318 Morpho genetic Factors 



unless there was a high concentration of fat globules near the point of 

 origin. These authors believe that this is not a case of true photoperiodism 

 but that the low production under short days results from a limited 

 availability of food. 



Klein (1948) reports that in the fungus Pilobolus there is a definite 

 cycle of asexual reproduction caused by periods of light and darkness, 



100 



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u 



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id 60 



u 50 



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 O 



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JULY AUG. SEPT. OCT. 



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 JAN^FLB. MAf\. 

 PLANTING 



Fig. 13-5. Graph showing percentage of reversal of staminate flowers to pistillate ones 

 in genetically staminate plants of Mercurialis annua planted at different dates. Day- 

 length markedly affects sex expression. ( From Schaffner. ) 



sporangiophores maturing at the end of a dark period and new ones re- 

 maining immature at the end of the light one. Light is essential to growth, 

 but a dark period seems necessary to establish a periodicity of growth 

 and maturation of the fruiting bodies. Periodicities other than those 

 found in nature could be established in this plant by artificial illumina- 

 tion. Among these were light-dark cycles (in hours) not only of 12-12 



