914 
Journal of Agricultural Research 
Vol. XXXI, No. 10 
LONGEVITY OF UREDOSPORES 
During the summer of 1923 no material was collected primarily for 
the purpose of studying the longevity of uredospores. However, in 
the course of the studies to determine the longevity of teliospores it 
was found that practically all of the leaves which had produced telial 
columns had also a generous number of uredospores present. It is 
often found that leaves apparently bearing only telia also have fresh 
uredospores borne around the bases of the telia. These probably are 
the source of the new uredinial sori which often appear on new leaves 
late in the seas.on. With the above material, in each test in which 
teliospores were germinated, the germination of the accompanying 
uredospores was also noted. This means that observations were 
made only on such uredospores as were floating on the glasses of 
water together with the telial columns. 
Tests of longevity of uredospores of other rusts have been made by 
a number of workers {12). The results with uredospores of Cronar - 
tium ribicola range from 7 to 270 days {17) under various conditions. 
Table VI gives the number of days which the uredospores from the 
various Ribes species remained living after telial columns had formed 
and after the leaves had been picked. From Table VI it will be seen 
that no germination of uredospores was accomplished on Ribes triste , 
while on R. nigrum the uredospores lived as long as 59 days. On 
leaves collected from the ground the uredospores lived 50 days, and 
on material kept in the house they remained viable 36 days; hence 
the length of time that uredospores can live on leaves after teli¬ 
ospores have been formed varied from 0 to 59 days, in these tests of 
the writers. The uredospores, as explained under discussion of 
Table IV, actually lived slightly longer than these figures indicate. 
Table VI .—Longevity of uredospores of Cronartium ribicola 
Ribes species • 
Date of 
collec¬ 
tion, 
1923 
Last 
date 
alive, 
1923 
Num¬ 
ber of 
days 
living 
Ribes species a 
Date of 
collec¬ 
tion, 
1923 
Last 
date 
alive, 
1923 
Num¬ 
ber of 
days 
living 
A mftrirannm (13) 
Aug. 13 
Aug. 20 
Aug. 6 
Sept. 6 
Aug. 3 
Sept. 5 
Oct. 3 
24 
Nigrum (10). 
Aug. 11 
Aug. 23 
Aug. 7 
0 
0 
Ampriranmn (17) _ _ 
45 
Nigrum (19).. 
Oct. 10 
49 
riypftfjhat.i (6) 
Aug. 8 
Sept. 9 
Aug. 29 
3 
Odoratum (9). 
Aug. 29 
23 
Gynnshati (21) _ _ 
4 
Odoratum (18)_ 
Aug. 23 
Aug. 4 
Oct. 3 
42 
Glandulosum (4)_. 
27 
Rotundifolium (5)_ 
0 
0 
Glandulosum (11). 
Glandulosum (14). 
Aug. 11 
...do. 
19 
Rotundifolium (15)._ 
Aug. 15 
Aug. 20 
6 
Aug. 15 
Aug. 20 
6 
Triste (3). 
Aug. 3 
0 
0 
Nignim (1) _ 
Aug. 1 
.do... 
Sept. 5 
Sept. 19 
Oct. 3 
Aug. 15 
36 
Triste (12)... 
Aug. 11 
Aug. 16 
Aug. 26 
0 
0 
Nigrum (2) _ 
50 
Vulgare (16). 
Aug. 20 
5 
Nigrum (7).. 
Nigrum (8). 
Aug. 6 
...do. 
59 
10 
Vulgare (20). 
Sept. 12 
18 
« Figure following species name is the number of collection given in Table IV. 
The viability of uredospores in old material was tested at the 
same time (January, 1924) and from the same material as here 
reported for teliospores. Examination of each of several collections 
showed a very few uredospores with persisting old germ tubes. 
Spores which had been floated on water had a few similar persisting 
old tubes but no new ones. The fresh uredospores germinated 
abundantly. M. W. Taylor found similar persisting germ tubes 
among old aeciospores of this fungus. In making germination tests 
of old spores, it is necessary to examine first for these persisting old 
germ tubes. 
