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lichen may be referred to a species of algal. 2. The connection 
of the hypha with the gonidia is of such a nature as to exclude 
all possibility of the one organ being produced by the other, 
and the theory of parasitism can alone explain it satisfactorily. 
This alone, he urges, can account for the gonidia of very diverse 
lichens being almost identical, as well as for the marked 
differences between the gonidia of certain other lichens of 
which the thallus and fructification are identical. In the same 
way, too, he thinks can only be rightly explained the origin of 
dead gonidia found in the interior of lichens, as also the 
occurrence in the same thallus of dissimilarly coloured gonidia. 
As had been suggested by De Bary, various experiments have 
been made in the way of lichen- and alga-culture, in order to 
ascertain with certainty whether the germinating lichen-spore 
developes gonidia or not, and whether these latter in a free 
state form from themselves hyphse or not. Accordingly 
Professor Beess, in order to test the applicability of the theory 
with respect to the Collemacei , made certain experiments, which 
were recorded in October, 1871, in 66 Monatsb. der k. Akad. der 
Wissensch. zu 'Berlin.” These consisted in sowing the spores 
of Gollema glances cens, Hffm., upon Nostoc lichenoides , Vauch., 
which readily germinating sent forth numerous filaments that 
penetrated into and spread within the substratum (see our 
Plate CXII., fig. 6). After undergoing various phases of develop- 
ment, they at length surrounded the moniliform gonidia, and 
formed the “ collema-mycelium,” or hypha-mass, so that in 
this way, in process of time, the Nostoc becomes converted into 
a Collema, although no fructification could be obtained. Hence 
Reess inferred that every Collema is in free nature a “ nostoc,” 
which should no hypha come to it remains so, but which, 
should it be thus inoculated, undergoes the above transforma- 
tion. We may here observe that while Reess’ experiment 
appears to confirm Schwendener’s theory as to Collema being a 
compound organisation (and it has constantly been adduced as 
one of its main supports), he at the same time strongly 
suspects, nay, even plainly asserts, that the fungus-hyphas 
represented by the latter (Schwend. t. x. figs. 19-21) as 
attacking a nostoc, are in reality those of a true mould. But 
whether this be so or not, both writers agree in regarding Nostoc 
as an independent algal, which may either normally continue 
so, or become the host of a parasitical fungus, and by it 
be converted into Collema. Strongly impressed by the argu- 
ments put forward by De Bary, Schwendener, and Reess, as to 
the nature of the Collemacei , some, amongst whom is Professor 
Cohn, while regarding the theory as untenable with respect to 
the other families, would exclude the Collemacei altogether from 
the class of lichens. 
