388 THE POPULAR SCIENCE MONTHLY. 



same, chiefly involving greater degrees of complexity in the latter, 

 and that we must apply the same principles for the recognition of dis- 

 ease in each case. This view was expressed so long ago as 1846,* and 

 receives confirmation in the expressions of some of our best patholo- 

 gists of the present day.f Frank J tells us that " disease is eveiy de- 

 viation from the normal condition of the species " ; while Sorauer * 

 says, " We must recognize as a disease every distui-bance of the organ- 

 ism which detracts from the final end of its labor, the accomplishment 

 of its purpose." 



In considering the diseases of plants, it is important to bear in 

 mind that we have to deal with subjects which on the one hand are 

 cultivated, and on the other hand not. In forest-trees there has been 

 no modification through cultivation, and disease would not be likely 

 to become complicated from this cause. In cultivated trees, and 

 plants, as in the peach, pear, strawberry, rasjiberry, etc., a high degree 

 of cultivation has I'esulted in a corresponding modification upon which 

 the pecuniary value directly depends. This strong divergence from 

 the original type involves a debility in one or more directions, and is 

 quite parallel with the changes known to occur in more highly civilized 

 communities of men, by reason of which diseases are not only likely 

 to be more prevalent but more complicated. This analogy, as well as 

 general principles, would show us that the more highly cultivated the 

 varieties of fruits or plants, the more susceptible are they to the influ- 

 ence of environment with the introduction of disease, and this is con- 

 firmed, not only by personal observation, but by the experience of 

 practical fruit-growers. 



Again, cultivated fruits always tend to revert to the original form 

 when the conditions of their high state of development are withdrawn. 

 Moreover, such organs often show that this excessive development has 

 obliterated, wholly or in part, those important functions connected 

 with the reproductive processes which they were originally designed 

 to fulfill. These are some of the evidences that all such monstrosities 

 as our modern apples, pears, strawberries — in short, all our cultivated 

 fruits — are in reality abnormal growths which we may designate as 

 hypertrophied structures, and are therefore evidences of disease. In 

 such cases, therefore, the questions of treatment are likely to become 

 somewhat complicated, since, while maintaining a certain form of dis- 

 ease, we must exclude, prevent, and cure all others. 



Diseases may be general in the system, or they may be localized, 

 and this is a consideration of obvious importance when we bear in 

 mind that, according as they are one or the other, they may be more 

 or less destructive in their effects or be controlled with greater or less 

 difiiculty. When a disease involves the entire system, as in peach-yel- 

 lows or pear-blight, it is often a matter of great difl5culty to deter- 



* Smee on " The Potato Plant." % " Krankheiten der Pflanzen," p. 2. 



t " Lancet," 1880,' vol. ii, pp. 605, 645. « "Handbuch," p. 56. 



