1896.] The Bacterial Diseases of Plants : 915 
though they exhibit no visible motion in the slime they can- 
not be entirely without motion in penetrating into the bulb.” 
(4) Spores—The bacillus produces endospores. Their de- 
velopment and germination was followed with so much care 
that it appears worth while to give a somewhat detailed 
account. 
“ In the cultures already described [those at room tempera- 
tures] no spores were found. These had, therefore, to be sought 
in some other way. They were finally obtained from the liquid 
cultures by keeping them at a higher temperature. Drops of 
nutrient fluid containing the bacteria were placed in an en- 
closure having a uniform temperature, night and day, of 35° C., 
i. e., at a temperature exceeding the mean temperature of the 
room by about 20° C. Ordinarily, at the end of ten days, 
spores appeared, and the characteristic agglomerations of small, 
motionless individuals did not appear. Subsequently it was 
found that a temperature of 35° C. was not absolutely neces- 
sary for the formation of the spores. In fact, during the sum- 
mer, when a rather high mean temperature prevailed in the 
room, some cultures produced spores without artificial heat; 
but these were never as numerous as those formed in the tubes 
kept at the uniformly higher temperature of the enclosure. The 
spores of Bacterium Hyacinthi (84, pl. I, fig. 1) have that lively 
bluish brilliancy which is usually so characteristic of the 
spores of bacteria, and which is caused by the strong refraction 
of the light. These spores are always a little longer than broad, 
and form in the interior of the largest rods near the middle, 
although ordinarily slightly nearer one of the extremities. In 
consequence of their strong refrangibility it is difficult to decide 
with certainty whether the rod is swollen around them, as has 
been indicated for several similar species. This swelling, if it 
exists, must be very slight, since the spore is not thicker than 
the bacterium itself. Besides the rods with ripe spores, there 
are, ordinarily, a great number engaged in forming spores, an 
these still move about in a lively manner. On the contrary, 
when the spores have reached full development, the rods which 
contain them remain motionless and their wall soon disappears, 
so that the spores become completely free. In this state they 
