316 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
As shown in Table III, plots receiving treatments by 14 chemicals 
remained wart-free through the three growing seasons 1921, 1922, 
and 1923. These chemicals were bichloride of mercury, Bordeaux 
mixture, chloride of lime, cleaning solution, copper sulphate, formal¬ 
dehyde, kerosene, lime-sulphur, crude oil, sodium carbonate, sodium 
chromate, sodium fluoride, sulphur, and a commercial weed killer. 
Many of the plots treated with these chemicals showed very little 
growth 7 of potatoes during the first season, 1921, some showed poor 
growth in 1922, and a few showed poor development in 1923. In 
the plots treated with sodium fluoride growth was entirely pre¬ 
vented during all three seasons. 
The gardens used for these experiments were reported to be heavily 
infected with Synchytrium endobioticum. Soil samples from different 
parts of each garden were prepared in 50 per cent sugar solutions and 
centrifuged in order to secure visual evidence of the presence of wart 
sporangia. As a further check, designed to show whether or not the 
sporangia present were viable, two 10-inch pots were filled with 
composite soil from each plot before the plot was treated, and potatoes 
were planted in these pots the first year (1921). A “ C” is shown in 
Figure 3, beside a number of plots indicating that wart developed in 
one or both of the pots filled with soil from that plot. Previous 
experience with pot checks had indicated definitely that they could 
not be depended on to give an accurate indication of the presence of 
wart in the plot soil. The following tabulation (Table IV) of the 
occurrence of wart in the check pots in 1921 as compared to the 
occurrence of wart in the corresponding plots brings out this point. 
Table IV .—Check pots as indicators of the presence of wart in plots 
Gardens containing plots 
Wart present 
in check pots 
Wart not present 
in check pots 
Wart in 
plots 
No wart 
in plots 
Wart in 
plots 
No wart 
in plots 
1 to 20_ 
. 1 
5 
7 
7 
21 to 51 ..-.-.. -- 
1 
2 
9 
19 
52 to 76 . _ _ 
11 
8 
3 
3 
77 to 100 ___ 
0 
2 
B 6 
16 
13 
17 
<*25 
45 
• Five of these plots were untreated 
The pots were planted in 1921, only, but the plots were planted in 
1921, 1922, and 1923; and no distmctipn is made between plots 
producing wart one year, two years, and three years. 
It will oe noted that the check pots demonstrated the presence of 
viable wart spores in 30 plots and only 13 of these plots produced wart. 
However, 16 of the remaining 17 plots received treatments which 
prevented wart throughout the experiments. No wart developed in 
either of the check pots for 70 plots, yet wart developed during one or 
more years in 25 of these plots. The pots demonstrated the presence 
of wart spores in only 30 plots, whereas they were present in at least 
55 plots. 
7 The growth obtained is discussed in the section on Potato Growth Followin Certain Chemical Soil 
Treatments (Part IV). 
