Equilibrium Between Selection and Nutrition. 563 



into the variability of various animals {Forficula, Car- 

 cinus, Xylotropus, etc.), and repeatedly by Ludwig in 

 plants. Bateson^ in his work on discontinuous varia- 

 tion, has emphasized the great importance of such cases 

 to the student of variability, and given examples of 

 them.^ Tbe two-peaked curves are separated by him 

 as cases of dimorphism from the ordinary or mono- 

 morphic curves. 



The duplicate character of curves can be brought 

 about by the most various causes. Giard, for example, 

 has made the remarkable discovery that a dimorphism 

 of this kind may be brought about when some of the 

 individuals in a locality are infested by a parasite. Thus 

 Carcinus mocnas which were infected by Sacciilina car- 

 cini or Portunion moenadis differed widely from the 

 normal ones.^ 



But the double curves in plants can be dealt with ex- 

 perimentally much better than those in animals or men. 



Let us now proceed to the description of the experi- 

 ment with Chrysanthemum segetum. In 1892 this ex- 

 tended over an area of 2 square meters. The number 

 of individuals, when I came to select them was 97. For 

 making the curve only one head was taken from each 

 individual, the so-called primary one at the top of the 

 main stem. All plants whose terminal inflorescence had 

 14 or more ray florets were pulled up immediately; 

 fourteen plants with 13 such florets and one with 12 were 

 saved. 



^W. Bateson, Materials for the Study of J^an'ation, London, 

 1894, PP- 39-41- 



Comptes rendus, T. CXVITT, 1894, No. 16 (April 16). p. 870. 

 This case has now been thoroughly investigated by Geoffrey Smith, 

 Fauna and Flora of the Gulf of Naples. Volume on Rhizocephala 

 (Note of 1908). 



