BULLETIN OF THE BUSSEY INSTITUTION. 325 
In nature, the asexual spores appear principally on the under sur- 
face of the leaf and on the stalk, but, wherever the tissue of the plant is 
cut so that the enclosed mycelium readily reaches the air, we may have, 
them produced. ‘This may be shown, artificially, by making a section 
of a tuber affected by the rot, and placing it in a moist place. In 
a short time the cut surface will be covered with a layer, like cotton 
wool, which, on examination by the microscope, will be found to con- 
sist of mycelium and spores, precisely like those in Fig. 1, only much 
more luxuriant. It is only in the air, however, that the asexual 
spores are produced, never in the substance of the potato. When, 
however, the potato tuber has so far rotted that there are cavities in 
the interior, the spores may be produced in the cavities. 
As just remarked, the spores easily drop off, and, if we bear in mind 
that the greater part of them are on the under surface of the leaf, 
they naturally fall upon the leaves below and to the ground. ‘They 
may also be blown away to a distance. They are easily recognized by 
their oval shape, somewhat pointed at one end, and by their having a 
very short stalk at the blunt end, as in Fig. 2, a. If they fall upon a 
moist surface, no matter of what kind, they begin in a few hours, 
sometimes even in the course of a single hour, to germinate. The 
way in which they do this varies in different cases. The more common 
mode is as follows: The contents of the spore roll themselves up into 
several different masses which collect at the small end, and, finally, 
burst through, as is shown in Fig. 2, c, leaving the empty shell behind. 
Fig. 2, d, gives a more | 
highly magnified view of 
one of the bodies repre- 
sented in c, They move 
rapidly about over the 
moist surface on which 
we have supposed them ®% 
to fall for from fifteen 
minutes to half an hour, the motion growing constantly slower. 
Fig. 2. 
This motion is brought about by the vibration of two hair-like bodies, 
called cilia, attached as shown in the figure. From the fact that they 
move about like animalcules they are called zodspores. The number 
produced in each spore is generally from six to fifteen. At the end 
of about half an hour, having come to rest, the cilia disappear, and the 
