DISEASES OF PLANTS 
cated, the environment and the relations 
between the organism and the environ- 
ment. It is often difficult to distinguish 
between health and disease; because of 
the differences between the standards 
by which comparisons are made. For 
instance, whoever has seen an oak in the 
Appalachian mountain range, where it is 
“King of the forests,” and would com- 
pare it with the same species and vari- 
ety found in the semi-arid bluffs of 
Kansas and Nebraska, would incline to 
the opinion that the stunted specimen of 
the semi-arid section is diseased. How- 
ever, the short, scrubby specimen of the 
Central West is normal to that region 
and not diseased. It may be pointed out 
that certain specimens of that region 
are decaying, have been attacked by in- 
sects, broken by storms, are not properly 
nourished, the leaves turning yellow, and 
that these particular specimens are dis- 
eased while the normal specimens, with 
no visible decay, no external injuries 
and no apparent lack of nourishment, are 
healthy. Prof. A. D. Selby, Botanist of 
the Ohio Agricultural Experiment Sta- 
tion, says: “The idea of disease is not 
an easy one, though it may seem so be- 
fore trying to define it. In reality, the 
term disease as applied to plants means 
any change in the plant towards re- 
duced vigor from the ordinary behavior. 
To put it in another way, a plant is said 
to be diseased when it shows deviation 
from the average behavior of the plant 
in respect to appearance, growth, color 
of bark, foliage, fruitfulness, time of 
dropping the leaves, or length of life. In 
short, when the plant fails to perform 
those functions, or conform to those aver- 
ages which have been established by ob- 
servation for the species and variety 
in question, we say that it is diseased. 
Under such general definition, variegated 
or purple hued spots would be included, 
although diseased potentially rather than 
in reduced vigor.” 
In deciding the question of what are 
favorable and what are unfavorable con- 
ditions results obtained from  experi- 
ments or from observed phenomena 
would be determining factors as against 
any theory. The best conditions would 
887 
be those in which the best specimens 
were produced; average conditions would 
be those in which average specimens 
were produced; and poor. conditions 
those under which poor specimens were 
produced. By observations of this char- 
acter, it can be determined what envir- 
onments are most favorable for the 
health and vigor of the plant. In this 
manner we have come to know in a 
measure what are the conditions best 
suited to the different varieties of apples, 
peaches, pears, plums, grapes, straw- 
berries and bush fruits. We have by a 
general study of the subject, by infor- 
mation gathered from all available 
sources, from farmers, experiment sta- 
tions and experts who have traveled 
widely, made comparisons so that there 
is a general ideal or standard of judg- 
ing, by which plants are compared and 
the plants of normal growth, excessive 
growth and stunted or diseased condi- 
tions determined. 
It would seem that a comparison 
should not therefore be made between 
the most perfect specimens and any 
particular individual of the species, nor 
should it be made between the more 
stunted specimens and the same indi- 
vidual, but with the average, for it is 
the great law of averages that deter- 
mines the standard of any race, species 
or variety. 
Perfection as a Standard 
We have often urged that perfection 
should be the standard by which com- 
parisons are made, and we still insist 
on this when we are trying to improve 
the stock. But judging in reference to 
diseased specimens is another matter. 
Perfection is defined as “Having all 
properties and qualities necessary to its 
nature, of the best, highest, or most com- 
plete kind of type, without deficiency, 
fault or blemish.” Sometimes it is de- 
fined as “Finished, incapable of being 
improved upon.” In this latter sense 
the word is never used in reference to 
fruits, for like most other things in na- 
ture, there is no limit to the degrees 
of improvement. The apple of the future 
will perhaps be as much better than the 
apple of today as the finest specimens 
