JEFFREY: EVOLUTION BY HYBRIDIZATION 299 



contented himself mainly with pointing out that a general process of 

 variation has been going on from age to age in matter endowed with 

 life. He emphasized the fact that the struggle for existence on the 

 one hand and the selection exercised by environment on the other 

 provided an important directing influence upon the development of 

 new species of plants and animals. In recent years a doctrine of old 

 standing has been revived, namely the hypothesis of mutation. It has 

 been maintained that new forms or elementary species arise spon- 

 taneously from formerly existing species. This doctrine has been 

 particularly advanced by the activities of the Dutch physiologist De 

 Vries and his disciples in this and other countries. It is a general 

 observation in connection with the activities of the lower organisms 

 that in the process of their often extremely active development they 

 give rise to inhibiting substances. In the case of the common yeast 

 for example we have the formation of alcohol, which finally, by a high 

 degree of concentration in fermenting sugary solutions, brings the 

 activity of the yeast organism to a close. It is of interest to note in 

 this connection that it is precisely in Holland that scientific opposition 

 to the mutation hypothesis of De Vries has recently appeared. To 

 Dr. Lotsy we owe a recent volume on Evolution by Means of Hybrid- 

 ization, which attacks the mutation hypothesis at its very base 

 through the contrary hypothesis that all changes in living matter are 

 due to crossing or hybridization and are not the consequence of 

 spontaneous internal or mutational phenomena. The author argues 

 that since hybrids are notoriously variable all variability must be 

 due to hybridism. This appears to be reasoning in a vicious circle. 

 Clearly the most definite evidence in regard to hybridism as the cause 

 of new species should be demanded before the possibility of the 

 appearance of new types in this manner can be admitted. We 

 fortunately have extremely good testimony on this subject from the 

 earlier investigations published by Kerner in Austria and Brainerd in 

 this country. Kerner in his well-known Pflanzenleben as well as in 

 an earlier publication in the Oesterreiche Botanische Zeitung has 

 brought forward much evidence as to the origin of new species as the 

 result of hybridization in the mountainous regions of eastern central 

 Europe, where the floras of the Pontic, Mediterranean and Baltic 

 areas meet. It is impossible within the time at my disposal to make 

 more than a very brief reference to the results reached by this writer. 

 He has made it clear that the members of different floras are very 

 apt indeed to produce new species by hybridization in nature and that 

 these species, where they are advantageously equipped as compared 

 with the parent forms, flourish within the same region. In case they 

 have qualities which enable them to live where the parental species 



