Another curious instance of suggested mimicry is recorded by G.E. Stone[1243]. He spotted a number of bodies on the bark of some sickly elms in Massachusetts. They were about 1/8 of an inch in diameter “with a dark centre and a drab foliaceous margin.” They were principally lodged in the crevices of the bark and Stone collected them under the impression that they were the apothecia of a lichen most nearly resembling those of Physcia hypoleuca. Some of the bodies were even attached to the thallus of a species of Physcia; others were on the naked bark and had every appearance of lichen fruits. Only closer examination proved their insect nature, and they were identified as belonging to a species Gossypina Ulmi, an elm-leaf beetle common in Europe where it causes a disease of the tree. It had been imported into the United States and had attacked American elms.
It is stated by Tutt[1244] that the larvae of many of the Psychides (Lepidoptera) live on the lichens of trees and walls, such as Candelaria concolor, Xanthoria parietina, Physcia pulverulenta and Buellia canescens, and that their larvae pupate on their feeding grounds. Each species makes a “case” peculiar to itself, but those of the lower families are usually covered externally with grains of sand, scraps of lichens, etc. The “case” of Narcyria monilifera, for instance, is somewhat raised on a flat base and is obscured with particles of sand and yellow lichen, giving the whole a yellow appearance. That of Luffia lapidella is roughly conical and is held up at an angle of 30° to 45° when the larva moves. The “cases” of Bacotia sepium are always upright; they measure about 5·5 mm. in height and 2·75 mm. in width and present a hoary appearance from the minute particles of lichen with which they are covered, so that the structure is not unlike the podetium of a Cladonia.
c. Food for the Higher Animals. It has been affirmed, especially by Henneguy, that many lichens, if deprived of the bitter principle they contain, by soaking in water, or with the addition of sodium or potassium carbonate, might be used with advantage as fodder for animals. He cites as examples of such, Lobaria pulmonaria, Evernia prunastri, Ramalina fraxinea, R. farinacea, and R. fastigiata, all of which grow abundantly on trees, and owe their nutritive quality to the presence of lichenin, a carbohydrate allied to starch.
Fig. 127. Cladonia rangiferina Web. (S. H., Photo.).
Cladonia rangiferina ([Fig. 127]), the well-known “reindeer moss,” is, however, the lichen of most economic importance, as food for reindeer, cattle, etc. It is a social plant and forms dense tufts and swards of slender, much branched, hollow stalks of a greenish-grey colour which may reach a height of twelve inches or even more; the stalks decay slowly at the base as they increase at the apex, so that very great length is never attained. In normal conditions they neither wither nor die, and growth continues indefinitely. It is comparatively rare in the northern or hilly regions of the British Isles, and is frequently confused with the somewhat smaller species Cl. sylvatica which is very common on our moorlands, a species which Zopf[1245] tells us reindeer absolutely refuse to eat.
The true reindeer moss is abundant in northern countries, more especially in forest regions[1246] and in valleys between the tundra hills which are more or less sheltered from the high winds; it is independent of the substratum and flourishes equally on barren sand and on wet turf; but grows especially well on soil devastated by fire. For long periods it may be covered with snow without injury and the reindeer are accustomed to dig down with horns and hoofs in order to reach their favourite food. Though always considered as peculiarly “reindeer” moss, deer, roebuck and other wild animals, such as Lemming rats[1247], feed on it largely during the winter. In some northern districts it is collected and stored as fodder for domestic cattle; hot water is poured over it and it is then mixed with straw and sprinkled with a little salt. Johnson[1248] has reported that the richness of the milk yielded by the small cows of Northern Scandinavia is attributed by some to their feeding in great measure on the “reindeer moss.”
Fig. 128. Cetraria islandica Ach. (S. H., Photo.).