THE LICHEN GENUS PHYSCIA. 171 



Physcia hypoleuca is found in situations very similar to speciosa, but 

 is frequently in fruit. 



Physcia coiiiosa is very often found on the dead and green twigs of 

 cedar trees, usually in abundant fruit. The fibrils are conspicuous. 



Physcia aquila detonsa. — I do not know that I have ever seen the 

 species, but the variety detonsa is common among moss at the base of 

 trees and frequently abundant in fruit. 



Physcia pulicnilcnta. — This is found on rocks and tree trunks. Com- 

 mon on limestone fences. The thallus has a bluish cast in its younger 

 portions, the older portions soon breaking up. No more sorediate or 

 powder}' than some other species. 



Physcia pulvcnilenta leiicoleiptes. — In this variety the thallus has a 

 more distinct bluish or bronze tint. Found in similar situations. 



Physcia Icana. — This has been collected but once. The record of the 

 locality is so indefinite that the spot cannot now be determined. The 

 type specimen in the Tuckerman collection at Harvard is not readily 

 distinguished from other forms on the same herbarium sheet. 



Physcia stcUaris. — By far the most common species of the genus and 

 perha])S more common in our region than any other lichen. It is very 

 variable, often appearing in scattered bits of thallus, but frequently the 

 thallus may be called stellate. 



Physcia astroidca. — This I have never seen in fruit. It is often seen 

 on the bark of such trees as the basswood, papaw, and apple. Clings 

 closely to the bark ; white spots of soredia are conspicuous. 



Physcia crispa. — This much resembles the following tribacia, but the 

 thallus is more compact. I have collected it but once and that was on a 

 tree standing on the large circular earthwork of the moundbuilders at 

 IS^ewark. Ohio. 



Physcia trihacia. — A good place to find this is on the bark of such 

 trees as hickory and cedar. The thallus is whitish and broken up into 

 small bits. 



Physcia caesia. — This I have on granite rock collected in Iowa. It 

 seems to be infrecpient. It resembles the preceding. 



Physcia ohscura. — A common lichen on rocks and tree trunks. The 

 thallus is likely to be separated into fragments but is not obscure, al- 

 though of a dark gTcen color. 



Physcia ohscura cndochrysea. — This will be recognized by an appar- 

 ently diseased condition of the thallus. causing brick-red spots to appear. 

 Often found among mosses at the base of trees. 



Physcin sctosa. — This resend)les obscura but is lighter colored and the 

 fibrils are numerous on the edge of lobes. Found in similar situations. 



Physcia adylutiinata. — As the name inqdies this lichen appears closely 

 aiqu'essed to the substratum. It is frequent on the smooth bark of trees 

 like that of basswood and upon rocks. 



- Few of the remaining species occur in our region but are southern, 

 Avestern or Arctic. I should like to give here a synoptical key to the 

 arrangement of the genus but it could not be made reliable without the 

 use of microscopical characters. 



The lichens are delightful plants to study, but they have little if any 

 economic interest. No insects disturb them in the collection. The liter- 

 ature is sc-antv and scattered. 



