FUNGICIDES, PREPARATION AND APPLICATION 481 
That a fungicide must be non-injurious to the host is self- 
evident. Hosts, like pathogenes, vary in their sensitiveness 
to fungicides. Some, like the peach, are notably susceptible 
to injury from almost any toxic substance, while others, 
like the apple, will tolerate a wide range in kind and con- 
centration of fungicides. Varieties and even individual trees 
exhibit great variation in their susceptibility to injury, so 
that only after extensive testing may one say with safety 
what kinds and strengths are to be applied to the different 
fruits. Moreover, the liability to injury depends on a number 
of variable conditions, such as the stage of seasonal development 
of the host, or its vitality, climatic conditions, especially tem- 
perature, moisture and the like. It is common knowledge 
among growers that in rainy seasons bordeaux mixture is apt 
to be very injurious to apples, while in dry seasons little or 
no injury follows its application. Foliage on apple-trees of 
low or impaired vitality is much more liable to lime-sulfur 
injury than that of healthy vigorous trees. Grapes of Ameri- 
can origin are almost uniformly injured by the application 
of sulfur in any form while showing no evidence of injury from 
the application of copper fungicides. European grapes, on 
the other hand, are not injured by sulfur. Young, expanding 
leaves of the apple will tolerate a much more concentrated 
solution of lime-sulfur than will the fully expanded and mature 
leaves later in the season, strange as this may seem. 
Adhesiveness, especially where the fungicide is to act in a 
protective way, is a very necessary requisite of a good fungi- 
cide. The spores of most pathogenic fungi are disseminated 
and infect the host during rains. Not only must the fungicide 
be present on the host in advance of the rains, but at least 
enough of it must remain, in spite of the washing of the rain, 
to destroy or inhibit the growth of the spores. Adhesiveness 
may be due to the gelatinous nature of the fungicide as in the 
case of bordeaux mixture, or to the finely divided character 
