31 



same parts in the less perfect (where they are largest, most con- 

 stant in form, and most numerous) as rather resembling the asci of 

 aquatic alga?, and not so much in these last seminal as infusorial 

 in their nature. In his latest work (Lien, in Mart. Fl. Brasil. 

 1. p. 60) he denies that there is any certain limit between asci and 

 sporae in lichens, and further says, that it is amost impossible to de- 

 cide whether the annulate appearance of the asci is occasioned by 

 septa or strictures, or by included asci or spora?. I can only briefly 

 refer to these questions. The whole has been most fully illustrated 

 by F6e, in the second part of his "Essai sur les Cryptogames," &c , 

 Paris, 1837; with five plates; containing a vast amount of informa- 

 tion. The principles deduced by Prof. Fee, from the general re- 

 sults of his observations, will, perhaps, not be considered altogether 

 admissible, though certainly of great value. They lead him to pro- 

 nounce Peltigera, Nephroma, and Solorina distinct genera, which 

 is confirmed by a striking natural habit in each. But again 

 they compel him to separate Umbilicaria pustulata from the rest of 

 the genus, and to make two genera of this most natural group, a 

 construction irreconcilable with our definite knowledge of these 

 plants from all other points of view. In the same way, he is led to 

 refer Stereocaulon to Cladonia. But it does not seem to me that 

 the present views of the author are in any degree final, and they 

 will probably be hereafter developed more satisfactorily. 



Beside the propagation by Gonidia, and that by Sporidia, there 

 may be mentioned another, which is, however, rather accidental in 

 its nature, and perhaps only a modification of the gonidial propaga- 

 tion, that by the Hypothallus (Protothallus, Mey.). This, origi- 

 nally the elementary state of lichens, in which their layers are 

 confused, is afterwards discernible as cylindrical cells in the hori- 

 zontal lichens, and also as the pythmenes or fibres occurring at 

 their margins or on their under surfaces; and in crustaceous species 

 it forms the base of the thallus closely adnate to the matrix, of 

 various thickness, and in color varying from black or white. Crus- 

 taceous lichens, which had been scraped from rocks, were found 

 by Fries to grow again from the remaining portions of the hypo- 

 thallus. In like manner, Schaerer found that new individuals of 

 Umbilicaria were sometimes produced from the pythmenes or 

 fibres of a species alone. " Hypothalli vis individua propagandi non 

 deneganda; continet enim gonidia in potestate." Fr. 



Auct. de Genesi: Fries, Lichenogr. p. 52; Meyer, Entwick. 

 pp. 314, 319, &c.; Wallroth, Naturgesch. der Flechten 1. 255, &c.; 

 Eschweiler, Syst. I.e. ; Koerber, Dissert. 1. c. 



II. MORPHOSIS. 



The ulterior evolution of the thallus consists in the segregation 

 of organs, either together with, or from the hypothallus, which had 

 been primarily involved in it. The nisus of the young thallus is 

 either centrifugal, producing a thallus typically horizontally ex- 

 panded, or centripetal, producing a thallus normally arising verti- 

 cally from the matrix. These directions are not, however, in polar 

 opposition, since, by constriction, the centrifugal becomes centrip- 



