214 BACTERIA IN RELATION TO PLANT DISEASES. 
proved equally virulent to cucumbers, the disease occurring promptly and the signs being 
typical in all respects, including the presence of the sticky bacillus in the vascular system 
(plate 15, fig. r). The inoculation-experiments were repeated a few weeks later with the 
same positive results; squashes and cucumbers being infected with uniform success. Addi- 
tional studies should be made. 
In the inoculated plant, the primary foliar signs (a dulled green with absence of 
turgor) always appear first in the punctured area and immediately around it, but never until 
after a definite period of incubation covering at least several days. The signs of disease 
gradually extend until the entire blade of the leaf is involved. The loss of turgor and change 
to dull green is soon followed by shriveling, after which the leaf-blade becomes brown. 
Subsequently, and usually considerably prior to the collapse of the petiole of this leaf, the 
blades of other leaves up and down the stem suddenly wilt (plate 16 and text fig. 58). The 
first leaves to show this secondary wilting are ordinarily those which arise from parts of 
the stem nearest to the insertion of the inoculated leaf; exceptionally the first leaf to show 
secondary wilt is one standing over the inoculated leaf rather than one actually nearer but 
inserted on the opposite side of the stem. Gradually more and more remote leaves are 
destroyed until the whole plant is involved. 
Whenever this secondary stage of the dis- 
ease supervenes, the vessels in the stem 
(which still outwardly presents a green and 
normal appearance) will be found to be 
occupied more or less fully by the bacillus. 
Usually the organism is to be found in the 
vessels of such plants in extraordinarily 
large numbers. In the stem of the squash 
the writer traced the bacterial occupation 
microscopically in one plant to a distance 
of 210 cm. from the point of infection, and 
in another plant to a distance of 240 cm. 
Almost all of the writer’s inocula- 
tions have been made by means of needle- 
punctures into the blade of the leaf, at first 
often directly from plant to plant, but in 
recent years generally from pure cultures 
(descendants of poured-plate colonies) on 
agar, carrot, potato or in beef-bouillon, and 
other fluids. This method closely resembles 
the natural manner of infection and has given very satisfactory results. These inocula- 
tions now number over 700. A great many check-plants were held for comparison and 
the number of accidental infections (when insect-carriers have been excluded) has been 
practically nil, whereas the number of successful inoculations in susceptible plants has 
frequently amounted to from 75 to 85 per cent of the total number punctured. In certain 
experiments (pages 246, 276) every inoculated plant has contracted this disease, which is one 
of the most infectious known to the writer. So many experiments have been made, under 
such a variety of conditions, and with such good success (except in case of the squashes 
already mentioned) that not the least doubt remains, either as to the bacterial nature of 
this disease or as to the particular organism which causes it. 
*Fic. 54.—Cross-section of small portion of a cucumber-stem attacked by B. tracheiphilus showing condition 
of one of the outer bundles. The pitted vessels lie in the more heavily shaded lignified part of bundle and only a very 
few. of them are occupied by bacteria. All the spiral vessels are filled and the bacteria have formed conspicuous 
cavities in the primary vessel-parenchyma which is a living non-lignified tissue. Other tissues are uninjured. Drawn 
from a photomicrograph. 
