136 ORIGIN OF PLANT VARIATIONS 



plant or animal is definitely known it is probable that the varia- 

 tion of the offspring can be accurately forecast. 



It must be borne in mind that the variations referred to above 

 do not result in the formation of new characters but in the re- 

 combination of characters already existing in the parents. As 

 to the actual origin of new characters there is no universally ac- 

 cepted explanation. The view has been widely prevalent that 

 insignificant departures may appear in any form owing to some 

 circumstance of environment and that these departures may 

 gradually become intensified so that after a long lapse of time 

 they are sufficiently pronounced to warrant the recognition of 

 the forms possessing these characters as distinct species. Such 

 was Darwin's theory as to the origin of new forms but this 

 conception is purely theoretical and is not supported by any 

 demonstrable evidence. 



As opposed to this theory Bateson, and more recently deVries, 

 has called attention to the fact that entirely new forms may ap- 

 pear at any time in the offspring of the parents. These new 

 forms are called mutants because of their sudden appearance. 

 During the cultivation of Oenotheras, evening primroses, in which 

 only plants of the same kind were crossed, deVries found after 

 fifteen years of cultivation in which time over 80,000 plants had 

 been under observation that fifteen new forms had suddenly 

 appeared at one time or another. These mutants are distin- 

 guished by new characters not possessed by the parents and 

 furthermore they transmit these characters to their offspring. 

 This theory of mutation holds that the unit characters which 

 distinguish the individuals of a kind or species may be influenced 

 by external forces with the result that one or more of them may 

 be blotted out or changed in its nature, or new ones may be 

 added. The offspring therefore will be characterized by the 

 absence of certain parental characters or will appear with new 

 ones not possessed by the parents. That this sudden appearance 

 of new characters has been an important factor in establishing 

 new forms of plants and animals is not to be questioned. Illus- 

 trations in addition to those previously noted, will repeatedly 

 occur later in the work, showing that plant life is profoundly 



