522 THE UNIVERSE. 



clouds, traverses oceans, and then effects a descent upon some 

 distant shore. We are told that after certain hurricanes it is 

 not unusual to see the soil of Spain covered with different 

 aerial seeds brought from America. It is to the action of 

 the winds that Linnaaus ascribes the importation into Europe 

 of the Conyza ccerulea of Canada, which now infests the 

 north of France. 



The air does still more ; in its commotions it carries away 

 entire plants and bears them to a long distance, to let them 

 fall there like an abundant living shower. 



Certain lichens from the mountains of Asia, travelling 

 thus amid the clouds, suck up watery vapors from them, 



217. Edible Air-Borne Lichen: Lecanora esculenta. 



and grow during their accidental peregrination. Torn away 

 from the soil when they are scarcely so large as the head 

 of a pin, they have reached the size of a small nut by the 

 time when, their aerial journey over, they fall far from 

 their native rocks upon the ground below them. This hap- 

 pens with many edible species, which after a storm are soon 

 scattered over the sand of the deserts. 



These plants, which seem thus to fall from the sky, some- 

 times form thick layers on the soil, and yield the exhausted 

 traveller an agreeable food. The providential manna, on 

 which the Hebrews fed while wandering in the desert, 

 doubtless arose from showers of edible lichens ; for it is 

 these plants which seem always to produce such showers. 



