30 



ture, Light). They are not to be confounded with certain other 

 regular excrescences, first distinguished by Wallroth, (stauromata,) 

 which arise in and consist of the cortical layer alone, of the outer 

 cells of which they are only anamorphoses. 



Gonidia propagate either, 1st. in the matrix, or original thallus, 

 forming leaves, scales, &c., thereon ; or, 2d. by forming new thallus 

 external to, and apart from, the original thallus, new individuals, 

 that is, of the original thallus, but not of the species. To the frequen- 

 cy of the gonidial propagation is to be ascribed as well the great 

 excess of abnormal states in lichens, as the numberless variations 

 into which the species run. 



Obs. G. G. Koerber (De Gonidiis Lichenum, Dissertatio, BeroL 

 1839) has given the most comprehensive view of the Gonidia with 

 which I am acquainted. He has embraced the most of Wallroth's 

 important conclusions, and set them forth in a clear and somewhat 

 improved form. I repeated myself some of Koerber's important 

 experiments on the spot, with a powerful microscope, and with suc- 

 cess. He concludes that the gonidia are the most essential parts 

 of Lichenes, as they are taken by Fries to be the principal distinc- 

 tion of Algae in general from Fungi : that in fine the gonidium is 

 the ultimate living atom and elementary monad of lichens ; and 

 hence that every lichen is a synthesis, a systematical individual 

 which may contain countless numbers of true individuals ; all of 

 which flows directly from our primary views of the structure of 

 lichens and the nature of the gonidia. Eschweiler dissents from 

 some of the above views (Fl. Bras. 1, p. 56). 



The second mode of propagation in Lichenes is by Sporidia. These 

 are cells produced by a metamorphosis of gonidia. They are the ana- 

 logues of seeds, and produce new individuals of the species, and the 

 propagation by them is the typical and primary : just as the gonidia 

 are the analogues of buds, produce new individuals of the parent 

 only, and are the medium of the succedaneous and secondary propa- 

 gation. The sporidia are eubglobose or elliptical, and either naked 

 in the thalamium,or contained in elongated subvertical cells (asci; 

 which are again sometimes themselves included in other asci), which 

 are formed in the thalamium, or that part of the lichen which is the 

 analogue of the blossom. The asci are very variable in form, but 

 always elongated, and more or less cylindrical, clavate, or elliptico- 

 cylindrical. They are commonly more obsolete in the higher and 

 more perfect lichens, and most remarkable in the lower divisions. 

 Very different genera have asci perfectly similar. The spores, 

 when they occur naked, are for the most part collected together 

 without order ; frequently somewhat coherent ; and black, or more 

 rarely purple and lemon-colored : when included in asci, they ap- 

 pear either in a simple or in binary, ternary, or quaternary series, 

 and are either colorless, or lightly tinged, gray, yellowish, reddish. 

 They germinate by simple elongation into threads, by the conflu- 

 ence of which the hypothallus is formed. 



Obs. Eschweiler (Syst. p. 9,) has pointed out some differences 

 between the spores of lichens and those of fungi, and comparing 

 the asci of more perfect lichens to those of fungi, he considers the 



