360 THALLOPHYTES 



True Molds (Mucorales). There are a number of Molds 

 some of which belong to other divisions of the Fungi. The 

 Molds of this order are characterized by a zygosporic reproduc- 

 tion, on which account they are called Zygomycetes. Of the 

 nearly 200 species known, Bread Mold is the most familiar one. 



FIG. 311. Conidia of the Late Blight of the Potato developing zoospores, 

 and zoospores growing hyphae. X about 400. After Ward. 



Bread Mold (Rhizopus nigricans) . Bread Mold is very 

 common about homes, producing a fluffy tangle of hyphae on the 

 surface of bread, fruit, and other favorable nutrient substances 

 when left exposed (Fig. 313). It is sometimes injurious to 

 Sweet Potatoes and other vegetables in storage. The fluffy 

 tangle of hyphae is white while young but becomes dark when old, 

 owing to the dark color of the mature sporangia. 



A strong poison has been found in connection with Rhizopus 

 nigricans, and it has been suggested that some of the diseases of 

 stock, such as the " cornstalk disease " and the " horse disease," 

 prevalent in some of the Western states, may be due to the toxin 

 which stock get in moldy fodder or other feed. The toxin 

 apparently is only effective when introduced into the circulatory 

 system. This is shown by the fact that rabbits can be fed the 

 Mold without any injury, but when a little of the sap is expressed 

 from the mycelium and injected into the blood, the animal dies 

 almost instantly. 



The mycelium consists of numerous coenocytic branching 

 hyphae. Some of the hyphae penetrate the substratum and 

 gather food, while others gro\v above the substratum and produce 

 the visible fluffy mass. The surface hyphae with more or less 



