MISSOURL BOTANICAL GARDEN BULLETIN 49 
increased from 45° to 50° F. at night and 10 degrees higher 
during the day until the maximum of 70° at night and 80° 
during the day is reached. Sudden changes in temperature 
will promote mildew, as well as check the growth and fruit. 
When artificial heat is discontinued similar troubles appear 
if the house is kept tightly closed. Vines enjoy fresh air com- 
bined with a humid atmosphere and ventilation should be 
given, avoiding direct drafts. 
When starting into growth the plants should be sprayed 
several times during the day up to the time of flowering. 
During this period water should be withheld from the foliage 
so as not to interfere with pollination. After the setting of 
the fruit overhead spraying may be resumed, but it should 
be reduced to a minimum when the fruit begin to show color ; 
otherwise the fruit will become spotted. Ordinarily, vines 
are rank feeders, responding with maximum fruit production 
when fertilizers are applied. Potash is the most essential for 
fruit development and is frequently applied in the form of 
nitrate of potash. Wood-ashes and bone-meal are likewise 
beneficial, especially if mixed with the soil when the bed is 
under construction. For local application when the vines are 
established organic fertilizer in the form of cow manure is 
most commonly used, being applied first when the grapes are 
thinned and again after they have passed their stoning period 
or when the fruit begins to swell. Many so-called grape fer- 
tilizers are on the market, but the grower must learn from 
experience which to use, as much depends upon the nature of 
the original soil. 
An important factor controlling crop production is correct 
pruning. There are two systems of pruning in general prac- 
tice, the spur system and the long-rod system. The spur sys- 
tem is the one usually adopted in this country. The young 
canes, the first season, are cut back to about one foot above 
ground. The following season they are pruned to about four 
feet, the subsequent cutting of the terminal depending upon 
the desired height of the vine. This may seem a rather drastic 
method, but it is necessary in order to produce strong growth 
for future development. The interspacing of the spurs or 
lateral shoots should be about fifteen inches apart so as to per- 
mit east training along the supporting wires or trellis. In 
pruning the lateral dormant shoots they should be cut back 
