SPECIES AS TO VARIATION, ETC. 187 



Community of descent of all the individuals of species 

 is of course implied in these and all similar reasonings. 



An obvious result of such partial extinction is 

 clearly enough brought to view. The European oaks 

 (like the American species) greatly tend to vary ; 

 that is, they manifest an active disposition to produce 

 new forms. Every form tends to become hereditary, 

 and so to pass from the state of mere variation to that 

 of race ; and of these competing incipient races some 

 only will survive. Quercus Robur offers a familiar 

 illustration of the manner in which one form may in 

 the course of time become separated into two or more 

 distinct ones. 



To Linnaeus this common oak of Europe was all of 

 one species. But of late years the greater number 

 of European botanists have regarded it as including 

 three species, Q. pedunculata, Q. sessiliflora, and Q. 

 jyabescens. De Candolle looks with satisfaction to the 

 independent conclusion which he reached from a long 

 and patient study of the forms (and which Webb, Gay, 

 Eentham, and others, had equally reached), that the 

 view of Linngeus was correct, inasmuch as it goes to 

 show that the idea and the practical application of the 

 term species have remained unchanged during the cen- 

 tury which has elapsed since the publication of the " Spe- 

 cies Plantarum. " But, the idea remaining unchanged 

 the facts might appear under a different aspect, and the 

 conclusion he different, under a slight and very sup- 

 posable change of circumstances. Of the twenty-eight 

 spontaneous varieties of Q. Robur, which De Candolle 

 recognizes, all but six, he remarks, fall naturally under 

 the three sub-species, peduncidata, sessiliflora^ and 



