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By that time , a debate emerged focusing on the origin of the asexual generation of land plants ( i.e. , the sporophyte ) and is conventionally characterized as a conflict between theories of antithetic ( Čelakovský , 1874 ) and homologous ( Pringsheim , 1876 ) alternation of generations .
 Čelakovský, Pringsheim
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Čelakovský, Pringsheim