106 THE NORTHERN MICROSCOPIST. 
they contain simple, short, thickish stalks, or stoutish cells, called 
basidia, which generate and bear on their apices stylospores. 
These are pyriform or oval bodies, something like ordinary spores. 
The function of pycnides like that of spermogones, is still very 
much shrouded in mystery, and until this is understood, we cannot 
truly know the real difference between them. They are illustrated 
by Fig. 16. 
We have already hinted that the Lichen has no axis and no root. 
Therefore it does not nourish itself from the soil, or place of 
growth. It is an aérial plant, and what the water with its solutions 
is to the Alga, so the damp atmosphere is to the Lichen. The 
whole plant imbibes nourishment alike, and its growth is, therefore, 
much affected by the purity, dryness, or humidity of the air. A 
polluted atmosphere is destructive to Lichen growth, while a flou- 
rishing condition of these plants, is a sure indication of the purity 
of the surrounding aérial medium. On account of their spongy, 
cellular nature, Lichens are strongly hygrometric. After being in 
the herbarium for years, on the application of moisture which they 
greedily absorb, they will freshen up and appear almost as bright 
and green as when first gathered. While humidity promotes their 
growth yet they are capable of enduring great drought. The 
crustaceous Lichens are of very slow, and frequently very long 
growth. Some are said to grow for hundreds of years. They 
cover, and emboss in grey and gold, the rocks on our highest 
mountains ; to which they cling so closely, that no storm affects 
them. The foliaceous plants, contrary to the crust-forms, attain 
their highest development at low attitudes, and in shaded places. 
Some of the softer and less thalline plants grow to maturity in a 
short space of time. I gathered myself, Odontotrema longius 
(LVy2.), in considerable quantity on an old rail, near Asby, Cum- 
berland, in the autumn of 1879. In the same month of last year 
(1880), I visited the same spot, and upon the old cuttings of the 
previous year, upon the very knife marks, I found the same plant 
regrown. No thallus was visible, but some of the apothecia, when 
examined under the microscope, were fully developed. This 
growth of the Lichen had been made in one years 
The habitats of Lichens are almost all objects on the surface of 
the earth. ‘They grow abundantly on rocks, old walls, rails, the 
bark of trees, the ground, old stumps, exposed tree roots, the 
withered fronds of ferns, on mosses, sheep’s dung, mortar, and 
some have been found on glass. They are natives of the whole 
country side. 
‘* With such a liberal hand has Nature flung 
Their seeds abroad, blown them about in winds.” 
Although our remarks partake more of the character of hints 
