394 



THE POPULAR SCIENCE MONTHLY, 



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 di- 

 rect 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 disor- 

 dered 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 condi- 

 tions 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,* that in 

 certain cases of disease the normal and abnormal conditions are corre- 

 lated 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, 

 the 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. 



* '-Transactions of the Massachusetts Horticultural Society, 1882.' 



