118 OBSERVATIONS ON THE CALIFORNIA VINE DISEASE 
that the disease will first appear in this or that variety. We only 
know that at A the disease may affect almost exclusively +; at 
В that у is worse than ғ; and at C that у, и and v are equally, 
or almost equally affected. But such observations as these are 
only good for the season in which they are made; they may not 
be true for the year before, nor yet in the year to come. Ina 
word, the past is no criterion of the future: this is true whether 
the vines become diseased suddenly or progressively, and I mean 
by this latter term an intermittent addition rather than a natural 
sequence of symptoms. 
I have said that the past is no criterion of the future. This 
statement, while true for the individual vine, is not necessarily 
true for the vineyard as a whole. When a large percentage of 
the vines in a vineyard are affected, not suddenly! but pro- 
gressively, it is not infrequent that the disease reappears the 
following years and becomes chronic, as it were, in a large 
number of vines, though it is impossible to select with certainty 
the vines in which it will be so, and gradually, in bad cases, 50 
weakens them that they die. 
From the behavior of diseased vines, both as individuals and 
collectively, it appears that the California vine disease is suffi- 
ciently variable in its mode of action to be considered as pos- 
sessed of two forms, differing from one another in immediate 
virulence. The one we may call apoplectic, from the suddenness 
of its action ; the other chronic, from its lesser destructiveness and 
predisposition to recurrence. These two forms, identical symp- 
tomatically, conduce, the one rapidly, the other slowly, to the 
same end, the death of the vine. It is, therefore, unnecessary, in 
describing the disease, to state specifically which of these two 
forms one has in mind, the line of demarcation between them 
being, to all intents and purposes, but a line in point of time. 
This being so, the following description determines the Cali- 
fornia vine disease, provided the characters of the affected 
organs are considered in conjunction with one another and not 25 
separate and sufficient entities; for, and it cannot be too strongly 
urged, the disease we are considering cannot be surely and safely 
1 When a vine is affected салалары in all its shoots it en dies of ` 
chlorosis the following зеазо 
