30 
LICHENS. 
minate and produce a normal thallus, thereby indicating that these 
organs are analogous with the conidia of the Ascomycetes. (3) 
The fact that the trichogynes are in general divided into several 
cells by transverse septa, a condition opposed to the idea of their 
being intermediate organs in the fecundation of the ascogonia. For 
the above reasons it is considered that the presumed sexual organs 
afford no essential point of distinction between the two groups 
under consideration. It is furthur suggested that the ascogonia 
represent a special kind of receptacle containing nutritive material 
for the formation of the ascospores, or constitute a stage of develop- 
ment of the hyphas preceding the formation of asexually produced 
asci. It is also suggested that the so-called trichogynes are 
nothing more in structure or function than hairs in general, acci- 
dental prolongations of the ascogonium, which, owing to the excess 
of nutritive material, grow with exceptional vigour. 
A characteristic feature of the higher lichens is the highly 
organized thallus, comparable with the stroma of the Ascomycetes ; 
but here again a transition can be traced through the lower lichens 
until a type of stroma occurs distinguishable from that of the 
parent group — the Ascomycetes — only by the presence of 
gonidia. 
Again, the presence of lichenine is characteristic of lichens, and 
can be demonstrated by the use of iodine in the hymenium of most 
of the higher forms, but gradually disappears in the lower lichens 
approximate to the Ascomycetes; consequently, although 
characteristic of lichens, lichenine cannot be considered as a crucial 
test. 
From the above statements it will be seen that the only general 
character separating lichens from fungi is a biological one — their 
symbiosis with alg£e. 
Intermediate forms between Lichens and Ascomycetes . — Many 
authors, adhering to the hypothesis that the gonidia are produced 
by the hyphal elements, have placed amongst the lichens numerous 
species not possessing gonidia, i.e., species of Arthonia , Calicinm , 
etc. ; also numerous species parasitic on lichens. So far as the 
parasitic species are concerned, it is possible that they may be true 
lichens, and for their symbiosis, profit by the gonidia of the plant 
on which they are parasitic. 
The parasitic species without gonidia technically belong to the 
fungi, although in many cases giving the same reaction with iodine 
as the greater part of lichens. 
It cannot be disputed but that the Pseudo-lichens — so-called 
lichens without gonidia — resemble so very closely the corresponding 
genera of lichens, that they are distinguished solely by the absence 
of gonidia. 
The above statements illustrate clearly the great affinity between 
the Lichens and Ascomycetes, and at the same time form a con- 
necting link between the two. 
At the same time this transition of the genera of Lichens to 
