[Vor. 1 
4 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
defined at the close of the season, or at the time of the first 
killing frost, the sprayed plants are almost invariably more 
vigorous. Often, in the practical absence of any disease, 
sprayed plants may remain healthy until killed by frost, while 
unsprayed plants may have died from a few days to а few weeks 
in advance of frost. 
Following a recital of notable increases of yield in Connecticut 
as a result of spraying potatoes with Bordeaux, Clinton (5) ex- 
presses the conviction that an explanation must be found in the 
conservation of water. His statement follows: 
“The question naturally comes up, why did the sprayed 
potatoes give this increased yield over the unsprayed if there 
was no particular injury caused by the late blight fungus? 
Some little benefit was no doubt derived from the prevention 
of the early blight, but this must have been scarcely appreciable 
because this fungus was not at all conspicuous these years. 
Again, some very small benefit may have been due to lessening 
insect attack, since potatoes sprayed with both Bordeaux and 
Paris green keep off the insects somewhat better than where 
sprayed only with Paris green. This is especially true as regards 
the potato flea beetle. But here again the gain was of a very 
minor kind. .Ordinarily botanists have explained this increase 
as due to some stimulative effect the Bordeaux mixture has on 
the chlorophyll of the potato leaves in increasing starch pro- 
duction. Personally, the writer believes that the results are 
largely due to conservation of moisture in the leaves in dry seasons 
by clogging up the stomata and water pores with the sediment of 
the spray. The reasons for this belief are (1) that the potato 
leaves, through their numerous stomata and terminal water 
pores, lose water very easily, and are especially susceptible 
to what is known as tip burn in dry seasons; (2) that the un- 
sprayed vines uniformly suffered earlier and more severely 
from tip burn than the sprayed, which were green for about 
two weeks after the unsprayed were dead; (3) that in 1910, 
which was a season like the preceding years, except with а 
little injury from blight at the very end of the season, spraying 
with ‘Sulphocide’ and commercial lime-sulphur, sprays with 
comparatively little sediment, did not prolong the life of the 
