23 



détermination of this latter character only tlie umbellets 

 of the oldest umbel of each plant were taken. Of Banunculus 

 arvensis the number of fruits per flower was determined 

 and of Gardamine hirsuta the length of the silique, of each 

 plant the siliques of the principal stem being measured. 



For each of the characters mentioned I took of each of 

 the cultures on fertile soil and on sandy soil 300 measure- 

 ments or countings, a number which, according to the 

 calculations of Prof. Kapteyn, gives in investigations of 

 this kind a sufficient guarantee of accuracy. For certain 

 characters I had to be contented with a smaller number 

 since the material in thèse cases was déficient. For those 

 cases in which the variability concerns the number, the 

 numbers were noted increasing by unity ; for those charac- 

 ters that vary in length, the length was determined in 

 fractions of a millimètre, in milimetres or in centimètres, 

 depending on the absolute size of the parts. By means 

 of the numbers obtained, curves were plotted in order to 

 hâve a gênerai survey of the observations and to facilitate 

 a comparison of the observations of the culture on fertile 

 soil with that on sandy soil. In most cases the observa- 

 tions were combined into groups, so that from seven to 

 seventeen intervais were obtained. In this way curves 

 are obtained that admit of easy inspection and in which 

 the smaller irregularities hâve disappeared. Only for the 

 number of branches of the third order of Iberis amara, 

 fig. V, the observations of the plants on the fertile soil 

 had to be combined to 28 groups, since only then a com- 

 parison with the plants from the sandy soil was possible. 



The curves for the various characters are reproduced 

 on the accompanying plate. Since for ail cases the fre- 

 quencies hâve been calculated, ail the curves hâve the 

 same area and can be mutually compared. For each cha- 

 racter the curve of the well-fed plants has been drawn as 

 a continuons line and that of the badly-fed plants as a 



