DURATION OF DISEASE. 67 
by Bacillus tracheiphilus, the progress of the disease is rapid after the incubation period has 
passed. In squashes, onthe contrary, theresistance is much greater, and it may be several 
weeks after a vine shows the wilt before it entirely succumbs. At night, or in moist weather, 
it becomes turgid, to again collapse with the reappearance of sunlight and dry air. In the 
growing season, pear-blight is usually a rapid disease, but in 
the cool weather of autumn and winter there is frequently an 
almost balanced activity between host and parasite, result- . 
ing in what is known as “hold-over”’ blight. In this way 
the disease is carried from one growing season to the next. 
Vascular diseases, such as those of sweet corn and sugar- 
cane, already mentioned, kill the plant very gradually, if it 
is of good size when infected or when the constitutional signs 
first appear, but after the vascular occlusions have reached 
a certain volume the destruction of the plant is speedy. In 
maize, which has reached this stage, the leaves dry out 
within a few days, and the green stem then shrivels. In 
case of the olive-tubercle, the tree as a whole does not, so 
far as we know, become infected but only particular parts 
of it, yet there may be wide metastasis especially in young 
trees. Individual knots live for several months, and fre- 
quently portions of them for several years, the knot enlarg- 
ing from some particular part which has not been injured 
beyond the power of cell-division. Terminal twigs girdled 
by tubercles are frequently starved and die, but not very 
promptly. Knots and cankers due to bacteria are generally 
of slow progress and correspondingly long duration. The 
life of a shoot of chrysanthemum, sapped by a big tumor 
due to Bact. tumefaciens, varies from 6 months to a year or 
more. Often the plants live many months. Peach trees 
attacked by crown-gall generally live for several years. 
Galled apple trees may live indefinitely. In the recently 
discovered tuberculosis of the sugar beet due to Bacterium 
beticolum (Vide Crown Gall, etc., Bull. 213) decay is rather 
prompt. 
FINAL OUTCOME. 
Plants, like animals, are affected to very different 
degrees by the various bacterial parasites. This must be 
apparent from what has been said under duration of the 
disease. In the animal world there are protracted bacterial 
diseases and rapid ones, diseases terminating fatally or end- 
ing in recovery. The same is true of plants. The simplest 
cases, perhaps, are the stomatal infections resulting in leaf- 
spots and fruit-spots. The leaves are more or less disfigured, 
and the fruit may be destroyed or so spotted as to be unsal- 
able, but generally it is beyond the power of the organism 
to destroy the plant, or even to render it wholly unfruitful. In bacterial blights, such as 
that of the mulberry or pear, much larger portions of the plant may be destroyed, twigs 
or even large branches, and yet it may recover. In a majority of cases, after running a 
Fig. 19.* 
*Fic. 19.—Coconut budrot of Eastern Cuba. Outer enveloping leaf sheaths removed to show condition of inner 
undeveloped leaves—sound below, rotted above. Tree No. 11. Bud itself not dead, but enveloping sheaths rotted. 
Color of decayed part was a mixed gray and brown. Photographed by the writer at Baracoa, Cuba, April 20, 1904. 
One-third natural size. 
