Explanation of Plate 3.—Aster ericoides pilosus, reproduced from photographs taken late in November. Figures 1 and 2 show plants with abundant, and Figure 3, with few young shoots close to the ground. Plants shown in Figures 1 and 2 had the tops removed in summer. Figure 3 shows the common appearance at the end of the growing season of undisturbed plants.
GEOPHILOUS PLANTS OF OHIO.
F. J. Tyler.
Geophilous—meaning earth loving—is a term which has recently been applied to such plants as have some special adaption, which enables them to withdraw beneath the surface of the ground when adverse conditions, such as extreme heat and drouth, cold, etc., overtake them. Such adaptions may be classified as
Rhizomes,
Bulbs,
Corms,
Crowns.
Rhizomes are underground stems and like other stems may be simple or branched. The branched rhizome is, however, the most common form since it combines vegetative reproduction with the other advantages of a rhizome habit. The Brake Fern (Pteris aquilina L.) is an example of a much branched rhizome and Solomon’s Seal (Polygonatum biflorum Ell.) of a nearly simple rhizome.
The stem of a rhizomatous plant may remain permanently underground, as is the case with all ferns except the tree ferns of the tropics. An annual stem is, however, usually sent to the surface and this may be a lateral branch from the main subterranean stem or it may be a continuation of the rhizome, in which case the next year’s rhizome will be a lateral branch and thus the whole rhizome will be made up of a number of distinct segments. Various members of the Iris group are good examples of this. In at least one genus of Ohio plants—Smilax—there are some members having both a perennial woody stem and a well developed rhizome. It may be that these plants are leaving the rhizome habit and are taking up the woody stem habit.
Perhaps in most cases rhizome plants became such through the gradual covering of trailing stems. It is a protection and a saving of building material to a plant if its stems are trailing or creeping, still more so if they are covered by leaf mould or soil. If rhizome plants were once trailers there should be every gradation between the two and so we find. The Trailing Wahoo is a good example of this, since some of its stems are often covered by leaf mould or soil while others are on the surface or some inches above. Many of the Ericaceæ are in this transition stage between trailers and geophytes. The Wintergreen (Gaultheria procumbens L.) has a long, creeping stem which is often or usually covered by leaf mould. It roots freely and sends up perennial woody branches to the surface. It is hard to say in such cases whether the plant is geophilous or not.
Many geophilous plants of the rhizome type were doubtless once crown formers and here again we find a transition stage which contains every gradation between the two groups. The Compositæ are mostly crown formers, but some are true rhizome plants and some are transitional.
The advantages of a rhizome habit are very apparent. The first and most important advantage is the protection from frost which this habit affords. By taking up this habit many plants have been able to withstand a climate, which would otherwise prove fatal. The Alpine Willow is an example. Rhizomes are often storehouses for food and become swollen and distorted in consequence. Vegetative propagation is usually combined with the geophilous habit and with great advantage to the plant. In most cases a rhizome dies off at the back as fast as it grows in front so that any part of it lives a definite number of years. The individual segments of the Solomon’s Seal, for instance, live from three to five years. In this way a branch soon becomes a separate plant. In some cases, however, the rhizome may live for many years and thus hundreds of seemingly independent plants may be connected beneath the surface of the ground. The Brake Fern (Pteris aquilina L.) is of this class and an entire hillside may be covered with a much branched specimen of this plant.