and Laboratory Methods. 2185 



Laboratory Outlines for the Elementary Study of Plant 



Structures and Functions from the Standpoint 



of Evolution. 



FOUR PHYCOMYCETES SHOWING VARIOUS HABITATS. 



XXIV. Mucor stolonifer Ehrenb. Black Bread Mould. (Rhizopus nigri- 

 cans.) 



Class, Zygomycetes. Order, Mucorales. Family, Mucoraceae. 



This fungus can nearly always be obtained by placing a piece of old bread 

 for several days in a moist chamber. An ordinary glass or jar with a cover will 

 do very well for making the culture. Enough water should be added to keep 

 the bread moist without soaking it too much. The fungus forms a white floccu- 

 lent mass of cottony filaments (the mycelium made up of hypha;) over the sur- 

 face of the bread and later also spreads out over the walls of the glass. Some 

 of the hyphae will be seen to rise vertically into the air and end in rounded black 

 heads. These are the sporangia containing the non-sexual spores. 



1. Describe the naked eye characters noted above. Notice habitat and 

 color. Notice also (1) the hyphae passing down into the substance of the bread, 

 (2) the horizontal stolon-like hypha;, and (3) the upright sporangiophores. 



2. Cut off a flake of the mycelium with a pair of scissors and mount in 

 water, taking great care not to injure the delicate hyphae. Study under low 

 power and draw some of the hyphae showing mode of branching. 



3. Under high power draw part of a hypha and describe carefully. Any 

 transverse septa (cross walls)? If not, what kind of a fungus is it? (Compare 

 with Vaucheria.) How does this plant differ from the green algae in general ? 

 Difference in mode of obtaining food ? Why is this plant called a saprophyte ? 



4. Study and draw a cluster of sporangiophores showing the rhizoids at the 

 base and the sporangia at the tips. The best are those taken from the walls of 

 the dish. Color ? Draw a single unbroken sporangium showing the columella 

 on the inside, and the non-sexual spores. Do not mistake the columella of a 

 broken sporangium for the entire body. Describe the structure of the sporan- 

 gium. What does the columella represent ? The sporangia burst readily because 

 of the presence of an intermediate substance which swells readily in water. Of 

 what use is this ? 



.5. Draw and describe the non-sexual spores. Color ? About how many in 

 a sporangium ? 



l». This plant has a partial development of sexuality, and under proper con- 

 ditions produces zygospores. If any of these are at hand or material from 

 another species, study and draw showing the following stages : 



a. Two neighboring, swollen branches of the mycelium, which are about to 

 conjugate. 



b. The stage in which the two branches have fused. 



c. The stage in which transverse septa are formed, cutting off the apical 



