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taken in its net to more rapid activity ; nay, to more vigorous 
increase.” 
Now this hypothesis seems to have been suggested to Schwen- 
dener from two different sources. Of these the one was an 
observation made (of course not seriously) by Nylander in 
“Lapp. Or.” p. 117, to the effect that if the gonimia in the 
various cephalodia of lichens were parasitic algae, then it would 
be necessary to regard all lichen-gonidia as such parasites, 
seeing that in an anatomical point of view they all agreed. 
And the other and more immediate source was an alternative 
more seriously put forward by Professor De Bary in “ Hoffmeist. 
Handb. der Phys. Bot.” ii. p. 291, where, in speaking of 
some genera of the Collemacei , he says : “ These are either 
perfectly developed states of plants, whose imperfect forms 
have hitherto stood amongst the algae, as Nostocacece and 
Chroococcacece ; or these latter are typical algae, which assume 
the form of Collema , Ejphebe , &c., through certain parasitic 
Ascomycetes penetrating into them, spreading their mycelium 
into the continuously growing thallus, and frequently attached 
to their phycochrome-bearing cells.” Taking the alternative 
thus proposed as his starting-point, Schwendener, commencing 
with the Collemacei , made various observations and experiments, 
which were afterwards extended to other tribes and genera, the 
result of which was to lead him to the conclusion that lichens 
consist of the two primarily distinct elements already men- 
tioned — that the lichen-gonidia are algae, and the lichen-thallus 
a parasitic fungus. This position he endeavours to support by 
the following considerations : — 1. That as yet the genetic 
relationship of the gonidia to the hyphae (that is the colourless 
filamentose tissue which in conjunction with the coloured 
cellular portion, or the gonidia, constitutes the lichen-thallus) 
has in no case been directly proved, but only assumed for ana- 
tomical reasons. 2. That chemically the gonidial membranes 
differ from the hyphal membranes, the former having an algal 
and the latter a fungal reaction. 3. That the various gonidia- 
forms, alike in structure and mode of increase, correspond to 
parallel types of unicellular and filamentose algse. 4. That as 
the germination of the spore has not been observed further than 
the commencement of a hypothallus, this is probably owing to 
the want of the co-operation of the requisite algal. 5. That 
between lichens and Pyrenomycetes there is a very striking 
correspondence in the development of the fructification. In 
the second of the two papers above mentioned, he enters into 
further details, and enumerates the various algal-types, which 
he regards as constituting the gonidia. These types, which are 
eight in number, he includes under two groups, viz. “ Phyco- 
chromacese,” and tc Chlorophyllacese,” so called from the colour 
