viii INTRODUCTION, 
Zygnemacee, and meet it by the assertion that, as far as our 
experience goes, this suggestion is not supported, and the 
evidence produced is far from satisfactory. The larger and 
more complex hypothesis of the combination of Alge and Fungi 
in the production of Lichens, has been combated elsewhere,* 
and to this we have nothing to add, save that we have since 
encountered no facts or arguments which would induce us to 
modify that opinion. Even should hereafter the terrestrial 
Nostocs be united with the Collemacew, the saxicolous Stigo- 
nemee be relegated to the Sirosiphei, and the corticolous 
Chroolepide be transferred to some other relationship, the true 
aquatic Algz would still remain in sufficient number to interest 
the student, and maintain for some time to come the distinctive 
group of Fresh-Water Alge. 
* “ Grevillea,” Vol. vii., p. 102. 
