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full development and produce smut pustules and spore beds on every 
spot of the still undeveloped parts of the plant into which they have 
penetrated. The action of the germ is narrowly localized—only those 
parts of the young plant become smutty which have been attacked 
directly by the fungous germs; all the rest remain normal and sound. 
The formation of the smut pustules begins quickly, at longest, 3 weeks 
after the infection. 
The complete result of all the here-cited infection experiments with 
dusty smut, millet smut, and corn smut affords, in the first place, indis¬ 
putable proof that the germs of smut fungi which live sapr ophytically 
outside of the host plants can produce smut diseases. 
When the smut was nourished saprophyticallv longer than a year in 
continual reproduction outside of the host plant, then only did the out¬ 
growth of the conidia into germ tubes cease. Along with this the 
power of infection was extinguished, i. e., with the disappearance of a 
comprehensible morphological character, for the germs can only pene¬ 
trate into the host plants by means of their germ tubes. 
The earlier view that only young seedlings of the host plants are 
receptive to the fungous germ has not been sustained. On the con¬ 
trary, the fungous germs can penetrate into all sufficiently young parts 
of the host plant. 
In the grain-infesting smut fungi, e. g ., in the dusty smut and millet 
smut, of all the fungous germs which have penetrated into the young 
parts of the plant, of course, only those come to maturity, i. e ., to 
the production of smut diseases, which reach the growing point and 
the place of the here-included nascent inflorescence. This takes place 
only in the germs which have penetrated into the young seedling in 
the vicinity of the root nodes during the first stage of germination. 
For all the other germs which have penetrated later this is already 
impossible. The vegetative tips with their incipient blossoms, the later 
place of development of the smut, have already grown away from these, 
and consequently are entirely out of reach inside of the plant. 
The relative rapidity of germination in plants receptive to smut dis¬ 
eases aids materially in determining the subsequent appearance of the 
smut, i. e., the development of the germ which has penetrated. This 
may vary according to the accidental temperature prevailing at the 
time of germination, therefore according to external influences; but 
from internal causes it will also be dissimilar in particular individuals, 
which accordingly may show an individually different receptivity. 
In the peculiarities formerly stated, and now clearly established by 
me, the natural explanation is given, so far as regards smut diseases, 
to the terms “periodic receptivity,” “ subsequent immunity,” and “in¬ 
dividual predisposition to an infective disease.” 
Especially noteworthy is the long incubation period from the pene¬ 
tration of the fungous germ to the outbreak of the disease. The germ 
of the destructive disease is taken up in the earliest youth of the plant 
