THE 60 
GARDEN YARD 
the plant. The “best temperature’ varies 
with the species and variety. Usually, if the 
soil is hotter than that, growth stops, and if the 
greater heat is kept up, the plant dies. When 
the temperature is lowered, growth ceases before 
freezing point is reached. Some few plants may 
be frozen without injury if they are allowed to 
thaw slowly, but most of them are easily killed 
by the frost. Too great heat or too much cold 
acts the same as lack of water; the heat causes 
too great evaporation, the cold prevents the 
roots taking in the water. 
Shingles stuck in the ground on the sunny 
side will serve to protect young plants from sun 
and rain, while cool soil may be had by using the 
shady places, or by sheltering the ground with 
flat sheds the roof boards of which have open 
spaces between them as wide as the boards. 
This is done in some southern tobacco fields. 
It is the law of nature that living cells must 
have a constant supply of oxygen, that is why 
a tar wash sometimes kills plants by cutting 
off the air supply. In the same way, too wet 
soil or too hard a crust smothers the roots and 
the plants die. The surface soil should be kept 
loose and sufficiently dry, so that the air can 
circulate. If this be prevented, the soil be- 
comes hard and sour and unfit to feed plants. 
