the membrane
of the conidium detaches itself from the expelled portion, and while
this is undergoing changes takes the form of a vesicle, which is
destroyed with the membrane. It is very rare that the protoplasm is
not evacuated, and that the conidia give out terminal or lateral tubes
in the manner that is normal to other species without papillae. The
germination just described does not take place unless the conidia are
entirely surrounded by water; it is not sufficient that they repose
upon its surface. Besides, there is another condition which, without
being indispensable, has a sensible influence on the germination of
_P. macrocarpa_, and that is the exclusion of light. To ascertain if
the light or the darkness had any influence, two equal sowings were
placed side by side, the one under a clear glass bell, the other under
a blackened glass bell. Repeated many times, these experiments always
gave the same result--germination in from four to six hours in the
conidia under the blackened glass; no change in those under the clear
glass up to the evening. In the morning germination was completed.

The conidia of _P. umbelliferarum_ and _P. infestans_[L] show an
analogous structure. These bodies, if their development be normal,
become zoosporangia. When they are sown upon water, one sees at the
end of some hours the protoplasm divided by very fine lines, and each
of the parts furnished with a small central vacuole. Then the papilla
of the conidium disappears. In its place appears a rounded opening, by
which the parts of the protoplasm are expelled rapidly, one after the
other. Each of these, when free, immediately takes the form of a
perfect zoospore, and commences to agitate itself. In a few moments
the sporangium is empty and the spores disappear from the field of the
microscope.

The zoospores are oval or semi-oval, and in _P. infestans_ the two
cilia spring from the same point on the inferior border of the
vacuole. Their number in a sporangium are from six to sixteen in _P.
infestans_, and from six to fourteen in _P. umbelliferarum_. The
movement of the zoospores ceases at the end of from fifteen to thirty
minutes. They become motionless, cover themselves with a membrane of
cellulose, and push out slender bent germ-tubes which are rarely
branched. It is but seldom that two tubes proceed from the same spore.
The same development of the zoospores in _P. infestans_ is favoured by
the exclusion of the light. Placed in a p