LICENSE. 209 LICHENS. Licenses of the former sort are either execu- tory, where the act authorized has not been done, or executed, where it has been done. At law all such licenses may be revoked by the grantor, un- less the license be coupled with an interest in the land, and the same rule prevails in equity courts, except that the latter sometimes hold that an executed license, where the license was based on a consideration, is not revocable at the pleas- ure of the grantor. A court of equity re- gards sueli an executed license as an executed contract, one of the parties to which, the licensee, has gone too far to be put back into his furmer position. A license, though revoked, saves the licensee harmless from liability or re- sponsibility for such acts as he has done there- under. A license in regard to land is not to be confused with an easement (q.v.). An executed license' which puts an end to an easement of the grantor in the licensee's land is irrevocable. The most common licenses of the second sort are licenses to sell liquor, to exercise the trade or calling of a peddler, to give theatrical or other public entertainments, to hold public meet- ings, to use the streets for processions, etc. Such acts are in themselves innocuous and do not con- stitute a violation of the common law, but are gcneralh' restricted by statute or by local mu- nicipal ordinances in the interests of public order and safety. Such licenses are a matter of statutory regulation. The term license is used in international law for the authority given by a State engaged in war to its subjects or the svibjects of the State With which it is at war, to engage in a trade forbidden in time of war. The right to give such licenses is original with the sovereign power, and they may be given by commanding officers in the army or navy as its delegates. A license in patent law is a permission to make or sell a patented article. LICENTIATE (:ML. licentiutus, p.p. of licen- tiiire. to license, from Lat. licentui, license). A university degree between that of bachelor and doctor, or one holding that degree. It is used somewhat in Europe to indicate a person who has taken certain examinations and is licensed to lecture. LICHAS, li'kos (Xeo-Lat., from Gk. Xix<is, space between the thumb and forefinger) . An inter- esting genus of fossil trilobites found in rocks of Ordovician, Silurian, and Devonian age. The genus is characterized by broad Hat carapaces, short wide head, small eyes, and peculiar lobation of the central portion of the head-sliicUl. The genus has several allies that have the most ex- travagant spinose ornamentation. One of the simpler forms, Lichas bigsbyi. is a well-known characteristic index fossil of the Niagara group. See TRirontTA. LICHEN, ll'ken (Lat. lichi'ii. from Ok. Xeixii", leichen. Xixr/Vjlichrit. tree-moss, ringwiu'm : possi- bly connected with Xcfx"", leirlieiii, Skt. rih, lih, OChurch Slav. Ihnti. Lat. Hntjere, to lick. OTr. liflim. I lick, OHG. Icokon. Ger. lecken. S. lie- f ioH.Eng. lirk) . A dry. papular disease of the skin. Formerly there existed considerable confusion in the use of the term: hut since the time of Hebra, the Vienna master, it has been limited tn (1) lirtirn xcyofulosum and (2) lichrn riihrr. The for- mer has now been definitely classed among the cutaneous tuberculoses, leaving lichen r»/)pras the only aiTection regarded by dermatologists as entitled to the name. In most cases, especially in neurotic sulijects, there is much itching, which provokes destructive scratching. The disease is an aUection of nervous origin, following sorrow or violent nervous emotions, and is often accom- panied by insomnia, agitation, and headaciie. Hot sedative douches, arsenic, and proper diet and hygiene produce good results, aided by external • application of carlji>lic acid, pilocarpine, mercury, lead, chrysarobin, and the curette. Consult Ka- posi, I'atlioloyy u,id Treatment of the Diseases of the Skin (New York, 1895). LICHENIN, li'ken-in. A starch-like body, found in Iceland moss and other lichens, from which it is extracted by digesting the moss in a cold, weak .solution of carbonate of .soda for some time, and then boiling. 13y this process the lichenin is dissolved and on cooling separates as a colorless jelly. Iodine impart.s.no color to it. LICHENS, li'kenz (Lat. lichen, from Gk. fiXVt leichen, Xix^", Hchfn, lichen). A very large group of plants, mostly northern and arctic in their distribution, some of the forms living at the very limits of vegetation. They have gen- erally flat, membranous, or crustaceous bodies, but some forms liave branching stalks. Lichens are exceedingly interesting in their structure and life activities, for they are known to be com- posed of two plants living together (smybiosis, q.v.). Every lichen is made up of two elements: (1) colorless threads (tilaments); and (2) cells (gonidia) containing gieen or blue-green pig- ment. These latter are blue-green (Cyanophyceae) or green alga" (Chlorophycea>) , and the colorless thready portion is a ftingns. The fruit of a lichen is that of an ascomycete fungus, generally a flattened or cup-shaped striu'ture with variously colored lining (black, brown, red, et<!. ). The colored lining of the cup or disk consists chiefly of the little sacs (ascil which contain the spores. There is a small group of tropical lichens whose fungus constituent is related to the mushrooms (Basidiomycetes) . Lichens generally live in ex- posed situations, where their only source of water is that from rain and fog. This water is used by the algal cells which manufacture organic food in the manner characteristic of all green plants ( photo.synthesis, q.v.). When the lichen dries up in the sumshine all vegetative activities cease for the time, to be resumed when the plants are again moistened. However, lichens are espe- cially adapted to retain moisture by the gelat- inous character of the thallus. There are also present thread-like outgrowths (rhizines) from the fungal part of the plant, which may draw up some water from the substratum, but probably serve chiefly as organs of attachment. The algal portion of a lichen manufactures the organic food that is absorbed by the fungal elements, which bear the same relation to the algal cells as does any parasitic fungus (o its host. The fungal portion makes no return at all commen- surate with the benefits it receives; indeed, it is well known that the fungus may injure and even destroy the alga. The algic are really slaves of the fungi, and under such conditions the latter are absolutely dependent upon the former. The nlca" are of course jierfectly able to take care of thcnisolvcs. anil do actually grow wild on many of the surfaces frequented by lichens. Some of the lichens are conspicuous in the landscape, e.g. many forms in barren highlands among the moun- tains, and on the rocky shores in the Arctic re-
