ORIGIN AND EVOLUTION OF THE FUNGI 



31 



By inoculating spores from different thalli on the two halves of a 

 Petri plate culture, it will be found that in some cases where the 

 two thalli come together tlie filaments will fail to fuse and form 



Fig. 25. Mucor Mucedo. Zygospores: 1, two hyphae in terminal contact; 

 2, articulation into gametangia a and suspensors b; 3, fu.sion of gametangia; 

 4, mature zygospore supported by suspensors; 5, germination of zj-gospore. 



After Bredfeld. 



zygospores, whereas with other combinations they will fuse. By 

 repeating this experiment with many strains one can demonstrate 

 that two sexes really exist, though they cannot be distinguished by 

 their appearance. These "sexes" are referred to as plus and minus 

 strains. 



Origin and Evolution of the Fungi. Certain of the Oomycetes, 

 like Saprolegnia, show resemblances to certain of the green algae, 



