44 PROTISTS AND DISEASE 



Zygomycetes. --This group includes Mucorineae and 

 Entomophthorineae. The former agree with Oomycetes in 

 general structural plan, but they differ in the absence of 

 zoospores and in forming zygospores in place of oospores. 



Material for study is easily obtained : a piece of bread 

 that has been exposed to the air for 2 or 3 days is dipped in 

 water, placed on a saucer and then covered by an inverted 

 tumbler ; in 4 or 5 days a growth of mould will appear. 

 Mucor mucedo can be recognised by its tall unbranched 

 conidiophores and dark round sporanges. The former are 

 generally about half an inch long, but I have seen the growth 

 like a piece of a sheep's fleece with conidiophores nearly 

 3 inches long. 



The mycelium or thallus is non-septate save when 

 injured or old. Zygospores are formed by fusion of pro- 

 jections from neighbouring hyphae, Fig. 9. They form 

 more readily in some species than in others, thus they abound 

 in Sporodinia grandis, which is parasitic on fleshy Hymeno- 

 mycetes, such as Bolets and Russulas ; while in M. mucedo 

 their presence is exceptional. The reason of this was shown 

 in 1894 by Blakeslee, who discovered that in this and some 

 other species of Mucor conjugating filaments belong to 

 different strains of mycelium ; a more vigorous, or +? 

 mycelium, and a less vigorous, or , mycelium. 



If growths of a + and a strain are started on opposite 

 sides of a culture-plate, they will meet near the middle and 

 form a dark line of zygospores, seen as black spots projecting 



