RESPIRATION AND OXYGEN. 81 



oxygen were 4 to 5 times shorter than in the case of those in the air. 

 He found further that the respiration intensity remained the same, 

 whether the seedlings were in oxygen or in air. 



Wortmann (1879) carried out an extensive series of experiments 

 with seeds, seedlings, and shoots in order to determine the nature 

 and significance of intramolecular respiration. His results indicated 

 that the latter was unable to furnish energy for growth processes, 

 though he concluded that life could persist for several days after the 

 withdrawal of oxygen. He was unable to find the slightest growth 

 in the absence of oxygen. 



Detmer (1881) repeated and extended the studies of Wortmann, 

 employing N 2 0, H, and C0 2 with seeds and seedlings of Pisum and 

 Triticum. He found neither germination of seeds nor growth of 

 seedlings to occur, while both heliotropism and geotropism were 

 suppressed, as well as the formation of chlorophyll. The plants 

 suffered markedly and quickly perished. 



Wilson (1882 : 93) repeated the experiments of Wortmann with 

 seedlings of Vicia faba and confirmed the observation that, for a 

 short period, CO 2 was excreted just the same, whether oxygen was 

 available or not. When the experiment continued in the absence of 

 oxygen there was a gradual decrease in the production of C0 2 , be- 

 cause the plant became injured. With other seedlings, as with 

 flowers and other plant parts, just as soon as the access of oxygen was 

 cut off a direct decrease took place in the evolution of CO 2 . This 

 decrease was usually one-half to three-fourths of the normal respira- 

 tion. In an atmosphere consisting of one-fifth air and four-fifths 

 hydrogen, the seedlings of Helianthus annuus showed no noticeable 

 decrease in C0 2 , but a mixture of one-twentieth air and nineteen- 

 twentieths hydrogen resulted in a marked decrease. 



Wieler (1883 : 223) determined that plants require atmospheric 

 oxygen for growth, with the exception of certain fungi of fermentation 

 and decomposition. Growth ceased at once in the absence of oxygen, 

 but the amount necessary for growth was very small, ranging from a 

 fraction of a cubic centimeter for Helianthus annuus and Vicia faba 

 to 1 to 7 c.c. for Brassica and Ricinus. With decreasing pressure, 

 growth was at first increased, then reached an optimum, decreased 

 with further rarefication, and finally ceased. The growth optimum 

 was determined for Helianthus annuus and Vicia faba. For the 

 former it was about 3 per cent and for the latter 5 to 6 per cent of 

 oxygen in relation to the contents of the bell-glass. A slowing down 

 of growth in comparison with growth in normal air occurred at 0.14 

 to 0.5 per cent for Helianthus, 1.45 per cent for Vicia and Lupinus 

 luteus, and 5 to 6 per cent for Cucurbita pepo. In pure oxygen, 

 Helianthus and Vicia grew more rapidly than under normal pressure. 

 In an oxygen-content corresponding to an air-pressure of 2 to 2.5 

 atmospheres, growth seemed to be slowed down in comparison with 



