6Q 



of research : instead of attempting to find an answer ready made 

 for our questions we propound our question and set living things 

 in action and seek our reply in their behavior under conditions 

 which we may vary to suit our interrogation. It is obvious 

 that the only way in which we may determine the method of 

 origin of new species is to observe the formation of a species. 

 The recent work of de Vries dealing with this subject is a record 

 of the notable attempt made by him to obtain information upon 

 the subject in this manner.* 



De Vries' observations extend over seventeen years and the 

 first volume of the great book in which his work is described 

 deals with the origin of species by mutation, while the second 

 now in preparation gives consideration solely to the subject of 

 hybrids. According to de Vries species may arise by the fol- 

 lowing general modes : 



i . Progressive species-formation by the construction or acqui- 

 sition of new qualities. 



2. Species-formation without the construction of new qualities, 

 in which three cases may be distinguished. 



A. Retrogressive species-formation by the lapse or latency of 

 existing qualities, partly atavistic. 



B. Digressive species-formation by the awakening or energiz- 

 ing of latent characters, partly in the formation of anoma- 

 lous structures and partly in atavistic phenomena. 



C. Hybridization. 



De Vries assumes that any group of individuals which are 

 independent, self-perpetuating and sufficiently distinct by taxo- 

 nomic characters to meet the requirements of systematic botany 

 constitutes a species irrespective of origin, and in the consideration 

 of his results the importance of his conclusions is not lessened 

 materially whether the forms with which he has dealt are consid- 

 ered as species or varieties so long as they are shown to consist of 

 distinct and independent individuals capable of transmitting cer- 

 tain characters which are assumed to be constant within the limits 

 of ordinary fluctuating variation. 



* De Vries, II. Die Mutationstheorie. Versuche und Beobachtungen iiber die 

 Entstehung von Arten im Pflanzenreich. I. Die Entstebung der Arten durch Muta- 

 tion, xii -|- 648 pp. PL 1-8 -\- f. 1-181. 1901. 



