452 EXPERIMENTS WITH PLANTS 



normally colored flower be pollinated from its own 

 flowers it will produce white flowers only and prove 

 constant. Such varieties, he considers, are really 

 species. 



Every one who has opportunity should be on the 

 lookout for sudden variations, both in garden and 

 field. Should one be found it should be kept under 

 observation, protected from crossing by paper bags 

 (as described on p. 289), and hand -pollinated. The 

 seed should be saved and sown, in order to see 

 whether it proves constant. 



Professor de Vries offers a satisfactory reply to 

 the opponents of evolution, who contend, first, that 

 species are constant and, second, that if evolution 

 were going on we should be able to see the process. 

 He says that species are constant except at mutation 

 periods: moreover, evolution is going on and he has 

 seen it, not once merely, but year after year in his 

 garden: he has furnished seed to other botanic gardens 

 in various parts of the world, and the same phenomena 

 have been observed. The seed sown at the University 

 of California produced about 8 per cent of mutations, 

 which I have had the privilege of personally observing. 

 Further, his theory makes it unnecessary to seek for a 

 continuous series of "missing links," since it assumes 

 that they never existed in such a series. His dis- 

 coveries demonstrate conclusively that evolution can be 

 studied experimentally in a manner hitherto unsus- 



