8 
represents the entire difference between Lichens and the classes 
above them in the scale of vegetable organization, but it is one 
sufficiently obvious in the great majority of species, and it is the 
character which gives name to the group of plants to which Lichens 
belong. The distinction between Lichens and other lowly organisms 
of the same group—the so-called Algze and Fungi of our botanical 
books—must be looked for in other morphological differences, and 
we had better defer its consideration. 
Suppose us now upon our hunting-ground and ready to begin 
our search. All around us, overspreading the rocks, covering the 
walls from foundation to coping stone, and encrusting such portions 
of the ground as have been left bare of other vegetation, we see 
countless stains and patches ; some small, hardly an inch across, 
others a foot wide or more ; many of them nearly circular in outline, 
others of no definite shape, but extending themselves vaguely and 
diffusely. Very various in colour are these patches, grey and white 
being perhaps the most common, though shades of yellow, bronze, 
and olive abound, while not a few deepen nearly to black. All 
spread flat upon the surfaces they grow on, clinging so closely 
that the thinner and duller patches hardly seem distinct from 
the substratum itself. A greater contrast than they present to the 
rest of vegetation can hardly be conceived: earthy, arid, to all 
appearance dead, they seem the last things to which a name 
originally meaning “full of life,” could be applied. Every one has 
seen them, comparatively few reflect on the mystery of their being, 
nor many note their exceeding variety in form, consistence, and 
colour. 
These patches, earthy-looking, powdery, or filmy, are individual 
plants. For the species to which they belong they represent and 
perform all the functions of the roots, stems, and leaves of higher 
plants. Botanists have given the name of ¢had/us to such vegetable 
structures as these, in which we can recognise no differentiation of 
parts, no member of separate origin, no organ with definite function. 
And however greatly we might at first sight be inclined to ascribe 
leaves or stems to some Lichens, in these we can make no such 
mistake. Their upper surface from centre to circumference is of 
