56 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 
localities. (For range of observed dates in various sections of North 
America, see Table V, p. 72.) 
In the White Mountain region of New Hampshire, York 35 found 
fresh urediniospores in 1918 on May 16 and as late as November 17. 
Urediniospore production there continued on some bushes for 185 
days, while under average conditions it continued about 120 days. 
At this place the following species were under observation: Riles 
cynosbati, R. glandulosum, R. lacustre, R. nigrum, R. odoratum, R. 
oxyacanthoides , R. reclinatum, R. triste, and R. vulgare. Uredini- 
ospore production continued the longest time (185 days) on R. nigrum 
and the shortest time (65 days) on R. lacustre. In general, it can 
be stated that the urediniospores continue to form as long as there 
are susceptible leaves on the Ribes bushes of a given locality. 
York 35 found that the maximum urediniospore production in 1918 
occurred about July 14 to 16 and in 1919 about July 25 to 26. After 
these dates came the maximum sporidia production, and then the 
bushes became almost completely defoliated. 
DISTANCE OF DISSEMINATION OF THE TJREDINIO SPORES. 
In the early work upon Cronartium ribicola in North America the 
wide dissemination of the fungus from a given center appeared to 
take place by means of the urediniospores. Stewart and Rankin 
(151), who had an especially good opportunity to study this point, 
concluded that the urediniospores were blown at least one-half mile. 
Early general observations of the spread of this stage indicated that 
a wet season greatly favored it, while a dry season just as markedly 
retarded it. 
McCubbin (87) found that urediniospores fall in still air* about 8 
feet in 5 minutes. He calculated that a 30-mile breeze would carry 
them 2J miles in this time. Theoretically they may be distributed 
long distances if located on a hill or if picked up by convection air 
currents. But most of these spores are actually produced within 2 
feet of the ground in most localities, so that they are not picked up 
by the wind as readily as the seciospores, which are commonly pro- 
duced a number of feet above the ground. When set free, the 
urediniospores adhere in masses, so that they are not as readily 
blown by the wind as are the seciospores, which tend to fall apart 
when dislodged from the aecium. 
York and Overholts (cited in Spaulding, 145) in 1918 at North 
Conway, N. H., found urediniospores in spore traps up to 300 yards 
distant from the known source. This was where rain was plentiful 
practically all summer. Observations on infections of Ribes glandu- 
losum and R. cynosbati plants indicated that the disease spread by 
urediniospores up to 100 yards. In some cases where the bushes 
35 York, H. H. Op.cit. 
