518 Influence of Nutrition and Selection. 



good result : it will bring out more prominently the fun- 

 damental distinction between variability and mutability. 

 There are still so many cases in which it is difficult or 

 even, for the present, impossible to define the limits be- 

 tween these fundamentally different principles, that every 

 contribution to a solution of the problem is of value. 



Therefore it is most essential from the point of 

 view of the theory of mutability to have a perfectly clear 

 conception of the nature of variabilit}^ in the narrower 

 sense of the term. Absolute constancy and high varia- 

 bility are regarded by many as diametric opposites; in 

 fact it is believed by those who hold the modern theory 

 of selection, that variability leads to inconstancy, that 

 is to say to the production of new forms. According 

 to the mutation theory however constancy and variability 

 are perfectly compatible and, in most cases, usually asso- 

 ciated. That which is constant is the type or mean, on 

 both sides of which fluctuations may occur. 



The ray florets of the common cornflower are variable 

 in number ; the weaker the plant or branch the smaller is 

 this number, according to Mac Leod.^ The secondary 

 fruits of Papaver somniferum polycephalum exhibit the 

 same correlation,^ the tongue-florets in the heads of 

 Othonna crassifolia diminish if the nutrition of the plant 

 is artificially curtailed.^ ' The same thing happens in 

 Chrysanthemum segetum"^ and other Composites.''^ And 



^ Page 135 of this book. ^ Pages 138-143. 



' Page 147 and Othonna crassifolia in Kruidkundig Jaarboek, 

 Gent, 1900, p. 20. 



* Over het periodisch optreden van anomaHen, Kruidkundig Jaar- 

 boek Dodonaea, T. XI, 1899, p. 54; Sur la periodicite des anomalies 

 dans les plantes monstrucuses, Archiv. Neerland. d. Sc. exactes et 

 nat., 2d Series, T. 3, p. 403. Ueber Curvenselection bei Chrysanthe- 

 mum segetum, Berichte d. d. bot. Ges., Bd. XVII, 1899, p. 84; Ueber 

 die Periodicitdt der partiellen Variationen; ibid., Bd. XVII, p. 45. 



^ A. Weisse^ Die Zahl der RandblUthen am Compositenkopfchen, 



