126 MISSOURI BOTANICAL GARDEN BULLETIN 
out injury to the grass, it having been found that all plants 
with broad leaves will be destroyed while the narrow-leaved 
_ plants will not. The grasses are especially protected because 
they have not the extended absorbing surfaces of the broad- 
leaved weeds. Besides, they are intermediate growers while 
young, growing from the inside outward at the stem ends, 
the young or growing point being protected at the base. The 
parts which come into contact with the spray are the tips 
and these have already done their chief physiological work. 
Even if the tips are killed the basal portion continues to 
grow, furnishing new surface to the sunlight. The grasses 
also have a waxy covered cuticle which causes the chemical — 
spray to remain in round spheres which rattle off at the first 
wind. In the case of the wide-leaved weeds the drop of mois- 
ture extends at once over the entire surface and comes in 
direct contact with the juices of the plant. This readily 
explains why crab grass and quack grass do not succumb to 
the treatment by chemical sprays, as both are narrow-leaved — 
and grass-like. 
The use of chemicals for weed eradication has been suc- 
cessfully employed at the Garden, and it has been found 
that the one which is most efficient and which causes no 
injury to the grass is iron sulphate. It should be applied to 
the lawns by means of a compressed-air type of hand 
sprayer or a traction or cart sprayer, depending upon the size 
of the lawn. Sufficient pressure to make a fine spray is neces- 
sary, for too much solution at one place may cause injury 
to the young grass shoots just beneath the surface, which 
have only a slight power of resistance. If a hand sprayer 18 
used it should Tie fitted with three feet of compression hose 
and a three-foot extension rod for swinging the nozzle over 
the lawn. The solution is made by dissolving two pounds 
of iron hie a in one gallon of water, and, to be effective, 
lawns should be sprayed five to six times during the season 
in order that each set of new leaves may be destroyed as they 
appear. The solution should be applied on bright days, for 
if the rain comes too soon after spraying it may wash ol 
the iron sulphate before it has had a chance to act. It is 
not advisable to spray until two to three days after mowing, 
and the grass should not be mowed until two to three days 
after raying. Care must be taken not to get the solution 
upon clothing or stone walks, on account of discoloration. 
Copper a mie sometimes used in a similar way to 
that described for iron sulphate, except that, as it is about — 
ten times as destructive as iron sulphate, the solution should 
be weaker—about eight to ten unds of copper sulphate 
to fifty gallons of ee = geeeials P : 
