COMMON KART'S TONGUE. 
125 
advance toward maturity ; till at last they open down 
the centre, one indusium turning up and the other 
down, the two lines of spore-cases becoming confluent 
and confused. 
This is the normal condition of Scolop endrium ; but 
the genus is one of the most remarkably prolific in 
varieties, and in remarkable varieties, among all known 
Ferns, the greater part of these, though not unfre- 
quently altogether monstrous, permanent and retain- 
ing their peculiarities in cultivation. Several forms 
very distinct in themselves, and distinct also from the 
parent, have been produced from the spores by arti- 
ficial treatment, indicating how probably the same 
process is going on in a state of nature, more slowly 
perhaps and imperceptibly, but as certainly, giving 
rise to new forms, some transient, but some to be 
perpetuated. 
The fructification of S colop endrium is, of course, as 
being one of the Polypodiacece, normally dorsal ; but 
in some of its varieties there is a very curious deviation 
from the law : the sori are produced on the upper as 
well as the lower surface, and sometimes abundantly 
so. This occasionally happens from the elongation of 
the normally-placed sorus on the underside, which ex- 
tends to the margin and returns on the upper side 
when the sori are placed opposite the marginal crena- 
tures. But it also frequently happens that the sori 
are produced on the upper side distinctly within the 
margin, and where there are no corresponding sori 
beneath. Those varieties which have the margins 
toothed (crenated) or lobed seem most liable to assume 
