Dec. 3, 1917 
Podblight of Lima Bean 
497 
flowering plants, because of the different methods 01 experimentation 
and standards of measurement, the spores of fungi show equally great 
variability and sensibility to copper salts and other toxic substances. 
Clark (3) found that Penicillium glaucum was injured by copper sulphate 
at a concentration somewhere between iV/2,04^ and Nj 1,024, while 
Aspergillus flavus would endure a concentration of N/512 to NI256, two 
to four times as great. Crandall ( 12 ), on the other hand, showed that 
the apple scab fungus is quite resistant to copper sulphate, the spores 
being only slightly retarded in germination in a solution of 1 to 100,000, 
while a concentration of about 1 to 10,000 was necessary to entirely 
prevent germination. At this latter concentration some of the common 
molds, however, grew quite well. Temperature was found by Brooks 
(1) to influence the percentage of germination of the spores of certain 
fungi in the same concentration of a toxic substance. By an extensive 
series of experiments he found that Penicillium glaucum gave medium 
growth in N/128 copper sulphate at 20° C., Monilia fructigena did not 
germinate in N/16 copper sulphate at 25 0 to 30° C., but at 15 0 C. 12 per 
cent, at io° C. 30 per cent, and at 5 0 C. 49 per cent. 
No attempt has been made to review all the extensive literature on the 
effect of toxic substances on plant growth. The results of the work of 
the different investigators are very conflicting, due, perhaps in part at 
least, to the different methods of experimentation employed and the 
different standards of measurement. 
During the time the podblight fungus of Lima bean has been under 
investigation many interesting observations have been made from time 
to time on the effect of certain chemical substances commonly used in the 
laboratory on the germination of the spores. The use of a solution of 
mercuric chlorid for disinfecting field specimens preparatory to isolating 
the fungus led to a study of the strength of this solution necessary to kill 
the spores in a given time. A similar study was made with formaldehyde 
because of its possible use in disinfecting infected seed, and with copper 
sulphate, a well-known constituent of Bordeaux mixture, sometime rec¬ 
ommended as a spray in controlling the disease in the field. 
method of experimentation 
Preliminary experiments showed that the use of Van Tieghem cells 
to determine the toxic limit for the germination of the spores was ex¬ 
ceedingly unreliable and was consequently abandoned. Although this 
method has been generally used, it is likely that many of the conflicting 
results may be attributed to it. In fact, the writer found that each 
test in Van Tieghem cells might be expected to give different results, 
probably owing to the variation in vapor pressure or to some slight 
accident overlooked, unexpected, and unaccounted for. After con¬ 
sidering the different methods that might be used, the writer concluded 
23716°—17-4 
