WHITE-PINE BLISTER RUST. 
61 
currant plants which had been previously set out in an isolated garden for the pur- 
pose. After inoculation the plants were covered for two days by a box having a glass 
lid. In all cases, water was sprinkled three or four times daily on the plants and 
on the inside of the box, to keep a high humidity. Unfortunately, during the whole 
of the period covered by this series of inoculation the weather was exceedingly hot 
and dry, and it was evident from a study of field conditions that infections could take 
place at this time only with the greatest difficulty. The adverse nature of the weather 
conditions will serve to explain the meager results. . . . 
The only positive result from this experiment was that the spores would retain 
their power of infection for a period of nine days at least; but so many failures oc- 
curred all through the course of the work that this period can not be regarded as 
establishing a maximum limit of life. 
It is interesting to note that the spores kept outside underwent a complete decolori- 
zation in two days, whereas those stored in the laboratory retained their normal 
color, with but little change throughout the whole time of the experiment. 
The inconclusive results obtained from the first set of inoculations in the field led 
to another later attempt with plants kept in the laboratory, for this purpose a number 
of small plants being used from which the leaves had been stripped, so as to induce 
the formation of secondary foliage. The methods employed in this case were the 
same as for the first set, exept that after inoculation the shoots were kept covered 
and moistened for the usual 48 hours inside large glass jars. (See Table IV.) 
Table IV. — -Inoculation of currants with uredospores of different ages. 
Series. 
Age of 
spores 
(days). 
Date of inoculation, 
1916. 
Number 
of leaves 
used. 
Date of examina- 
tion, 1916. 
Result. 
I 
2 
4 
7 
8 
11 
13 
18 
24 
27 
31 
16 
16 
16 
14 
11 
16 
5 
7 
7 
7 
September 19 
September 22 
September 25 
September 26 
September 29 
5 pustules on 2 leaves. 
67 pustules on 11 leaves. 
II 
September 2 
September 5 
September 6 
September 9 
September 11 
September 16 
September 22 
September 25 
September 29 
III 
IV... 
10 pustules on 5 leaves. 
8 pustules on 2 leaves. 
2 pustules on 2 leaves. 
V 
VI... 
VII 
October 6 
VIII... 
October 12 
October 15 
October 19 
Do. 
IX 
Do. 
X 
Do. 
The results from these inoculations were somewhat better than those from the first 
set; infections were obtained from spores kept for 13 days after collection, as shown 
in the tabulated record. It is still thought that this period is far below the maximum 
period for which the spores will retain their vitality. 
In 1917 Gravatt and Taylor made a series of tests of urediniospores 
together with asciospores and teliospores. (See p. 38 for details 
of the experiment.) They were tested weekly beginning May 8. 
June 16 gave the last germination in lot A, while lot B persisted 
until July 2. Although germination persisted longer in lot B, it 
weakened decidedly somewhat earlier and was poorer practically 
throughout the test. (See Table II, p. 38.) 
In 1918, Duff (30) experimented on the longevity of urediniospores 
placed in a refrigerator at 2° to 5° C. two weeks after collection and 
tested in hanging drops of distilled water. He states that when 
placed in the refrigerator — 
A negligible percentage of spores were germinable, but reduction in temperature 
stimulated them to greatly increased germination. By this means a continually 
