8 SN HENRIK PRINTZ — [1920 
and with greater certainty, at least if they are examined at various 
times. 
Another feature of general biological interest I will point out, 
viz. that the subaérial algae form natural plant-communities. The 
various species do not occur spread around, mixed arbitrarily, but 
species with the same demands on their environments unite in 
natural plant-communities. I have thus noticed that Physolinun: 
monile primarily occurs associated with certain liver-mosses, 
partly also with Trentepohlia aurea; associated with species of 
Protococcus is usually found Acanthococcus, etc. However, it must 
be remembered that this interdependence, as far as less known and 
less investigated species are concerned, may indicate a genetic 
affinity. On plants with a smooth and hard trunk, e. g. bamboo, 
it is only a few species that are able to find hold, and here usually 
only occur plants that have an adhesive growth, e. g. Phycopeltis 
arundinacea, and some others, a flora very different from the one 
found on rugged bark. However, my material is too scanty and 
accidental and wanting the necessary information about the nature 
of the habitat for making further conclusions from it. 
In the following account I have for each species put down the 
number of all the samples, wherein the alga concerned has been 
observed. This I consider as not being without interest. as it gives 
an idea of the relative frequeney of the different species. 
