Sunshine, Rain, and Wind 



a special lamp. Even with all these precautions one of 

 his twenty flasks was contaminated. 29 



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 



