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How a Lichen Is Made

According to this theory, if a wandering fungus spore meets a group of algal cells with which it can live in harmony, a lichen-fungus-company may be founded on the spot. This lichen may grow and flourish and may from time to time send forth representatives to found new colonies.

By another method, which is somewhat analogous to the budding of higher plants, the partners for the new colonies arise within the parent lichen company. Certain groups of cells (Soredia) separate from the rest, each group consisting of one or more algal cells enmeshed in a dense weft of fungus hyphae. At the proper time the surface of the parent lichen ruptures, and the numerous social groups appear, giving to the old lichen that attractive hoary or frosted appearance they so often have. With the aid of the wind these easily travel, to form new companies.

The fungus spores (ascospores) which enter into partnership with groups of alga cells are produced in sacs (asci, singular ascus) in organs of various shapes, knobs, or flat disks (apothecia), or cup and flask-like cavities (perithecia). In addition to these large spores (ascospores) of the knobs and cups there are smaller spores (conidia) produced in smaller cavities scattered over the thallus. There is much conjecture as to what may be the function of these spores.

In tropical countries there is found a very beautiful fanlike, greenish-yellow lichen (Cora pavonia) having a thallus marked with concentric ridges. This lichen bears its spores on the under surface on tiny clubs (basidia) instead of in sacs. The algal partner is one of the unicellular blue-green algae (Chroococcus) often found in mucilaginous masses in damp places. Another tropical form (Dictyonema) grows as delicate blue-green, felt-like plates standing out from the tree-branches to to which they are attached. The algal partner in this case is a blue-green, branching, and thread-like species (Scytonema) found enveloped in a mucilaginous mass in fresh water. The fungus-partner in both the Cora pavonia and the Dictyonema is one of the group which forms leathery crusts on twigs and tree trunks.

Another lichen, Laudatea, has the same partners as the Dictyonema. It is a crustaceous form and in it we find the exception to the rule, that the fungus is the leading member of the lichen firm. In it the alga has the upper hand and determines the direction of the growth.

One lichen (Emericella variecolour), which resembles a tiny puff-ball, is known to be due to the confederacy of a member of the pouch-fungi group (Gasteromycetes) with an alga (Palmella).

In the majority of lichens the algae are arranged in definite layers, sometimes--as in the gelatinous lichens--they are distributed through the whole thickness of the thallus. The fungus partner which, with but few exceptions, directs the growth of the lichen, determines whether it shall encrust the surface so that it cannot be removed without injury, or whether it shall form shields and ribbons lightly attached, or corals and fringes fastened at one point.

Although it is impossible without microscopic examination to determine the exact relations of one lichen to another, much pleasure may be derived from an acquaintance with their external form alone. No plants are more readily preserved and none will so satisfactorily respond to one's effort to revive them. Even after they have been dry for years they will become as beautiful as ever if placed in a moist atmosphere. One may find them every-where and at all times of the year. Their power of absorbing moisture is truly wonderful. It is stated that if living lichens which have become dry in the air, are left in a place saturated with moisture, they take up 35 per cent. of water in two days and as much as 56 per cent. in six days. Certain lichens after a long continuance of dry weather will absorb one-half their own weight of water in ten minutes and will lose it as quickly when exposed to dry air. It is an interesting experiment to put a mass of Reindeer-lichen in a glass of clear water, and note how quickly it will expand into a beautiful fresh plant. One may appreciate their wonderful absorbing power by comparing the dry forest trail with a wet one. The old tree stumps are decked, as for a banquet, with branching, coral-like Cladonia, a lavish display of fairy candelabra! The red tips of Cladonia cristatella and the brown tips of Cladonia mitrula are in rich contrast with their frosted green branches. The gray goblets of Cladonia pyxidata and Cladonia gracilis are suggestive of many a wood-sprite revel. In cedar woods and on sunny mountain slopes, Reindeer-lichen (Cladonia rangiferina), covers the ground with a carpet of loveliest grays, crisp and crumbling when dry but soft as a sponge when moist, and "O'er yon bare knoll the pointed cedar shadows drowse on the crisp, gray moss." J. R. Lowell--An Indian Summer Reverie.