such genus. Some consideration of the numerous, sometimes 

 sufficiently significant instances, in which nature appears to 

 point in this direction, may be found in the author's Genera 

 Lichenum ; from which work these observations on spore-values 

 are taken. Suffice it here to say that Parmelia proper, Ach., 

 will thus fall into Theloschistes, Parmelia, and Physcia ; and 

 Lecanora into Placodium (DC.), Naeg. & Hepp, Lecanora, and 

 Rinodina. Excluding the sub-Biatorine forms of Placodium 

 from the Lecideei, the latter family will have no examples of 

 the polar-bilocular sub-type ; but Heterothecium, corresponding 

 to Physcia and Rinodina, will be distinguishable from Biatora, 

 and Buellia similarly from Lecidea. And the whole Class may 

 be conceived as in like manner passing into 1, a Colourless 

 Series, especially prominent and characteristical in the higher 

 tribes ; and 2, a Coloured Series, having its chief development 

 in the lower; series which, tabularized, will be found significant 

 as well of the relations of the genera, as of the systematic value 

 of the spores. 



It is yet important to distinguish between spores typically 

 colourless, and what are rather to be taken for decolorate con- 

 ditions of spores typically coloured. There are sufficiently nu- 

 merous instances of such decolorate spores ; and we need per- 

 haps scarcely hesitate to argue from them to some other cases 

 in which the evidence is possibly less clear, and thus to keep 

 certain natural genera entire. And, on the other hand, it is 

 conceivable that a genus may rather be referable to the Colour- 

 less Series, notwithstanding that many of its species exhibit 

 spores which, in respect at least of colour, look often the other 

 way. Difficulties of this sort are however to be expected in 

 every stage, from the first step, of our endeavours to study the 

 life in nature. What responds to our intelligence there is in- 

 deed of kin to that intelligence, is the ideal ; but the ideal im- 

 prisoned in, and subjected to all the inordinate fortuitousness of, 

 the natural. (Gen. Lich. pp. vi-viii.) 



There occur also, beside the apothecia, and very generally. 



