will recognize a well-devised system of irrigation, which may be applied to all his orchards and cultivated fields when necessary, as an indispensable part of the machinery which a successful business demands.
The conditions which produce disease in plants, as well as the direct and secondary effects of their operation, are likely to be more or less complicated, and thus render a direct course of diagnosis and treatment correspondingly hard to reach and apply; but we can hardly form a correct estimate of these difficulties by analogy with a disordered condition of the animal. We have, at the outset, structures of widely different organization, which not only depend upon very different conditions of nutrition, but which are placed in widely different conditions of environment other than this. On the one hand, we have forms which, once developed, occupy a definite position, and their relations to environment—soil conditions, food-supply, etc.—are in a measure fixed. On the other hand, we have more highly organized bodies, which are continually changing their location, and they are thus brought into new relationships, to which they must adapt themselves, and this is liable to complicate the phases of disease already present. I think it will appear, however, that—at least in many cases, especially where nutrition is chiefly involved—we must apply the same general principles in the one case as in the other.
It was shown, not long since, by my friend Dr. Goessman,[1] that in certain cases of disease the normal and abnormal conditions are correlated to the presence of relatively greater and less quantities of certain food-elements. This was demonstrated by chemical analysis of the diseased wood or fruit, the naturally healthy structure, and, again, he diseased structure after being restored by a course of treatment which involved an application of the elements supposed to be wanting. In the case of the peach-yellows, concerning which we have the fullest data, he found the potash to increase in the healthy and decrease in the diseased; while the lime decreased in the healthy and increased in the diseased; and furthermore that, under treatment, the appearance of greater or less quantities of potash was reciprocal with similar changes in the lime present. The following analyses will show this relation:
CRAWFORD'S EARLY PEACH.
| FRUIT. | Healthy. | Diseased. |
| Ferric oxide | 0·58 | 0·46 |
| Calcium oxide | 2·64 | 4·68 |
| Magnesium oxide | 6·29 | 5·49 |
| Phosphoric acid | 16·02 | 18·07 |
| Potassium oxide | 74·46 | 71·80 |
| Total | 100·00 | 100·00 |
- ↑ "Transactions of the Massachusetts Horticultural Society, 1882."
