9 
uniform character, presenting nothing like a stem; nor when we 
remove a portion of a plant from its base of support do we discover 
the slightest trace of a root. All parts of the thallus are perfectly 
alike, and, so far as regards the absorption and assimilation of 
food materials, whatever function one part of it can perform is 
equally shared in by the rest. 
In the great diversity of Lichen thalli of this kind, it is quite 
impossible, in a general survey, to notice and describe all their 
variations. We have supposed ourselves to be upon a botanical 
excursion, but reality is too strong for me, and language fails to 
convey correctly the many differences our eyes, armed with a 
magnifying glass, would readily detect were we actually among the 
plants in their place of growth. Let us notice a few species where 
the differences are more pronounced. 
The thallus of one, Zecidea lucida, which we meet with very 
commonly, may be taken as the type of several others. You have 
doubtless noticed it frequently, spreading irregularly over the shady 
parts of stones in walls. To the naked eye it looks like a thin 
powder of a pale yellow colour, but examined under a lens it is seen 
to have in reality greater consistence. The magnifying glass also 
reveals what the eye fails to distinguish—minute round bodies 
scattered here and there over the surface. ‘These are also yellow, 
but more shining than the thallus. They are the organs of 
reproduction, which I shall speak of presently. In other Lichens 
the substance of the thallus, instead of being powdery, is aggregated 
in little granular heaps, and the granulations vary greatly in size, 
not merely in different species, but also frequently in one and the 
same. Such a Lichen is Z. decolorans, or granulosa, which we 
should certainly meet with abundantly in the course of our search, 
covering large spaces of peaty earth, with its gray granulations. 
This Lichen has borne various names, for, from the different 
appearances it assumes, forms of it have often been mistaken for 
distinct species. One name formerly given to it was Z. guadricolor, 
from plants of it being sometimes parti-coloured, the thallus being 
gray, and the fruit varying from flesh colour when young through 
a livid green to a dull black in old age. 
