196 
FLORIDA STATE HORTICULTURAL SOCIETY. 
Amongst the diseases of the citrus, 
Dieback, Melanose, Yellow Spotting and 
Frenching have been classed as malnu- 
tritional diseases. But from recent in¬ 
vestigations it is concluded that Melanose 
is probably due to some organism. As in 
the case of all other malnutritional dis¬ 
eases, the primary cause of Dieback has 
not yet been traced; but it seems probable 
that it is connected with the nitrogenous 
feeding of the plant. The probable cause 
of Frenching is a disturbance of feeding 
conditions in the roots. 
O. Butler (Bui. 168, California Exper¬ 
iment Station) concludes, from his ob¬ 
servations, that' the grape-shrivel is a dis¬ 
ease of the fruit of grapes that is due to 
improper feeding conditions. 
The injurious effects of over-fertliza- 
tion and of chemical injury may be 
classed as malnutritional troubles. Many 
cases of injury to the citrus tree from 
giving very large amounts of readily 
available fertilizers are known. Quite 
frequently injury is reported from the 
use of bluestone, both beneath the bark 
and on the soil around citrus trees, for 
the treatment of Dieback. 
Headden (Bui. 131, Colorado Experi¬ 
ment Station) reports an injury of fruit 
trees which he concludes is due to arsenic 
in the soil, that had collected there from 
the continued use of arsenical sprays. 
Other instances of presumed malnu¬ 
tritional troubles might be mentioned. 
TREATMENT AND PREVENTION OF DIS¬ 
EASES. 
The method of treatment for a disease 
due to organisms is radically different 
from that which must be employed for 
a disease due to adverse conditions of 
growth. The purpose of the treatment 
for a disease due to an organism is to 
kill or prevent the growth of that organ¬ 
ism. For that reason, we use insecticides, 
such as whale-oil soap, for insects; and 
fungicides, such as Bordeaux mixture, 
for fungi; and we prune to remove the 
diseased portion which serves as a source 
of infection for healthy parts. But in 
the treatment of diseases due to adverse 
growth conditions, these methods are 
worthless. For these diseases it is neces¬ 
sary to right the conditions under which 
the plant is growing. These conditions 
are those which have been enumerated 
above. * 
conclusion. 
The facts presented in this paper may 
be summed as follows: 
1. A plant disease is an unsound or 
unhealthful stat$ that results from a fail¬ 
ure or disturbance of the normal living 
processes in the plant body. 
2. The causes of disease in plants are 
insects, fungi, bacteria, or adverse factors 
of growth. 
3. Diseases due to adverse factors of 
growth are known as Physiological Dis¬ 
eases; among which those due to im¬ 
proper feeding conditions are malnutri¬ 
tional diseases. 
4. Though there are many malnutri¬ 
tional diseases, it is difficult to prove that 
a disease belongs to this class. 
5. To treat diseases due to organisms, 
it is necessary to destroy or prevent the 
growth of the organism. 
6. To treat a physiological or a mal¬ 
nutritional disease, it is necessary to right 
the growing conditions of the plant. 
