132 TRANSACTIONS OF THE [ Sess. Lxxv. 
districts of France and Belgium seemed to have been caught 
up in a cyclone, carried right round by the north of 
Scotland, and reached his instruments at Kingairloch (28 
miles from Ben Nevis) with a north-westerly wind. 
These inorganic dust - particles must, therefore, be 
miscellaneous; they probably differ both in chemical con- 
stitution and in physical character, though they are all 
exceedingly minute. 
But the organic part of the dust-particles is perhaps even 
more interesting. 
It is hardly necessary to say much about the enormous 
number of germs, spores, pollen grains, and other organic 
material which seems usually to hover in the atmosphere. 
Dust-like seeds are characteristic of many phanerogams, 
and especially, according to Ridley, of many of those which 
have colonised oceanic islands. Fern-spores also must be 
abundant in the atmosphere. I need hardly recall the 
classic case of Krakatoa, for, even in this country, many 
kinds of ferns and even some flowering plants establish 
themselves on trunks of trees, bridges, and walls, sometimes 
miles away from their nearest neighbour. 
With mosses and lichens, the facts of their distribution 
both in the Arctic and Antarctic and on mountain summits 
are very remarkable. Fink (18) discovered no less than 
thirty forms of lichen on a wall that had only been built 
thirty years. One should also mention, perhaps, the trades 
dust which falls in the Atlantic, and which consists of an 
alga, Trichodesma Hildenbrandtii forma atlantica, the 
regular distribution of yeast-cells on fruits, Dietel’s experi- 
ments which showed that spores of rust-fungi could always 
be detected on plates left exposed during the summer. 
Many other instances could be mentioned, but this hardly 
seems necessary. One of the most recent papers, however, 
can hardly be omitted in this connection. 
Galeotti and Levi (19) studied the distribution of bacteria 
and fungus spores on the snow of high Alpine summits. 
From a cubic centimetre of water melted from the snow 
found on Point Strahling, at an altitude of 3116 metres, 
they obtained 147 colonies of bacteria and 20 colonies of 
Hyphomycete fungi. In one case (Lyskamm) they found 
only one colony of Hyphomycetes; yet on another summit 
