P TER IS. 
29 
When the frond is fertile the margin of the segments is strongly and stiffly recurved, and 
the doubling back is continued by a delicate membranous curtain continuous with the edge of the 
segment ; this is by some authors considered an indusium, by others as a portion of the frond, 
and it may be termed a false indusium. It covers the sporangia, which are arranged in a 
continuous line of sori along the whole length of the marginal vein above noticed, and it is worthy 
of particular remark that there is beneath the line of fructification a second membrane similar 
to, but shorter than, the first, and concealed by the sporangia ; both membranes have a delicate 
fringe of hair-like processes. The lower one must be considered as a true indusium, and its 
presence distinguishes P. aquilina from the other species of the genus here described ; it is said, 
however, to be sometimes absent. The spores are yellow, slightly granular, and tetrahedral- 
globose in shape. The peculiar double indusial membrane has led some botanists to make 
a separate genus of this plant, and it has been named Eupteris by Newman, and Ornithopteris 
by Agardh. 
It is scarcely an exaggeration to say that the Bracken is found all over the world, for, with 
the exception of the extreme north and south, this is almost strictly the case. The Fern, 
however, puts on a rather different appearance in different parts of the globe, and the list of 
names which it has consequently received is very formidable ; most of them are given in 
Hooker’s “ Species Filicum yet, considering the very great extent of its distribution, it cannot 
be considered a very variable species. The following are the varieties recognised by Hooker in 
the work above referred to : — 1. glabra, with the fronds smooth or but slightly downy beneath. 
This is abundant in Europe, North America, and North Asia, and extends into South Africa, 
South China, Java, the Pacific Isles, and Brazil. 2. lanuginosa, with the fronds silky-tomentose 
beneath, and the pinnules more regularly pinnatifid : this is even more widely distributed, and 
is especially common in hot countries, as throughout tropical Africa, India, Penang, Sandwich 
Islands, Mauritius, Jamaica. 3. caudata, a West Indian and Central American form, with narrow 
linear segments, with the false involucres nearly meeting across the smooth back. 4. esculenta, 
which also has remote linear pinnules often running together, and decurrent, narrow, coriaceous, 
and smooth ; the decurrent base usually forms a rounded lobe or short wing to the rachis ; 
this is the common form in the Southern Hemisphere, and is often reckoned a separate species ; 
it is abundant in Australia, New Zealand, and Norfolk Island, and is found in the Feejees, 
tropical America, the West Indies, and rarely in India. 
In this country P. aquilina grows abundantly in all suitable spots, and forms a familiar 
feature of English scenery. For its due growth in luxuriance a fairly deep and light soil is 
necessary, and hence, probably, it is a rarer plant on chalky and limestone formations than in 
other districts. Heaths, borders of fields, and especially open places in woods or forest lands, are 
the favourite habitats of the Bracken. The range in altitude in this country has been found to 
agree very closely with corn cultivation, and Pteris is thus never an alpine plant. In no parts 
of the Scotch Highlands does it reach higher than 1,900 or 2,000 ft., and it has been employed 
by geographical botanists as a convenient test of elevation and boundary line between alpine 
and non-alpine vegetation. 
Passing by slight varieties, a few words must be said about a puzzling little fern frequently 
met with in wet seasons in the chinks of brick walls and similar places, which has been mistaken 
for Maidenhair more than once. It is usually but a few inches high, very delicate in texture, with 
the frond slightly divided into wide segments, and never produces any fructification. This 
is nothing but the young “ seedling ” state of the Bracken, the spores of which have germinated 
in an unsuitable position ; such little ferns are often seen on walls in cities ; thus on the Tower 
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