166 
HISTOEY OF BRITISH FERNS. 
ment, dependent on the circumstances in which it grows. 
Its more usual size is from three to four feet in height. 
Sometimes in dry, very sandy soil, the plant becomes a 
pigmy, not reaching a foot in height, and being merely 
bipinnate. The opposite extreme occurs when the plant 
is growing on damp hedge-banks, in warm shady lanes, 
where it attains eight or ten feet in height, and is 
proportionately compound in its development. Under 
circumstances which favour the most luxuriant deve- 
lopment, this common and usually vulgar-looking plant 
combines the most noble and graceful aspect, perhaps, 
which is borne by any of our indigenous species, its 
fronds scrambling up among the bushes, which sustain 
them at the base, while their graceful feathery-looking tops 
form, overhead, a living arch of the tenderest green. 
The Pteris is known among our native Ferns by having 
the edges of all the little divisions of its fronds furnished 
with a line of spore-cases. No other of our native species has 
the fructification arranged in continuous lines except this 
and the Bleclinum ; and the Pteris may be readily known 
from that by the lines being in it confined to the margin, 
leaving the centre unoccupied, while in BUchnum the 
extreme margin is unoccupied by the sori. 
