49 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 
perses the spores widely through the field and causes. a marked 
downhill spread of infection. 
MOISTURE CONDITIONS FAVORING INFECTION. 
Judging from the evidence already presented under the considera- 
tion of water dissemination, it seems quite evident that the very 
agency of dissemination in that case furnishes the proper condition 
for spore germination and subsequent host infection. In view of 
the even-aged “‘crops’’ of new lesions followimg each rain, it appears 
that infection with anthracnose generally occurs while the plants 
are still wet from a rain. 
However, it was pointed out that some incipient infections are often 
to be found after periods of prolonged drought, and this was attrib- 
uted to delayed penetration by spores already present. Whether 
these spores were present as such or as appressoria is not known, 
although it seems quite probable that the latter may represent a 
resistant resting stage. 
Now, as to the conditions favoring such cases of delayed infection, 
it is of importance to recognize that durmg August in Wisconsin 
heavy dews occur at night and cucumber foliage is heavily coated 
with moisture. Observation has shown that this water of condensa- 
tion remains in drops on the lower epidermis of cucumber leaves, 
while it spreads over and thoroughly wets the upper epidermis. This 
daily wetting of the leaves no doubt affords favorable conditions for 
germination of the spores or penetration from the appressoria. 
Furthermore, there is a possibility that infection may be facilitated 
by guttation water. Large drops of guttation water often collect 
about the margins of cucumber leaves when evaporation is retarded, 
as, for example, in the case of plants under cloth cages. This water 
is sometimes exuded in such quantities as to run down over the epi- 
dermis of the leaf. Marginal anthracnose lesions are common. Two 
samples of guttation water were collected from caged plants, Septem- 
ber 6, 1916, and tested as a medium for spore germination. While 
only a very low percentage of germination was obtained, proof was 
afforded that the liquid was not toxic. 
Examination of watermelon fruits in the South showed the fre- 
quent occurrence of dense masses of incipient anthracnose lesions, 
or ‘‘pimples,”? about the periphery of the bleached area where the 
melon was in contact with the soil in the field. Subsequent exami- 
nation of fruits as they lay in the field revealed that this region of 
their surface was coated with a layer of minute droplets of condensa- 
tion water, while the part in actual contact with the soil was thor- 
oughly wetted. This condition obtained even during the heat of the 
day. It seems quite probable that the exposed band of condensation 
moisture on the under side of the fruit would afford conditions of 
moisture and oxygen supply very favorable to spore germination, 
