68 
MORPHOLOGY 
Sexual reproduction. Sexual reproduction occurs under special 
conditions, when suitable individuals are brought together. The two 
kinds of individuals are called strains, and have been distinguished as 
(+) and ( ) strains, which 
apparently correspond to 
female and male individuals. 
In general, the two strains 
are not recognizable by sight, 
but are known to be sexually 
different by their behavior. 
Fertile branches (suspensors) 
are developed by pairing in- 
dividuals, come into contact 
(fig. 163), and a terminal cell 
FIG. 162. Mucor: showing the development (gametangium) is cut off by 
ofasporangiumattheendofasporophorejinthe each , fi lfi N These ^ Q 
last member of the series the spores (s) and 
columella (c) are evident. abutting gametangia are 
multinucleate, a perforation 
is developed at the contact, and the two protoplasts fuse, a very 
large and heavy-walled zygospore being formed (figs. 165, 166), from 
>vhich a new mycelium is developed (fig. 167). In many cases the 
pairing suspensors and gametangia differ decidedly in size, in which 
case a differentiation into male and female individuals becomes visible 
(figs. 164-166). It has also been observed that the larger gametangia 
and suspensors arise from more robust mycelia, and these in turn from 
larger sporangia than do the smaller gametangia and suspensors. It 
seems possible to arrange a series of pairing gametangia, ranging from 
such inequality in size that the pair may be regarded as an oogonium 
and an antheridium (as in Albugo}, to absolute equality. Such a series 
suggests a line of degenerating sexual organs, in which distinct heter- 
ogamy passes into isogamy; but of course it might be read in the 
opposite direction. 
Pilobolus. This mold is abundant on stable manure, and resembles Mucor, 
but it is remarkable for the method of dehiscence of its sporangium. The sporo- 
phore becomes very turgid and swollen just beneath the sporangium and finally 
bursts, hurling the sporangium with considerable force. This curious habit has 
given to the plant the name squirting fungus. If a bell jar is placed over the 
plants, the inner surface becomes dotted with discharged sporangia. 
Entomophthorales. These are parasites fatal to insects, the common house 
fly often being destroyed by them. The spore (conidium) in germination sends 
