86 THE BOOK OF NATURE STUDY 



also of the new growths produced by mosses and liverworts kept 

 in darkness. 



The rest of the ferns have the same general structure and 

 life-history as the bracken, though varying greatly in the form 

 of the leaf, arrangement of spore-masses, etc. They mostly 

 grow in moist, shady places, having as a rule thin, soft leaves 

 which can absorb moisture from the air, but are ill adapted to 

 withstand exposure to sun, wind, or drought, and are divided 

 up in a feather-like manner, so as to catch as much as possible 

 of the feeble light falling on them. 



The Common Polypody (Polypodium vulgar e) resembles bracken 

 in having a branching stem on which the leaves are spaced 

 out. The polypody, however, grows on leaf -mould in hedge 

 banks, or walls, or on the trunks and branches of trees, 

 the stem, which is covered with golden-brown, pointed scales, 

 creeping over the surface while the roots are inserted in the soil, 

 or between the crevices of bark or old stone walls. It is the 

 largest British plant, which regularly grows perched upon trees, 

 sending its roots into the scanty soil composed of matter washed 

 down by rain from the branches. It is not a parasite, like the 

 mistletoe for instance, for it does not get its food from the tree 

 it is growing upon. It is an epiphytic plant, like many mosses 

 and lichens which inhabit the bark of trees, and obtains its food 

 in a legitimate way from rain-water, dust, and the air. When 

 growing on trees, it occurs chiefly in the forks from which the 

 branches arise, but in damp woods it often clothes the horizontal 

 branches, or even creeps vertically over the main trunk, sending 

 its roots into the crevices of the bark. It is especially found 

 on oaks and polled willows. The leaf is oval or oblong in general 

 outline, from three inches to two feet long, and deeply divided 

 into rather broad lobes on each side of the stalk. The edges 

 of the lobes are usually even, though sometimes they are toothed. 

 The leaf is smooth on both surfaces, evergreen, and leathery. 

 Each lobe bears two rows of round spore-masses which have no 

 protective scale ; at first the spore-cases are straw-coloured, but 

 later they become orange. 



The polypody is rather exceptional among ferns in that 

 its leaves, which last for several years, are cut off when old, 



