THALLOPHYTA B47 
not important, as what are regarded as the most primitive of the 
Oémycetes have antheridia which produce sperms that swim to 
the oogonia, exactly as in the case of Vaucheria. From the above 
comparison it will be seen that Vaucheria and Saprolegnia have 
a great many points of similarity. If a holdfast of Vaucheria, 
instead of attaching itself to a rock, were to grow into the body 
of an animal and absorb nourishment, and if at the same time 
the plant were to lose its chlorophyll, we should certainly have a 
plant that would be very similar to some of the Odémycetes, such 
as Saprolegnia. We have already seen in the cases of certain 
flagellates that the same organism may under different condi- 
tions develop chlorophyll and manufacture its own food or lose 
its chlorophyll and live on organic matter. . It is therefore not 
hard to believe that some plant similar to Vaucherta changed its 
mode of obtaining food and gave rise to the Odmycetes. This 
seems all the more likely because a number of different kinds of 
green plants have saprophytic or parasitic relatives. 
Rhizopus nigricans. ‘The members of the order Zygomycetes are 
distinguished from those of the order Odmycetes by their method 
of sexual reproduction. In the Zygomycetes there are no motile 
cells, and sexual reproduction is due to the conjugation of two 
hyphe. 
Rhizopus is a typical example of the order Zygomycetes. ‘This 
fungus is the white mold which grows on bread and other sub- 
stances. Its distribution is world-wide, and it is exceedingly 
common. 
Structure. The vegetative body consists of branching fila- 
ments. Some of these penetrate the substratum and absorb 
nourishment, while others extend into the air and produce re- 
productive bodies (Fig. 359). The vegetative hyphe of Rhizopus 
are like those of Saprolegnia in being nonseptate and containing 
many nuclei. 
Reproduction. Asexual reproduction is by the formation of 
large numbers of spores in spherical sporangia (Fig. 359). 
Sexual reproduction is due to the conjugation of two similar 
filaments (Fig. 360). This takes place in the following manner: 
