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frondosum confusis, strato cortical! nullo, sed extus compactiores et 

 epidermidi vulgo tectse, fructificatione metamorphosi sirnplici enata. 



ULVACEARUM : Stirpes radice et foliis in unum corpus homoge- 

 neum et similare confusis ; metamorphosi ad sporidia formanda 

 nulla. 1 



The place of Lichenes in the System, and their relations to 

 other Thallophytal plants, as well as their more essential relations 

 to other sections of Alga?, being thus indicated, it is next in 

 order to describe their production, development, and the forma- 

 tion of their fructificative organs. 



Auctores : Fries, Lichenogr. prsel. i. ; Id. Fl. Scan. ; Endlicher, 

 Gen. PI. 1. 1. 



I. GENESIS. 



Original or equivocal generation has been assumed to occur in 

 the Lichenes, and Meyer has even ventured to describe the pro- 

 cess. But Fries declares that he has never been able to find any 

 grounds for it ; and moreover that the germination of lichens from 

 sporidia, as observed by him, presented appearances so exactly cor- 

 responding with what Meyer described, that he cannot but conclude 

 that sporidia were present in this case also. 2 



Lichenes are reproduced by, I. Gonidia, and, II. Sporidia. 



The gonidial propagation will be first described. The thallus of 

 lichens is disposed in four layers ; the cortical, medullary, sporige- 

 rous, and gonirnous ; or, more essentially, it is distinguished into three 

 layers: the cortical, medullary, and gonirnous, of which last the 

 sporigerous is a metamorphosis. The gonidia exist primarily as 

 the gonimous layer, and are a disposition of cells immediately be- 

 low the cortical, and above, or constituting the upper portion of the 

 medullary layer; the cells normally green, spheroidal, originally 

 composed of a hyaline membrane surrounding a grumose matter 

 without apparent structure. While existing only as the goniraous 

 stratum, it is evident that the gonidia cannot come to the surface of 

 the lichen, and in this state, though most perfect, they are incapa- 

 ble of propagation. They appear on the surface in the form of So- 

 redia, which, whether a powdery indumentum or rounded heaps, 

 consist of gonidia, with more or less mixture of cells of the other 

 strata. Here, then, the gonidia appear in their secondary state, 

 constituting subspheroidal globules of a uniform grumose matter, 

 which is scarcely or not at all cellular, and is apparently the same 

 matter which exists primarily within the cells of the gonimous stra- 

 tum. The first increment of the gonidia in the secondary state is 

 therefore a mere confluence of single cells, and thence a dilatation 

 and prolongation of the new mass. Soredia are exceedingly com- 

 mon in Lichenes, and the propagation by them is much more frequent 

 than by sporidia. Their evolution depends as well on the predis- 

 posing individuality of the species, as on external moments (Mois- 



1 Fr. Lichenogr. p. 35. 



2 De hac theoria non plura a me afferenda sunt; fatear, me illam non intel- 

 ligere, eamque mentis potius, quam oculorum acie, esse observatam, censere. 

 (Fr. Lichenogr. p. 173.) 



3* 



