XXV111 
INTRODUCTION. 
this volume to do more than enumerate and describe. As it is 
in animal diseases so it is with those of plants, that a time 
diagnosis must precede any attempts at remedy. All that a 
work of this kind can accomplish is to supply the data whereby 
the true character of the attacking fungus can be ascertained, 
its relationships, and its methods of reproduction, and hence 
conclusions may be drawn as to the best methods of applying 
remedial measures. Empirical methods may sometimes suc- 
ceed by chance, but the only real prospect of permanent success 
is based upon a certain knowledge of the character of the 
disease, and the life history of the parasite producing it. It 
must be remembered that these pestiferous fungi are primarily 
of two kinds, viz., those which are epiphytal, developed upon 
the surface of the green parts, and attaining their end by 
choking up the stomata, preventing transpiration and killing 
the plant by suffocation; or they are endophytal, being pro- 
duced within the substance of the tissues, and establishing 
themselves long before there is any external manifestation of 
their presence. The former class of diseases find a representa- 
tive in the disease of the vine called Erysiphe viticola, and its 
conidial stage, which is a species of Oidium, or effused white 
mould. In such a case, as in the allied European vine disease, 
caused by Oidium Tuckeri, and the common hop mildew, 
Sphcerotheca Castagnei, the application of sulphur has proved 
effectual, as the disease is external, and amenable to the action 
of fungicides. But in the other and larger class of diseases the 
fungi are either hereditary, or the mycelium, developed from 
germinating sporules, enter the young plants secretly, and com- 
mence the work of destruction by permeating the substance of 
the tissues. The latter class includes the rust, smut, and 
mildew of corn crops, and, in fact, all that group of fungi 
which arc described in this volume under the title of Hypo- 
dermece. In addition to these are the rotting moulds, included 
under Perotwspora and its allies, as well as the species of 
Fnsicladium, causing the “ apple scab,” and numerous other 
groups of more or less importance, notably of the genus 
Glceosparium. With these pests prevention is better than cure, 
since the application of external remedies will fail to reach the 
basis of disease, or either destroy tho parasite, or restore the 
diseased tissues to healthy action. Clearly, then, the only safe 
course is to ascertain accurately the nature of the disease, 
which can only be done by a patient microscopical examination, 
and, by taking advantage of the knowledge of its methods of 
reproduction, to destroy the germs, or sporules, check its 
extension, and “ stamp it out.” 
By means of a passing reference to those terrible moulds 
which attack the potato, tobacco, and tomato, and known 
generally as Peronospora, we may indicate what we intend to 
convey by “ knowledge of life history,” and how this know- 
ledge may be turned to account. As a starting point we take 
