GEOGRAPHICAL DISTRIBUTION. 879 
the sea. Many Hymenophyllee grow within the spray of 
cascades or on dripping rocks, and on mossy trunks of 
trees. Ceratopteris thalictroides grows in shallow waters, 
its sterile fronds floating on the water, and may be said to 
be the only truly aquatic Fern, and one of the very few 
annuals ; like many other aquatic plants it has a wide 
geographical range within or near the tropics of both 
hemispheres, 
Many have a great predilection for the works of man, 
whether elevated in the air or sunk below the earth, such 
as old castles, walls, embankments, hedge and road-side 
banks, quarries, or deep open pits or wells, this being 
common to species of both tropical and temperate countries, 
it is, therefore, not surprising to find the same species 
assume different sizes and forms, as, for instance, the 
common Hart’s-tongue Fern, Scolopendrium vulgare, which 
on walls and other dry places produces fronds only a few 
` inches in length, while in shady places or open pits or 
.. wells they may be found lining the sides with fronds two 
.. bo three feet in length. 
| . Another example of a Fern making itself at home under 
. very opposite conditions is Pteris longifolia, which is com- 
mon in or near the tropics of both hemispheres. On the 
island of Ischia (in the Bay of Naples) it is found luxuriating 
within the influence of the hot vapours rising from the 
. fissures of latent volcanic heat, growing in soft mud at a 
. temperature ranging from 140° to 160°. In hothouses its 
~ Spores vegetate abundantly upon all moist surfaces, and in 
. crevices close to hot water tanks. It also establishes itself 
| indry places, even in situations where the temperature is 
. often at or near freezing point. 
Ee Although Ferns thus conform themselves to different E 
. Climates, many being wanderers, yet on taking a view of — SZ 
