HEREDITARY FACTORS AND GERMINATION 



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anaerobic conditions for a few hours after treatment and then 

 placed under conditions favorable for germination, however, they 

 failed to grow. Activation and deactivation were therefore re- 

 versible reactions. In later work Goddard and Smith (1938) 

 sought to explain what portion of the respiratory mechanism is 

 activated by heat and what constitutes the respiratory block in 

 dormant spores. By subjecting spores to various partial pressures 

 of oxygen and carbon dioxide, they determined that the respira- 

 tory rates are not limited bv permeability of the spore membranes 

 to passage of these gases. Under anaerobic conditions carbon 

 dioxide was not evolved by dormant spores, an observation which 

 led Goddard and Smith to suggest that active carboxylase is not 

 present in such spores. On heating, however, this enzyme is re- 

 versibly activated. They interpreted their results to show that 

 two qualitatively different respiratory systems are present in the 

 ascospores of N. tetrasperma, the dormant system which func- 



