66 BACTERIA IN RELATION TO PLANT DISEASES. 
With Bacillus tracheiphilus, inoculating from young agar-cultures, potato-cultures, or 
bouillon-cultures into the leaf-blades of cucumbers and other very susceptible plants by 
means of needle-pricks, the writer has seldom been able to obtain signs of the disease in less 
than 3 or 4 days. Usually the first signs (wilt and change of color in the vicinity of the 
punctures) were visible in 5 to 7 days. Occasionally the wilt did not appear until after the 
tenth day, once it was not manifest until after 21 days, and once not till after 30 days. 
In leaves of hyacinths inoculated by needle-pricks with Bacterium hyacinthi signs of 
the disease.appeared in from 1 to 3 weeks. 
In one experiment in cabbage leaves inoculated by way of the water-pores with Bac- 
terium campestre, the serratures of the leaves showed a distinct blackening within 4 to 6 
days, buta period of 3 weeks elapsed before there was any visible spread of the disease down 
the leaf, 7. e., away from the leaf-serratures. In another experiment there was a distinct 
blackening in the region of the water-pores in 6 days. In Russell’s water-pore infections on 
cabbage, signs appeared in 2 to 3 weeks. Stem-inoculations, 7. e., needle-punctures without 
injection, cause signs of the disease in the nearest leaves, viz., yellowing, flabbiness, and 
brown veining after 7 to 28 days (Smith, Harding, Hecke). 
In sweet corn infected in the seedling stage by Bacterium stewarti, a period of 1, 2, or 3 
months may intervene between the first signs of disturbance in the seedling leaves and the 
general sickening of the plant, during which, of course, the plant has grown to many hundred 
times its original weight. There may be an equally long period between local infection and 
constitutional disturbance in case of sugar-cane attacked by Bacterium vascularum. 
In Savastano’s experiments with the olive-tubercle, knots began to appear upon the 
young shoots in a little over a month after puncture and were well developed in 2 months. 
In my own and Mr. Rorer’s experiments, incipient knots were frequently visible as early 
as the end of the second week, 7. ¢., sufficiently developed to be distinguished from the 
control punctures, and were very distinct in a month, but larger, of course, after several 
months (see vol. I, plate 2). Once ina later experiment, starting with cultures very recently 
plated from a knot and introducing the organism by needle-pricks from agar, I observed 
the beginnings of tumefaction on 5 shoots as early as the ninth day. 
In case of the soft-galls, due to Bacterium tumefaciens, the writer has sometimes obtain- 
ed the distinct beginnings of them asearly as the third or fourth day, using pure cultures, 
needle-punctures, and very susceptible tissues such as young shoots of the Paris daisy. 
Earlier than this it is not possible to decide whether the slight swellings are to result in 
tumors or are simply a reaction of the plant to the needle-thrust. Ordinarily ifthe organism 
is virulent, the tumors are distinctly visible in 8 or 10 days if the tissues are young and 
tender, but they continue to grow for several months, or even many months. 
The bacterial leaf-spot diseases are usually visible in 1 to 2 weeks from the date of 
inoculation. 
DURATION OF DISEASE. 
Plants show very different degrees of resistance to a bacterial organism once ensconced 
in the tissues. The soft-rot organisms, as already noted, are usually prompt in their action, 
and a week or two is often sufficient to destroy the susceptible parts. The writer has seen a 
good-sized potato-tuber half rotted in 5 days at ordinary autumn temperatures when 
inoculated with Bacillus phytophthorus by means of a few needle-pricks, this too, in a rather 
dry air; others wholly rotted in 8 or 10 days. Under favorable circumstances, inoculating 
from a young agar-culture, the flesh of a melon one decimeter in diameter may be rotted 
wholly by Bacillus melonis in 4 or 5 days (Giddings, Smith). In case of the leaf-spots, 
progress is much slower, and the disease is generally restricted to small areas, e. g., bacterial 
leaf-spot of the peach, which dry out and fall away from the sound tissue, especially if 
excised by a cork layer. After plain signs appear, a week or two is sufficient in most cases 
to accomplish the destruction of the affected part. In cucumbers and muskmelons attacked 
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