51<> A NEW THEORY OF THE OKIGIN OF SPECIES. 



a ([uite brief period the habitual invariability. In this it harmonizes 

 with Darwin to a certain extent. 



Hugo de Vries considers that the existence and invariabilit}' of species 

 are facts supported by daily observation. He refers to the memorable 

 experiments of Jordan and his followers, who made thousands upon 

 thousands of sowings of vegetable species and never observed the 

 passage of one into another — that is to sa}', a true vegetal mutation; 

 they only obtained ditferences now classed under the head of indi- 

 vidual variations. These, as is well known, are of such a nature that 

 if we avoid artificial isolation, segregation, and selection, the forms 

 revert to the primitive type. It is vain for transformism to deny this 

 remarkable tixity and to replace it by an h5^pothesis of changes so 

 slow, so miiuite, and so gradual that they become evident only after 

 the lapse of centuries, and inevitably escape our observation at the 

 moment. 



Another fact that accords with the theory of mutation is the exist- 

 ence, in certain genera, of animals and plants of a great number of 

 species that differ from each other but little anatomically. Botanists 

 are aware that most Linntean species are groups of living forms that 

 are constant, hereditary, and usually infertile when crossed; that is to 

 say, they are specifically distinct. Yet they differ so little in their 

 aspect that many naturalists mistake them or confound them with each 

 other. It would appear as if, at a given moment, in a crisis of muta- 

 tion, the parent stock had become resolved into a multitude of sec- 

 ondary species which have persisted. For instance, the group of roses 

 contains more than a hundred wild species so similar to each other 

 that the most experienced connoisseurs make mistakes in their deter- 

 minations. The thorn bushes, the willows, and the Alpine gentians 

 are other examples of the same peculiarity, as are also the pansies and 

 the sunflowers. In the animal kingdom many genera of insects pre- 

 sent the same phenomena. 



These, however, are merely agreements. H. de Vries has not con- 

 tented himself with noting them; he has sought direct proofs of his 

 hypothesis. The best one would bo to iind a plant that was actually in 

 its period of mutation and that might beget, by means of seeds, a 

 number of daughter plants in which there should abruptly appear the 

 characters of a new species. We may readily apprehend the principles 

 which would guide him in his researches. It would be necessary to 

 experiment with genera of wild plants that have a large number of 

 closely related species. Jordan has, indeed, established the fact that 

 the greater number of wild species now found in Europe are specifically 

 immutable. Yet it is possible that they may not all be so and that 

 some may, at the present time, be undergoing a crisis of mutation. 

 There would be more chance of finding such among the species that 

 present a great many subspecies, this being a sign of plasticity leading 



