168 Annual Report for 1905 of the Consulting Botanist. 
cultivation. The pure culture was placed on healthy potatoes 
which were infected, and after eight days the signs of the rot 
were obvious and its characteristic smell was given off. In 
these trials no other bacteria made their appearance, and all the 
infections of the healthy potatoes were successful. These, 
without doubt, showed that this particular bacterium was the 
cause of the rot. From the readiness with which healthy 
tubers became infected it is clear that this is a dangerous 
organism. One diseased potato in a pit would do serious 
damage, and as each diseased potato would pass on the bacteria 
to its neighbours extensive mischief would be done. It was 
found that when litmus paper Avas brought into slight contact 
with the disease it was instantaneously coloured red, showing 
a strong acid reaction. This justifies applying to this disease 
the name of acid rot. When the whole of the sugar in the 
potato is dissolved by the bacteria the tubers dry and shrivel 
up, often to such an extent as to make them into a flattened 
disc. If the dried tuber be broken a number of cavities are 
seen covered with a chalk-like powder. The bacteria in the 
diseased potatoes are small longish rods, 2'5 to 4^ long and *7 
to *8 y broad. In the cultures the size is slightly less. Both 
ends are rounded. They are identical with those described by 
Migula (, System d. Bcicterien , ii., page 573) and called by him 
Bacillus solaniperda (see Fig 2, a). 
7. A second bacterial disease was observed, which is called 
black leg or potato stem rot. It has been noticed in several 
counties in England, and it has been very destructive in 
Germany. It shows itself by killing the haulm just above the 
ground ; the leaves soon discolour and die. On cutting an 
injured stem, the cells near the skin are seen to be darkish 
brown in colour, and under the microscope these are seen to be 
filled with countless numbers of bacteria which freely move 
about in the liquid within the cell. The tubers become 
attacked either directly from the diseased stem, or by the 
dispersion of the bacteria in the soil from the decay of the 
stem. The bacteria move by the help of four to six minute 
flagella or small hair-like appendices. This bacterium is known 
to attack other plants, such as tomatoes, cucumbers, carrots. It 
is a short, stout, little rod, variable in length, and from *8 to 
TO /x broad. Its name is Bacillus phylophthorus Appel, (see 
Fig. 2, b). No satisfactory method can be suggested for 
dealing with these bacterial diseases in the field. A crop like 
that attacked should not be repeated in the field, but cereals or 
beet root may be grown, as these have hitherto not suffered. 
It is found that tubers kept in dry and well-ventilated pits 
remain free from disease, and that the disease does not spread 
in tubers that are slightly diseased. If used for seed the 
