18 



AERATION AND AIR-CONTENT. 



of new organs, and that an aerial supply was needed for the growth 

 of shoots and roots. 



Smirnoff (1903 : 26) has shown that wounding causes an increase 

 in the intensity of normal respiration in the bulbs of Allium, but 

 not of intramolecular respiration. This increase may sometimes 

 amount to more than 50 per cent. 



Kossowitch (1904), in studies with hemp, has reached the con- 

 clusion that the respiration of roots is significant, and that it can 

 not be left out of consideration in the biological processes of the soil. 



Putter (1904) found that Beggiatoa and Euglena, as well as Para- 

 mcecium and Spirostomum, were obligate aerobes that were harmed 

 by very low oxygen pressures, while complete withdrawal of oxygen 

 killed them with great rapidity. 



Duval (1904 : 76) has shown by studies of the seeds of beans, cab- 

 bage, carrot, lettuce, and onion that the respiration of seeds is in- 

 tense if moisture be present and is accompanied by a rapid loss in 

 vitality. Table 3 gives the results when seeds were allowed to ab- 

 sorb from 4 to 10 per cent of water. 



Table 3. 



When onion seeds were kept for a year and 13 days in sealed bot- 

 tles of air or illuminating gas, the vitality was not impaired except 

 in the case of those with additional moisture, which were all dead. 

 In this bottle the oxygen had completely disappeared and the amount 

 of CO2 was 13.35 per cent, while in the two other bottles containing 

 air, the oxygen was 8 and 12 per cent and the carbon dioxid was 

 18.8 and 6^8 per cent. 



Snow (1905 : 33) found that the absence of oxygen stopped the 

 production of root-hairs and retarded growth, while root-hairs also 

 developed better in tap-water than in distilled water. In the case 

 of corn, the reduction of the oxygen-pressure to zero completely 

 suppressed the development of hairs, even when the CO2 was re- 

 moved. The roots of wheat quickly died in the absence of oxygen, 

 but in the case of several roots that lived for a day, no root-hairs 

 were formed. The roots of willow twigs developed root-hairs in 

 about half the normal oxygen-content, but this may have been due 



