74 Wisconsin Academy of Sciences, Arts, and Letters. 
haustoria always present a turgid appearance even in old host 
cells, which have become nearly empty. The protoplasm of the 
haustorium proper usually seems quite dense', while that of the 
rest of the cell of which it is a part, particularly the more dis¬ 
tant portion outside of the host cell, has a much looser struc¬ 
ture. The nuclei of the haustoria are at the usual short dis¬ 
tance from each other which is characteristic for the conjugate 
nuclei. The nuclei are regularly of greater diameter than the 
neck of the haustorium through which they must have passed 
to reach their characteristic position inside the host, cell. But 
there is noi question that they are plastic enough to be elonga¬ 
ted and narrowed in order to pass through such a small open¬ 
ing. It is noticeable that the opening in the wall of the host 
cell is uniformly much larger than the neck of the haustorium. 
This condition is in sharp contrast with that in the Erysipheae 
as figured by Smith (7) and others'. Fig. 25 shows a case of 
a young haustorium into which one of the two nuclei has not 
yet penetrated. 
Fig. 7 shows the formation of a sterigma, from! one of the 
cells of a promycelium. The sterigma is rather thick and ir¬ 
regular and the nucleus is already well advanced toward its 
tip. The sporidium soon becomes binucleated by the division 
of its primary nucleus. The germination of the sporidium we 
have not been able to trace. 
If we summarize now the life history of the Coleosporium 
rust, we shall find that at certain stages the cell contains two 
and at other stages but one nucleus. The uredospore is a binu¬ 
cleated cell. When the uredospore germinates it gives rise to 
a mycelium whose cells also contain two nuclei, which divide 
by conjugate division. If this mycelium produces teleuto- 
spores, they will be binucleated, and will get their nuclei from 
the mycelium by the process of conjugate division. This will 
be the last binucleated cell of this series. In the teleutospore 
the conjugate nuclei fuse to produce an enlarged single 
nucleus. After fusion the teleutospore is stimulated to growth 
at once instead of after a resting stage as in Puccinia and forms 
the promycelium. The fusion nucleus next divides and the 
elongated teleutospore or promycelium divides, each daughter 
