78 
Journal of Agricultural Research 
Vol. V, No. a 
and after having nourished several plants to partial maturity. Two days 
later an examination showed that spores and conidiophores were develop¬ 
ing on two of the tubers; but no indication of infection was observed on 
either the leaves or stems which were placed in a moist chamber. 
Examination on the following day showed no further developments, and, 
as the potato plants were becoming very much discolored, the observa¬ 
tions were discontinued. It should be noted at this point that the fungus 
was alive and able to sporulate on the diseased tubers after being in the 
soil for 45 days at a temperature between 15 0 and 20° C. Had the fungus 
been latent in the potato leaves and stems, as claimed by Massee (20), 
it should have developed. The most interesting and important fact 
brought out in this experiment was the production of healthy vines 
by a tuber having in it the mycelium of P. infestans which remained alive 
for 45 days. 
The two pots which were kept at 23 0 to 27 0 0 ., one containing three 
infected tubers and the other three healthy tubers, came up a little earlier 
than those kept at 15 0 to 20° C. The first shoot came up on February 4, 
or 6 days after planting, and in 10 days all three of the diseased tubers 
had shoots up, some of them longer than others. The development of 
the tubers used as controls was several days behind that of the diseased 
tubers. Ten days after planting, the shoots were so tall in the pot contain¬ 
ing diseased tubers that the pane of glass had to be replaced by a bell jar. 
The control was treated similarly. Nothing of special interest occurred 
until March 8, or 39 days after the tubers had been planted, when it was 
noticed that one of the small shoots growing from one of the diseased 
tubers appeared water-logged at and a short distance above the surface 
of the soil. It did not have the normal appearance common to the stems 
of the other seven shoots in the pot. Upon examination of the water¬ 
logged area with a hand lens, a white glistening growth could be seen on 
the surface. Some of this material was carefully removed and exam¬ 
ined microscopically and proved to be spores and conidiophores of P. 
infestans . This infected plant was about 2 inches tall, spindly, light 
green, and less robust in appearance than some of the other plants in 
the same pot (PI. V). The soil was carefully dug away from the stem, 
and a portion of it below the soil was found to be diseased. This portion 
gradually became darker as it approached the mother tuber, being brown 
and doubtless dead at the point of attachment. The parent tuber was 
nearly all decayed, except one small portion, which was still firm and from 
which the diseased shoot in question had developed. Free-hand sections 
made of the portion of the parent tuber where the stem was attached 
showed the presence of a nonseptate fungous mycelium which was un¬ 
doubtedly that of P. infestans . The tissues of the stem nearest the 
mother tuber were softer than those higher up, which would indicate 
that the infection was of longer standing in that section of the stem. 
