THE FERN’S REPRODUCTIVE ORGANS 
The crescent-shaped masses found on the backs of many fern leaves are sori or aggregations of 
spore-cases. 
From a commercial viewpoint their presence is a drawback rather than 
an advantage—they are unsightly and not needed since in cultivation the fern is ordinarily 
propagated by runners rather than by spores. 
depth is filled to about 11% inches in 
depth with clean broken crocks and 
large pieces of cinders. Over this, 
finely screened leaf mold is placed and 
is packed down somewhat firmly. The 
surface of the leaf mold should be about 
34-inch below the upper edge of the pot. 
The leaf mold should never be sterilized. 
Sterilization of the leaf mold is not 
desirable because with the cooking or 
baking of the leaves during the process 
of sterilization toxic substances are 
produced. This process also kills all 
living organisms, so that when spores 
of fungi or molds fall on the surface of 
this sterilized medium, they are abso- 
lutely free from competition, and they 
grow rapidly over the surface of the 
pot, either destroying the fern spore or 
giving off poisonous products which 
prevent the spore from germinating. 
Since Nephrolepis ferns are not found 
(Fig. 19.) 
wild in North America, leaf mold which 
the grower procures from the woods 
may be considered absolutely free from 
such spores. The pots are to be filled 
with this compost, and boiling water 
then poured over the contents, to kill 
grass seeds, worms and insects which 
may be present. Most of the seeds 
present will be destroyed after 20 
minutes, and the surface of the leaf 
mold in the pot will then be almost 
sterile. As soonas it cools down, a little 
finely screened fresh leaf moldis scattered 
over it. The soil in the pot is thus inoc- 
culated with ordinary soil bacteria which 
grow very rapidly and spread over the 
surface; spores of fungi falling on a 
soil thus quickly populated with soil- 
bacteria will make a very small growth 
or none at all, but the germination of 
the fern spores is not interfered with 
in any way. 
227 
