- 7 8 — 
phrastus, and Pliny. However, as a class of plants they did not attract much 
scientific attention, nor did they become the subject of special classification until 
about the beginning of the 18th century. 
The ideas of earlier authors concerning them, of course, were very primitive 
and erroneous. Some believed them excrementitious matter produced by the 
earth, the rocks or the trees. Some believed that depending upon external media 
Lichens, Algae, or Fungi might arise, and even animalcules. Another form of 
belief was that they were merely the result of the decomposition of higher vege- 
tation. Sprengel speaks of the Lichens as formed of nothing but the vegetable 
juices, and except here and there, some slight rudiments of a cellulose organiza- 
tion. 
Up to the time of Tournefort, 1694, only such forms as were remarkable for 
their size, their color, or their supposed medicinal virtues received any attention. 
The abstraction of a purple dye from certain species of Lichens dates far 
back into history, and must have been quite a profitable industry — to-day, how- 
ever, it is limited to the abstraction of litmus, cudbear, and orchil. 
As to their medicinal virtues; it is not surprising that, at a time when people 
believed in the “doctrine of signatures” — that is, that a plant had stamped upon 
itself an indication of the purpose for which it is to be used — they believed that 
Lobaria pulmonaria, which so closely resembles lung tissue, was good for diseases 
of the lungs; and that Peltigera aphthosa, with the little eruptions all over the 
thallus, was good for the thrush; and that Xanthoria parietina, that beautiful yel- 
low lichen, was good for jaundice. To-day, however, Iceland Moss -^Cetraria 
islandica — is perhaps the only lichen that still is used. It at one time had a pro- 
minent place in our Materia Medicas, and was one of the articles in the U. S. 
Pharmacopoea even as late as 1900. 
Due to the fact that nearly all lichens contain a bitter principle, most dis- 
agreeable to the taste, they are used as food only in countries where nothing else 
is likely to grow, and then only in case of famine. The “ manna ” which supplied 
the Children of Israel during their sojourn in the desert, is generally supposed to 
be a species of Lecanora — L. esculenta. This lichen, loosely attached, is carried 
by the wind quite readily, and in countries where it occurs plentifully, is some- 
times brought in quantity from the mountain sides down into the valleys. 
The only discovery of especial interest that was made in this long period 
(that is, from Aristotle to Tournefort), was that of Malpighi, who discovered the 
. soredia 3 ; he understood them to be propagative organs, and for that reason con- 
sidered them true seed. 
It was Tournefort (1694), who first considered the Lichens as a distinct 
class of plants; up to his time they were given no definite position in the vege- 
table kingdom, and were classified variously, as Algae, Fungi, Liverworts, and 
Mosses. 
3 The little patches of powdery or mealy substance formed on the upper surface or margin of 
many lichens. 
