14 AERATION AND AIR-CONTENT. 



Miiller-Thurgau (1885 : 857) found that potato tubers respired 

 more vigorously just after being harvested than they did several 

 days later. But tubers that were separated from sound stocks re- 

 spired about doubly. Ultimately, however, the respiration sank to 

 about the same level and then remained constant for a long time 

 during the resting condition of the potato. 



In an investigation of the relation of cell-turgor in growing organ- 

 isms to respiration, Palladin (1886 : 328) reached the following conclu- 

 sions : Since the absorption of oxygen is necessary for the production 

 of substances which cause turgor, it is to be expected that the latter 

 will be reduced by lack of oxygen, and, in fact, plants that have 

 lived some time without oxygen appeared to be withered. In 

 growing organs the accumulation of the organic acids that produce 

 the turgor of the cells appears as a result of respiration. In the ab- 

 sence of oxygen, growth ceases on account of the interruption of the 

 formation of these substances. 



Molisch (1887 : 84) studied the secretions of roots and concluded 

 that they influence also organic materials, and in a higher degree 

 than mineral and rock constituents of the soil. He found that the 

 root-secretions have both reducing and oxidizing action. They 

 oxidize different organic substances, such as guaiaconic, pyrogaUic, 

 and gallic acids, and, most important of all, humus substances. As a 

 consequence, they favor in a high degree the decomposition of the 

 organic material of the soil of fields and of forests. The root- 

 secretion changes cane sugar to reducing sugar, and exerts a weak 

 diastatic effect. 



Kny (1889 : 163) found that a 12-day exclusion of oxygen pre- 

 vented the formation of cell-walls, but was not sufficient to kill the 

 cells completely. He concluded that the free oxygen of the air is 

 not only necessary for the beginning of the formation of cell-divisions 

 in the wound-periderm, but also for cutinization of the membrane. 

 The cell-divisions of the latter seem to be favored a little by the action 

 of a very small amount of hydrogen peroxide. 



Loven (1891) studied the respiration of a number of marine algae, 

 Ascophyllum, Laminaria, Ulva, Enteromorpha, Ceramium, etc., and 

 found that they are able to absorb every trace of oxygen present in 

 the water. In water entirely free from oxygen, algse can produce con- 

 siderable quantities of CO 2. He gave the oxygen-content per Hter 

 and also that of CO2 before and after the respiration experiments. 



Aubert (1892 : 280) showed that the internal air of fleshy plants 

 differed considerably from the atmospheric air in the relative pro- 

 portions of the component gases. The variations in the ^ ratio 

 in the fleshy plants bore a certain relation to the amount of water 

 they contained. They were greater when succulence was most pro- 

 nounced. Fleshy plants subjected to the same temperature in the 

 dark absorbed a nearly constant volume of oxygen, but evolved 



