among the fermentation products arising from 

 anaerobic respiration are amyl, butyl, and ethyl alcohols, acetic, 

 butyric, citric, formic, lactic, oxalic, propionic, and valerianic acids, 

 acid aldehyde, and acetone, while the decomposition products are 

 ammonia, fatty amido-acids, leucin, skatol, tyrosin, sulphureted hydro- 

 gen, mercaptan, etc. Hydrogen is a frequent product, and methane, 

 carbon monoxid, and nitrogen rarer ones (Pfeffer, 1900 : 533). 



