FIL1CINEAE LEPTOSPORANGIATAE 393 
process of budding ; a growing point developes from the cells of the 
prothallus. The cycle thus runs : 
Fern-plant ->• sporophylls -► sporangia 
t I 
prothallus 
The other case, apospory , is found in A thyrium Filix-fcemina var. 
claris sima, and in Polystichuni angulare var. pulcherrimum , &c. 
Here spore-formation is replaced by a process of budding, which gives 
rise to prothalli on the backs of the leaves, so that the life-cycle runs 
Fern plant 
t j 
fertilised ovum — spermatozoid — antheridium | _ thallus 
(ovum archegomum) 
This latter case must not be confused with the ‘vivipary* of 
Asplenium bulbiferum , &c., where the leaf-tissue buds out directly 
into new plants, which for a time remain attached to the parent, but 
ultimately drop off and grow independently. This case is analogous 
to that of many phanerogams (see p. 113, and cf. Bryophyllum &c.). 
Natural History of Ferns. A very large number of ferns are 
shade- and moisture-loving plants. This is comprehensible enough 
when we remember how dependent they are on water for their fertili- 
sation. Many however are xerophytes and alpine forms with reduced 
transpiration. These exhibit the familiar characters (see p. 163) of 
such plants — reduced surface, thick cuticle, hairiness, incurving of 
leaves (cf. Ericaceae), and even, though but rarely, succulence ( Poly - 
podium adnascens , Drymoglossum carnosum , &c.). The tree ferns and 
many others have water storage tissue in the stem. 
Many sp. are epiphytic, especially in the tropics, though wherever 
the air is sufficiently damp they may be found growing in this way, 
even in Britain (p. 173). The most interesting epiphyte is Platy- 
cerium ; see also Polypodium &c. 
The spores of ferns, consisting only of one cell, are of course much 
lighter than is possible for a seed, and may be carried by wind to 
enormous distances. Owing to this the ferns of to-day are much 
more widely distributed than the flowering plants — species for species ; 
and further, owing’ to the greater age of the family in geological time, 
it is as a family more widely distributed than the families of flowering 
plants. 
Classification (after Campbell) : there are 6 orders : 
1. Osmundaceae (sporangia shortly stalked with a group of pecu- 
liarly shaped cells at one side of the apex; they open by a 
longitudinal fissure on the other side; fertile and sterile 
pinnae). 
a. Gleichcniaceae (sporangia sessile, 3 or more in a sorus without 
