Some Diseases Due to Malnutrition 
B. F. Floyd. 
The average citrus grower can recog¬ 
nize the presence of disease in his trees, 
but he frequently fails to distinguish be¬ 
tween different diseases, and to ascertain 
their causes. Some will attribute all their 
tree troubles to unfavorable growth con¬ 
ditions; while others consider them to 
be due wholly to the attacks of insects, 
fungi, or bacteria. 
CLASSES OF PLANT DISEASES. 
All plant diseases may be included in 
two large classes: those that are due to 
the attacks of living organisms, and 
those due to unfavorable growth condi¬ 
tions. These two classes are not entirely 
independent of each other. It often 
happens that trees growing under unfa¬ 
vorable conditions are in consequence 
made more susceptible to the attacks of 
parasites, and vice versa. For example, 
citrus trees weakened by the cold are 
more susceptible to attack by the wither- 
tip fungus (Colletotrichum gloeosporio- 
ides) ; and also citrus trees attacked by 
the withertip fungus are more easily in¬ 
jured by cold than are healthy trees. Cit¬ 
rus trees badly infested with the white- 
fly are more susceptible to injury by cold 
than are healthy trees; but in this respect, 
as well as in other instances of insect in¬ 
festation, the contrary is not known to 
be the case. 
what is disease? 
The dictionary says that disease is a 
morbid condition resulting from a failure 
or disturbance of the normal living pro¬ 
cesses. It defines the word morbid as be¬ 
ing in an abnormal state; or, not sound 
and healthful. Therefore, a plant dis¬ 
ease is an unsound or unhealthful state 
that results from a failure or disturb¬ 
ance of the normal living processes in the 
plant body. 
v 
WHAT IS THE CAUSE OF A DISEASE? 
The cause of a plant disease is that 
thing or condition that produces the fail¬ 
ure or disturbance of the normal living 
processes in the plant body. These 
things and conditions are, first, hostile 
organisms, such as insects, fungi and 
bacteria; second, unfavorable growth 
conditions; and, third, a combination of 
these factors. 
From this it is seen that hostile organ¬ 
isms affect the plant in nearly the same 
manner as do unfavorable growth con¬ 
ditions, in that each affects the normal 
living processes. For example, the with¬ 
ertip fungus, in attacking the citrus tree, 
affects the living processes in that tree as 
truly as does lack of soil drainage or 
severe cold. 
♦ 
WHAT ARE THE LIVING PROCESSES IN THE 
PLANT BODY? 
Processes within the plant that are 
necessary to life are, respiration, nutri- 
