30 BOTANICAL GAZETTE [ JANUARY 
not yet been able to effect any tests by which their true place 
can be defined. 
We can easily see that the consequence of this abundance of 
forms ought to be a very considerable reduction in the capacity 
of the rust to propagate itself from one species of grass to 
another. To be sure rye and barley are able to infect one 
another with black rust, as illustrated in the table, and they also 
can be infected by Triticum repens, T. caninum, and several other 
grasses. In the same manner oats may be infected with black 
rust from Dactylis glomerata, Alopecurus pratensis, and several other 
grasses. For all the other eight forms of rust occurring on our 
cereals, however, as well as for the forms of rust on the wild 
grasses and the fodder grasses generally, it has not been possi- 
ble to discover any source of the disease among surrounding 
grasses of other species. 
But some one may ask if the proofs brought forward for the 
difference between the forms — proofs which have been gathered 
from experiments with the fungi in their uredo stage, as they 
occur on culms and leaves of grasses—are completely satisfac- — 
tory. If it is a fact, as seems to follow from the table, that all 
forms of black rust are like each other in that they are able to 
the query presents itself whether this bush is not able to serve 
as a connecting bridge between the forms which show their dis- 
a 
alternate on barberry, producing an zcidium upon it, of course — 
tinguishing features in the uredo stage; whether, indeed, an — 
zcidium that, for instance, arises from the black rust on oats é 
may not be able to produce an outbreak of black rust not only i 
on oats, but also on the other cereals, nay, on every grass that — 
1s susceptible to black rust. Many trials made during the last — 
SIX years have proved conclusively, however, that it is not SO — 
An ecidium arising from black rust on oats is able to infect, 
among the cereals, only oats, while an zcidium arising from 
black rust on rye or barley can produce rust only on rye OF 
barley, and so on. The different forms of black rust are thus — 
entirely separated one from another in all their stages —as 
uredo and puccinia on the grasses and as acidium on barberry — 
