OBSERVATIONS ON THE CALIFORNIA VINE DISEASE 151 
manifestation of an organic weakness, they are worthy of 
consideration. 
The California vine disease develops with greater intensity in 
sunshine than in shade, in wind-blown vineyards to windward 
rather than to leeward, and soil fertility and texture are not 
without influence. I shall examine more at length these factors, 
and independently of one another, though in reality, they 
cooperate more or less. 
Shade.—The effect of shade on the development of Ше 
disease is marked. Pierce notes that vines well shaded are but 
slowly killed; Ша“ shade has a marked retarding influence upon 
the work of the disease." My own observations confirm this 
view. Vines shaded at the time the rupture of equilibium be- 
tween transpiration and absorption is brought about in the open 
vineyard, whether by sudden insolation or insolation plus 
humidity or wind, are not affected except in extreme cases. 
Insolation.—The effect of excessive insolation has been ob- 
served by Morse, who remarks that “ many successive vines could 
be found with dead spurs of last year upon the sunny side, and 
not infrequently a line of dead wood extended with the fiber to 
or near the surface of the ground. No shoots started from this 
side. Suckering, if it occurred at all, came invariably from the 
north side, where the greenest wood was always found; in ас, 
I saw no line of dead wood upon this side.” 
The deleterious effect of intense sunshine following a deposi- 
tion of moisture is well known to all horticulturists. Morse 
thinks that water of condensation is not without effect in the 
burning of the foliage in some cases of the California vine 
disease. He writes: Those vines “which are protected more ог 
less by trees, present a scalded appearance; some leaves show 
three different stages: about the margin, and extending an inch 
or so outward, they will be perfectly red and dead; next comes 
a zone of light green color, followed by another only slightly 
lighter colored than the healthy part of the leaf. These are 
usually most exposed to the sun. In the early morning large 
drops of moisture, almost equal to that from a heavy rain, are 
1 е 
Loc. cit., 111. 
* Loc. cit., 177. 
