OBSERVATIONS ON THE CALIFORNIA VINE DISEASE Ht 
of the disease is subject to marked variations. These variations 
are both individual and inter-individual. Тһе symptomatic differ- 
ences between two plants are often found in replica on the shoots 
ofa single vine. Тһе disease, in fact, appears to work, to use a 
colloquialism, without rhyme or reason. It may affect а single 
shoot, or several shoots; one side only, or the whole of a vine. 
One vine may show all its characteristics, manifold though they 
be, and another, a part, perhaps only one, of them. The disease 
may never proceed beyond the first stages, a not uncommon 
feature, or it may develop slowly until all its characters are 
patent to the most casual observer; more often, however, its 
development is rapid. 
Тһе California vine disease, though it may appear at any time 
of the growing season, usually develops to a noticeable extent 
only when the vines are ripening their fruit, that is, at the most 
critical period of their yearly development. This fact is brought 
out very clearly in the accompanying graphic, which may be con- 
sidered representative when 25 per cent. or more of the vines in 
a vineyard are diseased. When less than twenty-five vines in 
one hundred are affected, the curve may become either flatter or 
sharper: flatter, if the malady develops gradually throughout the 
growing season; sharper, if the disease develops very rapidly. 
As soon, however, as one quarter of the vines become diseased it 
tends to assume the form shown in the graphic. 
The development of the disease is sporadic; and the malady 
always develops in the following general manner whether few or 
many vines are affected: 
A certain number of scattering vines show the ominous symp- 
toms; then more vines, unrelated positionally to the others, be- 
come affected, and thus, by the continued addition of diseased 
individuals, a vineyard becomes, to a greater ог less extent, in- 
fested. There is no such thing, however, as spreading by ef 
tiguity, no *oil spots." Such a thing as a diseased center, using 
exist, nor is there in the 
lves to 
the term in its narrower sense, does not 
different varieties of the grape-vine, if we confine ourse 
the Viniferae, any marked difference in predisposition. One can- 
not predict, as in the case of the powdery mildew, 
for instance, 
