260 
ON THE LICHEN-GONIDIA QUESTION. 
Br the Rev. J. M. Crombie, F.L.S., &c. 
[PLATE CXIL] 
S INCE the time when lichens were definitely separated from 
mosses, algae, and fungi, under one or other of which they 
were indiscriminately included by the earlier writers, they 
have until quite recently been regarded as constituting a 
distinct class of plants. Not only lichenists, but cryptogamists 
in general, have in all modern systems of classification viewed 
them as entitled to as definite a position in the vegetable 
kingdom as the algae and the fungi. Between these two 
classes they have universally been held to occupy an inter- 
mediate place, though their connection with the one or the other 
is, in most of the proposed arrangements of their families and 
tribes, not sufficiently manifest. In Nylander’s arrangement, 
however, which, in its main features at least, is the most natural, 
and consequently the most scientific yet propounded, lichens 
are connected with the algae on the one hand by means of the 
inferior genera of the Collemacei , and with the fungi on the 
other hand by means of the inferior genera of the Pyreno- 
carpei. At the same time it has always been difficult to draw 
very definitely the boundary-lines between the three classes; 
though of late years, with the consent both of algologists and 
mycologists, the lichen territory has gradually been enlarged at 
the expense of its neighbours. Alike from the algae and the 
fungi it has made various important acquisitions, which of 
right belonged to it all along, though its title-deeds to 
them were written in characters so minute or obscure that 
it required both microscopical aid and keen research rightly to 
interpret them. The result was that lichenists supposed that 
they had good grounds for believing that their much-loved, 
if in some respects difficult science, was at length in a fair way 
of having its limits well defined, with respect to the other 
two neighbouring classes of cryptogamics. Very recently, 
however, a theory has been started, which, should it be 
