The Food of Plants. 347 
tree, the general structure of the bark becomes altered in a 
conspicuous manner, while in both bark and leaves, the 
accumulation of starch is most unusual. These features are 
so characteristic of the disease, and appear so early in its 
development, that a correct diagnosis may be made through 
the aid of the microscope, even before the external 
evidences of disease are pronounced. In the new wood 
formed after treatment, the bark presents all the features 
of normal structure, both with reference to tissue and 
distribution of starch. 
We thus note certain important facts as the result of 
these experiments : 
Ist. That a specific disease is cured by a certain course 
of treatment. 
2nd. That potash and chlorine are essential to restored 
functional activity. 
3rd. The disease may be regarded as primarily due to 
deficiency of these elements in the food supply. 
But we should also point out that for this disease, any salt 
of potash will not answer, 7.e. the sulphate or the phosphate 
will not be equally efficacious with the muriate, but that does 
not permit us to infer that diseases of other plants may be 
similarly cured by the same salt of potash, for on the con- 
trary, the same investigations have shown that for different 
plants, different salts of potash must be used, so that while 
in some cases the chloride is best, in others it is the sulphate 
or nitrate. 
We have here, however, a definite fact established, 
namely, that the nutrition of the plant bears a most 
important relation to its normal condition, and while we do 
not wish to rashly assert that all diseases to which plants 
are subject may be cured in this way, yet we do feel con- 
fident that, when the bacteria craze has passed its fever heat, 
and the pulse of the investigator has once more returned to 
a normal rate, he will turn his attention more fully to the 
question of nutrition as affording a rational explanation of 
many of the vexed problems which now confront him. 
Before taking final leave of this part of our subject, I will 
