LIFE HISTORIES OF FUNGI 257 



stratum is also usually moist. Partly as a result of 

 their presence, the substratum on which they grow is 

 usually disintegrating with decay. From these facts 

 Rhizopus is called a saprophyte} The most common 

 species is Rhizopus nigricans. 



249. How Obtained. — Rhizopus, or almost any other 

 filamentous fungus, may be readily obtained by sowing 

 its spores on a suitable substratum. But, unlike the 

 higher plants, Rhizopus may ordinarily be obtained merely 

 by exposing moist bread, or other nutritive substance, to 

 the air. In the course of time, without one's sowing any 

 spores, colonies of the plant will appear, and this clearly 

 demonstrates the very interesting fact that these spores 

 are always floating in the air in greater or less abundance. 

 When the moist bread is exposed, some of the floating 

 spores come to rest upon it, and there, under favoring 

 conditions of moisture, temperature, and light they 

 germinate, and develop new plants. 



250. Description of Plant Body. — The plant body of 

 Rhizopus (Fig. 185) consists of a slender, thread-like 

 filament, called the mycelium, branching freely, devoid 

 of chlorophyll, and growing over the surface of the 

 substratum. The threads of mycehum are termed 

 hyphce. Careful examination with the microscope dis- 

 closes the fact that the hyphae are largely or wholly 

 aseptate, that is, not divided by cross-walls or septa. 

 The plant body, therefore, consists of one cell, though 

 there are several to many nuclei distributed through the 

 cytoplasm; such a structure is termed a coenocyte} 



^ From the Greek, sapros (aairpos), rotten, + phyton {ipvrSv), a plant. 

 2 Greek, koivos {koinos), common, -1- kvtos (kutos), a hollow (cell). 

 17 



