546 
THE PRINCIPLES OF BOTANY. 
This view induced Fries to form the opinion that Lichens 
“ are types of Algals horn in the air, interrupted in their 
development by the deficiency of water, and stimulated into 
forming a nucleus by light.” The same author concludes 
that Lichens have the vegetation of Algals and the fruit of 
Fungales. 
Agardh, according to Professor Lindley, “ considers Lichens 
more nearly allied to Fungals than to Algals : he remarks 
that if Sphserias or Pezizas had a thallus, they would be 
Lichens ; and that the same part is all that determines such 
genera as Calycium, Verrucaria, or Opegrapha to be Lichens 
and not Fungi. He adds that all the transitions from Algals 
to the state of Lichens which have been detected by modern 
enquirers, are mere degenerations into the form of the Lichen 
tribe, and by no means into Lichens themselves.” 
These opinions show how difficult it is in Nature to draw 
hard lines, and for the reason that she never made them ; 
and indeed our own observations with the microscope would 
lead us to conclude that the cellular initiative matter one has 
examined on walls, may develope Algals, Fungals, and even 
higher forms of vegetable life, according to the presence or 
absence of moisture and light. But whatever theory may be 
held as regards the physiology of Lichens, we shall not be 
far wrong in at least viewing them on rocks and stones as the 
pioneers of higher kinds of vegetable productions. 
As stated by Sir W. Hooker, “ They are among the first 
plants which clothe the bare rocks, and form a humus for 
others of a higher organization to live and flourish in.” 
( ( English Flora, 5 vol. v, p. 130.) 
The same idea has been noted by Professor Lindley. He 
says : 
Pulverulent Lichens are the first plants that clothe the 
bare rocks of newly-formed islands in the midst of the ocean ; 
foliaceous Lichens follow these, and then Mosses and Liver- 
worts.” (‘ Vegetable Kingdom, 5 p. 47.) 
These plants have been classified by Professor Lindley as 
follows : 
Alliance 3. Lichenales. 
Lichens contain two sets of principles which make them 
useful to man ; the one in a set of dyes, as Orchill, Orchall, 
Nucleus breaking up into naked spores Graphidacece , or Letter- Lichens 
Nucleus bearing asci ; thallus homoge- \ Colle or Ml Uchem _ 
neous, gelatinous, or cartilaginous 1 ^ 
Nucleus bearing asci; thallus hetero- 
geneous, pulverulent, or cellular 
| Parmeliaceee , or Leaf -Lichens. 
