WHITE-PINE BLISTER RUST. 69 
relate to instances where diseased Ribes bushes were found widely 
separated from Pinus strobus or from all 5-leaved pines (6). These 
necessarily depend for reliability upon the observer's complete and 
minute knowledge of the Ribes and pines within considerable areas. 
Hence, such observations are of very uncertain value. Investiga- 
tions showing that the aeciospores of this fungus are distributed for 
miles largely invalidate such observations so far as overwintering is 
concerned. 
In North America, investigations of overwintering on Ribes plants 
have been along the following lines: (1) By means of spores adhering 
to dormant Ribes plants, (2) in dormant or partially opened Ribes 
buds, (3) in living Ribes leaves which themselves lived over winter, 
(4) on dead Ribes leaves, and (5) on infected Ribes stems. 
Overwintering by means of spores adhering to dormant Ribes 
plants has been investigated in several ways. A great many field 
observations have been made upon bushes diseased heavily one year 
and not infected the succeeding year. Cases where bushes were 
shipped from known diseased localities and have shown the rust the 
next season in their new locations, have been considered, but the 
evidence has been too incomplete to be seriously considered except 
as it might help to confirm or refute other stronger evidence. A 
great many Ribes plants have been used by the writer in greenhouse 
experiments ; they shed their leaves and become dormant for several 
months, yet there has been no hint of the carrying over of the fungus 
upon them from one season to the next. A cooperative experiment 
was made with Stewart (151), using 500 plants of Ribes nigrum, which 
in the summer of 1912 were heavily infected. The leaves dropped 
normally. They were then dug and most of them heeled in out of 
doors until February, 1913. They were then brought into green- 
houses in six widely separated localities and allowed to put forth 
new leaves. Examination of some of these dormant plants by Arthur 
and Petry showed that plenty of urediniospores still adhered to the 
stems and buds. Inoculations with these spores did not give any 
infection, so that they presumably had lost their viability. The 
results reported by six different investigators showed no infection 
appearing on the new leaves. 
Howitt and McCubbin (56) in attempting to solve the overwinter- 
ing problem, made the following tests : 
(1) In the fall of 1914, 16 black and 7 red currant bushes and 1 gooseberry bush, 
all badly rusted, were stripped of leaves and placed in cold storage, where they 
remained until March 16, 1915. At this date they were removed and planted in a 
greenhouse. All grew well and produced healthy leaves and fruit and were entirely 
free from rust throughout the summer. In addition, 17 black currant bushes, which 
had been badly rusted in 1914 and which were wintered in the field, were added to 
the above on April 21, 1915. These also grew normally and without rust. 
