114 



KNOWLEDGE. 



[Mav, 1902. 



is characteristic i>f sandy or gravelly ground. The 

 Commou Polypody selects walls, rocks and tree-trunks for 

 its home, and most of the S[)leeuw()rts are wall-plants ; in 

 the case of the first, its fieshy, creeping stem stores up 

 water and food for the dry seasou, while the lattin* send a 

 network of roots deep into the stonework from the 

 sheltered crevices which they choose for their abode. It 

 may be noted also, that all the wall Ferns vegetate in 

 spring and early summer, and even if completely shrivelled 

 by summer drought, they lie dormant till autumn rains 

 awake them : they possess enough of the impervious 

 cliaraeters of xerophytes to prevent entire drying u]) of 

 their root-stocks. The Bracken grows abundantly on 

 sand-dunes, but its far-creeping rhizome lies deep buried 

 in the sand, beyond the reach of summer suns. In the 

 much-divided nature of their fronds, Fems also show the 

 characters of a damp-loving and shade-seeking ancestry; 

 where compactness of growth to prevent excessive trans- 

 jiiration was unnecessary, and a spreading out to catch 

 the maximum of light an advantage. 



Ferns are classified according to the manner in which 

 the spore-cases are arranged. Of the eight families into 

 which living ferns have been divided, the Pohjpodiaceie, 

 characterized by the incomplete chai'acter of the annulus, 

 or ring of thickened cells which encircles the wall of the 

 stalked spore-case, is far the largest, and to it belong 

 all our British ferns except the Filmy Ferns, which are 

 the simplest forms, and the Royal Fern, Adder's-tongue 

 and Moon wort, of which the last two belong to a strangely 

 aberrant group. 



Since form of stem determines style of growth, it is 

 worth while considering this character in our British 

 Ferns. We find a considerable variety of stem-forms. 

 Of short, upright stems, such as characterise so many of 

 our higher plants, we have a number of examples. These 

 upright stems often elongate by degrees, as in the Male 

 Fern, Lady Fern, Hart's-tongue. Very old specimens of 

 the Male Fern, and one or two others, may have stems of 

 one to two feet in length, resembling in miniatui-e the 

 Tree-ferns of the Tropics, which, however, belong to a 

 family, Oyatheacex, unrepresented in our tiora. These 

 upright stems are much thickened by the persistence of 

 the bases of the stalks of bygone fronds. In other species 

 the stems are procumbent and slowly creeping ; the 

 Maidenhair, Cydo^te.vis fraijilis, and Ladrea spinidosa, 

 furnish good examples. The Common Polypody and 

 Killarney Fern have more rapidly creej)ing stems, which 

 rest on the surface of the ground. The Polypody is re- 

 markable among our Ferns for having its fronds articulated 

 to the stem, so that they eventually drop off, leaving a 

 scar. But the most far-creeping stems are those which 

 grow below the surface of the ground. The most familiar 

 examjile is the Bracken, whose vigorous branching stems 

 cover whole mountain-sides with a forest of green fronds. 

 In wind-excavated escarpments in sand-dunes, these black 

 rhizomes, knotted with the stumps of old fronds, may be 

 sometimes seen hanging twenty or thirty feet in length. 

 The Oak and Beech Ferns, the Marsh Fern, Mountain 

 Bladder Fern, and the two Filmy Ferns, have also sub- 

 terranean creeping stems, ami consequently form spreading 

 colonies, instead of the close tufts caused by the occasional 

 liranching of upright stems. 



To revert to those few British Ferns which are not 

 members of the family Pohjpodiace/e. The lovely 

 Killarney Fern and the two Filmy Ferns belong to the 

 Hymeuophyllace;e, which are the simplest in structure of 

 the Ferns and show some aftinities to the mosses. These 

 species are essentially hygrophile. Their delicate pellucid 

 fronds, formed of only a single layer of cells, shrivel at 

 once in a dry atmosphere. They differ also from most of 



our Ferns in the fact that their fronds are not annual, but 

 will last for a numb t of seasons. The fronds of Hyineno- 

 phyUurn. nnilaterale will even continue to grow for several 

 years in succession ; I have fronds nine inches in length, 

 the result of three successive seasons' growth under close 

 treatment. These delicate species usually seek dei;)) shad^' 

 dells, where the sun never penetrates ; here they clothe 

 damp rocks with their dark verdure, but in some parts of 

 our Islands, as on the west coast of Ireland, the atmosphere 

 is so charged with moisture that on a mountain-side facing 

 north, the Filmy Ferns may form a constituent of the sliort 

 spongy turf, freely exposed to the weather. 



The only British representative of the Onmiiudacem is 

 the well-known Royal Fern, Osmundu reynlis, which needs 

 no description here. Whereas in many of our British Ferns 

 certain fronds produce no spores, but conSne themselves 

 to the process of assimilation, while others, whose 

 chlorophyll-bearing area is restricted, bear spores, in the 

 Royal Fern the upper portion of the fronds is set apart for 

 the production of the fructification, the lower parts being 

 expanded, green and leaf-like. But pinna? may often be 

 found in which every gradation from flat green barren 

 I>innules to narrow fruit-covered ones is present. The 

 remaining ferns, the Adder's-tongue and Moonwort, 

 possess remarkable features. The prothallium, instead of 

 being flat, green and aerial, is a subterranean colourless 

 mass of tissue. The stem, likewise, is subterranean, and 

 very short, sending up each year an aerial branch which 

 divides into two, a spore-bearing portion and a barren 

 leaf-like portion. In the arrangement of the young 

 fronds, too, these jilants depart from the almost invariable 

 rule of Perns, the parts being folded straight instead of 

 coiled up. These Ferns likewise differ from their British 

 allies in their habitat, since their home is in open pastures 

 and heaths, the Adder's-tongue preferring the lowlands, 

 the Moonwort the uplands. 



As regards habitat and distribution, our Ferns exhibit a 



A 





FlQ. 3. — Pinna ol' Osmiuida regalis, showing liMn^iiion from 

 b;irren to fertile portions. 



wide diversity. Though none of the species are aiiuatic. 

 several of the Ladreie frequent wet marshes, notably 

 L. Thelypleris. Most of our Ferns are wood and glen 

 plants ; some, as already pointed out, seek rocks and walls. 

 While the majority are lowland, many delight in the 

 skirts of the mountains, and a few. notably the two species 

 of Woodsia and the Holly Fern, are Arctic-Alpine plants. 

 In opposition to these, the Maiden-hair and Killarney Fern 

 are plants of markedly southern type. One, Aspleniuin 



