METABOLIC ASPECTS OF PHOTOPERIODISM 299 



pattern of labeled compounds (malate, aspartate, glutamate, alanine, 

 glutamine, citrate, isocitrate, succinate, and fumarate) nor the relative 

 distribution of radioactivity in these compounds showed any significant 

 differences between leaves of induced and noninduced plants. 



In recent work, with total titratable acids, Neyland and Thimann 

 (personal communication) have found that while much of the fixation 

 goes into organic acids, which decompose again in light or warmth, 

 there is sufficient difference between CO2 fixation and organic acid 

 measurements to suggest that important fixation products remain un- 

 identified. 



Although at present it is impossible to say whether or not there is a 

 causal relationship between the CO2 metabolism and flowering, it 

 should be noted that this metabolic response is more amenable to in- 

 vestigation than the morphological responses most often studied. A 

 morphological response such as flowering involves ceU division, cefl 

 enlargement, and cell differentiation, and each of these processes must 

 include many distinct biochemical steps. The CO2 fixation response 

 would appear to be a much simpler system. In addition, these meta- 

 bolic responses may indicate less obvious metabolic changes which 

 could be causally related to flowering. 



EFFECT OF ANAEROBIC CONDITIONS ON FLOWERING 



In addition to treating Kalanchoe with COo-free air during the long 

 dark periods, we have also treated Kalanchoe and Xanthium with 

 anaerobic conditions and carbon monoxide. We wifl present only some 

 of the anaerobic experiments at this time. In 14 out of 15 cases where 

 Xanthium was given anaerobic conditions during 2 to 5 long (16-hr) 

 dark periods, flowering was inhibited. The one plant that flowered had 

 received five short-day cycles and showed a delayed marginal response. 

 Anaerobic conditions during the dark period had no effect on Kalan- 

 choe plants treated for 15 short-day cycles. Perhaps more interesting 

 are the experiments of Melchers and Claes (1945; Claes, 1947) with 

 the long-day plant Hyoscyamus niger. This plant was able to flower 

 under short-day conditions if nitrogen was given throughout the long 

 dark period. 



These experiments lend support to the idea that some of the dark 

 processes involve the aerobic metabolism of constituents formed in the 

 light. 



