GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 241 
complete exclusion of the native plants. Originally the 
whole of Atlantic North America was an unbroken for- 
est, with an undergrowth of delicate shade-loving plants. 
With the clearing away of the primeval forest these 
plants quickly perished, and a host of foreign weeds, 
grasses, thistles, dandelions, docks, plantains, rushed 
in to occupy the waste room. As civilization pushed 
westward, the hordes of these European immigrants 
were met by the prairie plants, which were able to cope 
with them successfully, so that now the farmer has to 
contend with two sets of enemies, the European weeds 
on the one hand, and the prairie weeds, rag-weed, bur- 
marigold, Rudbeckia, sunflowers, etc., on the other. 
These weeds are transported with grain in railway 
cars, or cling to the coats of animals or the clothes of 
human beings, and in these days of rapid transit, plants 
have also taken advantage of the improved means of 
travel. 
In most parts of California, owing to the long dry 
season, most of the weeds from northern Europe do not 
thrive, and instead we find weeds whose home is upon 
the shores of the Mediterranean. Probably introduced 
by the original Spanish settlers, wild oats, alfilaria, 
bur-clover, and other south European plants have es- 
tablished themselves in the sunny valleys of California, 
where they grow side by side with the poppies and 
lupines, which, however, are quite able to hold their 
own. 
