PHYLOGENY OP ANGIOSPEBMS 293 



tants. Of these 800, about 200 were the new species named 

 (E. lata ; that is, the same new species appeared about 200 

 times. Various other new species appeared, and were preserved 

 by culture. The mutants also occurred in every direction in 

 the same environment, showing no indication of being responses 

 to external conditions. In the great majority of eases the mu- 

 tants M-ere constant from the outset, there being no development 

 and fixation of characters through selection, and no transition 

 between parent and offspring. Experiments with other species 

 seem to indicate that the majority of species are at present 

 immutable, varying within certain narrow limits, but not giving 

 rise to mutants. 



Solms-Laubach 10 has shown that in all probability Cap- 

 sella Heegeri has arisen in this way from O. Bursa-pastoris ; 

 and Carlson 13 has suggested a similar origin for certain Swed- 

 ish forms of Succisa pratensis; while Jordan's work with Draba 

 verna has discovered about 200 immutable forms within the 

 old species limits, that probably represent true species derived 

 by mutation from a parent of great mutability. 



The experiments of De Vries seem to indicate that there is 

 a definite limit to individual variability, beyond which selection 

 can not go. Furthermore, it is claimed that selection never fixes 

 a character, but reversion may occur after any number of gen- 

 erations of culture. In short, natural selection can not create 

 anything new, but can modify within definite and narrow lim- 

 its ; while mutation brings into existence something new, which 

 will continue as a new species if it can survive the struggle for 

 existence. There is thus drawn a sharp contrast between muta- 

 bility and ordinary variability, the latter being governed by 

 environment, the former independent of it. Hence, while most 

 species are immutable, all are more or less variable. 



At its present stage such a theory can not be accepted or 

 rejected. Either alternative will demand a vast amount of care- 

 fully sifted experimental evidence. It should be remembered 

 that the subject lends itself readily to observations that are 

 really inferences, and a vast amount of data will doubtless be 

 forthcoming that can not be regarded as testimony. The stu- 

 dent of Angiosperms, however, is in a position to encounter 

 useful data, for the group is a very modern one and seems to 

 contain many mutable species. It should further be remem- 



