THE EVOLUTION OF SPECIES 205 



Then comes a period, relatively short, when, under the 

 stimulation, perhaps, of changing environment, the plant 

 loses its balance and begins to produce offspring uiilike 

 its3lf . Variations occur suddenly in many directions ; 

 some are useful, others are not. Each form, however, is 

 constant, and, if hybridization does not interfere, breeds 

 true to seed. These new forms, or mutants, arising from 

 a parent-plant during a period of mutation, are called by 

 De Vries elementary species. The fate of these elementary 

 species must be decided by Natural Selection. Those 

 that are adapted to the environment wiU flourish and 

 multiply, those that are not wiU perish. Natural Selection 

 is the sieve through which they all must pass. 



The value of these rival theories must be tested by 

 experience. There is little to guide us at present, but 

 such evidence as we possess seems to "be in favour of the 

 mutation theory. In the first place, it explains the absence 

 in Nature of transitional forms, and it does not involve 

 the supposition that acquired characters may be trans- 

 mitted. At the same time it alters the position that 

 Natural Selection, the theory of the survival of the fittest, 

 has occupied in the Darwinian theory. In the latter it 

 plays the first part ; in the former it plays only a secondary 

 part, sifting out from among the variations produced those 

 which are of importance to the race for perpetuation. 

 Last of all, De Vries has discovered one plant, a species 

 of evening -primrose— ffiJno^Aera Lamarckiana — actually 

 in a state of mutation, throwing off a number of ele- 

 mentary species. The Irish yews are all derived from 

 one plant in Ireland which was a mutation of the 

 common yew, and all the copper-beeches in cultivation 

 are derived from two or three sports which have arisen 

 independently in several localities in Europe. The peach 

 is regarded as a mutation of the almond, and the nectarine 

 is undoubtedly a mutation of the peach. 



The one conclusion which we can draw from the 

 Evolution theory, however stated, is, shortly, this : that 

 the present vegetable forms have been derived by modifi- 

 cation or amplification from pre-existing forms, and that 

 there has been no break in the development of the vegeta- 

 tion under the control of natural laws from the earliest 

 times to the present. We look upon the vegetation as a 

 great family of more or less related forms having a con- 



