THE OAK FERN 87 



like the leaves of trees, and do not simply wither down and leave 

 their ragged stumps on the stem. It is obvious that the poly- 

 pody differs a good deal from the bracken in its mode of life. 

 One of the best methods of investigating the adaptations of a 

 plant to its surroundings is to grow it under varying conditions, 

 and see which suits it best. The bracken, as might be expected 

 from its natural habitats, will grow quite well in almost any 

 kind of soil, so long as it is dug up in its more or less dormant 

 state in winter, and carefully transplanted. But to cultivate 

 the polypody successfully we must imitate its natural environ- 

 ment as closely as possible. It must be planted where it can 

 take undisturbed possession of the place selected, in soil con- 

 sisting of leaf-mould mixed with some clay or garden-soil. The 

 locality must be shaded, cool, and moist, but not too wet or 

 stagnant, and the soil light and porous, not stiff and retentive. 

 The stem should not be buried in the soil, but simply fastened 

 down to it, with only the roots covered. When once estab- 

 lished in such surroundings the growth of the branching stem 

 is rapid, but it generally takes three or four years for the plants 

 to become beautiful and flourishing. It is fairly easy to see 

 that the polypody is adapted for the special habitats in which 

 it grows. It requires a damp but well-drained soil, which need 

 not be deep, since the branching stems run over the surface. 

 The stem itself is green, hence it loves air and light, but the 

 younger parts have to be well protected against the cold and 

 drought to which they are exposed, hence its covering of scales. 

 The leaves last for several years, hence they are leathery and 

 able to withstand the cold of winter. On rocks, walls, and trees 

 the polypody has but few competitors among higher plants, 

 and its branching stems often overrun the mosses which grow 

 along with it. 



The Oak Fern or Three-branched Polypody (P. Dryopteris) 

 resembles the common polypody in bearing its leaves singly 

 on the branching stem, but the leaf is compound and feathery, 

 and is divided into three branches giving this fern a very 

 characteristic appearance. The oak fern grows most luxuri- 

 antly in rocky, mountainous districts, but is very rare in Ireland. 

 Its homes are shady woods and hedgerows, and though it occurs 



