Ge: HENRIK PRINTZ | [1920 
There is no doubt, on the contrary, that the tropics — where the 
climate is not too dry — have a far richer vegetation of subaérial 
algae than the temperate zones. It is particularly the Myxophyceae 
that are reported to be dominating, while the Chlorophyceae are 
playing å more modest part. On this comp. e. g. FRITSCH, Å 
General Consideration of the Subaérial and Fresh-water Algal 
Flora of Ceylon. Å Contribution to the Study of Tropical Algal 
Ecology (Proceed. Royal. Soc. Vol. 79, 1907) and Wire, Report 
on an Expedition to Porto Rico for collecting Fresh- water Algae 
(Journ. New York Bot. Garden, 1915). It is therefore not super- 
fluous to point out especially that the bulk of the algae that occur 
in the samples from South Africa, examined by me, are Chloro- 
phyceae, while the Myxophyceae have been observed only in åa 
few samples, and in none of them in any particular abundance. 
Thus, the total number of the Myxophyceae observed is only 5. The 
possibility is not precluded, however, that this, partly at least, may 
be due to the collecting. 
Ås is well known, the freshwater algae evince, on the whole, 
a striking cosmopolitanism in their distribution, a natural con- 
sequence of the uniform character of the surroundings. On the 
other hand, it is to be expected that the various subaörial algae — 
though they are at least as easily spread by their akinetes, aplano- 
spores, and in other ways — like the terrestrial flora on the whole, 
will appear to be more directly dependent on the climatic con- 
ditions, as dampness of the air, temperature, wind, 
size of the amplitudes, etc. Ås to the demands of life of 
the algae, their conditions in air will be exposed to greater variations 
than in water in the same places. It does not therefore follow that 
the freshwater algae are quite independent of the environments, 
but here, no doubt, the chemical and physical states 
of the water take a vital part. In an earlier paper: Kristiania- 
traktens Protococcoideer (Kristiania Videnskabsselskabs Skrifter, 
1914), I have, by the way, pointed out the rather essential diffe- 
rence in the composition of the algal vegetation of the tracts west 
of Kristiania, abounding in lime, and the localities poor in lime 
and abounding in humic acid in the eastern neighbourhood of the 
town. Indeed, to the freshwater algae the height above the level of 
the sea seems to be of no considerable importance, at least not 
before the absolutely arctic conditions begin to assert themselves. 
Most species of algae, at least the most general ones, the distribu- 
tion of which is known with some degree of certainty, thus are 
found nearly all over the world, apparently quite independent of 
geographic limitations as well as elimatie conditions. Under extreme 
conditions only, e. g. in absolutely arctic countries or high up in 
the mountains, there apparently occur a few particular species, e. g. 
