38 



the strains being cultured. It does not produce very many of the 

 moniHoid asexual spores. This is an advantage, because the de- 

 tails of the development of the asococarps can be more readily 

 studied on this account. Normally the mycelium is homothallic, 

 or haplomonoecious. One can always obtain heterothallic strains 

 by selecting small ascospores. In this case asocarps will be pro- 

 duced only when two mycelia of opposite sex are mated in 



S 6 



;^^ 





S 1 



Figure 3. Petri dish culture inoculated with two strains of opposite sex of 

 Neurospora telrasperma showing characteristic distribution of ascocarps. The 

 black smudged areas show where the ascospores have been discharged. 



culture. Figure 3 shows a petri dish culture in which the uni- 

 sexual strains Si and Se have been growing for several days on 

 corn meal agar. Fruit bodies are first formed along the line 

 where the two mycelia meet, after which they appear one by 

 one along the lines of radiately growing hyphae of the strain Se. 

 Just why the stimulus of fertilization results in a production of 

 ascocarps back along the lines of mycelial growth is not yet 

 known. However, the fruit bodies from this combination always 

 form on the mycelium of the strain Se, so that it looks as though 

 the sexes are differentiated and that strain Se develops the 



