160 MISSOURI BOTANICAL GARDEN BULLETIN 
DAMAGE TO GREENHOUSE PLANTS AT GARDEN 
DUE TO SMOKE 
During the month of November several heavy fogs oc- 
curred in St. Louis, the one on the 9th—because of the ex- 
cessive amount of smoke — causing considerable injury to 
the greenhouse plants at the Garden. Fog is usually accom- 
panied by high humidity, still atmosphere, and a fall of 
temperature. Under these conditions every floating particle 
becomes coated by a film of water, and, due to this extra 
weight, remains stationary or falls, considerably impeding 
the movement of air. This stagnation of atmosphere permits 
the accumulation of the products of combustion in the im- 
mediate vicinity of plants, which under normal conditions 
would be more or less dispersed by the circulation of air. 
It is a matter of common knowledge that soot and certain 
gases are injurious to plant life. Soot exerts a detrimental 
influence by blocking up the air pores of the leaf, thus im- 
peding the process of transpiration, as well as by coating the 
leaf, which reduces the action of sunlight and affects the 
food manufacturing function of the plant. Most plants are 
sensitive to these abnormal conditions, but out of doors the 
evergreens, with their persistent leaves and their deeply sunk 
air pores, which form efficient traps for the particles of soot, 
are unusually susceptible. This is one reason why conifers 
do so poorly in the smoky atmosphere of the city. 
The most injurious and wide-spread product of coal com- 
bustion is ie aati acid, produced by the burning of 
sulphur usually present in considerable quantities in soft 
coal. Not only is this gas directly injurious, but because of 
the readiness with which it combines with water, forming 
sulphuric acid, a corrosive action soon sets in, resulting in 
the drying, blackening or curling of more delicate portions 
of the plants, such as the tips and margins of leaves, young 
shoots, and expanding flowers. The extent of the injury is 
dependent to a degree upon the activity of the plant, and 
during the day when the rate of absorption is greater, the 
action of poisonous gases is apt to be more detrimental. 
Should the fog with its deleterious contents be of prolonged 
duration, complete defoliation may take place. Further- 
more, even though external evidences of damage may be 
slight, the internal injury may be great, since sae areas 
of growing tissue are generally affected, causing a weakened 
condition, with a subsequent susceptibility to fungous at- 
tacks and other troubles. 
The accompanying | rena, or 0 oe a made within a 
day or two after the fog, only partially show the extent of 
