Dec. 3, 1917 
Podblight of Lima Bean 
499 
Tabled II .—The results of exposing pycnospores of Diaporthe phaseolorum to different 
strengths of mercuric chlorid , copper sulphate , arid formaldehyde for different lengths of 
time 
Time of 
exposure. 
Copper sulphate. 
Formaldehyde. j Mercuric chlorid. 
NI12.5 
Nl 3 I .25 \ NI62.5 
1:100 
1:250 
1:500 
i 
| Nh 35 j Nh ,350 
j ; 
N12,700 
Nj4,050 
M inutes . 
1 
2 
4 
6 
8 
10 
12 
14 
16 
18 
20 
a IOO 
35 
5 
IOO 
65 
55 
25 
i5 
10 
5 
2 
IOO 
75 
0 
85 
30 
0 
IOO 
IOO 
8s 
10 
0 
O 
O 
O O 
5° 
0 
IOO 
IOO 
75 
5° 
0 
90 
75 
45 
20 
2 
a In this and corresponding columns are given the percentage of germination as estimated at the close of 
the experiment. Water controls were made in every case in which the germination was arbitrarily placed 
at 100 per cent. These plates, together with those poured from a 1 minute exposure, served as controls for 
comparison in estimating percentages of germination. 
Reference to the table will show that the spores were nearly all killed 
in four minutes in a N/12.5 copper-sulphate solution, and in 14 minutes 
in a N/31.25, and in 20 minutes in a N/62.5 solution. It is interesting 
to compare these results with those of Clark (5), who found that the 
spores of several fungi exposed in a copper-sulphate solution were killed 
or injured as follows: Aspergillus flavus (?) Link N/4 and greatly injured 
in Ar/256, Sterigmatocystis niger Von Tieghem N/8 and greatly injured in 
N/128, Oedocephalum albidum Sacc. N/64 and greatly injured at iV/256, 
Botrytis vulgaris Fr. greatly injured at N/128 , and Penicillium glaucum 
Link Nfi and greatly injured at N/256. As will be seen, there is a wide 
difference between the strength of the solution necessary to kill and that 
required to injure greatly the spores. The writer found that none of the 
spores exposed for one minute to a solution of mercuric chlorid at a con¬ 
centration of N/135 and iV /1,350 would germinate, and that only 50 per 
cent germinated when exposed for the same length of time in a concen¬ 
tration of N/3,7oo. At the greater dilution, iV/4,050, 50 per cent germi¬ 
nated after an exposure for six minutes. Clark (3) found that spores of 
A. flavus , S. wiger, P. glaucum were killed in a Nj4,096 mercuric chlorid, 
O. albidum in a N116,384, and B . vulgaris in a N163,336. % The spores of 
these fungi were killed in the solutions of the toxic substance more dilute 
than that required to kill the pycnospores of Diaporthe phaseolorum , but 
they were likewise subjected to the solution for a longer time. In 
another work Clark (4) has shown that Rhizopus nigricans was killed in 
75 seconds in a solution of mercuric chlorid 1 to 3,700. 
Formaldehyde was found to be very toxic to the spores, only 10 per 
cent germinating after a six-minute exposure in a i-to-500 solution, and 
