TYPES OF CRYPTOGAMS; THALLOPHYTES 259 
After about twenty-four hours examine another portion of the 
mould from the surface of the liquid and study the more fully 
developed mycelium. Sketch. ry 
309. Zygospores. — Besides 
the spores just studied, zygo- 
spores are formed by conju- 
gation of the hyphe of the 
black moulds. It is not very 
easy to find these in process 
of formation, but the student 
may be able to gather from 
Fig. 190 the nature of the 
process by which they are 
formed, —a process which can- 
not fail to remind him of the 
conjugation of pond-scum. 
THE STUDY OF WHEAT 
RUST (PUCCINIA 
GRAMINIS) 
310. Occurrence. — Wheat 
rust is common on cultivated 
wheat and other grains, and 
also on many wild and culti- 
vated forage cg In fact, 1, threads in contact previous to conjuga- 
this or similar rusts occur on tion; 2, cutting off of the conjugating 
avery large number of grasses, cells, a, from the threads, 6; 3, a later 
f stage of the process ; 4, ripe zygospore ; 5, 
and many species of such rusts germination of a zygospore and formation 
are recognized. A rust may of aspore-case. (1-4 magnified 225 diam- 
have one, two, or three kinds eters, 5 magnified about 60 diameters.) 
of spores, and when three occur one is known as the eluster-cup stage 
and the others as red rust and black rust, according to the usual 
approximate color of the spores. The rust called Puccinia graminis 
growing on wheat has its cluster-cup stage on the leaves of barberry 
in June. The spores from the cluster-cups are carried by the wind 
to the wheat, where they germinate and in a few days produce the 
Fie. 190.— Formation of Zygospores in a 
Mould (Mucor Mucedo). 
