SPECIAL MORPHOLOGY: LICHENES. 161 



most cases, a distinct cytoblast. The colour of the plant, in a 

 moist condition, depends upon whether the colour of the chloro- 

 phyll be yellow (as in the Parmelia parietina), brownish (in P. 

 stygia), or of a pure green colour (in the Borrera ciliaris), &c. 

 since the gelatinous cortical layer is then transparent. In a dry 

 state the colour is more or less blended with gray, according to the 

 different thickness of the cortex. If we suppose two Lichens of the 

 above-described structure laid together by their under surfaces, we 

 have the structure of the flat upright Lichens, as the Cetraria, of 

 which the filiform Usnece and Alectorice are the thinnest forms. 

 The sporangia of all Lichens, with the exception of those plants I 

 have added to them from the Fungi, are formed of a substance 

 (starch ?) which is rendered blue by iodine. In the Cetraria 

 islandica, the cells and the intercellular substance of the cortical 

 layer are coloured blue by iodine (moss starch). In Lichens with 

 a crustaceous thallus, the Lichen tissue is more or less frequently 

 wanting, being replaced by more gelatinous cells, but slightly 

 elongated, and mostly placed vertically upon the base. In the 

 Pyrenomycetes we find thin-walled, closely compressed, polygonal 

 cells, as in the Sphceria fragiformis ; in the Helvellacece a loose, 

 soft, interwoven tissue. Finally, the gelatinous Lichens consist of 

 convoluted filaments, composed of spherical cells containing chloro- 

 phyll, and imbedded in a softish gelatinous intercellular substance, 

 so that it is not possible to distinguish them anatomically from the 

 species of Undina. 



Lichens offer little worthy of notice. No trace has as yet been dis- 

 covered of a spiral deposit layer. The thickened walls of the spores 

 of the Lecidea sanguined give, however, indications of this arrange- 

 ment. Knotty deposits, projecting irregularly into the cavity, are 

 exhibited by the long cells of the Peltidea canina. We have a special 

 treatise by Korber * on the green, round, cells ; and our only regret is, 

 that the author should have adopted, and even enlarged upon, the ter- 

 minological waste of words introduced by Wallroth. Special stress is 

 laid upon the conditions under which these cells increase, become some- 

 what altered, break through the cortical layer, and then appear as 

 masses of dust (soredia Auct.) upon the surface, whence the individual 

 cells are distributed and grow into new plants. This is no peculiar 

 property of Lichens, and not a process to be compared with the forma- 

 tion of buds in the higher plants, but simply an evidence that, under 

 favourable circumstances, every vital vegetating cell of a plant may grow 

 into a plant ; and of this we shall have occasion, as we proceed, to ob- 

 serve many cases in point. There, as here, a strict individualisation of 

 each cell is at variance with the regular formation of organic fructifica- 

 tion, since, in the latter, the individuality of the separate cells appears 

 most circumscribed and checked. 



* DC Gonidiis Liclicnum. Berlin, 1839. 



M 



