COMMON HART'S TONGUE. 
127 
advance towards 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 Scolopendrium ; but 
the genus is one of the most remarkably prolific in va¬ 
rieties, and in remarkable varieties, among all known 
Ferns, the greater part of these, thougli 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 slowdy 
perhaps and imperceptibly, but as certainly, giving 
rise to new forms, some transient, but some to be 
perpetuated. 
The fructification of Scolopendrium is, of course, as 
being’ one of the Polypodiacece, normally dorsal; but 
in some of its varieties there is a very curious deviation 
from tbe law : the sori are produced on the upper as 
well as tbe lower surface, and sometimes abundantly 
so. This occasionally happens from tbe elongation of 
tbe normally-placed sorus on the under side, which ex_ 
tends to tbe margin and returns on tbe upper side 
when the sori are placed opposite the marginal crena- 
tures. But it also frequently happens that the sori 
are produced on tbe 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 
