Plant Diseases 
351 
adverse conditions arise, this multiplication stops until the 
conditions become more favourable for their growth again. 
All plants showing signs of this disease should be 
carefully dug up and burned, before there is any chance 
of the bacteria being liberated into the soil, and care 
should be taken not to injure the stems or tubers in soils 
where the disease has at any time been. Insects should 
be kept down also where the disease is feared, to prevent 
them carrying the germs and inoculating healthy plants. 
One example of such diseases must suffice for such a 
work as the present one. Very little has been done up 
to the present. The enormous difficulties in the way of 
carrying out experiments are responsible for such a state 
of affairs, but it may be hoped the time is at hand when 
the work will be taken up and thoroughly investigated, 
and much money thereby be saved. 
Only the fringe of this all-important subject of plant 
diseases has been touched upon here, but enough has been 
said to make clear the great need of a fuller knowledge of 
them being acquired by all those who have the cultivation 
of plants in their hands, not only for the sake of one’s 
own plants, but also because a neighbour’s plants may be 
infected by the spores of the diseases on plants in the 
vicinity. These spores are so very small and light that 
they practically float about in the atmosphere, and wher- 
ever one alights on a suitable host plant in the proper 
condition, with regard to moisture, &c., it germinates, 
creating a centre of disease from which the entire crop 
may be infected. Or, as has been explained, insects may 
carry them on their feet or bodies. Birds also may carry 
tnem on their feet or feathers, or even mammals, such 
