30
PLANT DISEASES AND FUNGI.
ceeding changes follow each other in regular order. But this is not
all, since another system of reproduction is going on within the plant
tissues. Certain of the threads of the mycelium produce internally
larger globose bodies, sometimes called "resting spores," which
acquire a thick outer coat, and then remain dormant in the plant
stems throughout the winter, only germinating after a period of
rest. It is these "resting spores" which carry over the parasite to
the following spring, and awake to life and vigour just at the time
when young host-plants are ready to receive them. During the
winter these resting spores are concealed within the old herb-stems
which lie and rot upon the surface of the ground. In the spring, it is
assumed, that by the decay of the stems of the original host-plant the
resting spores are freed, and under the influence of spring rains
undergo their final change, like that of a chrysalis to an imago. The
contents of the globose body become divided into a number of seg-
ments, each of which is at length enveloped in a thin membrane,
and furnished at one extremity with a pair of vibratile cilia. When
the thick coating of the resting spore is ruptured, all the contained
zoospores escape, and are washed on to the ground, or wherever the
moisture will carry them, fully competent to carry on the process of
reproduction, by germinating upon the leaves of such young foster
plants as may be growing in their vicinity. By the means of these
two processes of reproduction, the conidia in the summer and
autumn and the resting spores in the spring, the perpetuation of the
species is assured.
After a consideration of this life history, it will become manifest
that such a pest must be met and encountered, in no haphazard
manner, but with skill and perseverance. Burning all the debris of
old plants in the autumn will include the destruction of all the rest-
ing spores, and thus prevention will obviate the necessity of seeking
for a cure.
By this time it will have become evident that there is only one
way in which the fungoid diseases of plants can be successfully
encountered, and that is by the patient acquisition of knowledge,
and a course of action based upon that knowledge. It can no longer
be maintained that the study of fungi is a waste of time; it is no
longer possible to laugh at those who pursue the study as fanatics
and enthusiasts. The old cry of cui bono has no longer any potency,
for it is only by patient study, by the acquisition of knowledge, and
by the spread of knowledge of the life history and characteristics of