168 Observation of the Origin of Varieties. 



flowered altogether. I picked off and recorded a head 

 from each of these during the course of the summer. 

 On every plant I selected the terminal inflorescence of 

 the main stem as soon as it opened ; plants in which this 

 failed were pulled up before they flowered. Only pri- 

 mary inflorescences were, therefore, employed, and the 

 curve obtained was an index of individual variability, 

 that is to say each unit in it represented a whole plant. 

 The figures obtained are represented in the following 

 series; The upper row gives the number of ligulate 

 florets (L. F.) per inflorescence; the lower, the number 

 of individuals which possessed these numbers. 



VARIATION IN NUMBER OF RAYS IN C. SEGETUM^ 1892. 



L. F. 12 13 14 15 16 17 18 19 20 21 22 

 Individuals 1 14 13 4 6 9 7 10 12 20 1 



The curve based on this series of figures is given in 

 Fig. 30. One of its two apices corresponds to that of 

 the wild species, the other to that of the curve for Chry- 

 santhennun Leucantheniiun and C. inodonun. 



My next task was to separate the components from 

 this mixture and to do this in such a way as to place their 

 existence in the mixture beyond doubt. On account of the 

 inevitable interference of insects in pollination it seemed 

 to me impossible to do this for both supposed races at 

 the same time, so I determined to isolate the 13-rayed 

 form first, and the 21 -rayed later on from a new mixed 

 crop. I devoted the two years 1893 and 1894 to the 

 former inquiry. 



With this object in view, I eradicated every indi- 

 vidual of the mixed crop of 1892 wiiich had more than 

 13 rays, as soon as I had counted the rays on its terminal 

 flowerhead. In this way only 15 plants were saved, of 

 which one had 12 and the rest 13 ligulate florets; the rest 



