Types of Mutations and Their Possible Significance in Evolution

Abstract

THE beginning of the twentieth century saw the rise of two concepts which have profoundly affected biological thought and been of increasing influence in the trend of experimental study of plants and animals. The mutation theory of deVries based on the evening primrose, and the laws of Mendel based on the garden pea, settled the date of birth of the modern science lof genetics. The studies on these two plants have together formed a basis for the main bulk of our present genetic investigations. While the garden pea stands intimately associated with a conception of inheritance of wider application than was at first imagined, the evening primrose and the theory of mutation connected with it are by many considered to furnish an example of a valuable theory founded upoii incorrect interpretations. The belief is growing that most of the new forms which have appeared in cultures of the Enotheras are not mutations at all and that the evening primroses, as an abnormal group of plants, are not to be seriously considered as representative of the processes of evolution in normal forms. In the short time at my disposal, I wish to outline some recent findings in the jims'on weed (Datulr-a Stramoniutm) which it is hoped may throw incidentally some light on the more highly involved phenomena in the &notheras, and which may serve as a basis of a brief discussion of their possible evolutionary significance. The jimson weed is not supplied with a wide range of obvious Mendelian characters. The early studies of