158 
HISTORY OF BRITISH FERNS. 
one the other ; the free margin, therefore, is exterior with 
reference to the fascicle of venules to which it belongs. 
When very young there is no evident trace of separation at 
the part where they overlap, but as they advance towards 
maturity the separation becomes apparent, and they even- 
tually open down the centre, one indusium turning upwards 
and the other downwards, the two lines of spore-cases 
they had covered becoming confluent and undistinguishable 
without manipulation. 
This is the ordinary form of Scolopendrium ; but there 
are a great number of very curious and some very distinct 
varieties, differing only, however, rather in the form of the 
fronds than in the fructification. Of these varieties it is 
deserving of especial mention that they are for the most 
part perfectly constant under cultivation, although they 
have, no doubt, originated in aberrations— that is to say, 
accidental variations, from the original species, which have 
been perpetuated naturally or by art. It is, moreover, a 
curious fact, that most of them are reproduced from spores. 
One of the most beautiful of these varieties is that called 
crispum, in which, the same outline of frond prevailing, the 
leafy portion is so much more developed than the midrib, 
that the margin becomes excessively undulated, giving the 
