12 



all their characters, in their whole behavior." (Ber. Deutsch. 

 Bot. Ges. 13: 307. 1895.) . " Now if Von Wettstein's plausible 

 assumptions concerning the established causes of this dimorphism 

 are correct, then even the state of heredity is here a relatively 

 verj' 5^oung epliarmon {Epliarviosc) : for onl)' since the develop- 

 ment of an alpine habit [Alpcnwirtschafi) through regular mowing 

 would tlie effective forces have been in action. If only a phylo- 

 geneticall}' considered short period suffices in this case to fix the 

 form as hereditary, by how much more would nature itself, 

 which operates over such immeasurably long periods, be in a 

 condition to do it. Through heredity numerous helikomorpliic 

 structures obtain that independence which establishes new phylctic 

 courses for their posterit}'. They become, then, ' phylembryos ' 

 of new developmental courses. Their leaf-form, fixed in a 

 definite direction, undergoes either epharmonic or autogenous 

 variations, a new strain is developed out of the former phase-form 

 of the old stock." 



Chapter V treats of similar phenomena in the animal kingdom, 

 and Chapter VI is a resume of the preceding chapters. The 

 following is a free translation of Chapter VI, with omission ot 

 the examples cited : 



" The generative maturity of plants is not unchangeabl}' bound 

 up with a definite stage of vegetative development. Of course 

 it presumes a certain minimum of previous vegetative work ; if 

 this is exceeded, however, there follows a broad zone of variation 

 for the appearance of the floivers. The regulation of this varia- 

 tion takes place by means of complex and diverse conditions. 

 External circumstances have an important share in it, in the case 

 of cryptogams (Klebs) as well as in the case of Howering plants. 

 Of this we know but little ; but it is manifestl}^ evident that dry- 

 ness and a qualitative variation of nutrition favor flozvering, oppo- 

 site conditions are Jinfavorable. 



"The vegetative ontogeny of plants is consummated thi-ough 

 the cooperation of autogenous and external {exogener) factors. 

 The ground work comprises diverse potentialities. Thus it 

 postulates no rigid configuration. At first the environment is 

 rather ' the determining factor as to which of the various possible 



