33 



curves. If, however, the observations are arrangée! to a 

 number of groups equal to that of the other figures, the 

 curve thus obtained is not différent from those of the other 

 characters. For this culture the médian is 53, the quartile 



17.25 and the variability-coefficient ^ 0.32, the minimum 



number of side-branches being 1, the maximum 162. 



With this character now, bad nutrition does not resuit 

 in a simple shifting of the curve to the left, accompanied 

 by greater or smaller changes in the values of M, Q and 



-^, as in the other cases, but hère the symmetrical curve 



changes into a semi-curve of which the apex lies at zéro. 

 We can explain the origin of this semi-curve in the 

 following way. The lower limit for the number of branches 

 of the third order of Iberis amara is 0. Since the plant 

 also blooms on the principal stem and on the branches 

 of the second order, it may exist without branches of the 

 third order. Under favourable nutritive conditions the 

 development of the plant is so vigorous that in ail indivi- 

 duals branches of the third order are formed, but in greatly 

 diverging numbers, as is shown by the curve of fig. V 

 for this culture. With unfavourable nutrition, however, 

 also individuals arise in which no branches of the third 

 order are originated and as nutrition becomes worse the 

 number of thèse individuals will become greater. Hence 

 we see that with the very bad nutrition of the sandy soil, 

 a great number of plants has no branches of the third 

 order and so has reached the lower limit, the other spéci- 

 mens bearing a greater or smaller number of thèse side- 

 branches, as is shown by fig. V for this culture. This 

 leads us to the conviction that the semi-curve for this 

 character is a necessary conséquence of the fact that by 

 the unfavourable nutritive conditions the variation-curve 

 is shifted in such a way that it strikes against the lower 

 limit of the whole range of variation of this character, a 



