In some books a species called Polypodium calcareum (The Limestone Polypody) is described. In some quarters this plant is regarded as a variety of P. dryopteris, as it is similar in some respects. Mr. C. T. Druery considers it to be a distinct species. The chief points of difference are said to be the following. The whole plant is larger in growth, whilst the green of the fronds is not such a golden colour, even in the early days. Also the pinnæ are not arranged so definitely in the form of three branches, as is to be observed in the case of the Oak Fern. Finally, the unrolling of the frond does not present the appearance of three little balls, seeing that each pinnæ unfolds separately. The Limestone Polypody occurs chiefly in the North of England.
Polypodium alpestre. The Alpine Polypody. This is a most remarkable species, in that it bears a singular resemblance to the Lady Fern. By some authorities it is positively regarded as a Mountain form of the Lady Fern. The reason for linking the species with the Polypodies is found in the rounded sori, which have no indusia. The Alpine Polypody has a short tufted root-stock, and from this arise the fronds, which may be a foot or even more in height. The stipes is very short when compared with the leafy portion, and it is covered with brown scales. The general outline of the fronds is broadly lanceolate, and they are twice divided. The pinnæ are arranged in alternation on either side of the rachis, and these are divided into pinnules with blunt points. The pinnules have toothed edges. The sori are chiefly situated near to the inside border of the pinnules. Those who consider that the Alpine Polypody is a form of the Lady Fern call the species Pseudathyrium alpestre.
The Alpine Polypody seems to be exclusively confined, as far as the United Kingdom is concerned, to the highlands of Scotland. It is sometimes to be found at an altitude of four thousand feet above sea-level. In spite of its restricted locality the Alpine Polypody is an easy subject for the garden, if it can be provided with a well-drained situation.
CHAPTER IX
THE ROYAL FERN
Under the name of the Flowering Fern it is probable that most people are familiar with the subject we are now about to consider. The title has without a doubt arisen from the fact that the species bears its sori in masses at the termination of the fronds, quite apart from the leafy portion. The Royal Fern is the sole British representative of the family Osmundaceæ.
Osmunda regalis. There is great diversity of opinion upon the derivation of the name Osmunda. The name is thought to be of Saxon origin, and possibly was given to the Fern in honour of a personage who bore the name of Osmund. Osmunda was one of the titles of the great god Thor. In other quarters the name is said to be compounded of the two words os, “a house,” and mund, “peace.” Finally, a pretty story associates the name Osmunda with a certain Osmund, a ferryman, who, to hide his daughter from marauding Danes, placed her amongst the great clumps of the Royal Fern which grew so plentifully by the riverside. The specific name regalis is simply Latin for “royal,” and is an apt reference to the noble proportions of this Fern.
Osmunda regalis. The Royal Fern.
The Royal Fern has a sturdy tufted root-stock which in an old example may well be one or two feet in height. From the crown of the root-stock arise the fronds, which are of a yellow-green colour when they are young. The stipes is about the same length as the leafy portion, and the fronds themselves often rise to a great height. Cases are on record where, the plant being in a very damp situation, the fronds have been as much as twelve feet in height. Average specimens would range from three to six feet. The fronds are twice pinnate, the pinnules being oblong with uncut edges. Some of the fronds are barren and never bear any sori.
In the case of the fertile fronds only the upper portion produces the clusters of spore cases. Here the leafy portion of the pinnules is very much contracted, so that little or no green is visible. The sori are quite naked, no indusia being present at any time. A notable feature of the sporangia is that they split up into two valves when about to burst, and are not provided with the elastic ring (annulus) which assists in the rupture of the capsules in the case of most ferns. That the pinnules which bear the sori are exactly comparable to the leafy portion is often very plain. Here and there on a plant it is possible to find fertile examples which have developed partly in a barren, and partly in a fertile manner.