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10 BACTERIA IN RELATION TO PLANT DISEASES. 
These men repeatedly produced wet-rot of the potato by direct inoculations. Their 
method consisted of cutting out a little tetrahedron from a tuber, to a depth of 10 to 15 mm. 
A: drop of fluid containing the bacteria was put into this wound. The tetrahedral piece 
of the tuber was then put back and pressed in. When the tuber was placed with the 
wounded side up, the cut portion usually dried out, a cork-layer formed under the cut 
surface, and the wet-rot did not occur. On the contrary, when the tuber was placed with 
the wounded side down against wet paper under a bell-jar, in a saturated atmosphere, 
there was always more or less decay of the tuber, and sometimes within 2 or 3 days the 
whole interior became wet-rotten. In no case did Reinke and Berthold experiment with 
pure cultures nor could they have had any active parasite, but we are warranted in 
believing that sometimes at least their mixtures of bacteria were free from filamentous 
fungi. They found different tubers to possess very different powers of resistance, as will 
be mentioned in another place. 
The first edition of Frank’s Diseases of Plants, published in 1880, contains a brief 
chapter on root-tubercles of Leguminosae, but nothing on bacterial diseases of plants. 
The following translation from page 27 of Hartig’s Lehrbuch, published in 1882, shows 
the general attitude of botanists and pathologists at the time Burrill and Wakker were 
working out their interesting and beautiful results. 
With the pathological processes in plants they have nothing whatever to do; in fact, I have 
never on any occasion found the schizomycetes in the interior of a closed plant tissue, and they 
have nothing to do with the falsely so-called rotting processes of dead plant tissue. Of course, this 
does not exclude them from a share in the destruction of dead vegetable substance whenever they 
find an easy access to it. Evidently the interior of the plant is difficult of access to them because 
the open circulatory paths are wanting, which in animals make possible their rapid distribution 
with the blood. Also the circumstance that the wall of the plant-cell is nitrogen-free and is mostly 
very thick in comparison with the size of the schizomycetes, must be an obstacle to the wandering 
of the schizomycete from one cell to another. Finally, also, the formation of humus acids in the 
dead plant tissue will tend to prevent the multiplication of the schizomycetes. 
In Worthington G. Smith’s book (1884) there is nothing on bacteria as a cause of 
disease in plants, although two long chapters are devoted to ‘‘The Potato Disease,” as 
though there were but one. 
In 1884, in his Comparative Morphology, etc., De Bary considered the subject very 
briefly, but much more cautiously than Hartig: 
As Hartig has already pointed out, bacteria living in plants parasitically have scarcely been 
observed. The generally acid reaction of plant parts may be a partial explanation of this. Recently, 
however, Wakker has described as the yellow sickness, a disease of hyacinths.in Holland, in which 
the characteristic symptom consists in the presence of slimy yellow bacterial masses in the vessels, 
éte. = * More exact investigations upon this phenomenon must be awaited. 
The following year, in his Vorlesungen, De Bary devoted two pages to this subject. 
Parasitic bacteria as causes of plant disease have been only infrequently observed. The 
most of such diseases are due to animals and plants of other groups, especially to fungi. 
Wakker’s yellow disease of hyacinths is described briefly from that author’s first papers 
with the remark that “successful infection experiments and the exact following out of the life 
history of the bacterium are still to be awaited.’”’ In the same way, Burrill’s work on pear- 
blight and apple-blight is mentioned, without other comment than that ‘in Europe this phe- 
nomenon, so far as I know, is not known, or at least has not been carefully investigated.’’* 
Prillieux’s studies of changes in wheat-grains are mentioned with the remark respecting the 
micrococcus that “‘its importance as a cause of disease can not be judged with any certainty 
from the short account. It may turn out to be only a saprophyte appearing in consequence 
of other injuries.’’ Finally, De Bary mentions the wet-rot of potatoes, studied by Reinke 
*The disease of the peach tree, of the Lombardy poplar, and of the American aspen, mentioned by De Bary 
on Burrill’s authority as bacterial diseases are now believed to be due to other causes. 
