170 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
ACAROSPORA Mass. Ric. Lich. 27. f. 43-46. 1852. 
PLATE 32. 
The thallus varies from typically crustose to squamulose or subfoliose forms and is 
always closely adnate. In most of the species, and in all of ours, there is a good cel- 
lular cortex above. The algal and medullary layers are also usually more or less 
differentiated. The lower portion is scarcely different from the so-called medullary, 
and, indeed, the whole thallus is frequently more or less distinctly cellular throughout. 
The algal symbiont is Pleurococcus. The attaching organs are rhizoidal hyphe. 
The thallus varies greatly in color, white, yellow, greenish, and brown, and even 
blackish examples occurring. . 
The apothecia vary considerably in size and appearance, but are always more or 
less immersed in the thallus, at least in our species. The thalloid exciple is rather 
poorly developed and tends to disappear in all of our species. The hypothecium is 
pale and the hymenium of the same color or darker above. The asci vary considerably 
in form, and the paraphyses are simple or rarely branched. The spores are hyaline, 
minute, and very numerous in the asci. 
The genus is frequently placed with Lecanora, but it seems evident enough that 
species showing such pronounced spore differences should not be referred to that genus, 
In structure the thallus resembles that of some of the Lecanoras, and indeed the cells 
of the upper cortex are much better differentiated and more distinct in the present 
genus. However, the spores make it seem possible that there is a close relation between 
the present genus and Biatorella. But the present genus differs from Biatorella in 
having better developed thalli with good upper cortex and in making more or less of 
a showing of a thalloid exciple. Perhaps the thalloid and excipial development 
should not count for more than the spores in classification, and it may not, conse- 
quently, be unreasonable to suppose that the present genus is more closely related to 
Biatorella than to Lecanora. 
The genus is not large and is represented in our flora by only four species and sub- 
species. All occur on rocks, though one has been found on old wood also. 
Type species Acarospora schleicheri (Ach.) Mass. loc. cit. 
EXPLANATION OF PLATE 32.—Fig. 1, @, the apothecia; 6, the thallus on the substratum. Fig. 2; 
a single apothecium and a small portion of the thallus. Fig. 3, a section of an apothecium and part 
of the thallus; a, the hymenium; b, the hypothecium; c, the cellular medullary layer. Fig. 4, a section 
ofthethallus; a, the upper cortex; 6, the algal layer; c, the cellular medullary layer; d, the hyphal rhizoids. 
Fig. 5, paraphyses and an ascus. Fig. 6, free, simple, and minute spores. Fig. 7,algal cells (Pleurococcus), 
a, as they occurin the thallus; b, normal size. Fig. 1, natural size; fig. 2, enlarged about 35 diameters; fig. 3, 
enlarged 400 diameters; fig. 4, enlarged 300 diameters; figs. 5 and 6, enlarged 650 diameters; fig. 7, enlarged: 
a, 650 diameters; b, 500 diameters. From Schneider. 
KEY TO THE SPECIES. 
Thallus lemon-yellow..........-..--------------0++-------- 1. A. xanthophana. 
Thallus yellowish brown to chestnut, or rarely ashy white. 
Squamules scattered and usually plainly lobed; thallus 
yellowish brown to chestnut......-....--------++------ 2b. A. cervina fuscata, 
Squamules usually compacted into an areolate crust, not 
conspicuously lobed. 
Thallus yellowish brown to chestnut........--.------ 2. A. cervina. 
Thallus ashy white...............0...-------------- 2a. A. cervina cinereo- 
alba. 
1. Acarospora xanthophana (Nyl.) Fink. 
Lecanora xanthophana Ny]. Ann. Sci. Nat. Bot. LV. 15: 379. 1862. 
Thallus composed of peltate or round-lobulate squamules, which are usually com- 
pacted, except about the margin of the thallus, into an angulate-areolate crust, the 
