130 



Mycologia 



fertile in combination with the other after many transfers. The 

 first sub-cultures of strains 2 and I on dung in jelly glasses re- 

 mained sterile from October 10 to January 6, but produced asco- 

 carps within five days when both strains were grown together on 

 dung in a milk bottle. 



Behavior of Mycelia in Culture 



If a petri dish culture is inoculated on opposite sides with the 

 same strain (4 + 4), the mycelia grow out at the same rate from 

 both sides until they meet along a straight line through the cen- 

 ter. There is a narrow region between the two mycelia which 

 remains comparatively free from hyphae as though there was an 

 antagonism or repulsion between the two. Now, if opposite 

 strains such as 2 and 4 are planted in the same culture, the my- 

 celia grow out at about the same rate, meeting near the center of 

 the culture where there appears to be, for a brief period a slight 

 antagonism, at least the rate of growth is much reduced, then 

 the hyphae from either side can be found growing freely across 

 the line of meeting, making a zone plainly visible across the cen- 

 ter composed of hyphae from both strains. Numbers of asco- 

 gonia and antheridia soon make their appearance, not necessarily 

 at all in a line across the center, such as one finds in the cultures 

 of Rhizopus. The hyphae grow so rapidly that both strains are 

 soon found throughout the culture and ascocarps appear in any 

 region whatever. The largest numbers of sex organs, however, 

 generally appear first near the line of meeting of the mycelia and 

 one or two cm. from the periphery. 



In view of Blakeslee's discoveries of plus and minus strains 

 in the Zygomycetes and his theories regarding their sexuality, 

 and Burger's recent report on the " pseudo-heterothallic " con- 

 dition in Cunninghamella (15a), it is of importance to deter- 

 mine the question of the sexuality of the strains in this Asco- 

 bolus. Each of the strains so far isolated is self-sterile, and no 

 sex organs are produced in a one-strain culture. Ascogonia and 

 antheridia ordinarily arise from different hyphal branches. How 

 universal this rule is, I am not prepared to say. I have not seen 

 any good evidence of fertilization between structures arising 



