150 OBSERVATIONS ON THE CALIFORNIA VINE DISEASE ' 
about unless the plant has reached the proper stage of develop- 
ment. But once the plants have reached the required stage in 
their development then external agencies may hasten or retard 
autumnal changes in the foliage. In countries with a cold winter 
climate it is a matter of common knowledge that the weather 
influences very largely the brilliancy of autumn tints, their period 
of duration and time of development, but is not, I repeat once 
more, the determinant factor: the plant must first have reached 
а certain stage of functional activity. 
The changes occurring in the autumn leaves of vines, vacuola- 
tion and absorption of chloroplasts with, in cases, a slight pro- 
duction of globoidal and homogeneous matters—are similar to 
those observed in the California vine disease; one might say that 
they represent a diseased area of a leaf affected by the latter 
malady in a very mild form. If, therefore, in certain of its forms 
the California vine disease becomes microscopically identical with 
an autumn leaf it necessarily follows that Brunissure, Folletage, 
and Sun-scald are also related to it. In autumn leaves, then, and 
in the above maladies the same cause must be paramountly active. 
And as the changes observed in autumn leaves are due to à 
decrease in functional activity, the disease we are considering, 
i. е, the California vine disease, may be said to be due to the 
same cause. But the same functional inactivity need not neces 
sarily be operative in all cases: 
In autumn leaves the changes are due to a decrease of vegeta- 
tive activity; in the case of Brunissure, to overbearing, 25 
appears from the researches of Ravaz; in the case of Folletage 
Sun-scald, and the California vine disease, to a rupture of equi- 
librium between absorption and transpiration operating upon 
vines weak in their power of absorbing and translocating water, 
and brought about by external agencies favoring transpiration. 
That it is really to a weakened state of the vine that the 
characteristics of the disease above mentioned are due, may be 
deduced from the conditions favoring their development. To 
consider, however, only the California vine disease, these condi- 
tions taken individually could not be held responsible for its ` 
development, but when considered as factors favoring the visual 
