Fungi 



193 



nitely. We have a culture which has been furnishing illustrative 

 material for nearly twenty years. Once in a while, when a particu- 

 larly good culture appears, lay aside some of it to start the next 

 culture. The best series of stages generally appears between the 

 fourth and seventh days. Dr. Blakeslee shows why zygospores are 

 so infrequent. The conjugating filaments belong to different strains 

 of mycelia which he calls 

 plus and minus strains, and 

 which, f o r convenience, 

 may be called female and 

 male strains. The more 

 vigorous mycelium is +, 

 and the less vigorous . 

 When the two strains come 

 together, zygospores are 

 formed along the line of 

 meeting. If + and 

 strains are started at op- 

 posite sides of a dish, they 

 will meet near the middle 

 and form a dark line of 

 zygospores. 



Even for elementary 

 study, it is worth while to 

 make permanent prepara- 

 tions of the zygosporic 

 stage (Fig. 50). Fix in 5 

 to 10 per cent formalin. 

 Stain some in eosin, some 

 in Delafield's haematoxylin, some in Magdala red and anilin blue, 

 and leave some without any staining at all. A slide with material 

 treated in these four ways will show all stages at their best. 



For sections, use the chromo-acetic acid as indicated for sporangia. 

 The nuclei are very small and have never yet yielded much, although 

 many have tried to study them. Professor Klebs had no success 

 in trying to induce the zygosporic condition in Mucor. 



FIG. 50. Rhizopus nigricans: various stages 

 in the development of zygospores from a culture 

 on bread ; preparation stained in eosin and mounted 

 in Venetian turpentine. X80. 



