3 74 American Horticultural Society. 



its normal condition, and still find in the latter the same parasites which 

 accompanied the former, we not only demonstrate that the action of the 

 parasite can be controlled, but that it probably has no direct pathogenic 

 value in that particular case. Such results have been obtained.* It therefore 

 becomes a most important question to determine whether these organisms 

 have a true pathogenic function, or if they are simply concomitants of disease. 

 In general it may be considered that the growth of one organism upon 

 another is at best a struggle for supremacy which must be decided in favor 

 of that individual which is capable of bringing the greatest vital resources 

 to bear upon its antagonist for the longest time, and there are many facts 

 which would justify us in believing that the influence of these organisms is 

 of a secondary rather than primary nature. At the same time, however, we 

 must recognize that these parasites develop according to the same laws, and 

 that their action is probably similar, whether in the plant or animal ; and 

 the various investigations concerning the relation which these organisms 

 bear to animal pathology, offer, therefore, convenient means of examining 

 their probable influence in the promotion of diseases in the plant. 



In certain destructive diseases of the animal, it appears to have been well 

 demonstrated that some of these organisms are most active and direct 

 pathogenic agents, and yet it remains an open question as to whether the 

 results are due to the physiological activity of the parasite in breaking down 

 organic substance, or in the production of deleterious compounds which by 

 first causing neci'osis, permits the secondary influence of the plants in the 

 promotion of disorganization to come into operation. As Sternberg ex- 

 presses it,t " It is not alone by invading the blood or tissues that bacteria 

 exhibit pathogenic power. Chemical products evolved during their vital 

 activit}^ external to the body, or in abscesses or suppurating wounds, or in 

 the alimentary canal, may doubtless be absorbed and exercise an injurious 

 effect upon the animal economy. Indeed, we have experimental evidence 

 that most potent poisons are produced during putrefactive decomposition of 

 organic matter. The poisons resembling the vegetable alkaloids in their 

 reactions, called ptomaines by Selmi, who first obtained them from a cadaver, 

 are fatal to animals in extremely minute doses. These ptomaines have also 

 been obtained by Gautier from putrid blood and from normal secretions of 

 healthy persons— saliva, blood, etc." What is thus true in the animal may 

 likewise obtain in the plant. 



Whether they arise from the action of these parisites or from other causes, 

 pathological conditions are doubtless to be regarded as developed in the 

 vegetable kingdom in accordance with the same general laws which control 

 them in the animal ; the laws which primarily control life are the same in 

 each case, and departures from them must result similarly. Diseases origi- 

 nate in disturbance of the protoplasmic functions, and through this involve 

 the entire organism. 



■■Diseases of Plants. Penhallow. Series III, No. 2, p. 36. 

 i Bacteria, p. 257. 



