152 POTATO- FUNGUS. 



stalks had come into direct contact with the diseased one. Repeated 

 examination with the microscope showed that the sickly shoot actually 

 contained Phytophthora ; kept moist under a bell-glass it formed 

 conidia, but while in the open air no conidiophores were observed. 

 The weather during tlie 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 Mr. Jenkins, the Secretary of the Society. 



Still, it would not have been justifiable to come to a final judg- 

 ment from a single failure in an experiment dealing with such com- 

 plicated 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 accordingly repeated the experiment during 

 the present year (1875). In March about fifty healthy Potatoes were 

 inoculated at the eyes by fresh conidia. No exact test was applied to 

 ascertain whetlicr the infection had taken place ; the result, however, 

 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 distinguishel from the 

 rest, as 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 Ph/tophthora, and on the lower surface of the leaves 

 where these spots occurred, conidia were produced ; no further in- 

 dications 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 same time several other diseased tubers also gave off small 

 shoots, into which the mycelium of the Fungus had passed from the 

 tuber; no further observation, however, was made on them, because 

 the disease was then far advanced everywhere. Most of the shoots 

 were still quite healthy at their base. They could not, therefore, have 

 received the infection from their tubers, but it could only have come 

 from the conidia produced on the five diseased shoots. To remove all 

 doubts on this point, several stocks were entirely dug up and closely 

 examined in all parts. Two red kidneys had the old tuber still turge- 

 scent, and altogether free from the Fungus ; the base of the shoots was 

 likewise entirely free from the Fungus, while in the upper part the 

 Fungus spots existed in abundance. During all this time to the end 



