THE ENTRANCE OF BACTERIA INTO PLANTS—THE QUESTION OF PARASITISM— 
WHAT CONSTITUTES A PARASITE. 
Among various writers there appears to be more or less confusion of ideas on the sub- 
ject of bacterial parasitism in plants, and on the relative importance of the various 
factors concerned in the production of disease. This has arisen partly from a confusion of 
terms and partly from ignorance of the facts. Wehmer’s argument that “bacterial decay 
is only the last stage of the injury begun by environment,’’ proves too much. It applies 
equally well to animal diseases and, if pushed to its logical extremity, ends in a 
reductio ad absurdum. No one denies that the host-plant or host-animal is more or less 
favorably disposed for the attack of a bacterium according to a variety of external circum- 
stances influencing growth, nutrition, and vigor. Some disturbance of the normally acid 
condition of the stomach allows the cholera vibrio or typhoid bacillus to pass undestroyed 
into thealkaline intestine where it thrives. A slight rawness of the throat, with the death of 
a few cells under certain bodily conditions, allows the diphtheria or tubercle organism to 
obtain a foothold. Awoundsoinsignificant asto be given scarcely a second thought, affords 
an opportunity for arthritis, septicemia, anthrax, plague or tetanus to develop. Are these 
and similar diseases any the less diseases due to bacteria because the entrance of the patho- 
genic organism was favored by some wound or exudate, or other abnormal con- 
dition of the host? By no means! Under ordinary conditions the dead cells would be 
sloughed off, the wounds would heal, and the organism as a whole would continue in its 
normal physiological course. The introduction of the pathogenic organism is the real 
fundament of the situation. It begins a new train of phenomena, and by no amount of 
argument can it be made clear to practical men that, to quote again from Wehmer, “the 
first sort of decay,’’ 7. e., the primary lesion which allowed the bacterium to gain an 
entrance, ‘‘is of interest practically to the exclusion of the other.’”’ To the individual who 
experiences it, the puncture of a pin or thrust of a knife which ends in tetanus must always 
be of considerably more importance than one which is followed only by temporary pain or 
inconvenience, and so of every other injury ending in a bacterial disease. 
It is not denied that general conditions of the host-plant or animal are at times espe- 
cially favorable to the development of the disease, and at other times unfavorable. Neither 
is it denied that the death of a few cells, by suffocation or otherwise, may afford just the 
necessary foothold for the beginning of a destructive disease. These may be the predis- 
posing causes, but they are not the actual cause, neither has the fact that there are pre- 
disposing causes been generally overlooked by animal or plant pathologists, although 
it must be admitted that they are often difficult to disentangle from a multitude of non- 
essentials and to bring into clear relief. There are many degrees of individual 
predisposition to parasitism, as De Bary pointed out long ago, and as every working path- 
ologist recognizes.| The exact determination of the factors leading to special predisposition 
TAs may be seen from the following paragraph, Reinke and Berthold pointed out as long ago as 1879 that some 
potato tubers are much more subject to bacterial rot than others: 
Differenzen im Widerstands-Vermégen gegen die Infection zeigen sich aber auch zwischen verschiedenen Knollen, 
welche vollkommen frei von Phytophthora sind. Wir haben beobachtet, dass solche Knollen, die in einer Wundegeimpft 
und unter eine Glasglocke gelegt waren, binnen zwei Tagen sich vollstandig in eine jauchige Masse umgewandelt 
hatten, wahrend andere die Bacterien nur auf kurze Strecke in das Parenchym eindringen liessen, und dann die nass- 
faule Stelle durch eine Korkplatte aus ihrem Organismus auszuscheiden wussten. * * * Jedenfalls miissen zwei 
Momente zusammentreffen, ein dusseres und ein inneres, damit die Nassfaule in einer Kartoffel ihren rapiden Verlauf 
gewinne, welcher bereits in wenig Tagen zur vollstandigen Auflésung fiihrt; erstens inficirende Bacterien mit ihren 
Fermenten, und zweitens Dispositfon des Kartoffel-Individuums. Wo sich in letzterer Hinsicht zwischen verschied- 
enen, ausgereiften Kartoffeln Unterschiede zeigen, da sind dieselben theilweise vielleicht in der Race begriindet; es 
ware denkbar, dass die wasserreicheren, starkearmeren Sorten leichter der Zeresetzung zur Beute fallen. Doch muss 
diese Frage durch speziell darauf gerichtete, ausgedehnte Versuchsreihen entschieden werden. 
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