Parasitic Fungi of Illinois. 158 
taneously, or nearly so, on the infected area of the host, but 
most often on the opposite sides, if of a leaf. In some cases 
the other fruit forms subsequently develop in the order named. 
upon the same mycelium, but in others only on a new mycelium 
produced from the germination of the ecidium spores, and 
either on the same or different hosts, according to the habit of 
the species. These alternations may be best understood by 
consulting what is said under the genus Puccinia. 
But this full series of forms is not found in all the spe- 
cies. Indeed, there are comparatively few which are really 
known to have in their regular course of development all the 
stages as necessary requirements of growth. Ina few instances 
it is known that species, which under some circumstances have 
this or that form produced, may, under other circumstances, 
perpetuate themselves though one or more forms are omitted. 
In very many cases the genetic connection of different fruit 
forms has not been satisfactorily made out; but contributions 
to knowledge of this kind are from time to time gained, and 
through the interest now taken in the matter more rapid ad- 
vance may be expected in the future. For this purpose artifi- 
cial cultures, with the most painstaking care to avoid mistakes, 
are required. The spores: must be placed on the proper host 
under proper conditions, and the development carefully fol- 
lowed through the season. It is believed that in some specie 
only teleutospores are produced, in others only uredo and teleu- 
toforms, and these from the same mycelium; in still others only 
ecidium and teleutoforms. The office of the spermogonia has 
not been conclusively ascertained. Cornu, of France has seen 
the spermatia from them germinate in certain nutritive fluids, 
but not in water, and he has supposed they may under certain 
conditions reproduce the plants like other spores. Many have 
attributed to them sexual functions, but the proof is unsatis- 
factory. It has been observed that some spermogonia are fra- 
grant, and insects are known to visit them, hence the inference 
that the special office may be for dissemination. 
In most cases the mycelium of these plants wanders little 
from the point of penetration of the host tissues—in this 
strikingly differing from the usual growth of the species of 
Ustilaginee and some other groups of fungus parasites. In 
