26 MISSOURI BOTANICAL GARDEN BULLETIN 
Temperature.—This is an important factor in plant 
growth and is usually subject to considerable variation in 
the home. It is a popular belief that most, if not all, plants 
do better when the temperature is lower during the night 
than during the day, a condition which usually obtains in 
greenhouses, and normally in the home. Plants vary con- 
siderably in their temperature requirements, some failing 
to grow at temperatures much above 60°F. House tem- 
peratures ordinarily run considerably higher than this, and, 
in fact, are high enough during the day for the growing of 
tropical plants. It is obviously impossible to regulate the 
temperature of the house exclusively to suit the needs of the 
plants. It is, therefore, necessary to choose such plants as 
will tolerate the temperatures ordinarily obtaining in homes. 
The attempt to grow plants at temperatures above their 
optimum growth temperatures is a common cause of failure. 
As regards systems of heating, hot-water is probably the 
most satisfactory for growing plants in the house, because 
it has less tendency to produce an excessively dry atmosphere 
and great and abrupt changes in temperature. — 
Humidity—The methods ordinarily used in heating 
houses tend to make the atmosphere excessively dry, and 
unless some provision is made for raising the humidity of 
the air, ety frequently wilt and ultimately die. ere 
many plants are “te together, as in the bay-window or 
house-conservatory, the tendency is to raise and stabilize the 
humidity of the air by the moisture constantly being given 
off from the plants and the soil. But where this is not the 
case, it is necessary to increase the moisture content of the 
air, either by periodically spraying the plants, placing 
vessels of water on the radiator or elsewhere near by, or by 
keeping sphagnum moss—saturated with water—on the sur- 
face of the pots. 
Injurious Gases.—Certain constituents of illuminating 
gas are—even when present in very small quantities—ex- 
tremely poisonous to plants, and unquestionably are fre- 
quently the cause of injury to plants in the house. The 
amount of these gases escaping in small and unnoticed leaks, 
as well as in lighting and turning off gas flames, is doubtless 
sufficient to cause appreciable injury. It has, for instance, 
been shown that one part illuminating gas in 40,000 parts 
of air is sufficient to hers carnation buds from opening, 
whereas exposure for three days kills the young buds. Su 
jecting carnations for twelve hours to an atmosphere con- 
taining one part nertiag re | gas in 80,000 parts of air 
causes all flowers to close. It has further been demonstrated 
that one part of ethylene—a constant constituent of illumin- 
