88 EXTRACTS AND ABSTRACTS FROM FOREIGN JOURNALS. 



decomposed leaves of the Chesnut. M. Roberge, to whom I am in- 

 debted for a sufficient number of specimens to illustrate my work on 

 Cryptogamia, observed it also on the leaves of the oak. It is scattered 

 or arranged in groups, and at those parts where several meet together, 

 they appear of a greyish-brown colour, while the rest of the leaf is of a 

 reddish tint. On these irregular and more or less extensive patches, a 

 lens brings into view small discs or perithecia, depressed in the centre, 

 where a small elevation is to be observed. These discs, of which the 

 diameter scarcely attains ^-th of a millimetre, are blackish, slightly shi- 

 ning, of a leaden hue, especially around the papilla, or elevation. They 

 are readily and easily detached entire from their support, and, submitted 

 to the microscope, they are found to be composed of a very delicate 

 semi-diaphanous membrane, furnished with a network of opaque fibrillae, 

 radiating from the centre to the circumference, and traversed by other 

 fibrillae, crossing them exactly similar to the delicate tissue in the spider's 

 web ; in the centre is also found an opening, which corresponds to the 

 elevation above alluded to. Beneath this small membraniform disc the 

 thecse are found, which are fixed, concealed, and circularly arranged, 

 their base corresponding to the opening of the disc. These thecse, de- 

 void of paraphysa, are in a mass, and sometimes in a slight degree 

 swollen towards the middle of their length, which does not exceed the 

 ^th of a millimetre. The enclosed sporidia are oblong, slightly fusiform, 

 straight or a little curved, about -g^th of a millimetre in length, and 

 furnished with three sufficiently distinct divisions. 



The characters of this new genus and species, as given by Desma- 

 zieres, are : 



MICROTHYRIUM. Desm. Perithecium simplex, superficial, membra- 

 naceum, adpressum, scutiforme, centre perforatum, obtegens ascos fixos 

 subclavatos. 



M. microscopicum. Desm. PI. Crypt. e"dit. 1, No. 1092 ; edit. 2, 

 No. 492. M. epiphyllum ; maculis magnis, irregularibus, fusco-cineras- 

 centibus; peritheciis sparsis, minutissimis, tenuissimis, nigris, subni- 

 tidis, papillatis ; ascis clavatis ; sporidiis septatis, oblongis, subfusifor- 

 mibus. 



Habitat. In foliis exsiccatis Fagi, Castanese et Quercus. Autumno. 

 March, p. 138. 



Explanation of the Figures. 



PLATE III, Div. 2, Fig. 1. a, Membraneous Perithecium of Microthyrium micro- 

 scopicum, seen with a power of 260 diameters, b, Vertical Section, c, Thecae, con- 

 cealed and arranged in a circular manner beneath the perithecium. d, Oblong fusi- 

 form sporidia, usually furnished with three rather distinct divisions. 



Desmazieres on the differential characters of Sphceria insidiosa and S. 

 caulium. These two Lichens are so nearly allied in external characters, 

 as to render it almost impossible to decide upon each species without 

 the aid of microscopic investigation. The differences detailed by Des- 

 mazieres are the following : The membrane of the theca of our Sphce- 

 ria insidiosa is so thin and transparent, that no idea would be entertained 

 of its existence, were it not for the sporidia it contains. These spori- 



