498 
Journal of Agricultural Research 
Voi. xi, 
■■ IO 
to employ the method frequently used in medical bacteriology to de¬ 
termine the germicidal value of certain chemicals. This takes more 
into account the actual death of the organism rather than the strength 
that inhibits growth. It seems that the same method should apply 
equally well to fungi and is easier of determination and more reliable, 
since the length of time the organism is exposed plays an important 
part also, and can be more accurately gauged. It is a well-known fact 
that a fungicide may merely inhibit growth when the spores are exposed 
to it for a certain length of time but may kill them on prolonged ex¬ 
posure. In these experiments the time the spores were exposed to the 
fungicide was relatively short, the concentration of the solution being 
proportionately strong to produce death in a comparatively short time. 
This method eliminated the necessity of taking into account, among 
other things, the temperature which Brooks (r) found to play such an 
important part in germination of the spores of some fungi. 
The pycnospores of Diaporthe phaseolorum were found to grow well in 
beef agar +15 on Fuller’s scale; and therefore this medium was used in 
which to test germination. The spores from a culture on Melilotus alba 
were transferred by a small platinum loop to a solution of the fungicide 
of the desired concentration and mixed by a wide circularly swinging 
motion of the arm with the plugged end up, or by vigorous shaking. At 
the end of one minute, two minutes, and every two minutes thereafter 
up to the suspected limit of endurance, a loopful of the mixture was 
transferred to a tube of liquefied agar and, after mixing by shaking, a plate 
was poured. Control plates were made by transferring a loopful of 
spores from the same test culture to a sterile water tube and a loopful 
from this tube to a tube of liquefied agar. This method was followed 
with each of the fungicides and repeated as often as necessary to establish 
the toxic limit. The plates were kept at room temperature in the 
laboratory. The colonies in the control plates appeared in about two 
days. Notes were taken from time to time for seven days, after which 
they were thrown out, for, if growth took place at all, it would do so 
before that time. 
RESULTS OE EXPERIMENTS 
The results of these experiments are given in Table II. 
The mercuric-chlorid and copper-sulphate solutions were made in 
advance and kept corked in the ice box until needed. Because of the 
instability of the formaldehyde, the solutions were prepared just before 
using and in such a way that the fractional parts given in Table II are 
based on a hypothetical formaldehyde solution of a strength of 100 per 
cent. 
