Partial Variability and Vegetative Propagation. 143 



acters; they depend, as far as our scanty information 

 goes, almost entirely on external conditions; which in 

 their turn, however, need some generations in order 

 to exert their full effect. 



The only way to decide this point is to carry out 

 extensive and numerous experiments in selection, deal- 

 ing with the general significance of nutrition in its widest 

 sense. 



§ 17. ON PARTIAL VARIABILITY AND SELECTION BY 

 VEGETATIVE METHODS OF PROPAGATION. 



Partial variability, that is, differences in homolo- 

 gous organs of the same individual, plays a much more 

 important part in the vegetable than in the animal king- 

 dom. It is as universal as the differences between in- 

 dividuals and is usually more pronounced. 



It conforms to exactly the same statistical laws. -The 

 size of leaves, of flowers and of fruits, the number of 

 leaves on a branch and of the parts of the flower, the 

 rays in the inflorescences of Umbelli ferae and Com- 

 positae even if determined on a single plant can be tabu- 

 lated by means of frequency curves. The phenomenon 

 of regression in partial variability has been made the 

 subject of special study by Verschaffelt : and the laws 

 describing it were found to be the same as those formu- 

 lated by Galton for individual variability.^ Lastly, the 

 principles of selection apply to these phenomena as well 

 as to individual variability.^ 



This great similarity between individual and partial 



^ Ed. Verschaffelt. Galton's "Rcs^ression to mediocrity" by on- 

 ^eslachtelyke Voortplanting. Livre jubilaire dedie a Charles van 

 Bambeke, Bruxelles, 1899. 



^ See the end of this section. 



