"SWEAT OF HEAVEN" 



stupid, and scarcely move from their birthplace. They live 

 out their life wherever their long, lancet-like proboscis 

 needles have pierced the plant's skin, but it is their power 

 of multiplication that makes them really formidable. 



Huxley calculated that if all the offspring of one " green- 

 fly " lived, and if their broods also lived for ten generations, 

 then the tenth brood of that original green-fly would con- 

 tain more animal matter than the entire population of 

 China. Green-fly would, as a matter of fact, go on increas- 

 ing at this rate, were it not for the enormous number of 

 enemies that prey upon them. A mathematical friend of 

 Mr. Buckton calculated that in 300 days the produce of 

 a single green-fly might be 210^^, that is 210 multiplied 

 by 210, and then again by 210 up to 15 times ! 



In summer time one may often notice, especially on syca- 

 mores and lime trees, a peculiar shining, sticky, honey-like 

 substance which covers the leaves. It is often so abundant 

 as to drip like a rain of honey from the upper branches. 



This " honey-dew '■" was a puzzle which greatly intrigued 

 learned minds in the ancient world. Pliny speaks of it as 

 the " sweat of heaven " or " saliva of the stars."" 



In reality, however, it is nothing but the excretions of 

 hundreds of millions of these green-fly or aphides, which 

 will be found established on the under side of the leaves, where, 

 moored by their little anchoring talons and with their pro- 

 boscis inserted in the fresh green leaf, they are sucking hard 

 and steadily at the sugary juice. In twenty-four hours it 

 was observed that a single individual gave forth forty-eight 

 minute drops of honey. 



Bees are very often tempted to collect this honey so 

 abundantly produced, but this turns their own honey black, 

 and may even make it poisonous. 



293 



