240 EVOLUTION OF PLANTS 



tainous districts of the north. Instead of dense forests, 

 with an undergrowth of dogwoods, rhododendrons, 

 brambles, roses, and with the ground carpeted, with 

 mosses and ferns, we find the floor of the valleys and 

 the rolling foot-hills covered with annual grasses, with 

 which, in the spring, are mingled numberless showy 

 flowers, unfamiliar to the eastern botanist except in 

 gardens. Fiery Eschscholtzias, blue Nemophilas, pink 

 and yellow Mariposa lilies, and numberless other 

 flowers, make masses of brilliant color of unrivalled 

 beauty. Here and there are scattered spreading ever- 

 green oaks, and on the hillsides are thickets of low- 

 growing shrubs, " chaparral," made up of Manzanita, 

 Ceanothus, and other western types, while the streams 

 are bordered with beautiful madronos (Arbutus), bay- 

 trees, and big-leaved maples, as well as the more fa- 

 miliar alders and cottonwoods. The central part of 

 the state is the meeting-ground for the two diverse 

 floras, the northern types often following the canons 

 down to the valleys, where they mingle with the south- 

 ern flora. 



While the natural conditions of topography and 

 climate have, of course, been the most potent factors 

 in the present distribution of plants, animals have also 

 played an important part, and especially man. The 

 advent of man into many regions has quite transformed 

 them, so far as the flora is concerned. In the tropics 

 many of the most characteristic plants, such as the 

 banana, breadfruit, cocoa-palm, and mango, as well as 

 many weeds, like the sensitive plant, have become nat- 

 uralized everywhere. So in temperate regions many in- 

 troduced weeds have taken possession of the soil to the 



