Origin of Species and Varieties 577 



It is manifest that we must be very careful and 

 conservative in dealing with new facts that are 

 brought to our attention, and every eif ort should 

 be made to bring additional evidence to light. 

 Many vegetable anomalies are so rare that 

 they are met with only by the purest 

 chance, and are then believed to be wholly 

 new. When a white variety of some common 

 plant is met with for the first time we generally 

 assume that it originated on that very spot 

 and only a short time previously. The discov- 

 ery of a second locality for the same variety at 

 once raises the question as to a common origin 

 in the two instances. Could not the plants of 

 the second locality have arisen from seeds 

 transported from the first? 



White varieties of many species of blue-bells 

 and gentians are found not rarely, white-flower- 

 ing plants of heather, both of Erica Tetralix and 

 Calluna vulgaris occur on European moors; 

 white flowers of Brunella vulgaris, Ononis re- 

 pens, Thymus vulgaris and others may be seen 

 over large areas in the habitats of the colored 

 species. Pelories of labiates seem to occur 

 often in Austria, but are rare in Holland ; white 

 bilberries {Vaccinium Myrtillus) have many 

 known localities throughout Europe, and nearly 

 all the berry-bearing species in the large heath- 

 family are recorded as having white varieties. 



