128 ORIGIN OF PLANT VARIATIONS 



species. This view is purely theoretical and is not supported 

 by any demonstrable evidence. 



As opposed to this theory deVries has called attention to the 

 fact that entirely new forms may appear at any time in the off- 

 spring of the parents. These new forms are called mutants 

 because of their sudden appearance. During his cultivation of 

 Oenotheras, evening primroses, in which only plants of the same 

 kind were crossed, he 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 distinguished 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. The offspring therefore will be characterized by 

 the absence of certain parental characters or will appear with 

 new ones not possessed by the parents. To what extent this 

 sudden appearance of new characters has been a factor in estab- 

 lishing new forms of plants and animals remains to be seen. 

 Illustrations in addition to those previously noted, will repeatedly 

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

 influenced by the stimuli of its environment. Gager has recently 

 shown that marked variations may be induced in the offspring 

 of Oenothera by subjecting the parents to the emanations of 

 radium and MacDougal reports like results from injecting solu- 

 tions into the ovaries. It seems altogether probable that the 

 hereditary substances may be similarly affected by the varied 

 stimuli which the plant is constantly receiving in nature. 



Later in the work it will be seen that nearly all plants have 

 devices of various kinds that assist in the transfer of the micro- 

 spores of one plant to the stigmas of other plants. In this way 

 the sexual generations are brought together that have been de- 

 rived from plants that may differ more or less from one another. 

 All these differences in so far as they are due to the hereditary 

 substances must be transmitted to the gametospore, consequently 



