THE EVIDENCE OF EVOLUTION. 373 



group remains wholly unaffected by the production of new species. 

 After eighteen years it is absolutely the same as at the beginning, 

 and even the same as is found elsewhere in localities where no muta- 

 bility has been observed. It neither disappears nor dies out, nor is 

 it ever diminished or changed in the slightest degree. 



Moreover, according to the current conception, a changing species 

 would commonly be modified into only one other form, or at best 

 become split into two different types, separated from one another 

 by flowering at different seasons, or by some other evident means 

 of isolation. My evening primrose, however, produces in the same 

 locality, and at the same time, from the same group of plants, quite 

 a number of new forms, diverging from their prototype in different 

 directions. 



Thence we must conclude that new species are produced sideways 

 by other forms, and that this change only affects the product, and 

 not the producer. The same original form can in this way give birth 

 to numerous others, and this single fact at once gives an explanation 

 of all those cases in which species comprise numbres of subspecies, 

 or genera large series of nearly allied forms. Numerous other distinct 

 features of our prevailing classification may find on the same 

 ground an easy and quite natural explanation. 



To my mind, however, the real significance of the new facts is 

 not to be found in the substitution of a new conception for the now 

 prevailing ideas; it lies in the new ways which it opens for scientific 

 research. The origin of species is no longer to be considered as so- 

 mething beyond our experience. It reaches within the limits of direct 

 observation and experiment. Its only real difficulty is the rarity 

 of its occurrence; but this, of course, may be overcome by persevering 

 research. Mutability is manifestly an exceptional state of things if 

 compared with the ordinary constancy. But it must occur in nature 

 here and there, and probably even in our immediate vicinity. It 

 has only to be sought for, and as soon as this is done on a suffi- 

 ciently large scale the study of the origin of species will become an 

 experimental science. 



New lines of work and new prospects will then be opened, and 

 the application of new discoveries and new laws on forage crops and 

 industrial plants will largely reward the patience and perseverance 

 required by the present initial scientific studies. 



(Science, N. S. Vol. XX, No. 308, Pag. 395-401, 

 September 23, 1904.) 



