88 THE NORTHERN MICROSCOPIST. 
thallus may be said to comprehend the whole plant, inasmuch as 
it contains within its tissues, or bears upon its surface the reproduc- 
tive organs, both male and female, with their fruit. The form 
which the thallus assumes in growth, is very variable. So is its 
consistence, size, and colour. It will sometimes expand to one or 
two feet in diameter ; while, in other forms, it will present a small 
grey or coloured spot ; and often nothing but the fruit will be seen, 
the thallus being evanescent. The typical forms of the thallus 
are vertical and horizontal. ‘The vertical, or free thallus, is divided 
into fruticulose and filamentous. The former is a shrub-like aggre- 
at 
~ (Ge Nene 
A mone s 
Hig. i. 
gation of segments or portions, springing from a centre ; and they 
are either narrow or broad, round or compressed, simple or 
branched. Cladonia and Ramalina are fruticulose forms, The 
Jilamentous species are more elongated than the fruticulose. They 
are round and thread-like, more or less clothed with divergent 
fibrils. Usnea barbata (fig. 11,) shows this form of Lichen. 
The forms of Lichens just named, are those which give the aged 
and venerable appearance to many of our forest trees; and present 
them to our sight so shaggy and hoary, as almost to move our pity, 
while they command our reverence. Wordsworth’s “Thorn” must 
have been covered with these Lichens. He tells us :— 
‘‘There is a Thorn, it looks so old, 
In truth you’d find it hard to say 
How it could ever have been young, 
It looks so old and grey. 
* * * * 
Like rock or stone, it is o’ergrown 
With lichens to the very top, 
And hung with heavy tufts of moss, 
A melancholy crop,” 
