58 BULLETIN" 95*7, U. S. DEPARTMENT OF AGRICULTURE. 
resulted in due time. Many of these insects are, of course, accidental 
visitors, but quite a number feed or breed upon the Ribes plants. 
All of those which frequent the Ribes bushes by preference may carry 
many spores of both uredinia and telia. Such insects would be 
most likely to spread the disease, since upon leaving one Ribes plant 
they would seek another, thus scattering the spores exactly where 
they could start new colonies of the disease. But the accidental 
visitors, in a locality where Ribes bushes are abundant, could also 
spread the spores locally, but in a much more indiscriminate manner, 
so that but a very small percentage of the spores would ever reach 
leaves of Ribes. 
Aside from carrying spores on their bodies, some insects feed 
directly on the uredinia and telia and a few of the excreted spores 
are known to retain their viability. Still other insects may be leaf 
eaters and ingest the rust spores only accidentally. These would be 
of minor importance in spreading the disease. 
At Lewis, N. Y., where the Ribes bushes overhang narrow cattle 
paths which wind through a heavy cover of blackberry, raspberry, 
and other low shrubs, observations by Pennington and Snell indicate 
that cattle, sheep, horses, dogs, and berry pickers may carry the ure- 
diniospores from an infected bush to neighboring healthy ones. 
The remarks on the carrying of seciospores by automobiles, steam 
trains, and electric cars on page 36 apply also to some extent to the 
urediniospores. 
GERMINATION OF THE UREDINIOSPORES. 
The urediniospores of Cronartium ribicola have been generally 
found to be erratic in germinating. At one time excellent germina- 
tion occurs; at another, none at all. In the greenhouse experiments 
it seems that urediniospores produced in newly formed uredinia have 
greater infective power than those produced later in the same ure- 
dinia. Such early urediniospores seem to give as good results as 
fresh aeciospores. The former are usually produced in limited quan- 
tities while the latter are usually abundant. This results in a more 
liberal use of the latter, so that a fair comparison of the two is not 
possible from the usual inoculation work. Gravatt made compara- 
tive tests and concluded that seciospores and urediniospores from 
newly open sori were about equal in infective power. More such 
tests should be made before any conclusive statement is made on 
this point. 
Gravatt and York found that newly matured urediniospores pro- 
duced out of doors were decidedly more viable than older ones. 
This agrees with general experience hi making inoculations in the 
greenhouse. 
Gravatt found that cooling the urediniospores on ice stimulated 
germination. Uncooled spores gave 15 to 23 per cent germination 
