39 



Eschweiler, Lich. in Mart. 1. c.; Koerber, Diss. 1. c.; Turner and 

 Borrer, Lichenogr. Britt. passim. 



V. CHROSIS. 



The intimate connection of color in lichens, both with the struc- 

 ture of the parts, and the progress of evolution of the whole plant, 

 was indicated by Eschweiler (Syst. p. 6) in 1824. Observing the 

 general occurrence of a black apothecium with a white thallus, and 

 of a red apothecium with a green thallus, he inferred a chemico- 

 polar secretion of coloring matter, the operation of which he com- 

 pared to the separation into red and green of the purple tincture of 

 Roccella, and many other lichens, at the poles of the Voltaic pile. 

 Hence he further argued the remarkable distinction in this respect 

 of Lichenes from aquatic AlgaB and Fungi ; their nearer approach 

 to phanerogamous plants; and their intimate dependence on light. 

 Fries (Lichenogr. 1. c.) concludes, that the vital color in lichens is 

 green, becoming more or less altered by external moments, and 

 either normally 5 or abnormally; that of the fructification red, re- 

 gressively passing into black ; and that white arises in every series of 

 variation of color, and is apparently never normal. Nimium ne crede 

 colori sed crede colori. In the infinite variety of hues in lichens certain 

 primary types of color can be discerned and indicated; and these 

 are observed to characterize, more or less distinctly, certain series 

 of species, which vary within the limits of their types. And these 

 series, if distinct, are sometimes so conspicuous, that species of the 

 most different form, but congruous in their normal color, seem to 

 possess more true affinity than others agreeing in form but differing 

 in their normal color. The native and primitive color, as in all 



AlffflB Or Piotophyltt, is green, (ra, iivrto y^s %Xuga, vravrav Quoftivtov ro 



xfir'ov iff-rt. Arist), which in the perfect lichen we find pure and 

 persistent only in the gonidium, or vital principle. 



The Hypothallus, where this is perceptible, is either palish (hy- 

 potk. albus), or blackish (hypoth. ra'ger); the latter verging here and 

 there to lurid, bluish, &c. The color of the Thallus, of primary 

 importance in determining the affinity of species, inheres only in the 

 cortical layer, and shows itself in four well defined series: e locte 

 viridi glauca, e flavoviridi ochroleuca, e saturate viridi/wsca 

 1. olivacea, e luteoviridi citrinn. But these colors are variously 

 aberrant. In the lower tribes the series are not defined ; in those 

 with ^thallus hypophlfeodes the color depends on that of the epider- 

 mis of the matrix, though this itself is variously changed by the 

 lichen. Other mutations are dependent upon station: thus, in moist 

 places the normal color becomes greener; in those too dry this ap- 

 pears whiter. White is peculiar to no series, and either as gray, or 

 whitish, results manifestly in each. The cycle of variations of 

 each series is best learned by use; in genere glaucfB pallide viridis, 

 glaucus, caerulescens, stanneus, albus; fusctB saturate viridis, oliva- 

 ceus, cinereus, griseo-fuscus, badius; ockroleucce flavo-virens, ochro- 

 leufus, albescens; citrina viridi-luteus, aurantius, miniatus. 



The Thalamium (possibly from the resinous principle ti-ylhrinum 



