Researches into the Nature of the Potato-Fungus. 
267 
fection spread to its healthy neighbours all through the sum- 
mer, though several healthy stalks had come into direct contact 
with the diseased one. Repeated examination with the micro- 
scope showed that the sickly shoot actually contained Phyto- 
phthora; kept moist under a bell-glass it formed conidia, but 
while in the open-air no conidiophores were observed. The 
weather during the experiment was not unusually dry. 
The negative result thus obtained caused me to doubt 
whether my previous explanation could hold good in the open 
field, and this opinion I stated in a letter to the Secretary of 
the Society. 
Still, it would not have been justifiable to come to a final 
judgment from a single failure in an experiment dealing with 
such complicated materials as two kinds of living plants, 
and the phenomena connected with their relation to each 
other, and the influence of the weather upon them. I ac- 
cordingly repeated the experiment during the present year 
(1875). In March, about 50 healthy potatoes were inoculated 
at the eyes by fresh conidia. No exact test was applied to as- 
certain whether the infection had taken place ; the result, how- 
ever, showed that it had succeeded in most cases, though not in 
all. On the 2nd of April the tubers were planted in common 
garden-soil, in a box without a bottom, and open to the air — 
that is to say, in a miniature garden, which, in order to be more 
easily looked after, was thus fenced in. The tubers sent out 
shoots in a normal manner ; many, even of the specimens known 
to be diseased, producing undoubtedly healthy foliage. One, a 
red kidney, was specially distinguishable from the rest, because 
the six shoots which it sent above ground remained in a wretched 
condition. On May 12th these shoots had become brown ; I cut 
off one of them for microscopic examination and found the living 
fungus in it ; the presence of the fungus in the tuber was also 
afterwards confirmed. The other five shoots were left, and, up 
to the 17th, remained unchanged, without any appearance of 
conidia. On the following night a warm heavy rain fell, and 
on the morning of the 18th the stalks and petioles of the five 
shoots were thickly covered by conidiophores with mature conidia. 
On the healthy foliage of the other plants there was no trace of 
the fungus as late as the 20th ; but on the morning of the 21st 
two leaflets on the upper part of a branch, which was near the 
five sickly shoots, presented the characteristic spots of the Phyto- 
phthora, and on the lower surface of the leaf where these spots 
occurred, conidia were produced ; no further indications of the 
disease were visible to the naked eye. From May 25th onwards, 
the fungus spots were to be seen plentifully scattered without order 
on the stalks, petioles, and leaves of all the plants. About the 
