102 THE NORTHERN MICROSCOPIST. 
fresh, often presents the appearance of a small clot of jelly. The 
presence of lichenine constitutes a point of difference between the 
the medulla and paraphyses of Lichens, and the hyphoid parts of 
fungi. The hypha and paraphyses of the latter, are generally brittle 
and non-elastic; and they dissolve away in a solution of hydrate of 
potash. But those of Lichens are thicker, and more flexible, and 
do not readily dissolve in the said solution like the filaments of fungi. 
On the ground of this difference, Dr. Nylander says, “No fungus 
is present in the formation of Lichens. This is demonstrated 
Fig. 13. Fig. 14. 
from their very first beginnings; for the spores and primary fila- 
ments of germination at once show themselves to be of a lichenose 
nature.”* Beside, the three layers of cells already described as 
- constituting the thallus, there is, particularly in crustaceous Lichens, 
a hypothallus. This is the first vegetation of the germinating 
spore, which underlies the thallus; and, eventually, from the 
increasing growth above it, becomes a dead mass. It is generally 
of a black or brown colour, though sometimes it remains white. 
It will be often seen bordering the thallus, or protruding through 
it; or, if scattered, filling up the intervening spaces. 
The “ biological action” of the Lichen-thallus is mostly super- 
ficial. It does not increase in thickness beyond a certain point ; 
but it grows upward, or outward from a common centre, according 
to the form it assumes. ‘The outer portions of the thallus are 
consequently always the younger. It is not an uncommon thing 
in foliaceous species, to see the centre of the thallus—the oldest 
part, entirely decayed and gone, while the periphery still adheres to 
the rock or tree, and grows on. The centre of vegetative action in 
the thallus, is undoubtedly in the gonidial cells. They are the 
* Vide Grevillea, Vol. VI., p. 44. 
