569. The ostrich fern.—Similar changes were also produced in the case of the ostrich fern, and in [fig. 319] is shown at the left a normal fertile leaf, then one partly changed, and at the right one completely transformed.
570. Dimorphism in tropical ferns.—Very interesting forms of dimorphism are seen in some of the tropical ferns. One of these is often seen growing in plant conservatories, and is known as the staghorn fern (Platycerium alcicorne). This in nature grows attached to the trunks of quite large trees at considerable elevations on the tree, sometimes surrounding the tree with a massive growth. One kind of leaf, which may be either fertile or sterile, is narrow, and branched in a peculiar manner, so that it resembles somewhat the branching of the horn of a stag. Below these are other leaves which are different in form and sterile. These leaves are broad and hug closely around the roots and bases of the other leaves. Here they serve to catch and retain moisture, and they also catch leaves and other vegetable matter which falls from the trees. In this position the leaves decay and then serve as food for the fern.
Fig. 320.
Ostrich fern, showing one normal sporophyll, one
partly transformed, and one completely transformed.
[CHAPTER XXIX.]
HORSETAILS.
571. Among the relatives of the ferns are the horsetails, so called because of the supposed resemblance of the branched stems of some of the species to a horse’s tail, as one might infer from the plant shown in [fig. 325]. They do not bear the least resemblance to the ferns which we have been studying. But then relationship in plants does not depend on mere resemblance of outward form, or of the prominent part of the plant.
Fig. 321.
Portion of fertile plant of Equisetum arvense
showing whorls of leaves and the fruiting spike.