Dec. 1910.] BOTANICAL SOCIETY OF EDINBURGH 133 
(4560 metres), Gnifetti, there were no less than 40 bacterial 
and 3 fungus colonies from a cubic centimetre of melted 
snow. 
However much allowance may be made for the share 
taken in the transport of spores by insects and birds, these 
instances are enough to show that even at altitudes of 
13,000 feet the air contains living spores in great 
abundance. 
When rain falls, a very large proportion of the floating 
dust-particles is washed out of the air and falls upon the 
foliage of plants. When the drops reach the leaves, the 
water is carried down to the petioles and stems by a series 
of grooves and gutters or flat surfaces which differ almost 
in every particular type of leaf. 
These ingenious contrivances for carrying off rain-water 
are much too complicated to describe, but the result is to 
deposit all dust contained in the rain on certain well-defined 
lodging-places, usually about the base of the lamina or of 
the petiole. 
I examined this dust microscopically, collecting it from 
about 26 species of plants. The results were too mon- 
otonous for it to seem worth while to go further into this 
side of the question. 
In every ease I found such easily recognised objects as 
lichen soredia, spores of rust-fungi, algal cells, pollen, yeast 
cells; in every case bacteria were to be seen. The pro- 
portion of these organic particles seemed to me extra- 
ordinarily high, at least in all cases when the leaf was more 
than 18 inches above the ground. 
The point which most impressed me was the extra- 
ordinarily high manurial value of this plant-dust. 
Not only does the inorganic part consist of very tine 
particles of the most varied mineral character, but the 
organic part not only forms a large proportion of the dust, 
but consists mainly of spores, etc., which must contain the 
most concentrated nutritive material. 
Not only so, but there are grazing animals, the mites, 
to devour this combined nitrogenous matter, and, as I have 
pointed out, bacteria are available to break up and transform 
the waste products. 
If this material, when dissolved in rain-water, enters 
