266 Researches into the Nature of the Potato-Fungus. 
its way to the foliage and attack it. The proof of this gives 
the answer to the question raised by me at the outset. 
The facts which have been observed establish that there are 
two "methods by which the conidia may pass from the tuber to 
the foliage. 
First, it is known that the mycelium of the fungus in the 
tuber, even when in the ground, is able to produce conidiophores 
bearing conidia directly from the tuber. We can easily see 
how the conidia thus produced could reach the foliage — they 
might be carried up either by the growing plant which may 
have touched them, or by small animals which frequent both 
situations. Neither of these methods can be easily detected,. 
Moreover, the formation of conidia in the soil cannot be very 
frequent. There should, therefore, perhaps, be little weight 
attached to this method. 
The second method can be easily observed and with great 
exactness. It consists in the mycelium growing from the tubers 
in and with the young plants, and producing conidia on them 
in the usual way ; and these, of course, extend the fungus to the 
healthy plants beside them. 
In 1861* I called attention to the fact that tubers containing 
Phytophthora, when they are growing, not unfrequently send out 
shoots into which the fungus passes from the tuber. The fungus 
advancing slowly in its growth, at last kills the shoots which, for 
the most part, were always in a sickly condition. The same 
tubers, as is known, may also send out healthy shoots. At the 
same time I further showed, that under special circumstances the 
fungus in these diseased shoots develops conidia, which become 
centres for the further spread of the disease. These were not 
conjectures, but facts observed in experiments. The observa- 
tions, however, were not made in the open field, but in the 
house and laboratory, and had not been confirmed by myself or 
observed by others in the open field. It was, therefore, a ques- 
tion whether these results were only to be obtained artificially 
or really occurred in the field, and this could not be decided 
except by experiment. Accordingly, in 1874, in prosecuting 
the investigations undertaken at the request of the Council 
of the Royal Agricultural Society, I made an experiment in 
the garden. A potato, with a tolerably well-developed shoot, 
containing Phytophthora, was planted in the garden with 
several others which had vigorous and healthy foliage. The 
diseased shoot was discoloured for some distance along the 
stalk, but continued to grow for a while ; the brown places 
died off by degrees, were completely dried up, and no in- 
* ' Die gegenwartige Eartoffelkrankheit.' 
