Sunshine, Rain, and Wind, 
a special lamp. Even with all these precautions one of 
his twenty flasks was contaminated.” 
Such dust is of the most varied character. It may be 
volcanic ash or desert sand, or carbon and soot from 
household fires, or the poisonous waste of chemical works, 
but a very large proportion of it is organic. Where 
there is a close vegetation of wood, or grass, or, for in- 
stance, in a garden, pollen, microbes, lichen-, fungus-, and 
algal-spores will be extremely abundant. But even in 
deserts or open and bare places, bacteria and these other 
minute spores are not necessarily absent, for if the dust 
of the Krakatoa eruption really went three times round 
the world, a bacterium might come to land anywhere. 
Quantities of these dust particles are washed down 
upon the earth’s surface in rain (indeed every raindrop 
or mist-globule condenses upon one particle at least). 
This is useful as a manure to the soil ; spores and germs 
are also distributed in this way. But a large amount of 
the rainfall and of its organic and other dust is inter- 
cepted by the leaves and stems. There are most 
interesting arrangements to utilise this atmospheric 
manure, of which some are described and figured in 
Kerner van Marilaun’s “ Natural History of Plants.” 
Until recently many botanists refused to believe that 
the rain-water could be directly absorbed by leaves and 
stems. Desert and rock plants are in some places 
obviously kept fresh and vigorous by sea-fog and mist ; 
it was also shown by direct experiment that plants can 
be revived by moistening the leaves even if the roots are 
dry, but still this prejudice survived. 
The probable reason is not without interest. Pro- 
fessors of botany feared that their students might become 
confused and bewildered, and so were unwilling to admit 
that water with anything dissolved in it cannot help 
entering the leaves. 
192 
