56 BULLETIIT 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 ^^ 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: Ribes 

 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 ^^ 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 OP THE UREDnSTIO SPORES. 



In the early work upon Cronartium rihicola 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 acium. 



York and Overholts (cited in Spaulding, 145) in 1918 at North 

 Conway, N. H., found urediniospores in spore traps up to 300 yards 

 distant froru 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 



s^York, H. H. Op.cit. 



