LIFE ON THE EARTH. 21 



migration, have traversed large tracts without hy- 

 bridism, and have been subject to various physical 

 influences without suffering any sensible change. 

 Ranunculus aquatilis in India and Britain every 

 where retains the little nectary at the base of each 

 petal, to mark the genus, still spreads its white 

 blossoms on the water, and extends its filmy leaves 

 beneath. Still Ranunculus lingua distinguishes itself 

 by its leaves, and Ranunculus arvensis by its prickly 

 seeds. 



Instances of purely local species of plants are 

 very common ; sometimes defined by impassable 

 boundaries as broad oceans or crested mountains ; 

 but not unfrequently contracted to small areas from 

 a once wider distribution, or confined to such areas 

 by the successful rivalry of other and more pros- 

 perous races. Thus the huge cypresses in the Sierra 

 Nevada of Upper California, known to us as Welling- 

 tonia 1 , are now confined to a small district, and 

 indeed rear their prodigious heads 400 ft. high, mostly 

 in one valley, where they have lived for a thousand 

 years and more near the head-waters of the Stanis- 

 laus and St Antonio rivers, lat. 38 N., long. 120 

 10' W. 2 So in the valley of the Cherwell, in Ox- 

 fordshire, the Fritillaria adorns but a few meadows, 



1 Sequoia Wellingtoniana is perhaps the right appellation. 



2 Seemann, Ann. Nat. Hist. March, 1859. 



