TORREYA 



Vol. 30 March-April, 1930 No. 2 



Material for Demonstrating Sexuality in the Ascomycetes 



B. O. Dodge 



Nothing since the time of Pasteur and Koch has done more 

 to revolutionize our ideas regarding the nature of fungi than the 

 art of culturing them from single spores. When our corn, wheat, 

 cotton and fruit crops aggregate several billions of dollars in 

 value annually and we realize that pathogenic fungi frequently 

 take toll of a large percentage, it would seem that the student in 

 Botany and Biology should be privileged at least a nodding 

 acquaintance with a representative of each of the large groups of 

 fungi. 



The question is, what is the best form in each case for class- 

 room demonstration. Any species, to fulfil these requirements 

 should first of all be readily available. It must be one that will 

 go through its life cycle in culture. It should show both types of 

 reproduction, asexual and sexual, and produce fruiting bodies 

 readily demonstrable, at least under the low power of the micro- 

 scope. Other things being equal, a form which is heterothallic or 

 haplo-dioecious* will prove far more interesting to students. For 

 example, among the Phycomycetes, Rhizopus nigricans and 

 Phy corny ces Blakesleeanus serve admirably for the purpose. Any 

 student who inoculates a petri dish culture with the two strains 

 of the latter species and sees for the first time the row of zygo- 

 spores developing along the line where the two mycelia meet, 



* In dioecious flowering plants the stamens and pistils are borne on differ- 

 ent individuals. A heterothallic or haplodioecious fungus is merely analagous 

 to a dioecious flowering plant. It is one in which an individual haploid gameto- 

 phytic mycelium is either of one sex or the other. Sexual reproduction occurs 

 only when two mycelia of opposite sex are mated or grown together. A homo- 

 thallic or haplomonoecious fungus is one in which each individual mycelium is 

 capable of reproducing sexually and if differentiated sex organs are developed 

 both kinds will be formed on the same mycelium. 



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