36 THE SCOTTISH BOTANICAL REVIEW 
outward visible effect on the plant. This may be called the 
symptomatology of the disease. Then comes the study of the etiology, 
or the investigation of the cause. Then, after the cause is known, 
we are in a position to find out the cure and future prevention, 
namely, the therapeutics and prophylaxis. The first and last of 
these, namely, the diagnosis and prophylaxis, are the most important 
from the economic standpoint. 
Everyone interested in the cultivation of plants should endeavour 
to make himself familiar with the appearance and effect, and 
possibly the botanical names, of the commoner disease-causing fungi, 
also the general preventive measures to be adopted to prevent their 
spread. Itis of the highest importance that a plant disease of any 
kind should be recognised in its earliest stages, as it is then that 
its spread may be prevented either by a timely spraying or by the 
more drastic method of removing the diseased individuals and 
burning them to make sure the disease-causing fungus is destroyed. 
It usually happens that before the advice of the plant pathologist is 
sought, the disease has made itself strikingly apparent by the amount 
of damage done. It is then often too late to effect a cure. 
On broader lines these remarks which apply to the individual 
apply equally to the State. We have seen how the Governments of 
other countries have established Departments to watch over the 
health of cultivated plants, and they are ready at a moment’s notice, 
so to speak, to aid these Departments by special legislation should 
occasion arise in the shape of a threatened epidemic. 
True, our own Government has passed special Acts with the view 
of preventing epidemics, but, unfortunately, these special laws have 
been so tardy and so long delayed that their effect on the disease 
may be the same as the proverbial delay in locking the stable door, 
and in any case there is not sufficient supervision to ensure that 
these special laws are carried out so as to be of real value. 
From the earliest times we have records that cultivated plants 
were subject to blights, pestilence, and disease, which the earlier 
cultivators of the soil attributed to various causes (moon, stars, 
etc.), but we also find the weather, climate, and soil held respon- 
sible for various brands, rusts, and cankers. The existence of para- 
sites or the phenomenon of parasitism among plants was undreamt 
of. Still, we have here a foreshadowing of the study of the effect of 
the physical environment on the health of plants. We know now 
that certain kinds of weather and climatic conditions predispose 
plants to certain kinds of disease, whose life histories we know, 
and we also know that their relationship to their host plants is 
regulated by external physical conditions which may render the host 
plants more vulnerable, and thus enable the parasite to attack and 
cause disease. The weather as a physical factor may predispose 
plants to certain organic diseases, so that the observers in these 
early times were quite correct in their observations, but their con- 
clusions were inaccurate or incomplete. 
Bacteriology has mainly owed its development to the work and 
