94 MISSOURI BOTANICAL GARDEN BULLETIN 
Construction.—Pools for the growing of water lilies may 
be made of either concrete or clay. Where the subsoil is 
clay, as is the case generally in this section of the country, _ 
the latter type of pool is much more cheaply constructed and 
has the additional advantage of appearing more natural. 
However, in cases where the subsoil is such that free drain-. 
age results, it sometimes becomes necessary to construct con- 
crete pools. All the new pools made in the Garden this 
spring were built of clay. The clay subsoil in the Garden 
lies only a few feet below the surface, so that it was only nec- - 
essary to dig through the surface loam to uncover it. When 
the clay itself was reached, a basin with vertical sides was 
dug out two feet deep. After the clay had been removed, the 
basin was refilled with one foot of well-mixed soil containing 
a large percentage of cow manure. Finally, water was 
allowed to run in until one foot of water covered the foot of 
good soil. A mistake is often made in thinking that lilies 
need nothing but water. for their growth, but a soil layer for 
properly feeding the plants is just as important. As the 
plants become older the depth of the water can be gradually 
increased by adjusting the overflow. Pools constructed in 
solid clay, as above, practically never leak. 
Where a solid clay subsoil is not available, a process of 
puddling is employed. This consists, essentially, of plaster- 
ing the sides of the excavation with a layer of clay—the 
addition of water making easy the application of the clay. 
Pools so constructed need very little attention and leak but 
little more than solid clay pools, and have an advantage 
over concrete in that they can be enlarged or remodeled at 
any time without much expense. 
The construction of concrete tanks usually requires the 
assistance of a mechanic and does not lend itself well to nat- 
ural surroundings. The formal concrete pool should not 
be used except in conjunction with other formal sur- 
roundings. 
Water Supply—aAfter the initial filling of the pools, it 
requires but a small stream to keep the water fresh and 
clean. It is necessary, of course, to prevent scum from 
accumulating on the surface of the water, as well as to avoid 
providing a place for the breeding of mosquitoes. If a half- 
inch stream of water be allowed to run slowly into the ee 
the slight overflow will usually carry off any scum which 
might accumulate. If unsightly scum growths appear, 
it may be necessary to add copper sulphate in quantity 
