rOTAXO-FtJNGUS. 151 



We have thus two ways in which the living Fungus that has sur- 

 vived the winter, may in the spring find its way to the fields with the 

 seed. The second is, perhaps, the more usual way ; at all events, it 

 is the more dangerous, because, even with great care in the choice of 

 seed, it cannot be avoided with certainty. 



In both cases the Fungus is placed in the earth along with the 

 tuber, and cannot there leave it ; the Fungus must die and become 

 corrupt in and with the tuber. It can, however, find 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 established 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 mycelinm 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 developes conidia, which become centres for the further 

 spread of the disease. These were not conjectures, but facts observed 

 in experiments. The observations, 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 question whether these results were only to be obtained artificially 

 or really occurred in the field, and this could only be decided by ex- 

 periment. Accordingly, in 1874, in prosecuting the investigations 

 undertaken at the request of the Council of the Royal Agricultural 

 Society, 1 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 discoloui-ed 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 infection spread to 

 its healthy neighbours all through the summer, though several healthy 



* "Die gegenwartige kartoffelkrankheit.'' 



