114 PLANT-LIFE ON LAND [ch. 



The results of successful dispersal combined with 

 high fecundity in any given organism come out clearly 

 in cases of invasion of areas j^reviously untenanted 

 by it. Darwin, in the Voyage of the Beagle, 

 quotes the case of the Cardoon Thistle in various 

 districts of South America. Its germs are spread by 

 the wind. Though not a native, it has by this means 

 occupied hundreds of square miles of country to the 

 exclusion of the native Flora. Similarly in Ceylon, 

 Lantaua, though introduced not long ago as an 

 ornamental garden plant, has spread throughout the 

 island, and forms dense thickets wherever the land 

 falls out of cultivation. The dispersing agents here 

 are birds, which greedily eat the pulpy fruits. But 

 we need not go so far afield as South America or 

 Ceylon for our examples. A very striking instance 

 of the ubiquity of germs, and the occupation by them 

 of any suitable nidus, is seen in the almost invariable 

 appearance of the Common Cord Moss (Fimaria 

 hygrometrica) on cinder paths, or places where the 

 ground has been burnt. There may apparently be 

 none of the Moss in the near neighbourhood : the 

 ground has been sterilised by heat. It can only be 

 that the spores are conveyed by currents of air, in 

 which countless numbers are present, but relatively 

 few find a spot for germination. The case is similar 

 for the appearance of Moulds on bread recently 

 baked, but kept in a confined atmosphere. Such 



