THE STANDPOINT OF BOTANY 59 



every direction, the intergrades are innumerable, 

 the habitats are exceedingly diverse, and Natural 

 Selection would seem to necessitate just the re- 

 sult observed. In fact, the greatest American 

 student of the genus, after a prolonged effort to 

 detect and define the boundaries of its species, 

 gave it as his private opinion that " there are no 

 species in Aster." Of course this must be under- 

 stood as an expression of despair rather than of 

 behef, but it emphasizes the situation. With the 

 wide-ranging genera showing this condition, it 

 was not difficult to imagine that the sharp differ- 

 ences among isolated species are to be explained 

 by the breaking up of their continuity ; and so all 

 species were swept into the category of Natural 

 Selection. 



On the other hand, when the botanist came to 

 enlarge the horizon of his observation, and in- 

 cluded the whole phylogeny of some great group 

 of plants, or even the phylogeny of the whole 

 plant kingdom, he began to have doubts as to the 

 adequacy of Natural Selection as an explanation 

 of all the changes. He has learned to regard this 

 selection as a factor that perpetuates and perhaps 

 develops certain characters, and that eliminates 

 others; but he cannot discover how it can really 

 originate new characters. The genus Aster, for 

 example, is defined by a definite group of char- 

 acters; and the species may be regarded as the 

 selected variants of these same characters. The 

 pattern changes, as in the kaleidoscope, but noth- 



