506 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
was introduced to this country some years ago, and its name was changed from 
'Paul Kruger,' or < President Kruger ' (by which it was also known), to 'Presi- 
dent,' and under that name it was widely grown both in Scotland and England. 
It was found to suffer increasingly from leaf-curl, and at last was practically 
discarded, not before an attempt was made to select healthy tubers and so to 
secure an immune stock, which was put on the market under the name of ' Iron 
Duke,' and which succumbed too. 'Magnum Bonum,' another old variety, and 
others now in commerce are liable to the disease. 
Two or three years ago Dr. Quanjer published an account of observations he 
had made going to show that in plants affected with leaf-roll the phloem was 
altered and its function interfered with. He has extended and confirmed 
his observations, which met with some amount of criticism at the time 
they were first published — mainly on the part of those who confused the form 
of leaf-curl with which he was dealing with other forms — and has made a 
series of experiments with the object of ascertaining the cause of this diseased 
condition of the phloem. 
Since the first appearance of the disease, watch has been kept upon it, and it 
has been found to increase in a district after its first introduction ; while, as 
already noted, selection has given anything but certain results, although at first 
they appeared quite favourable. This uncertainty suggested that the disease 
was either communicable or that the Potato was subj ect to sudden and frequent 
mutations, or changes produced by no assignable cause. Dr. Quanjer has now 
experimentally proved by well-controlled experiments that (i ) the disease attacks 
plants from healthy tubers placed in diseased surroundings. (2) If diseased pieces 
of Potato plants were grafted upon healthy stocks, the latter also became diseased, 
while other plants from the same tubers not so grafted remained quite healthy. 
Tomato plants similarly grafted also contracted the disease, but to a much 
slighter extent. (3) Infection took place when pieces of diseased tubers were 
grafted upon healthy ones. (4) Soil in which diseased plants had been grown 
carried the infection, and the infective power of the soil may (in badly tilled 
ground) be retained for so long as five years. (5) Plants growing in the neighbour- 
hood of diseased plants often contract the disease, although frequently not to a 
serious extent in the first year, but in the succeeding year their tubers will 
produce diseased plants. (6) Experiments made with seedlings were somewhat 
inconclusive, but suggest the probability that the disease is also transmissible 
to seedlings. 
All these experiments point to the contagious character of the disease, but the 
microscope and cultural experiments have failed so far to demonstrate the nature 
of the contagium, nor has injection of the juices of diseased plants reproduced 
the disease. It seems apparent, however, that some sort of virus is concerned, 
and that it often enters the plant by way of the root and may spread quite early 
in the season from diseased to neighbouring healthy plants, although the 
symptoms in these may not be very marked. 
k$p From the grower's point of view the practical points that emerge are these : 
Tubers from diseased plants, even when the disease is but slight, will produce 
diseased plants, and the symptoms of disease will be most marked when the con- 
ditions of cultivation are least favourable to the Potato plant, Susceptible 
varieties (perhaps all are susceptible, more or less) are likely to contract the 
disease when planted in infected soil ; but in the first year the disease is not 
likely to be very serious. The remedy lies in the cultivation of Potatos intended 
for seed purposes in uninfected soil and from healthy tubers. Considerable 
difficulties lie in the way of this, but until at least the nature of the contagium is 
known, and the actual method of transference made clear, this is the only means 
likely to lead to the production of healthy stocks of this most important crop. 
F. J. C. 
Potato " Leak" Disease. By L. A. Hawkins {Jour. Agr. Res. vol. vi. No. 17, 
July 1916, pp. 627-640; 1 plate, 1 fig.). — Two organisms are found to be the 
cause of Potato " Leak " Disease, namely Rhizopus nigricans and Pythium 
Debaryanum, the latter being more frequently found in the infected tubers. 
Infection takes place through wounds in the skin, and soon a wet rot is set up 
which ultimately destroys the entire tuber. ~ - 
The control measures suggested are a careful sorting of wounded tubers, and 
care in harvesting and storing the potatos. — A. B. r 
Potato " Silver Scurf " caused by Spondyloeladium atrovirens. By E. S. 
Schultz (Jour. Agr. Res. vol. vi. June 1916, No. 10, pp. 339-35°; 4 plates). — 
The author finds that although the conidia range in size from 18 to 64 p., there 
is but one species oi^Spondylocladium . 
