172 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM, 
typically crustose species, Some lichenists, however, admit to the genus plants hav- 
ing fruticose thalli. In our foliose species there is a well-developed upper cortex, 
which is much gelatinized and seems to be most commonly composed of hyphe 
rather than pseudocellular, In these the lower cortex is similar but commonly 
thinner, or sometimes scarcely at all developed. In these foliose species the algal 
and medullary layers are also well developed, while rhizoids are few or entirely 
absent. The better-developed crustose forms show some suggestion of an upper cor- 
tex and algal and medullary layers, but the great majority of them do not; in the 
latter there are found the simple hyphal rhizoids as attaching organs. Cystococcus 
is the algal symbiont. 
The apothecia are commonly of medium size, usually sessile, though adnate and 
immersed forms occur. The thalloid exciple is commonly somewhat raised, though 
it may disappear entirely, leaving a biatoroid apothecium. The exciple is most 
commonly entire or crenate and the disk flat orslightly convex. The hypothecium 
is pale or only slightly colored, and the hymenium is of the same color, or darker 
above. The asci are clavate, as a rule, and the paraphyses commonly simple, though 
compound forms may doubtless be found in any of the species. The spores are sim- 
ple, but vary greatly as to size and form. 
The foliose species are sometimes placed in another genus, but there is a gradual 
transition to the crustose forms, which may be represented to some extent, at least 
externally, in the most foliose species, and for this reason it has not seemed best to 
attempt a division. As to thallus structure, the genus is as a whole most closely 
related to Haematomma and Acarospora, and only less closely with some of the 
better-developed Lecideas. Also, there is a not very remote relationship between the 
present genus and the one last named as to spores and apothecial structure, 
transitional forms between thalloid and lecideoid exciples occurring in both genera. 
Lecanora shows also affinities with Parmelia. 
Some forty forms occur in the State. Mostly on trees and rocks. 
Type species Lecanora tartarea (.) Ach. loc. cit. 
KEY TO THE SPECIES. 
Section 1. Thallus usually lobed at the circumference (as also in two species of 
Section IT). 
Thallus rather thick and often scattered, greenish straw- 
colored. 
Apothecia pale yellow to yellowish brown...............-. 1. L. rubina 
Apothecia of the same color as the thallus or pale brown.... la. L. rubina heter- 
omorpha. 
Thallus thinner, smaller, and more compact. 
Thallus some other color than sea green. 
Thallus light-colored and sometimes white-powdery, often 
breaking away at the center or one side... 2.2.2.2... 2b. L. muralis ver- 
sicolor. 
Thallus becoming yellowish brown or reddish brown; the 
lobes short and often black-margined............... 2d. L. muralis dif. 
fracta. 
Thallus sea-green. 
Thallus lobes much flattened..............02202.022.-5.-.-. Za, L. muralis sax- 
icola. 
Thallus lobes not so much flattened. 
Thallus lobes somewhat elongated. ..................- 2. L. muralis. 
Thallus lobes much elongated and flexuous........... 2c. L. muralis garo- 
vaglii. 
